Rotary broaching on a budget!

Hello, I just thought I'd share a little experiment I've just done. I have made a crude rotary broach for use on my mill.

After making an 2 degree angled clamp fixture, and a crude 6 position indexer (an ordinary nut drilled out, with a set screw :D), I made a 4mm hexagon shape with a 2 degree relief angle from a piece of 10mm drill rod. The other end is center drilled 4.5mm.

A second piece of the bar is made and drilled off-center, and a 4mm steel dowel pressed in. This part goes into the chuck on my mill, and engages the crude broach, to make it wobble. :)

I did not harden the broach as it was only going to be used as a test in aluminium.

I guess the pictures will explain it better!

Cool. How about a video of it running?

Very interesting, but I don't quite understand how you used it. Can you post a photo, or video, of it setup for use?

I'd love to be able to do rotary broaching, but I don't think my little Grizzly lathe is rigid enough to handle it. My power-drawbar and auto-toolchanger products have several hexagonal holes, to fit over hexagonal gearbox shafts. I'm doing those now using standard (expensive!) broaches in my hydraulic press - a slow, tedious process. I'm actually planning to make a dedicated power broaching fixture using linear rails, a ballscrew, and a large stepper motor with gear reduction, eliminating the hydraulic press entirely. This would make both the broaching speed, and distance, programmable, and make the whole process both easier and much faster.

Regards,
Ray L.

I've closed up my shop for tonight, and am already in my PJ's and slippers! :p

But here is where I stole the idea from. He explains it a lot better than I did!
Rotary broaching on the mill - mikesworkshop

Clever! I'll have to add this to the list of tools to make.
Jake

That's an interesting approach. Any idea how accurate the resulting hole is, in terms of distance across the flats? Does it basically closely match the broach dimensions?

Regards,
Ray L.

Yes it matches the broach size.
If anything you'll want to make it slightly oversize by about 0.05mm, so that the allen wrench goes in easily, without getting stuck.

Looks simple enough to make. I have seen the commercial models, I can only imagine how much they cost.

Nice work there Memran. Not the commonest thing to see in the home machine shop.

Its kind of like wood broaching. I like it. Might not work too well in some hard materials, but I bet with good cutting fluid and a nice sharp cutting edge it did a wonder on aluminum. Is not really what I was expecting when I read the title, but I like it none the less.

Yes, definitely consider clearances when making bolt heads and wrenches. I've had that one bite more than once when I have forgotten.