Group Project: Rotary Broach-- Building complete, all shipped out!

[GunsOfNavarone]

Ave's crazy version

 

[bill70j]

There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.

FWIW, I made that "Hemingway" broach. Their broach is pretty small, so I scaled up their drawings and made a tool capable of making much larger squares and hex's. I got permission from the Hemingway guys to share the drawings. Let me know if interested.

Also for the broach, I would suggest O-1, which you can harden with oxy-acetylene, then sharpen by grinding.

 

[GunsOfNavarone]

@bill70j ABSOLUTELY! Thank you!

 

[ErichKeane]

Shank diameter. a 3/4" boring bar holder could be used to hold it in an Aloris type tool mount. Or, half inch with a sleeve.

Where does material come from? I'm considering joining the project.

In the other two group projects everyone buys the materials for the parts they are making. The boring bar holders are dependent on the size of the tool holders (mine are 1.250 with a 1" sleeve), but I'm up for whatever size the group is.

Questions....lots of dimensions missing....what provision is made for thrust bearing surfaces? or is that the "grease"?

I think this design is just grease The face of the 'broach holder' and the 'body' are the bearing surface it seems.

I was wondering the same thing, however, if you have seen the AVE guy on Youtube, it did it with two divits (one off center) in a couple of pieces f steel...with a ball bearing sandwiched between the two. It's a crazy simple device, but yeah, if we could find plans that made a higher level tool, that's awesome.
There is a British company that makes these and everyone copies those...I'll see if I can't find those plans or instructions, something.

I've seen a couple withe the ball-bearing in the middle, I'm definitely up for whatever designs we come up with. That design above was just the one I found in my machining folder.

 

[ErichKeane]

Instruction

This is a pretty nice one! I'd almost definitely make the tool 1/2" and scale it up for a 1/2" bit simply so we can use commercial broaches though.

 

[T Bredehoft]

Size of final product.... I can't imagine broaching anything larger than 1/4 hex, (Allen Wrench driven). I could hold a 1" shank in my PM25 mill, but not my lathe... (10-30).

I've yet to wrap my mind around the motion of the 'cutter.' It does rotate, driven by the piece being broached, does it pivot about it's long axis, or does it pivot on a point? Or are these two differing processes?

O-1 vs HSS for the cutter? So long as we have a grinder and it's operator we should use HSS, it's much better for its job than hardened O-1. Harder, too.

 

[Brento]

Most of them i believe pivot on an axis i believe.

 

[bill70j]

@bill70j ABSOLUTELY! Thank you!

Here is a photo of the Hemingway broach holder and its scaled-up companion. Both use 1/2" shank broaches made from hardened O-1 tool steel. The larger one can make hex's for screws up to M12 and up to 1/2".



The attached drawing includes the holder body and spindle showing the two radial bearings and the single thrust bearing.

If this helps you guys in any way and you want the as-built drawings, just let me know.

 

[Illinoyance]

I made my rotary broach a few years ago. It resembles your design but has radial and thrust bearings. made interchangeable shanks, 5/8 and MT2. That allows me to use it in the lathe tailstock, the turret on the lathe, in the mill, or even maybe the drill press.

 

[ErichKeane]

Hmm.... it would be interesting to build one around a tapered roller bearing, but sadly they tend to have a pretty massive OD for any reasonable ID.