Machinist

[Lawrence London <lfljvenaura@gmail.com>]

How would a guy make this small part? I'm stumped.. - Page 3
http://www.practicalmachinist.com/vb/general/how-would-guy-make-small-part-i-m-stumped-276509/index3.html

Just Google "home made" or "shop made" rotary broach.

Home build rotary broach - YouTube

Here's video of one in action, clearly on home shop equipment. About half way through the video it's shown being used on a mill, and because the workpiece isn't turning it's easier to see how they work. Essentially it's just a tool ground to the shape you want, normally with about a 2 degree relief ground behind the cutting face. The unit works by having about a 1 degree eccentricity on the back face of the tool, effectively "wobbling" the tool through a pilot hole in the work. In essence the only thing involved are some bearings set up with that 1 degree eccentricity. It's probably not a very good explanation of how the tool is made to wobble, but again if you Google rotary broaching you should find better explanations than my pathetic attempt.

The tool itself can be ground up from HSS lathe tool blanks. However they're also commercially available so I'd check that before going too far in case the shape you need is available.

Pete