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Keyway Broach

If you want to cut sideways your HSS has to be very rigid. For small stuff like 3/16 I did in the video you cut full width. Cut, move 1/1000 or so and cut again. It may flex at 1/1000 so you move another 1/1000 and again and 3rd time it cuts. So on and so forth. Plenty of lube.

This thing has to be RIGID setup. The more rigid it is, the better. My boring bar in the video is too long - hence issues with cutting just 1/1000 - it flexed away. If it was shorter it would probably be quite OK with that cut.
 
YYCHobbyMachinist said:
I'd be using the mill if I had something bigger than a mini-mill. Can't picture using a drill press? How would you advance the tool to achieve the desired keyway depth?
Click to expand...

If you have a "boring tool head", they have a fine "sideways adjustment" that would make using a drill press a charm, otherwise you would be down to using a dial gauge & re-clamping after every cut.
 
There are two way vices available or a milling table for a drill press. Or boring head. Given it takes a lot of strokes I don't think re-clamping is an option unless you really have lots of time or figure out how to do it in just few seconds. Maybe also there could be a jig made for a drill press.
 
I think it's time to give up trying to use the lathe to broach and go a different route.

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Modified the blade profile to match @RobinHood suggested profile.

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Hardened the blade and ground a keen edge on her.

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Rigged up this RIDGID tool post/holder.

Things were going better until I realized the saddle was now lifting and twisting on the ways:oops:


EDIT - It just occurred to me, flipping the blade over and cut the keyway towards the out board side of the lathe should prevent the saddle from lifting. I'll try that.
 
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Good choice on making a solid tool post.

I would really shorten up your tool. Make it just long enough so that it passes through your part plus 100thou.

You could also try to use the tail stock to push the tool post from behind. It would stop the carriage from lifting. The push force would be in line with the tool, thus no lifting moment on the carriage. It is almost like using a mill quill...
 
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