Making and using a broach

Some advice please.

I want to make a gear change lever for my 1971 Triumph T100 motorcycle out of aluminium.

The gear change shaft is finely splined.

Therefore the hole in the lever will have to be similarly splined, but I don’t have a dividing head to make the splines.

So as this will be a one off I was thinking of obtaining another shaft and modifying it so it had a lead. I would then be using it as a broach to press the splines through the aluminium. The shaft is steel but not hardened and didn't intend to harden it when using it as a broach as the alloy isn't that hard.

Is this likely to work and if not what alternatives do I have?

Thanks

John H

Hi John

if you use old shaft i would put a decent point on then get a bit of scap ally bar in lathe drill a hole a bit smaller then loc

k lathe in backgear then use tailstock chuck to hold your shaft and push through and se how it turns out before using it on finnished peice first,Kev

Tried it years ago but not successfully. A broach needs to take fine cuts so it needs length using a dummy shaft means it has to remove all the material in under an inch and two things happened. A lead won't broach, it will act as a tapered punch.

One is it drags the material out instead of cutting and secondly it takes the path of least resistance and tips so you get a ragged seized up looking hole that's on the piss.

If it's a one off and not a production run look towards turning an existing lever into a splined bush and pressing this into your pattern one.

If you have access to a dividing head or rotary table I would think it would be quite easy to use a single point tool to Cut each spline one at a time.

Mike

I made a gear lever for a pre unit triumph box, out of dural as it was for use with rear-sets on a triton. what i did was to lightly press the lever onto the shaft and i could see where the serrations were starting to mark the dural, i then simply filed a groove at each mark with a three sided needle file. It worked perfectly when it was all assembled. Another idea suggested to me by my workshop lecturer in tech, if the serrations were worn away, to work out where you want the lever to sit and then fit a french key. A french key on a british bike, that cannot be right ?

This of any use?

**LINK**

Its about the same method I use to fit/press pinions in brass wheels, it works very well but you need a rigid set-up and the parts must be lined-up absolute centered, square and straight and stay that when you press it in, either by the set-up or by a pivot or bush that keeps it centered, otherwise it will find its own way. The profile is not formed but cut, I turn the edge of the pinion I want to press in to get a ring of sharp "cutters". For brass the steel need to be tempered at around 35Rc, if it is softer it will not work, perhaps you can use softer for aluminium but I doubt. Also you will need considereble force, the tailstock of my Myford will not hold on a diameter of around 5mm, the largest diameter I fitted by this method was (I guess, long time ago) 15mm and for that I used a 10ton press. Niko.

Edited By speelwerk on 08/01/2015 23:27:26

Edited By speelwerk on 08/01/2015 23:38:33

Maybe use the old shaft as a dividing device, perhaps at the back of the headstock - then single point the splines by racking the lathe carriage back and forth.

Or if that's not precise enough (because of small diameter) print out a sheet of paper with the divisions on it and attach to a large disk at the back of the headstock to do the dividing - just need a pointer to line up the divisions, and (maybe more tricky) some way to lock the spindle. Or use a gear with an appropriate number of teeth...

Some sort of improvised dividing system for the headstock would probably be handy for future use too...

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For a very convenient way of doing that ... go here

MichaelG.

As usual, John is right; the only way to go if I was continue with the aluminium lever would be to turn the existing lever into a splined bush to be inserted in the lever.

Because of how close the gearchange shaft is to the kick start shaft and where the clamp bolt is the aluminium lever idea is not going to work.

I will have to weld the splined boss of the existing lever to a fabricated steel lever.

Thanks for all the suggestions - they made me think a bit deeper about how to proceed.

John H