It's back to the wheels again.
It took a while for the parts to appear but they did arrive at the end of September -
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...1000 tyres and 500 axles.
I was held up a bit by a bout of sciatica - a knock-on from carrying a heavy portable sound recorder around on my shoulder for a good few years. But I managed to get started on trying to set up a method for batch production. My previous methods were very much on a one-off basis per axle, taking several minutes to complete the axle with a lot of changing around on the Cowells during the job. With the prospect of making hundreds of axles I started investigating ways of doing things in batches and also on an easier setup than using a lathe,
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The tools developed so far are, from left to right, a holder for pressing axles into wheel centres. next right is the small brass insert to use in the axle press and above it is a piece to set up the press accurately. The next part along is a holder for the wheel when the centre is being reamed for the axle. Next right is a holder for ten wheels to assist putting the resin centres in the tyres and applying the cyanoacrylate. The three holders were CNC machined. Next along is the 2mm hand reamer with an adjustable stop to ream the axle holes in the wheels. The short brass rods are used to locate and press the axles into the centres. Above them is a split chuck to hold a tyre in the lathe, or to hold a wheel by hand. The brass bar beside it is a pusher to eject wheels from the split chuck.
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Just a couple of closer shots of the axle press. In the upper picture, a steel 8BA screw pokes through into the bottom of the recess and this is adjusted to stop the axle at the correct depth to give the correct back-to-back with the wheels equi-distant from the axle centre. In the lower picture, the small brass insert is placed in the recess and this provides a stop for the centre boss of the wheel so that it doesn't move during the pressing action. I found that the resin was distorting longitudinally when pressing the axle home and that was often giving inaccurate results when it settled back at the end of the action.
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Gluing the centres into the tyres using the cyanoacrylate, using a very fine nozzle. This particular glue takes about thirty seconds to set with the steel tyre and resin, so there's plenty of time to adjust things if need be. I started by applying the glue to the centre then pushing it into the tyre but that could get a bit messy at times, so I opted to change to inserting the centres in the tyres and applying the glue to the joint - much cleaner and no stuck fingers.
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Lining up the plate used to hold the wheel for reaming. The tool in the drill chuck is a tightish fit in the recess and the plate bolts are tightened while being held in alighnment using the tool.
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Reaming the axle hole.
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Pressing the axle into the first wheel using the press plate.
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...and the second wheel going on to complete the assembly.
The press tool being used is a light bench drill that I got many years ago in the 1970s from a model engineering supplier in South Queensferry under the approaches to the Forth bridge. I had gone over for a set of castings for a light bench drill and he offered me this machine ready built. I think I remember that he asked £10 for it. I got a good Jacobs chuck to go with it and the motor driving it is an ancient BTH 1/4 horse which powered a washing machine owned by the parents of a good friend. They got the washing machine when they were married in the 1930s so it's over eighty years old.
The drill is square and there's no play on the quill so it makes quite a good light bench press.
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The results of the first trial production run using the tools. They were not quite so good as my earlier tests, with the TIRs spanning from 0.003" to 0.008" with the majority being around 0.006" TIR. This is still better than the TIR of wheels supplied by one of our commercial suppliers, but I would like to get down to the 0.002" - 0.003" range, to match our other supplier. Today I ran the process as a production run - i.e. fit and glue all the centres in the tyres, then ream all the axle holes, then press all the wheels on. I'll do a stagger through of the process and check at all stages with the DTI in the Cowells and see where the problems are happening. I have been relying on the resin printed centre hole for accuracy and I may have messed something up in all the other adjustments to outer diameters when adjusting for the new tyres.
Jim.