Square Peg, Round Hole

[polygon]

I saw a post here about EDMing some holes in a custom made wrench. Here's another way to do it using a rotary broach tool holder. Rotary broaches can be made as a hex, square, spline, etc.

[ame]http://www.youtube.com/watch?v=uTsPXFy7Xx0[/ame]

 

[Paulsv]

Cool video! That would be a fun tool to own, but at $700 for the holder, plus $50 to $75 for each broach, I for one will have to take a pass. I'm sure there are many here who could make their own tool holder a lot cheaper, tho!

http://www.buybroaches.com/half-inch-diameter-rotary-broach-tool-holder

I wonder if you can do blind holes that way, or do they have to be through holes?

 

[Paulsv]

Being able to do internal splines that way would be very cool.

 

[tel]

Think I'll stick to the ol' Douglas shaper just the same.

 

[polygon]

Blind holes are no problem, except there needs to be room in the bottom of the hole for chips. This holder has a hole that runs through the center of the broach and then ports out the side of the body so that any air, cutting oil, or coolant that gets trapped can escape.
You can broach a wide variety of splines and serrations this way, but the tooth height is limited to about .020" in mild steel and .030" in aluminum or brass.

 

[shred]

Somewhere I ran across a site on making a 'wobble broach' holder. It's a pretty simple thing in theory-- a slightly off-axis spindle, but I bet there's a lot more to it in the details (which is why they can get $700 for the holders-- if it were simple some discounter would have knocked it off by now). Frank Ford's FRETS site has some info on making a broach for one out of drill rod. Someday I'll give it a try.

 

[polygon]

Another option is renting the tool instead of buying. Polygon Solutions offers broach holder rentals if cost is an issue.