How to cut a square hole?

[alandarkdale]

Are you making just one?

WARNING: Hillbilly engineering ahead: If so, I would mount the blank end up in my drill press. (vise, clamped to a metal block, etc.) Drill the four corners of the square with a 1/16" bit. Drill the center out with a larger bit that just reaches to the sides of the square. That takes most of the material out of the way.

8tnsane's tool could finish it. The lathe is not running. I believe he is using the chuck to hold things and running a corner tool in to cut one corner and the adjacent sides at a time. The carriage is simply cranked from sided to side to run the cutter in and out of the hole.

I would make a small chisel from tool steel ( or recycled old wood chisel or maybe even a cut concrete nail) and use it to cut the excess brass out of the hole. An alternative might be a small cutter in a Dremel tool. In my hands the chisel would be faster and much cleaner, but then again, I am a hand tool monkey.

 

[Hawkeye]

The broach 7HC linked is basically a square (or hex or ??) chisel that the toolholder wobbles down one corner at a time. That's as close as most of us will get to the one in this link:

http://www.youtube.com/watch?v=ALiqAXiTQBg

Not for the faint of budget. Pretty cool to watch, though.

 

[lohring]

Rotary broaching is great if you need to make a lot of holes. Look at Ebay for some low cost tools. However, you can make a simple tool holder like the one shown below using the offset of your lathe's toolholder.

Lohring Miller

 

[jerryhawthorne]

Thank you gang, gives me a little understanding of how a broach works. That square hole tool looks really complex and no doubt expensive! With my limited need and working mostly in brass, I will probably go with the simpler solution of several holes drilled and a lot of filing!
Appreciate the videos and explanations.
Jerry

 

[wolframore]

You should cut your own broach, if you're only making one square hole you can pretty much get away with using any steel lying around... especially for brass. you drill the center of the tool tip using a large drill bit to give it a bit of a convex. Then mill or grind the four sides to shape. I suppose you can heat treat it if applicable. The easiest would be to use an arbor to cut the corners out of the work piece after drilling out the center. Keep working up and down to clear chips until you hit your depth. Sorry about no pictures. I saw this online somewhere but can't find the link.

 

[alandarkdale]

Hey Auto.

Here is another view of the broaching subject. He builds his own with step by step photos. I have a much better idea how it works now.

http://www.docsmachine.com/projects/rotarybroach/rb01.html

I've enjoyed poking around on his site for the last hour or so.

Dale