Entry posted by buffalo
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Earlier today I posted a short note on the Dapol Class 22 thread about my first attempt at converting the Dapol wheels to P4 using tyres from Gibson coach wheels. With the aid of a fan heater, I'd survived the cold garage for long enough to produce my first wheel.
Since then, I've made three more so it is probably worth explaining how I did it in greater detail. The next two photos show the various stages of the process from the original Dapol wheel at the left to the new P4 wheel at the right. The brass objects in the first photo are the two halves of a simple tyre press that I knocked up to help ensure the tyres seated correctly.
The wheels appear to be made of aluminium or aluminium alloy and are tightly pressed onto the axles. The latter are non-magnetic, so I assume they are made of stainless steel. The fit is almost, but not quite, tight enough to machine the wheels with the axle held in the chuck. I managed to do this first one this way but there was occasional slipping so, for the remaining wheels, I held the axle in a collet that was adapted to also hold the wheel. This was done by drilling a hole in the front of the brass collet and inserting a short piece of 1mm diameter silver steel rod. This then passed through a pair of the spokes to provide a dog drive to the wheel.
The first stage is to turn the wheel down so that it is a tight fit to the inner diameter of the Gibson tyre. This appears to be a nominal 13mm, though my measurements did vary, perhaps affected by temperature differences indoors and in the garage. In practice, I aimed for about 12.98mm for this cut and two of the four wheels needed a fraction more to get a good press fit.
The Gibson tyre has a small flange at the outside end of this surface to ensure the tyre sits squarely on the centre. The next step (third wheel from left) was to cut a 0.4x0.4mm step at the outer end of the previous cut to match the flange on the tyre.
Next, the wheel and tyre were cleaned and the tyre pressed on to the centre until the slot and flange were firmly seated. The brass press was intended to be used between the chuck and tailstock on the lathe but, in practice, it was just as easy to do this in the vice.
The photo above shows how a thin piece of metal extends beyond the new tyre at the back of the wheel. This is all that remains of the original inset part of the Dapol wheel in the area beneath the flange. The final machining operation is simply to face this off to give a clean back to the wheel in line with the flange of the new tyre.
Finally, the wheels were re-fitted to the bogie using the original Dapol muffs, brass bushes and plastic washers. additional brass spacer washers were added to take up sideplay.
With luck, I'll get the other four wheels done tomorrow. Before everything goes back together, the bogie sideframes will need trimming to clear the new wheels and, perhaps, to adjust their height. Others have commented on how the axle boxes are not in line with the axles.
Coincidentally, Geoff (sparky) has drawn my attention to a new development on the Ultrascale web site. Putting two and two together, it looks like they may be considering offering to do something similar with customers wheels. Either that or they've managed to get a supply of the standard Dapol wheels.
Nick
Update, 14:40, 20th Jan 2012:
All eight wheels done and after a quick test on the rollers D6331 assists with track laying at Camerton (though strangely devoid of bogie frames):
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