Internal keyway cutting

[RayW]

I would be interested to hear if any forum members have made their own broaches for cutting internal keyways, such as in the bore of a flywheel. I am looking, in particular at cutting a keyway with a taper of 1:100 to match the standard flywheel key taper.
I have read articles about making broaches from mild steel, then case hardening, but does anyone have experience of doing this or any tips on the shape of the cutting teeth?
I only have a couple of keyways to cut, one 3/32" wide, and the other 1/8" wide, so I am reluctant to pay out something like £60 for a couple of commercial broaches. I intend to cut the keyways on the lathe, effectively using it as a shaper. I have done this in the past using a parting-off type tool to cut a parallel keyway, but have never tried a tapered one.

[mklotz]

I wonder if it would be possible to tilt the flywheel in the chuck/faceplate by the appropriate amount and use the parallel keyway cutting technique.  If it's doable it may be easier than trying to manufacture a broach.

[Jasonb]

If you want to do them on the lathe then I would think taking out the topslide screw and moving the topslide with a lever would be the best bet then set topslid to your angle. The usual way of using the carrage won't work for tapered keyways. Alternative is to make a slotting tool, several designs about.

You don't need a broach as such just a HSS bit held in a boring bar with a vertical cutting edge and ground to the required width, I've done quite a few parallel ones that way but now have broaches and just make a tapered bush if needed.

[simplyloco]

I've cut many a parallel keyway on the lathe using a boring tool as Jason suggests: it is quite straightforward provided you can put the spindle in the lowest gear and it stays in position whilst cutting! Once the basic shape has been cut it is not difficult to file a taper to suit your key.
John

[Mcgyver]

I've made broaches, but for hex and square.....its enough work that I bought them for keyway cutting.  O1 worked well and I can't see why it wouldn't work for a keyway broach.  To make the tapered keyway, I use a standard broach and a shop made bushing with the groove cut at an angle.  I've also done them in the lathe and mill.....holding the part (solidly) at an angle in the mill might be a way to get there with minimal tooling