Here is another wheel conversion job
The 3'6" wheels for Bamburgh need to look finer and thinner. It has been suggested that the Gibson 3'8" bogie wheels should be reduced to 3'6" so they have finer rims. The wheels also need to be thinned from 2mm to about 1.75mm Light railway wheels are much lighter than main line engines.
Because I need to thin the width down on these wheels it will not be possible to reduce the 3'8" tyres to 3'6" so the other option is to make the 3'6" tyres fit the 3'8" centres and the reason is I will loose the lip on the front of the wheels.
This is a picture of what I need to do to make the small tyres fit the larger centre and thin the tyre down to keep a lip at the front.
The shaded parts are to be removed.
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This job is being done using collets in the Myford lathe. I have fitted an ER25 Collet holder and check that it running correctly.
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As the tyre is tapered I need to check that it is running perpendicular using the dial gauge.
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Because when I tighten the collet holder it moves the tyre closer to the holder I need to make sure all the tyres are in the same place when I start to take out the inside. To do this I mark the collet holder an arrow. I put a paint dot on the cap for this sort of job when I bought it.
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Some of the Gibson tyres are very hard to remove from the centre so I destroyed the smaller centres and cut the larger tyres off.
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Tyre fitted in the Collet.
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I will be using a Boring bar to remove metal from the centre of the tyre.
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Now to cut where I want to I need to start or finish the cutter in the same place each time so that the recess for the tyres match each other so I need to know the backlash on the cross slide and the I already know its 3 thou but to check I use the dial indicator on the back of the boring bar.
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The pen written numbers are where I need to turn the handle to when going into the tyre and the 05 is how where I need finish when I am cutting the depth I need to cut although the arrow should be facing the camera as I am cutting the inside of the tyre.
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Tyre being cut.
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Once cut the inside need to be cleaned with 800grit emery paper held in forceps clamp and also the sharp corner needs softening so the centre cam be pushed in without damage.
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To do the front I have moved it to the Step Collet on the watchmakers lathe.
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The finished tyre on right
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When the insert is fitted it is slightly proud at the back and can be removed in the watchmakers lathe as well.
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and again the front needs to be taken back so that a etched front with crankpin position can be added.
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Left are original right have new centres.
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The last thing is to check the wheels concentricity from the centre hole, using a tapered axle with the tyre slotted on and the dial indicator to check the hole is still central. I did have a couple of failures which is the reason I cut the larger tyres rather than just push the centres out which were the failures.
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Next job is to make new shorter axles.
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