Shop Made Rotary Broach with plans

[hook86]

Here is a nice working rotary broach of a type that has been around for a while.
I just used some hot rolled stock for the housing and arbor and drill rod for the bits.
Bits were ground on my shop built "universal grinder".
The 4 retaining screws and nuts are 4-40 and are only used to hold the tool holder in place.
I backed them off by 1 1/2 turns after bottoming them out in the groove.
The ball bearing is a 0.5" old ball bearing!
Both the arbor and the tool holder have concave ends that were made with a 0.500" ball end mill.
I went about 80% of half the diameter of the ball for the depth,which was about .200" deep. That
leaves plenty of space inside the tool for the tool holder to "rock" on.
The prints show most of the details for the build.

I thought it was not working until I realized that broaching is not very effective at low rpm.
After getting the rpm up around 900 it started to work well.

The grease zerk is very helpful since you can grease it without taking it apart and it does
need plenty of grease to work without squealing like a stuck pig! Nice and happy with lots of grease.

My bits are for 1/4" and 5/16" made of drill rod and hardened to cherry red then quenched.
Over all the tool is simple and works great in the home shop. I did not want to invest in a $700 tool just for my use.

While my original use and tests were on the lathe this tool should work just as well on the mill and maybe even on a drill press.
Just watch out for the spinning set screws and that grease zerk!


Cheers, JR

Great idea like the look of it.