Cutting a Colchester gear spline
Colchester lathes have what I consider an awkward design feature, in that the change gears are not a round bore with a key, but an 8 tooth spline. In the factory they would be broached with a purpose made (all at once) broach, but in the home workshop that is tooling that we don't have.
John Stevenson (MBE) showed a technique once and here I have copied it to achieve that special spline.
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Love the mixing of imperial and metric - both are good in their own ways
@occasionalmachinist
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The reason is a bit dull in a way. My lathe is imperial and the mill is metric, so round bits usually are measured and referred to in inches, milled bits in metric (and thou's are a nice unit for measuring small amounts too!).
This turned out really well.
@occasionalmachinist
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It's an interesting technique, although I initially underestimated the difficulty of getting the bush spot on.
How did you index your broach --- from Spline to Spline ?
@occasionalmachinist
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Yes. I spoke about putting another slot in the bush at 135 degrees. That was for a small key (shown right at the end of the clip) to lock the bush to the previous slot that was cut. If the bush is accurate (and I had to repeat the process to get one accurate enough as the first was out slightly) it allows indexing around to get the 8 slots in position.