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Screwcutting Indicator Dial |
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I've had this lathe since 1985 and the only
screwcutting that I've done on it had threadcounts that were a multiple
of four. That is because it doesn't have a threading indicator dial and
I've never really needed one before, having access to other machines. I
now need to cut some 6 TPI threads and need an indicator to fit my 4 TPI
leadscrew but, as the lathe is eighty years old, finding one would have
been difficult, to say he least. They are not hard to make, though, so I
knocked on up over the weekend. The first thing I had to make was the gear
that engages the leadscrew and, on the basis that one makes a gear with
four times the number of teeth as the leadscrew pitch, that was a 16 TPI
gear with 1/8" wide teeth cut on a blank a little over 1.1/4" diameter.
However, 1.1/4" will do, this doesn't need to be particularly precise. A
bronze blank was machined up with 5/16" wide for the teeth and a 5/8" x
5/16" wide boss for fixing onto a 3/8" diameter shaft. Because I don't have
a dividing head, I checked my lathe changewheels for one that was a multiple
of 16 to make up an indexer and found this 32 tooth wheel. |
| With the gear blank made, I had to knock
up a mandrel to hold both the blank and the changewheel so that I could
index the thing round. I managed to cobble together a somewhat Heath-Robinson
setup with a vee-block held in the vice and a detent mechanism bolted onto
an old milling fixture. It looks very ramshackle but it's suprisingly sturdy
and accurate. The cutting tool is a broken centre-drill which I've ground
to form a 1/8" wide cutter, which is clamped into an offcut of 5/8" diameter
bar and held in a collet. |
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I decided to try and combine my saddle/carriage stop and
this thread indicator into a single unit so had to modify the carriage stop
by milling away a section at the top. A 3/8" diameter hole was drilled and
reamed through and the unit refitted to the lathe using the single bolt.
The gear was fitted to a length of 3/8" diameter bar and offered up to the
leadscrew to check both size and fit, as well as orientation of the stop
block. The rotating barrel with the five adjustable stops have been temporarily
removed. Next up was the indicator dial which was made from a piece of 1.1/8"
diameter brass with an angled face and parted off about 5/16" wide. The
hole through was drilled and reamed 3/8" diameter, and a cross-hole drilled
and tapped to take an M4 grubscrew. It was then clamped to a short length
of bar, held an a square collet block and loaded to the tilt-and-turn vice
to mill four indicator grooves. I don't have any engraving tools so a 1/4"
centre-drill was ground to a fine point instead, the four lines being "engraved"
by indexing the block in the vice. |
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The stop block was reassembled, a collar made for the
gear spindle to stop it climbing up the block and the indicator stamped
with four numbers. Although it is barely visible, I also used an end mill
to create a small pocket at the top of the block to take an "O" ring. The
dial rests on this and keeps the crud out plus adds a little bit of friction
to the spindle. Finally, the whole thing was fixed back onto the saddle
and adjusted for fit. When not in use, The stop block can be slightly rotated
to disengage the gear but without making the stop go out of line. There
are sixteen positions where I can engage the screwcutting lever but I will
use just the four marked positions, which will enure that all whole-number
threads can be cut without creating the dreaded two-start thread. Another
worthwhile additon to the lathe and it cost precisely nothing because all
materials were sourced from the scrap-box. |
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New Lathe Cross-slide |
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The cross-slide on my lathe, a clone of the
Denham Junior, doesn't really provide a means of mounting a vertical slide
because the whole thing is too tall, although the circular tee-slot does
provide direct mounting and swivelling for the compound slide. The one advantage
the lathe does have, however, is the ability to remove the whole slide very
quickly by undoing two coverplate screws and two leadscrew fixing screws.
Needing to machine the saddle of the chimney for my loco, I decided to make
a new cross-slide for my machine which would allow for direct fixing of
alternative tooling and a vertical slide. The dovetail section is 1/2" high
so I reckoned that the table needed to finish at 6" long by 5" wide by 1.1/4"
deep. |
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I started with a lump of cast iron cut to just over the
above dimensions. After setting up in the 4-jaw chuck on the lathe, the
two faces were cleaned up and finished about ten thou oversize, them the
edges were squared and finished to size in the mill. I don't have a vice
large enough to mount this workpiece flat so all subsequent operations were
done with the work mounted directly to the mill table. First of these was
roughing out the underside, followed by milling the slots for three tee-channels
with a 10mm carbide end mill. Having a table feed was an absolute godsend
as this took quite a few hours of cutting. |
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Next, a 12mm diameter tee-slot cutter was passed up and
down each channel, setting over to 1.1mm for the first pass and 2mm for
the second, finishing with a 16mm wide slot. I have deliberately made the
slot-spacing assymetrical to allow for a wider range of clamping solutions.
Next I drilled and tapped a large quantity of M8 boltholes, again using
different patterns for greater options. Clamping the work to machine the
dovetail was always going to be problematic because it's neary as wide as
my mill table. The power of the cut will be a bit too heavy for cam-button
clamps. I got round this by modifting four clamps so that the tongues would
fit into the tee-slots, then turning a length of angle iron into an extension
of the table by bolting it to the front where the stop collars fit. I did
have to dismantle the table feed operating arm to get it to fit but I was
still able to use the feed by operating the lever between the microswitches. |
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This is the cross-slide mounted on the table and the dovetail
cutter ready to do it's work. It's a left-hand cutter so I have to run the
machine in reverse and cut left-to-right. A friend lent me the cutter for
which I've had to make a mandrel because I couldn't use his 2MT mandrel.
I made one with a 16mm diameter stem to hold in a collet; my mill has an
R8 spindle. Before setting up to mill the dovetail, I trammed the head.
These mills are notorious for going out of alignment after heavy use in
the same direction because there is no locking dowel to keep the head aligned
at 90o to the table. I knew it needed doing because I was getting tail-cutting
when sending the tool left-to-right. After cutting the dovetail, the workpiece
was offered up to the lathe to check the clearance over the centre section
and a 10 thou feeler fits in there quite nicely. |
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The jib strip was next and I made this from a piece of
1.1/4" diameter cast iron bar, milling it down to form a flat bar 3/4" wide
by 1/2" high. I set up my angle table to exactly 30o by clocking out on
an angle gauge. Next, a fence was clamped to the top, clocked square and
the work fixed to the fence using a pair of engineer's clamps. The work
needed to be on and off the fixture a number of times until a nice, sliding
fit was obtained and this seemed the quickest and easiest way to mount the
work. |
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The jib strip was faced to length, then a pair of recessed
holed were drilled to take M5 cap screws and the jib strip lightly clamped
the underside of the table. The centre of the five jib-adjusing grub screws
was replaced with a long caphead screw to act as table lock. Also drilled
and tapped were the two holes for the leadscrew block and the holes for
the bedway cover. And, finally, a picture of the new table ready to carry
some tools. It takes less than two minutes to undo this one and replace
the original cross-slide so I expect to be swapping between the two on a
regular basis. |
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Home-made Keyway Broach |
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I've just spent ages trying to purchase a
1/8" keyway broach but could only find sets from DuMont or Steelman which
require an extension to the overdraft or some single items from Australia
which were attractive until the carriage charge was noticed. After getting
back on my chair, I decided to try and make my own broach. First, the maths.
I need to be able to cut the keyway to about 0.064" deep and would like
to plane off one thou per tooth. Any more would probably require a press
tool of some description and I only have my drilling machine available.
Assuming three passes, I need about twenty teeth on the broach and would
like to complete a pass in about four inches. I will use a 4mm carbide slot
drill to cut the teeth in a length of 1/2" x 3/16" ground flat stock. I
don't have 1/2" x 1/8" GFS and I'm not about to buy a piece in case it doesn't
work. First job was to saw off a 7.1/2" length of GFS, load it to the mill
table on some sacrificial packing and clock it true to the table. Then the
cutter was offered up to the edge of the workpiece until touch-on and then
moved in a further three millimeters and locked. |
| A suitable starting point was chosen about
half an inch along the bar and the table locked and the first plunge cut
made to create the front form of the first tooth. The table was then wound
along six millimeters and the next hole plunged through. This was repeated
until I had twenty one holes. Next, I had to relieve the back of the teeth
leaving just the tiniest of flats showing on the tip. I started by repositioning
the cutter to 2.5mm in from the face and 1mm nearer the starting end and
then plunge-cut the back of the teeth, moving 6mm along each time. Then
I set up my tiny angle plate with the work rest set at ten degrees. The
work was clamped to the faceplate with the edge of a tooth in line with
the end of the faceplate and a crosscut taken with the 4mm cutter. Then
the work was moved to the next tooth position and the process repeated.
The last operation on this edge was to relieve the leading and trailing
edges by about five thou to prevent any form of binding after which the
broach was removed from the vice. |
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Now it was time to reduce the thickness of the teeth
to 1/8" and for this I mounted the work directly to the table, using the
clamping bolts as a fence. I needed to move the work along after milling
the first section because my total travel in the x-axis is only 75mm. Three
passes each side at ten thou per pass saw the teeth reduced to the correct
size. The last bit of milling was the front-to-back size of the broach.
I needed about twenty thou difference between the first tooth and the last
tooth and this was set up on parallels using feeler gauges to tip the workpiece.
I'm aiming to get the major size to about 3/8". Much bigger and the guide
bush will be practically cut in half but if I go too small there is more
chance of distortion during hardening. Actual size is unimportant as I will
make the guide bush and shims to suit. |
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I have also drilled a hole in the end because I want to
hang the broach vertically whilst heating and also when plunging into the
clean engine oil, again to reduce the risk of distortion. Before heating,
I cleaned the whole thing up with slipstones, tied on the hanging wire and
then degreased it. Then it was time to harden. First, I took the broach
gently up to dull red and held it there to soak for a minute or two before
carrying on up to cherry. Then it was a straight vertical plunge into the
oil, keeping the thing moving gently for a few minutes while it cooled properly.
At this point it was glass-hard and I took care not to drop it! It was gently
stoned down the sides and back until bright all the way along and then I
tempered to about mid-straw for approx 60RC. I could have done it more accurately
(about 200° C) in the kitchen oven but senior management may well have objected. |
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All I need now is a guide bush and shims to fit Britannia's
driving and coupled wheels and I'm ready to cut some keyways but I will
cover this as an entry to the diary in a few weeks time. I have, however,
made a collar from one of my sash weights and used this to test the broach
and am happy to say it works a treat. And measuring the depth of this one
allows me to correctly calculate the final shim thickness required for the
wheels. And one other tip - if you use a plastic bottle like I did, stand
it in another container. When I plunged the broach into the oil, I forgot
to allow for the expansion of the oil due to heating and it promptly overflowed
all over the bench. Then, to cap it all, I must have hit the bottom of the
bottle and the heat in the broach was still enough to melt a small hole
in the bottom so I now had leaks at both ends. I must have had a brain-fart
when I set that up. |
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Combined Beam Compass & Drill Jig |
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for Britannia accurately placed, one needs to know the exact distance between
centres of each of the axles so have I made a combination beam compass and
drill jig to help keep things accurate. It's not the correct term but is
sometimes called a trammel. The two arms are made from 25mm x 3mm flat bar
one of which has had a 4mm slot milled into it and the other has three M4
x 0.8 holes tapped into it. I have set bushes into the adjustable arms with
1/8" reamed holes in them. The bushes are shouldered and on opposite sides
so that the device always sits level on a surface. I have also made a pair
of trammel points from 1/8" silver steel with a sixty degree inclusive angle
to suit standard centre drills and have filed a notch on the centre-line
at each end to aid alignment. The first use will be to set the trammel points
across the leading and driving axles, lock the beam screws and transfer
the holes to the front side rods using a 1/8" drill. |
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Next item... |
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Fitting a DRO to the mill |
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There are plenty of references across the
various forums concerning fitting DROs to lathes and milling machines but
the information tends to be a bit scattered and piecemeal so I have jotted
these notes down covering the start-to-finish process of puchasing and fitting
a 2-axis DRO with glass scales to a small milling machine. My own milling
machine is an SP2217-III from SPG Tools but it is physically identical to
the Warco WM-16, the Amadeal AMA25LV and the Chester 20V and all these machines
have a 700mm x 180mm table. The first thing one needs to do is decide whether
one wants a 2-axis or 3-axis measuring system and source the product accordingly.
I only want 2-axis because my machine already has a small DRO on the quill,
and this will suffice, so it is left to the reader to devise how they may
fit the third axis if required. The next important thing to know is the
size of the scale to use on each axis and a scale slightly longer than the
overall travel of the table needs to be chosen. However, there is no point
in choosing a scale that is much larger than the table travel because such
a scale will probably overlap the ends of the table and be prone to accidental
damage. Another thing that needs to be taken into account is that the scales
come in various sizes in 50mm increments and the overall length of the glass
scales is 140mm longer than the travel length. |
| In my case, the longitudinal travel (X-axis)
of the table is 485mm and, therefore, a scale length of 500mm was chosen
while the cross traverse (Y-axis) is 175mm and a 200mm scale was chosen.
Remember, however, that the physical length of the scales are 640mm and
340mm respectively but it is 500mm and 200mm scales that one is ordering.
There are many suppliers listed on a certain auction site and the price
for a full kit of parts is about £ 180 delivered to the UK and one has to
let the seller know what size scales one requires. I have issues with this
auction site (my own personal hang-up) so I bought the self-same thing from
one of these companies through Amazon and paid £ 192 for mine. As soon as
I placed the order, I used the Amazon email service to contact the seller
and advised them that I required scales of 500mm and 200mm and a reply was
received next day confirming that these sizes would be dispatched. Just
prior to delivery, I was contacted by the carrier with a request for a payment
of £ 19.00 for the VAT that was due. All the sellers on both Amazon and
the auction site state that VAT or duty may be payable on the goods as they
originate outside the EU so was not unexpected. The order was received seven
days after being placed and was immediately unpacked and checked for completeness,
arriving as two separate packages. The first package contained the display
unit and this is what was in the box. |
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The second package contained the scales with
their read-heads. Be aware that they come with a small transit locking screw
holding the read-head firm on the scale and which needs to be removed before
attempting to move the read-head. Everything appeared to be in order although
the instruction manual appears to be one of the worst translated documents
I have ever seen and will probably be discarded. Common sense and an internet
search will sort out most things rather that trying to decipher this gibberish.
Containg my impatience to hook it all up and conduct a test, I sorted out
the brackets and mounted the display unit in position to the right of the
machine and then went off to find a spare computer lead to apply power because
the one supplied was the European format. It all assembled easily although
I have placed a couple of fibre washers between the wall bracket and the
arm to fill the space and allow for easier adjustment of the display unit.
After this, I removed the transit screws from the scales and plugged them
in to their respective ports on the rear of the display unit which was then
turned on. The unit automatically set both scales to zero and I slid the
read-heads along both scales to check that they were working properly, also
changing from metric to imperial units to check this function and all was
fine. A word of caution. Don't be tempted to slide the read-heads up and
down at high speed whilst connected and turned on. I don't know the reason
why but have been advised that it is easy to damage the electronics if overspeeding
occurs. These things are too expensive to find out if that is just a myth
or not so I treated them with respect. |
| After offering up the scales to see how best
to fit them, I then marked up their respective limits and centres of travel
because the scales are not symetrical. I also centered the table and saddle,
making loads of marks with a felt-tipped pen, and then removed the table
and saddle as a single unit from the machine. I had decided that it would
be too much hassle trying to drill and tap all the fixing holes with everything
in situ. This involved removing all the paraphernalia from the front of
the table, the jib strip with its front adjusting screw, the rubber bedway
cover at the back and the Y-axis leadscrew and handle. Once these were removed,
the saddle was slid as far forward as possible and the two screws that hold
the leadscrew nut were loosened and the nut allowed to fall down so that
the saddle would come off the knee completely. I chose to fit the Y-axis
first as I thought that would be the most awkward and the first job was
to mark out, drill and tap two M5 holes in the knee to allow the scale to
be affixed. These were done freehand using a 3.0mm bit in a pistol drill
to act as pilot followed by a 4.2 drill, taking care to keep things as square
as possible and not too much force. Then I tapped them M5 freehand with
a spiral-pointed tap because they are less likely to break than any other
type and because they self-align as well. |
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I also made a couple of spacer bushes from some 1/2"
brass but they needed dressing by hand at one end because of the shape of
the casting. I suppose I could have spot-faced the M5 holes but I couldn't
be bothered to gring a drill up for it. Next I had to make a bracket to
couple the read-head to the saddle and a hunt through the scrap box produced
a door-mounting coat hanger and this was promptly modified to suit. The
table and sadlle were then upended on a workbench and the saddle marked
out from the bracket and then drilled and tapped M5. |
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Tapping was proving to be a bit problematic because of
access but eventually I managed it by using a small drill chuck. I didn't
want to separate the table and saddle, too much work. After offering everything
up to check that it would all work, it was time to fit the X-axis and I
have fitted it to the rear of the table even though I have lost about 25mm
of travel. I feel this is less important than losing the dead-stop adjusters
and the slideway locks. Even the embedded rule on the front will be useful
and mounting the glass scale on the front would have meant that all these
facilities would be made redundant. This time the scale and read-head will
be mounted with M4 screws and I was able to use the mill to drill the holes. |
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Unfortunately, I got a bit carried away and forgot to
take pictures of the next couple of stages but basically everything was
centered and holes were spotted through, drilled with the mill and tapped
by hand. Finally, the mill saddle and knee were thoroughly cleaned and given
a film of hydraulic oil prior to reassembly. The only awkward part is getting
the leadscrew nut aligned before locking into place but even this was not
too much effort. Then the scales and read-heads were fixed to the machine
and carefully aligned, and the leads taken to the DRO. The pictures should
be self-explanatory. |
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Vertical Slide for the Lathe |
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I've been chewing over how best to finish the bores of
my cylinders based on the limited equipment I have. The usual way that this
is done is to mount them on a vertical slide on the lathe and use a between-centres
boring bar. A good example is the Myfords vertical slide which bolts directly
to the cross-slide giving that required third axis adjustment. However,
I don't have one, and it looks like it would be awkward to mount one anyway.
To help visualise the space and to see what I could come up with, I started
to strip the compound slide off of the lathe and that's when I realised
I did have a vertical slide, I was just looking in the wrong place for it! |
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I was holding it, all I needed was find a way to mount
it vertically on the cross-slide. None of my angle plates were any good
for the task so I cast around for something to use and eventually converted
a lump of 100mm x 50mm steel box section into a mounting box. The walls
are a bit thin but, by retaining the box section, the overall lump is quite
sturdy and when the compound slide was mounted to it, the whole setup was
quite rigid. I've made it slightly overhanging so that I can use the full
travel of the slide but the fixed part of the slide sits on the cross-slide
to enhance rigidity. And there I have my vertical slide! It can be mounted
as shown or swung to face the chuck and still retain the full travel but
can also be mounted at any angle with limited travel. |
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At some point in the future, I will make or buy a tee-slotted
table to mount on the slide but, for now, I have made a mounting plate which
bolts to the top of the slide. This is needed because the cylinder blocks
are bigger than the top mounting face of the slide and there would be no
means of securing the cylinder to it. Because I wasn't sure whether I would
be able to get the requisite adjustment, I have made the plate with the
clamping bolt holes offset from the centre-line so that I can turn it up
the other way if neccessary. And so it proved, the first way up I chose
fouled the saddle so the plate was reversed. Two of the photos show me checking
to make sure I can machine both bores without having to unbolt the cylinder. |
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Once I knew that this part would work, I then made a clamping
arrangement to hold it all firm. Although this all looks a bit Heath-Robinson
the important thing is that it has cost me nothing, all the bits of plate
and bar are from the scrap box and the clamp bolts are from the mill clamping
set. Now it's just a case of swinging it round, clocking each cylinder true
in all planes and machining the bores. But before I do any of that, I need
to make a between-centres boring bar first. |
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Between-centres Boring Bar |
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It seems easy enough to be able to load locomotive
cylinders (or anything with a long bore) to a four-jaw chuck or a face plate
and machine the bores using a boring bar in the lathe tool post. The problem
that I see with this method is it can introduce a taper to the bore of the
cylinder because of misalignment of the headstock or twisting of the bedway
and the only way to ensure a parallel bore is to use a reamer or similar
tool in the tailstock to size the bore, quite an expensive solution in the
larger sizes and still no guarantee of a parallel bore if the reamer is
out of line and cuts at the back. Another problem is that the valve bore
is way off the centre of mass of the casting and swinging this lump around
in a four-jaw chuck would have the lathe oscillating like a rocking chair.
It could be mounted on a large faceplate with a balancing weight but, since
I don't have one, that option is not open to me. Cylinder bores could be
machined successfully using a boring head in a vertical mill but it seems
that the majority of our hobby-sized machines, my own included, do not have
enough travel in the quill to complete the operation. Winding the table
up and down (z-axis) on a turret mill, where the milling head remains static
and the knee moves, would work well enough but on our smaller hobby mills
adjustment is often made by winding the head up and down the column and
this introduces it's own set of problems. In fact, it is impossible in round-column
mills to stop side-to-side movement and even dovetailed vertical columns
need to be quite closely adjusted on the gib strips to prevent any wander. |
| When it comes to parallel bores, between-centres
boring in the lathe cannot be beaten. In fact, if you think about it, it
is impossible to introduce a taper to the bore, other than for tool wear
in a single pass. The reason for this is because it is a single-point cutter
and the tip of the cutting tool is following a fixed circular path which
will not deviate (unless the operator changes something, such as tightening
the tailstock centre during the cut which may cause the bar to move sideways).
The only inaccuracy that can occur is in the alignment of the bore or size
of the bore, both of which are the responsibility of the operator during
initial setup. However, a parallel bore is guaranteed! It is called between-centres
boring but, in fact, the boring bar doesn't actually need to be between
centres. The only requirement is that both ends of the tool need to be supported
to ensure that there is no lateral movement. The advantage of using the
bar between centres is repeatability because, once the size is set, it can
then be removed from the machine and the next workpiece set up. Then the
boring bar can be reloaded and machining of the next item continue. It is
usual, therefore, to use a centre in the headstock and drive the bar using
a driving dog fixed to the bar and driven by a catch-plate. However, to
ensure good repeatability, it is normally neccessary to lock the tailstock
in place and adjust the pressure to the same setting each time. |
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If there is only one workpiece that needs
machining, then it is possible to hold the driven end directly in a three-jaw
chuck and with a live centre in the tailstock supporting the other end.
It doesn't even need to be running perfectly true at either end because
this is not what controls the diameter of the cut, it just needs to be held
rigid so that the tip of the cutter rotates around a fixed circle in space.
All adjustment of size is made by varying the height of the tool tip above
the centreline of the boring bar. Measuring the bore, however, is a different
matter and this is where being able to remove the boring bar and return
it accurately pays off. If the bar is designed well enough, then it shouldn't
need to be removed from the machine as it would be possible to use digital
or vernier calipers to measure one end of the bore. There is no need to
measure both ends because the bore WILL be parallel. However, if greater
accuracy is required then removal of the boring bar would be an asset so
that a bore gauge or plug gauge could be used instead. This first boring
bar that I have made is designed to finish the valve bore at 1.1/4" diameter
and is made from 25mm diameter mild steel and is a little longer than twice
the length of the cylinder. The tailstock end has been centre-drilled with
a No3 Slocombe and I intend to hold the bar in the 3-jaw chuck so have turned
a shoulder to rest against the chuck jaws. The cutter is an old No.3 centre
drill suitably ground and can be adjusted to produce a bore in the range
1.1/16" to about 1.1/2". Adjustment is with an M6 grub screw beneath the
cutter and side-locking is provided by an M5 grub screw. |
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Modifying a pair of Drill Press Vices |
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Having a need to hold some long flat bar on the mill,
I purchased a pair of drill press vices from Toolstation for the princely
sum of £ 12.90 each. They are pretty rough and ready, definitely not square
or level but they are made of cast iron so I decided to re-machine them
as a matched pair for general purpose milling jobs. I first spent ten minutes
or so on each one flatting the bases on some wet and dry on my surface table
and then dismantled them to leave the main casting. The jaw facings that
have been provided are just strips of some unknown gash material as are
the sliding jaw catch plates. These are going straight in the bin, along
with the screws. |
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I trued them up as best I could on the mill and machined
the slideways first, the difference in heights being seen by the size of
the chips on each one. Then I put the large angle plate up and milled for
a clean-up on the two sides followed by squaring up and milling the front
and back. This gives me the option of aligning the vices using a square
or butting up to my tee-slot packers if I don't need super accuracy. In
hindsight, it would have been smart to do this set of operations first.
While I had the angle plate set up, I also drilled and tapped an M5 hole
in each end of the fixed jaw section to allow work-stops to be bolted on
at either side. |
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Next, I trued each vice body in turn and milled the fixed-jaw
face for a complete clean-up and also made the lower step where the jaws
sit exactly the same height as the slideway. The picture shows just how
rough the original machining is! I was also going to give the insides of
the slideways a quick lick to square them up but I didn't have enough travel
to do them in this setup. In the end, I didn't bother, it's the least important
part of the whole job.Once the machining of the upper surfaces was complete,
I then machined the underside of the slideway. This needs to be dead parallel
to the upper surface of the slideway so that the jaw catchplate rides smoothly
along the underside while the sliding jaw moves along the bedway without
jamming. The more accurate this part is, the less jaw lift there will be
during tightening. |
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Now it was time to machine the sliding jaw
castings. To start, I bolted the existing jaw faces to my small angle plate
and machined the top to get them square to the jaw faces. These were then
clamped to the mill table and the two sliding surfaces machined followed
by re-positioning the clamping arrangement and milling the catchplate mounting
to size. I have left these a couple of thou proud of the size of the vice
body as mentioned above and will lap these down later to suit each vice.The
jaw-mounting faces were the last to be machined, the castings being mounted
in a small vice and skimmed to clean up. Then it was time to deburr all
round and give each of the machined faces a bit of a rub on some wet and
dry before offering each jaw to the main casting and checking for a nice
sliding fit. |
| It was at this point that it became obvious that the clamping-screw
hole in the sliding jaw was about forty thou lower than before and would
need bushing and each jaw was mounted back on the mill, the hole clocked
out and then the table moved to the offset position. A 5/8" dia slot drill
was then plunged down to the original depth. Meanwhile, on the lathe, a
pair of brass bushes were made from 5/8" dia bar, drilled 3/8" and parted
off. These were then loctited into the sliding jaws and left to set, followed
by drilling through the existing retaining screw holes and tapping M5. The
ends of the clamping screws were also in poor order so I cut off the front
section completely and then remachined them with flat ends and the retaining
undercut in the correct place. |
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Finally, a length of 3/4" x 3/16" ground flat stock was
cut up to provide two sets of hard jaws and two underside catchplates. The
holes in the jaws have the same side-to-side spacing as before but had to
be compensated for in the vertical plane to allow for the material removed
during milling and are held in place with M5 countersunk screws. To see
how much jaw lift I had, I nipped up a thin parallel in each vice in turn,
set a clock on the moving jaw and then tightened up fully. Originally the
deflection was in the region of three to five thou on each but after a few
sessions back and forth on the surface plate, I've got that down to about
a thou. On one, I went a tad too far and the jaw locked up but a polish
of the slideway underside freed it off. The final picture shows them being
used as a matched pair for the first time. |
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Power Feed for the Milling Machine |
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| After sitting at the end of the mill winding
the handle for a very long time facing up a 12" length of black, flat steel
I decided that a table feed was an essential extra. Although there are feed
boxes available for my type of mill, they are around £300 each and as rare
as hen's teeth and, unless I'm missing the obvious, don't have automatic
disengagement. After spending a couple of days trawling the internet and
watching endless youtube videos, I decided to make my own based around a
windscreen wiper motor. As made, this project will work directly with a
Warco WM-16, Chester 20V, Amadeal AMA25LV and SPG SP2217-III which all use
the same 700mm x 180mm table, and is easily adaptable to mills of other
sizes. Total cost of bought-in parts was under £30, everything else came
from the scrap box. To make a useful power feed five things are needed;
a motor, a way to mount it, a power supply, some sort of speed control and
a means to engage and disengage the drive. The first item on the list was
purchased from the local car breakers and cost £8. Although it doesn't seem
to matter what vehicle it comes from, front wiper motors are larger than
rear wiper motors, probably because they drive two blades. I'm told that
mine came from an Audi A6. |
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On getting it back to the workshop, I hooked
it up to my battery charger and tested it in both directions by swapping
the polarity: it worked fine and the current draw was 2A under no-load conditions.
This will probably rise to somewhere between six and ten amps when driving
the table, especially if the table locks are lightly nipped up, and a power
supply will be chosen or built once this figure is known. Meanwhile, a car
battery and ammeter will suffice to get started. The next thing to buy or
make is a pulse width modulator (PWM) whose job it is to act like a dimmer
switch and slow down the feed rate. This is just a simple device which generates
a square-wave signal with adjustable mark-space ratio and applies this to
one or more power transistors that provide power to the motor. These are
easily made using the long-standing NE555 timer chip but I found some ready-built
ones on Amazon for £2.83 with free postage so two were ordered. They are
not worth building at this price! |
| Before designing the motor mounting, I had
to choose what sort of clutch arrangement I wanted and decided to use a
sliding drive-dog layout that could be automatically disengaged by the machine
using stops. The advantage of this is that if my attention gets diverted
for any reason while a cut is running, the stops will ensure there is no
disaster. After much internet research, and not finding exactly what I wanted,
I decided to design my own system using a sliding brass sleeve arrangement
that would work in both directions with a centre-off position. The framework
for the motor and clutch would be mounted at the left-hand end of the table
and the operating controls at the right-hand end where I always stand to
wind the "X" axis handle. To get started, I removed the M8 nut and washer
holding the right-hand handle followed by the handle itself. This revealed
a key set into the shaft which was also removed and put away safely with
the other parts. The next item on the shaft is a thrust bearing and this
needs to be retained in place and a way found to adjust the pressure on
it. This function was previously undertaken by the Nylock nut on the end
of the shaft. |
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Measuring the shaft showed it to be 10mm dia
and a sleeve was designed to fit this and become both the bearing adjuster
and the drive mechanism for the table. It is a 40mm length of 1/2" hexagon
mild steel which is drilled and reamed 10mm to a depth of 20mm and the balance
drilled and tapped M8. The sleeve is screwed onto the shaft and adjusted
until it just locks the table, then backed off a tiny amount and a grub
screw fitted in the end of the sleeve acts as a locking device. The wiper
motor has a knurled and angled face with an M8 threaded section so this
was dissassembled and put in the lathe so that a 10mm dia spigot could be
machined on it. For this, the sleeve is 25mm long with a 10mm dia hole reamed
to a depth of 10mm and the rest tapped M8. There is also an 8mm wide undercut
on the O/D machined to the root of the hexagon and the reason for this will
become obvious later. The grub screw in the end is still needed to ensure
that the sleeve doesn't unscrew itself from the shaft when going in reverse. |
| The motor mounting was now started and the
main requirement was to get the ends of the two shafts in line and about
half a millimeter apart, the idea being that a sliding collar can connect
the two. After working out the PCD for the motor mounting holes, a piece
of aluminium plate was sawn and then drilled to suit followed by the bolting
on of the motor. This assembly was then offered up to get some idea of spacings.
It obviously needed some way of being connected to the table and this meant
that some fixing holes had to be placed in the table end-plate. A piece
of 25mm x 3mm steel angle was chosen as the starting point and a 150mm length
was drilled with a pair of 5mm clearance bolt holes and a relief section
milled away to clear the leadscrew boss on the end-plate. The end-plate
itself, which is made of cast iron, was drilled and tapped with two M5 holes
in corresponding positions. |
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At this point, I decided to discard the first
motor mounting plate and, instead, made a frame from some more of the steel
angle. Hole positions for joining the pieces together were first calculated
and these were drilled M5 clearance or drilled and tapped M5. The end piece
also had a pair of M6 clearance holes drilled to mount the motor. Everything
was assembled and it was obvious that some adjustment in all three planes
was neccessary and most of the clearance holes were made into slots instead. |
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Now it became relatively easy to adjust everything and
get the two hexagons exactly in line. The only downside at the moment is
that the motor has to be mounted as shown in the next picture but I believe
there are other motors that are the opposite hand, which would place the
motor rearwards, and I may try and find one. Now I needed to make the hexagon
sleeve and a piece of 1" diameter brass was faced to 48mm length and then
set up vertically on the mill table. Using the bolt hole circle formulae
from the Zeus book, and allowing for the size of the drill, a series of
six holes were drilled through the block using a long-series 2.5mm drill.
These form the points of the hexagon. |
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The block was then returned to the lathe and the centre
was removed using a 1/2" drill that I reground to have a 90 degree point
angle. This was to ensure that the drill followed the centre of the workpiece
and didn't get deflected by the six corner holes. At the same time, a 1/4"
wide undercut was made in the bore 1/4" in from the front and to just below
root diameter. A piece of the hexagon bar was cut about 2" long and a 1/2"
dia spigot put on the front, the idea being to use this as a broach in the
vice. It worked - just - but wasn't very good and the hole was cleaned up
with files instead. The broach came in handy as a gauge, though. |
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Everything was now assembled, with the motor mount adjusted
until the hexagon sleeve slid smoothly along the drive and driven shafts
and the PWM was wired up to provide variable speed. As there was no mechanical
means of moving the sleeve at this stage, it was engaged by hand. Everything
worked as expected and I was able to control the feed from a dead stop to
the equivalent of a fast turn by hand. Making all the mechanical linkages
was straightforward and the only new holes on the milling machine have been
confined to the table endplates. The first items to be made were the main
actuating rod and the two brackets to hold it in place. This required a
hole at the top of each endplate, which I have tapped M5, two pieces of
the 25mm x 3mm steel angle cut to suit and a length of 6mm dia mild steel
rod. A spare brake-rod eye has also been modified and fitted to the end
of the actuating rod. |
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The next items I made were the operating lever and it's
support bracket, which has been bolted onto the right-hand table endplate
using a longer M6 Allen bolt in the existing hole. The bracket was another
piece of 25mm x 3mm angle and the lever is made from an offcut of 1/2" x
3/16" flat mild steel which was turned down at one end and threaded to allow
a plastic handle to be screwed on. It is fixed to the bracket with an M5
shouldered bolt and to the actuating rod eye with a clevis pin. To be able
to auto-stop the feed, I then had to make a new block to replace the one
on the front of the table. This was drilled to allow the actuating rod to
pass through, and acts as a centre support as well. I have milled an angle
on the top so that I can still use the table rule if required. A pair of
stop collars were also made and loaded onto the actuating rod. |
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To be able to move the driving sleeve from side to side,
a gear selector fork arrangemant was made using a piece of steel box section
which has a 4mm wall thickness. A pair of pivots were made on the lathe
from some 5/8" dia mild steel and these have had tongues milled onto the
top to fit the groove that I have now put in driving sleeve. This was then
bolted to a legth of 3/8" square mild steel which becomes the operating
lever at this end. A bracket was now made to create the anchor point for
this sub-assembly and was bolted to the front of the motor frame. |
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Then the operating lever was offered up and the approximate
centre point marked to create the pivot point, followed by drilling and
reaming 6mm. An M6 shoulder bolt was made and the whole lot was then assembled.
This left only the coupling piece from the main actuating rod to the operating
lever left to make and this was machined from another piece of 3/8" square
mild steel. The bottom was turned to create a shoulder bolt once more, since
this allows the operating lever to pivot, and the top was drilled 6mm dia
and a cross hole drilled and tapped in the end. This allows adjustment of
the relative positions of the two levers at final setup. |
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Although the electrics are still jury-rigged together
at the moment, the whole lot was now tested for function and it threw up
a small problem. In "neutral", for want of a better word, and with no power
to the motor, the lever mechanism work really well. Applying power and engaging
the feed also works as expected. The bugbear is in the disengagement of
the feed. Under load, it is quite difficult to return the lever to the central
position and it seems that the problem is in the amount of friction between
the sleeve and the driving hexagon because slight forward pressure on the
winding handle is enough to free it instantly. I have made the fit quite
loose, polished everything up and applied lashings of grease but it still
sticks so I will now look at reducing the contact area during engagement. |
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I have remade the bracket that supports the sliding sleeve
fork and moved the pivot point nearer to the sleeve. This has gained me
a 2:1 mechanical advantage and is a great improvement on the previous pivot
point which was actually a 20% mechanical disadvantage, the pivot point
being nearer the actuating rod than the sleeve. So far, it appears to be
working quite well and the feed disengages at the stop point each time.
However, a little more work is neccessary before I will feel fully confident
of it. Last night, I made some bushes on the lathe while leaving the mill
to clean the face of some black bar, about twenty minutes a pass so rather
boring (and tiring) to just sit there winding the handle. |
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I have used it quite a bit lately and thing are loosening
up nicely now. The feed disengages when a stop hits the centre support but
I'm going to need to put some sort of spring bias on the lever because it
jumps out of drive occasionally in one direction but the other way is fine
- for now. I have added the microswitches that control motor direction and
these function as expected. Moving the lever in the opposite direction reverses
the motor and pressing the button makes it go flat out. However, it's more
like a mobility scooter than a Porsche and I can wind it faster by hand.
Still, it works. I was wondering where I could get a power supply to replace
the battery charger and my Dremel power supply has been sitting practically
on the end of my nose the whole time. 13.8 volts smoothed and regulated,
and good for 5 amps which is more than I need. I thought this motor might
need more but it doesn't. The other thing of note is that this windscreen
wiper is a permanent magnet motor and is a great swarf attractor. So not
such a smart choice after all. And I needed to get a new 10k pot from Maplins
because this Chinese one on the speed controller gave up the ghost. |
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Large Fixed Steady |
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I now have my smokebox material and it's a rather large
lump of metal which needs a few machining ops done on it. I am, however,
a bit light on tooling and this presents a challenge. I need some support
at the tailstock end but a large pipe centre won't solve all the problems.
So I decided to have a go at making a decent-sized fixed steady for the
lathe using whatever was in the scrap box. A fixed steady is usually a sturdy
lump of cast iron but as long as one is not greedy with the cuts it doesn't
need to be particularly strong and rigid. Pretty much all the effort is
outwards from the radial forces but there is very little lateral force involved
so this can simplify the design. I made mine from an old car disc brake
and this is how I went about making it. There were no drawings involved
with this, winging it with back-of-a-fag-packet sketches as I went along.
The first job was to make the bedway clamp and for this a lump of 3" x 3/4"
flat mild steel was sawn off 4" long. After finishing the size to fit between
the leading arms of the saddle, I made the angled recess to locate on the
rear way. I set up expecting to mill out the clearance slot first with a
small end mill and follow this with a large 45-degree cutter. |
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However, the cutter was nowhere to be found so I had to
change over to the angle vice and use a standard endmill instead. This is
a 16mm one I bought for a quid at the Midlands show, so it's paid for itself
already. Because of the large overhang, I had to do this with twenty thou
cuts down in the leading direction and twenty thou cuts out in the trailing
direction. Size-wise, I tried to attain the same width as the tailstock
vee. After checking that it sat flat and square across the ways, I cleaned
it up a bit and also made the underside clamp from some black steel. So
that was the easy bit done. |
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Machining the disc needed some thought. There was no accuracy
required here but I needed the ability to hold the part and once separated
from the hub, this would be nigh on impossible without a faceplate. Holding
on the hub, I skimmed the O/D to clean up and took a couple of cuts down
the face, then turned it round and took a cleaning cut down the opposite
side. I'm running at about 100 RPM and using the power feed to keep a steady
cut. I also cleaned up the bore of the hub to facilitate holding later on
and, because I didn't fancy trepanning this, started to bore out to the
finish I/D using facing cuts rather than sliding cuts. But before I cut
right through, I needed to get some milling done while I could still hold
it. So it was over to the mill and set up the rotary table, allowing me
to mill some guide slots for the bearing supports, or fingers, which I will
make later. I started milling with a 12mm cutter but it rang like a bell
because of the large overhang so I changed to a 6mm cutter which allowed
faster speeds and a better finish. |
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I also spotted the various drilled holes and the splitting
lines before returning the workpiece to the lathe and separating the flange
from the hub with more facing cuts. When there was about twenty thou to
go, I saw a witness of the cut start to appear on the rear of the workpiece
so stopped the lathe and gently broke the flange away from the hub with
a hide mallet. The bore was cleaned up with files and the part then split.
Offering up to the lathe it appeared that the base of the ring needed to
be 7mm above the bed clamp and because I needed to make a piece of angle
to fix them together I made this 7mm thick to get the required lift. The
lower section sits on the angle and is bolted through with three M5 cap
screws. In the photo the top section is shown. |
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A quick rummage in the "bearings" drawer produced three
626 bearings which are 19mm x 6mm x 6mm and this determined the size of
the fingers, which were made from 3/4" x 1/2" black bar, cleaned up all
round and milled to be a snug fit in the 16mm slots. A 6mm cross-hole was
drilled and reamed and the slot cut away with a 6mm carbide endmill to take
the bearings. To create the adjusting slot in the fingers, I stitch-drilled
the full length of the slot by centre-drilling at 5mmm intervals and using
a 4.7mm drill to clear the material followed by 5.1mm. The only suitable
slot drills I have are 3/16" HSS and, because this material was a bit rough
and abrasive, it was kinder to the cutter. |
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The slots were finished at 5.2mm wide by 40mm long which
will give a reasonable range at these large diameters. Different fingers
can be made as and when required for other diameters. That left the rear
hinge and the front clamp to make. The hinge was made from 1" x 1/2" bar
with a 1/2" section milled away from each piece and a pivot hole through
the middle and the clamp was made from 1" x 1" x 1/8" angle, held together
with a nut and bolt when in use. Here is the beast bolted together and on
the lathe with the smokebox held rather precariously in the chuck and resting
in the steady. Im running at about 100rpm again but not taking any cuts,
just making sure it runs OK. |
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General Purpose Tapping Fixture |
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I've always been comfortable with freehand tapping but
after breaking a 12BA on the third hole, and with thirty three still to
go, I decided that it was time to make a tapping fixture. Nowadays, my hands
aren't steady enough to keep these delicate little taps perfectly upright
whilst twisting the wrench. Once again, all these parts were made from surplus
materials except the little Jacobs 5/32" chuck which I have a pair of and
will take taps with 4mm or 5/32" shanks. I wont describe this in detail
because it's very simple; a 3" square baseplate, a 5/8" diameter mild steel
column and a head from the same material as the base. The shaft is 1/4"
diameter mild steel with a Jacobs No. 0 taper turned on one end. The bearings
are roller bearings salvaged from an old printer 7/16" O/D x 1/4" I/D x
7/16" long and the handle is turned from a lump or Delrin, fixed to the
shaft with a 3/32" taper pin. The locking screw on the side is M8 nylon
and is only to hold the chuck up whilst loading a tap. The head height can
be adjusted to suit the workpiece and the alignment is done simply by lowering
the chuck jaws down to the hole in the baseplate. |
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| The workpiece doesn't have to sit on the little
table, either. Just swing the head round and use the base to rest on any
flat surface thus keeping the tap vertical. By holding the fixture in the
bench vice it can be used in the horizontal mode, and I found this the most
comfortable working position. Tapping the other thirty three holes was achieved
inside half an hour and no further breakages occurred. The fixture took
a few hours to make but was well worth the time spent. These small taps
ain't cheap! And, luckily, I was able to remove the broken tap from the
third hole in the workpiece without damage so not quite a disaster. |
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Hand-held Dimple-forming Tool |
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I've never been particularly happy with any
of the methods for producing a dimpled effect on loco and tender steps.
I have tried using a punch directly onto the underside of the tread with
a backing block of wood, and lightly punching onto brass shimstock to produce
an inlay for gluing or soldering into place. I wanted something simple that
was repeatable, easy to use, and didn't distort the tread. Most punch actions
make the tread curve in the direction of the punching action and any effort
to flatten the tread out again flattens the dimple pattern. The other problem
is that these all work better if one has three hands, the third hand supporting
the work. My solution was to convert a heavy-duty leather hole-punch into
an indenting tool. The first job was to remove the brass anvil, which just
punched out, and the rotating punch holder which was slightly more problematic.
Although I used my advanced butchery skills (junior hacksaw, hammer, cold
chisel, verbal encouragement etc) it would have been simpler to just drill
straight through the carrier with a 5/8" drill. It was made of one of those
horrible aluminium-zinc alloys and not worth trying to adapt. I also discarded
the indexing spring as I only require one tool location and would like some
fine adjustment of its rotary position. |
| The tool carrier was remade from mild steel
using the same dimensions as the original and a solid mild steel pin made
to mount it on. The carrier has a flat milled on it and a 6mm reamed hole
to locate the tool bit. The tool bit is from 5/16" diameter mild steel with
a 6mm back and the front tapered at ten degrees except for the point which
is forty-five degrees. The anvil mounting point was opened up to 6mm and
the anvil made from 5/16" mild steel. The M6 thread on the back is to hold
it firmly in position but allow easy replacement and the front has a 1/8"
diameter nose with a small indent formed with a No.1 centre drill. All the
parts were fitted together and checked for alignment, followed by a couple
of trial indents. This is a close-up of the tool. |
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I found that the tool bit had a tendency to rotate away
from it's positon so an M5 bolt was used to lock the position after alignment.
The hole on view at the back of the tool carrier allows the tool bit to
be punched out if it get's stuck. This final picture shows three different
sets of dimples. On the left is 18swg material and the dimples are not particularly
well-formed, the middle is 20swg brass and they are much crisper. On the
right is 8 thou brass shimstock and the inset shows the graph paper that
I used as a guide. It just needs a bit of care and attention to get a perfect
pattern. Trying to dimple 16swg material failed miserably but may just need
more acurate and harder tools. Now that the principle has been proven I
am going to try different types of anvil, and may use silver steel which
can be hardened for the tool bit. The other tool bits and anvils that I
am going to experiment with are for riveting. I think it should be possible
to squeeze copper rivets in sizes up to 1/16" and also the smaller brass
sizes using this tool. Although there is limited throat depth, such a tool
could still come in handy for things like the smokebox rivets (I hope). |
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Next item... |
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Quill Stop for the Mill |
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One of the things that this hobby mill is
missing is a deadstop for the quill. Industrial machines usually have these
on the front of the quill housing and come in very useful when repeat drilling
or milling to a set depth. Our hobby machines appear to rely on using the
simple DRO to get to a depth and it's very easy to make a mistake and go
too far, ruining the workpiece. I've now made a quill deadstop to help overcome
this problem. I dismantled the safety guard and interlocking switch the
very first day I got the mill so decided to make use of the guard mounting
holes. A pair of blocks were milled up from some 30mm x 12mm flat steel
bar and a counterbored hole put in each to take M5 cap screws. A 5mm hole
was also drilled to take the vertical rod. With the blocks screwed to the
machine, it left a gap of 55mm between them and the maximum travel on the
quill is a tad under 50mm. A pair of knurled rings were made from 7/8" dia
bar, drilled and tapped M5 and parted off at 4mm thick. A length of M5 allthread
was used to make the rod. |
| To connect to the quill, I would have prefered
to make a collar with connecting bar but couldn't find any suitable material.
Therefore, I replaced the flimsy, plastic block connecting the DRO tail
to the quill with a more substantial block of steel and used a length of
flat bar to connect this to the bottom of the stop-rod. I also had to make
a new quill-locking screw but, not having any 12mm hex material, made an
extension instead. This ensures I don't trap my fingers or skin my knuckles
when using (got the tee-shirt). It's a little "spongey" in use but, combined
with using the DRO, certainly speeds up jobs like multiple plunge-cuts.
This took a couple of hours to make but well worth the time. When a suitable
chunk of material appears, I will make a quill collar and dispense with
the current connecting bar. Because of the need to dismantle the safety
guard, I can't recommend that others copy this exactly but a more able mind
than mine may well find an alternative method of mounting the deadstop and
keeping the guard. |
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Milling Fixture |
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I needed to make a large quantity of thin strips and angles
from offcuts of sheet steel but edge-milling vertically in a vice was never
going to be a sensible option. I decided to invest a couple of hours in
making a simple fixture for holding strips of steel and milling the edges
true. It is only a simple clamping fixture but allows quick and easily repeatable
operations. There was a 240mm length of 40 x 8 black steel in the scrap
box and this became the body of the fixture. The edges were milled flat
and true to create a clocking face. A series of M5 holes were drilled and
tapped at 1" spacings along the length for the clamps and another series
half-way between them for the distance fingers. Clamps were made from 1/2"
x 3/16" ground flat stock with 5.1mm holes for the clamp screws and M5 tapped
holes for the packing screws, grub-screws in this instance. The distance
fingers are from 1/2" x 1/8" BMS with a 5.5mm slot milled for most of the
length. A pair of 11mm holes were drilled for fixing to the mill table.
These four strips of 45 thou steel have been finished at 3/16" wide and
are just under 7" long. |
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By adjusting the grub screws, any thickness of material
can be easily clamped without the need for additional packing. The fingers
can be adjusted with a vernier caliper before setting the jig on the table.
The fixture can also be used for drilling holes in strips of metal, or angles,
assuming spacings are correct for the job. Here, an end stop has been clamped
into place and the strips rested against it. I was also able to use the
jig at the same settings for the roof that the strips will fix to by raising
the jig on packing blocks. These are 1.2mm holes for 3/64" brass rivets.
The gutter strips on the roof section were drilled with this fixture also.
The main advantage of the fixture, however, is the ability to true up thin
strips using the side of the end mill rather than the end. The cutting forces
are pushing into the fixture rather than at right-angles to it. And the
multiple clamps when drilling prevent the thin sheet lifting up at drill
breakthrough and raising a large burr on the opposite side. A very simple
piece of kit that took a couple of hours to make but well worth the time
invested. |
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