|Drawing 2 - Pony Frame and Pump
|1. Pony frame
|The next parts I made were the two arms of
the pony frame and the associated stretcher. Both of these items were very
easy to make but I am including all the parts I've made for completeness.
The pony frame arms are just an exercise in marking out followed by lots
of arm-ache and some swearing (or was it the other way round?). I started
with two plates of 3/16" black steel sawn to 11.1/8" x 3.7/16" and marked
out and drilled all the holes while the plates were still rectangular. Next
I marked out the profile and and then it was sawing, filing, sawing, filing,
sawing.....At least I managed to get the holes correct where they connect
to the mainframes. I don't know why I didn't use the CNC mill to profile
these at the time because it would have made light work of them. An ideal
job also for laser or waterjet.
|2. Pony frame stretcher
||The pony frame stretcher is four pieces of 1/4" x 1.1/4"
flat mild steel which I welded together and then milled to be a snug fit
between the two lots of frames, the width being set by clamping one of my
spacers close to the end of the mainframes. Then the fixing holes were marked
out and this time the holes are tapped 2BA so that bolts can be used to
pull the whole lot together. There is also a 3/8" reamed hole at the bottom
to take the pony truck pivot pin. The two cutaways at the front are to clear
the rear spring hangers on the mainframe.
|3. Pump Stretcher
||The pump stretcher is just a bit of 10 swg
mild steel plate and a couple of bits of 1/2" x 1/2" x 1/8" m.s angle. The
plate was marked out in the normal way and all the holes drilled, the only
awkward ones being the two 1" holes. The six pump mounting holes were done
using the co-ordinates from the Zeus book, a most useful reference book
in the workshop and a mine of information. I had a 1" blacksmiths drill
on a 1/2" shank but didn't fancy drilling this size from scratch so I used
a 24mm hole saw instead and used the 1" drill to open up to size. This was
done on a bit of 12mm MDF and I did make sure that the plate and MDF were
well clamped down on the table. I wasn't too worried about accuracy here
since the top hole is just clearance for some pipework and the lower hole
is for locating the pump body - I can machine the O/D of that to suit.
|My steel angle had a bit of a ropey finish
so I cleaned up one outer face on the belt linisher and marked out one of
the rivet holes on that face, making sure that, once assembled, the angle
would be about ten thou wider than the finished size. I also marked out,
drilled and tapped the three frame mounting holes on the other face of the
angle. After dropping a rivet into the one drilled hole and clamping similar
to how I did the top stretcher, the other three rivet holes were spotted
through and drilled with the rivet going in each time. After messing up
some riveting once before by getting the holes slightly out of position
and having to open them up I always follow this procedure of drill, rivet,
drill, rivet etc. Once the assembly was completed, it was clamped to an
angle plate and the outer edges were skimmed on the mill to clean the faces
and end up with a snug fit between the frames. I may leave the pump out
when I see how well the injectors work but the pump stretcher can stay,
though, as it helps to stiffen the frames.
|4. Drag Box
||The drag box came as two identical castings which are machined all over but, strangely, not bolted
together. These could just as easily be made from cast iron or mild steel billets which would be a lot
cheaper although a lot of pocket milling would be required. It acts as both a stretcher for the rear
of the pony frame and a pivot point for the drawbar to connect the tender. It also contains the cylinder
cock bell crank assembly fixed to a machined area on the lower part and with a drilled hole on the upper part.
The first thing I did was to clamp each casting to an angle plate, squaring up as previously shown, and milling
the four edges to final size.
||Then they were loaded to a milling vice and the top was flycut and, as can be seen,
my flycutter was smaller than the workpiece. It matters not because these surfaces have no function and cannot be
seen once built up. Having a cleaned-up surface makes marking out of the holes easier, though, so I felt it worth
doing. Also, the inside face of the boss of each casting was flycut to finished height and the area where the bell
crank assembly mounts to the lower casting was machined flat. After this, all the holes were marked out and then drilled
and tapped as appropriate. The drawpin holes I drilled 15/64" and will drop a 1/4" reamer through them, by hand, after
assembly to get them in line. I chose to make this assembly a little different to the drawing.
||I made the crank arm as per drawing but didn't bother to make the fancy pin and braze it to the crank arm.
The picture shows the simplified parts that I made and the pin, which is just a bit
of 3/16" unhardened silver steel, just pushes through the side of the casting, through the spacer and the crank arm and
into the bearing. It needs nothing to keep it in place because the whole assembly is trapped between the frames. I made
sure that the parts were a reasonably accurate fit between the pony frames and also made sure that they were square otherwise
they would probably put a twist into the frame when I bolted it all together. I also noted that the tapped holes in the
sides of the top half are at different positions to the lower half. It would have been easy to assume they were symetrical
and just mark out both halves the same.
|5. Pressure Brackets
||The two rear pressure brackets help connect the rear beam to the pony frame and also carry
the hemispherical pressure pads which sit in the sliding cups on the rear crossbar of the pony truck. I used gunmetal castings
but I think I would make these from mild steel bar another time. They didn't need much fettling and it was just a case of
milling them square and doing the holes.
||Although the picture shows all the holes drilled, I didn't mark out those for connecting
to the rear beam. After bolting the dragbox to the pony frame and the rear beam to the dragbox I spotted through the rear
beam (which will be made next) to the pressure brackets behind.
|6. Rear Beam
||The rear beam comprises the large full-width plate from
18 swg mild steel and the main beam from 10 swg mild steel. The main beam
has two rubbing plates for the tender buffers riveted to it, and the central
stand-off bracket which the drawbar passes through is bolted to it with
6BA bolts. Both plates were first marked out and cut to shape by hand, except
for the platform support cutouts which will be done later, and were then
co-ordinate drilled using the DRO on the vertical mill. I could have marked
out and free-drilled the holes with confidence but it was easier on the
||The drawing suggests marking off eight of the holes from
the pressure brackets but I have chosen to do it the other way round, spotting
through the beam to the pressure bracket. The central stand-off bracket
is a fairly rough gunmetal casting and a little thought went into the machining
sequence. I decided to first mill the top and bottom edges square to the
sides but left twenty thou up on finished size and then face the back to
the nominal size.
||To get it level, I set four screws into the
rear beam and adjusted them to the same height. This then went into the
bottom of the milling vice and the casting settled on top. There is no size
given on the drawing but scaling from the drawing, which is normally inadvisable,
worked out at about 125 thou. It wont matter as long as I remember to make
the drawbar to suit, not just to drawing. I could have made this bit in
the 4-jaw chuck but it's a bit quicker in the mill. Then it was back onto
the angle plate to finish the edges all round, a load of filing and sanding,
followed by marking out and drilling the 6BA clearance holes. Be aware that
the hole positions are different on the tender pivot block - 1.1/8"
apart instead of 1". I had to modify my tender front beam because I
didn't check this detail.
||It is essential that the holes for fixing to the pressure brackets are
drilled and tapped before riveting the rubbing plates on since they get
covered by these plates and tapping would be nigh on impossible after. The
photo shows the rubbing plates riveted on and the central stand-off bracket
about to be bolted on. Finally the two plates are fixed together with nineteen
10BA nuts and bolts
|7. Main Horns
||The main horns were supplied as gunmetal castings and
need machining all over, although there was not a lot of metal spare so
a little thought was needed to ensure a good cleanup. The important bit
is obviously the fit to the frames so I decided to try holding on the inside
edges. How I solved it was to use my self-centering 4-jaw chuck on the mill
which I first set up square to the table. By expanding the jaws, I was able
to get a good grip on the horns which allowed me to mill the tops and outer
edges of the flanges and the seating faces. These in the picture have been
finished but this is how I held them.
||Once I had a flat face and square edges, it was easy to
set up in a normal milling vice to machine the opposite side and drill the
holes. The trapezoidal edges were formed by using a sine bar and bolted
to an angle plate. The inner faces of the horns have yet to be machined.
There is only about twenty thou per side to come off and these may be milled
to size whilst bolted to the frames to ensure the axles are all parallel
to each other but I will need access to a larger machine for this. It was
at this point that the extra shaping was done on the frames to ensure a
snug fit for the horns. Here they are just held on with a couple of bolts
|I needed to think about milling the internal
bearing surfaces of the main horns and I considered it easier to make the
axle boxes to fit the horns rather than making the horns fit the axle boxes.
In an ideal world, I would plonk the mainframe assembly, complete with horns
bolted on, onto the bed of a Bridgeport, true it all up, load up a long-series
1" dia end mill and finish machine the whole thing in one visit. However,
using my little Cowells mill for something of this size is stretching the
envelope somewhat. I decided to try and use the precision milling vice to
grip the horns on the frame locating flanges but first I had to find a novel
way just to hold the vice because I ran out of y-axis travel if I mounted
it the usual way. Once I had worked out the best direction to work in, I
then loaded the first horn casting to the vice. They are all a good fit
to the frames and I would have no trouble with repeatability although to
help keep them square, I dropped a couple of large dia rivets through two
of the mounting holes to locate against the side of the vice. However, as
I tightened the vice the feel was wrong - too spongy - so I measured the
gap at the bottom of the horns, released the vice and measured again. I
was springing them closed by about seven or eight thou so this was no good.
I was also getting a slight lift from the moving jaw which was affecting
||I decided to treat the vice as a fixture and just lightly nip the jaws
up and then use clamps to hold the workpiece down. It's getting a bit busy
on here now, and it's going to take quite a while to machine the six horns.
I was able to clock off of the outer edges of the external flanges to find
the centre line and had to be quite accurate on this because, even though
they are symetrical, three of the horns are mirror-imaged (left and right
handed) but I can't reverse my fixture so any offset from the centre line
will be doubled once the horns are reassembled.
||Now it was just a case of taking multiple passes up one side, across the top and down the other side
until I had about twenty thou left to come out side to side. I used a 6mm carbide end mill for this as any of my smaller
diameter cutters have too short a flute length and I was taking about ten thou per pass. The top didn't need so much material
removed and was finished during one of the earlier passes. Before making the final cut on each, I re-checked my centre-line
position and calculated the offset either side. The finish size is 1.500", the cutter is 0.236" so the offset is 0.632" either
side of centre, not forgetting to allow for backlash. And to finish the job off the corners were filed out once all machining
was complete and the horns bolted back into the frames. I checked them with 1.1/2" worth of mild steel and they fit OK but they
can be eased to suit with some emery on a stick once the axle assemblies are made if neccessary
|8. Pump Body
|Although the drawing calls for the pump body to be made from a gunmetal casting, I decided to
machine mine from 2" diameter brass since I had some in stock. The first alteration I made here was the smaller diameter of
the pump body. The drawing calls for a 1" x 32 tpi thread on the end with a 15/16" relieved dia along to the 1" diameter locating
spigot. To me, this is a nonsense and I decided to make the diameter 24mm with a M24 x 1mm pitch thread on the end. I will also
change the plunger to 16mm and use a 4mm section O-ring. After facing my billet to length, I held on the last half inch using
soft jaws in my 3-jaw chuck and did all the maching in one visit, starting with centre- and drilling the bore, drilling the small
hole at the bottom, turning the two outside diameters, reaming the bore and finishing with screwcutting the thread. For this, I
used a standard screwcutting tool with a 1mm pitch insert. The advantage of using an insert is that as soon as you see the outside
diameter getting a light skim then you are close enough to size to stop cutting and you have a full-form thread. When I originally
made this part, I had the luxury of an Ainjest high-speed screwcutting attachment on a Colchester Triumph 2000 so there is no
discernable run-out point but if making it on my simple centre lathe today, I would just create a decent length of undercut and
run into that. The length of thread is unimportant as long as it is long enough to allow the nut to screw on fully.
||To form the back section, I held the part in a 3-jaw chuck
on the mill and machined the four faces to size. The suction
and delivery connections were made by holding the work in my normal milling
vice and drilling and tapping the first hole 3/8" x 32 tpi and then turning
the job over and doing the same again from the other side, bearing in mind
that the two holes are different depths. I also drilled the through-hole
at this point, being careful because I was breaking into the cross hole
that was drilled to depth while on the lathe. Final job
was to mark out and drill and tap the six mounting holes which are on a
PCD of 1.1/4". The drawing shows a distance of 7/16" between holes but this
is incorrect, the distance should be 0.442". When I made the pump stretcher,
I used the proper co-ordinates and have to do the same again here if I want
everything to fit!
|9. Pump Nut
||I made the pump nut, in one visit, from 1.1/4" diameter brass held in the 3-jaw chuck of the Colchester
Triumph and, once again, had the benefit of high-speed screwcutting. First, I drilled at 9/16" diameter to about 1" depth
and then bored it out to 0.635" to clear the plunger diameter of 0.629" (16mm). Next I bored it out to 23mm (the core size
of the thread) and finally created a 24mm diameter undercut, 3/16" long, at the bottom for the thread to run into. Using a
boring bar with a triangular tip meant I could do this all with the same tool. The "O" ring will sit in this undercut. Then
I screwcut the thread using a 1mm pitch insert and using the pump body as a gauge. Finally, the O/D was given a light skim to
clean up and the nut parted off. I haven't put the 6BA tapped holes in yet, they're only for locking the nut to the body.
||The plunger is just a bit of 16mm stainless steel with some simple machining applied to it. Here is a
picture of the pump assembled on its stretcher and fitted between the frames. The pump strap and eccentric will be made
after I have made the main axles. If I was making this assembly with the machines I have today, I think I would make
an M24 (or imperial equivalent, say 40 tpi) tap out of a bit of silver steel and make the nut first, tapping the thread.
Then I would make the body to suit the nut. This is because screwcutting upto a shoulder in a blind hole can be a bit daunting.
|10. Pump Eccentric
||With the pump eccentric my first instinct was to face, turn and form the groove as one operation followed
by loading to the four-jaw independant chuck and machining the bore and boss as a second operation. However, I felt that I
would likely damage the shoulders of the eccentric with the amount of work needed on the second op so I decided to do it in
three stages instead. Starting with a 1" long billet of 2" diameter mild steel, I faced the back to clean up and skimmed
the O/D to 1.7/8" diameter by 1/2" long, then turned it round and faced it to 7/8" overall length. This meant I could load
the billet to the four-jaw chuck and tighten it up firmly with little risk of damage.
||Next, I marked out the middle of the offset and centre-popped
it followed by loading to the four-jaw chuck and, since I didn't need a
high level of accuracy here, true-ing up with a hard centre in the tailstock.
Then it was a straight-forward matter to drill and bore the 3/4" diameter
hole and turn the boss to 1.1/4" diameter by 7/16" long. I don't have a
3/4" reamer so boring would have to do. It's locked to the centre axle with
a couple of grub screws, anyway, which will pull it square to the shaft.
The last job on the lathe was to hold the boss in the four-jaw chuck and
true up the outside before machining the bearing area of the eccentric.
For this I used a parting tool slightly modified with a notch ground out
of the middle. I did, however, play around with two saddle stops to control
the width as I didn't want the fit to be too sloppy. To finish, the eccentric
needs to have the two drilled and tapped holes in the boss, which I have
made M6 because I have grub screws that size. I decided to mount a piece
of 3/4" diameter bar in a vee-block and clamp it on the drill table.
|11. Next Item...