Tools, Jigs and other bits (page 1)
This section is for the various bits of tools and fixtures that I have made to help me build Britannia. There is nothing particularly clever or innovative in any of the following items and all will have been made before by someone else. If I have been directly influenced by someone elses design I have acknowledged that person but, just because something I have made looks like something that has been seen elsewhere, if I haven't seen it then I haven't copied it and cannot offer a credit for it. At the end of the day, there is nothing original to be found in day-to-day engineering, it's all been done before one way or another.
Simple Milling Table Backstop  
I made this very simple backstop arrangement for my micro-mill one afternoon after getting fed up of jury-rigged arrangements when doing any batch work. Nothing hard about it and not very pretty but it might be useful to anyone who doesn't want to drill and tap the side of their machine vice. It's made from a bit of 4mm thick mild steel box section and cleaned up to about 1" wide by an 1.1/2" high. The three slots were milled in with a 1/4" slot drill and the adjustable screw from an old 6mm bolt. It probably only needed one vertical slot but I chose two because it needed to be offset from centre and I can use it either side of the vice. Dead easy to adjust in all three planes.
Marking out a Pitch Circle Diameter  
Marking out a pitch circle diameter (PCD) can be a bit awkward at times and it is often easier to either use a template or use co-ordinate drilling on a DRO-equiped machine. However, some of us can't afford a DRO.... One of the essentials for marking out a PCD is having two edges at 90 degrees to each other as these are the two reference points needed to acurately find the centre of the circle. After this it is just a matter of following the formula and scribing the work accordingly. This is how I marked out my Britannia pump body which uses six of an eight-hole PCD. As can be seen, it's not the easiest of shapes to work around but there is always a way. Following the formula in the Zeus book I have a PCD of 1.250" so the heights of the holes above and below the centre line are 0 (zero), 0.183" (1.250 x 0.14615), 0.442" (1.250 x 0.35355) and 0.625 (half of the PCD). These are the only four dimensions I need.
I held the work in my milling vice as shown and, using my vernier height gauge, I first found the height of the top of the spigot. Since the O/D of this is 1.000" I lowered the height gauge by half of this to give me the centre of the PCD and then reset the scale to the nearest whole number. Now it was just a case of working plus or minus the worked out co-ordinates and using the height gauges facility for scribing. Next I turned the vice on end and did the procedure all over again, resetting the centre and marking out as before.
Now that I had marked out all my points, it was a simple matter to just centre-pop each position and then to spot-drill, drill and tap them. Because of the distance I used a long spotting drill, and the 2.3mm drill I held in a pin chuck. Tapping was done freeehand from the other side. Similar to above, I could have "blued" up the face of the work and set a scribing block with the various co-ordinates and marked them that way..
Home-made Keyway Broach  
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.
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.
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.
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.
Combined Beam Compass & Drill Jig  
In order to get the bushes in the side rods 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.
Radius Form Tool for the Lathe  
Chatting with a collegue I mentioned that I was writing up the bogie pressure pads for my loco and he asked how I had made the form tool with a decent enough finish to create the external radius. It's something those of us with a professional background learnt early on and take for granted but might not be that obvious to the less experienced modeller. So this is how I made the 5/16" radius (5/8" diameter) form tool. To create a complete quarter-circle, you need a piece of tool steel (or gauge plate if you want to harden your own) a little larger than your chosen radius, a grinding wheel from a dremmel-like set of tools, a short length of mild steel bar of your chosen diameter and a tub of grinding paste. First, I faced off the 5/8" dia bar and used it to mark the radius on the top of a blued-up piece of 3/8" square high speed steel. The other end was turned to 1/2" so that it would fit my drill chuck.
Then, just using the bench grider, I roughed out the lump of tool steel making sure there was plenty of clearance underneath. Next, I loaded my hobby grinding wheel in the lathe chuck and dressed it down to 5/8" diameter. Because you dont want grinding dust anywhere near your lathe bed, make sure you protect the bedway with an old towel or something, and don't forget to put your geartrain in neutral - you don't want your protective cover to end up wrapped around the leadscrew. To dress the grinding wheel, I set up a tool rest similar to what woodturners use to support the tool - don't try to do this freehand. Then the diamond dresser was rolled back and forth along the toolrest until a reasonable size was attained. Once made, I moved the grinding wheel to the pillar drill and set the machine on its highest speed, not really fast enough but it's what it is. It is much easier to work in the vertical plane than the horizontal.
A few minutes work here created a reasonable finish and form on the tool steel but it needs a final polish to make it just right. Now i loaded the 5/8" dia bar to the drill chuck and smeared a load of grinding paste over it. Now it was just a case of working the tool up and down the bar, topping up the paste when neccessary. Once finished, all it needs is a light dressing on the top with an oilstone and it's ready to use. This took me about fifteen minutes in total and will join my growing collection of form tools once the current job is finished. The pressure pads that I made have been described on the relevant page so wont be repeated here. I'm aware that most of you will have used this or a similar technique in the past to create your own radius tools but I hope someone out there found this useful.
Fitting a DRO to the mill  
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.
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.
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.
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.
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.
Vertical Slide for the Lathe  
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!
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.
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.
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.
Between-centres Boring Bar  
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.
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.