View Full Version : Square/Acme/Trapezoidal thread milling?

21-04-2017, 08:40 PM
Has anybody came across examples of Square, Acme, or Trapezoidal threads being milled?

I've got an idea for something I'd like to produce, and although I could use some standard metric threaded rod, I'd quite like to use something quicker/squarer. And that is where the problem starts.

Finding square threaded rod is akin to finding a blood donating stone. Acme and Trap on the other hand are available from a couple different suppliers for reasonable prices, which leaves me the problem of machining the corresponding female thread.
I had been considering 10 or 12mm, but even going up to 14mm to get a bigger minor diameter/hole size has yielded no results for thread mills. Given the width of the thread form, I fully expect to need to do the thread in multiple passes to get the required thread width.

Tapping in the lathe as a second op is looking like the only option, but given the length of taps involved, it's something I'd rather avoid, especially since one part will be awkward to quickly mount as it'll be rectangular.

I don't mind spending 2-300 on suitable tooling, but without going to full custom tooling, I'm drawing a complete blank. Anybody got any suggestions?

21-04-2017, 10:39 PM
I have had to make some aluminum blocks to mount very large castors with an acme thread. I found the best way was to make up a fixture to hold the block on the lathe then use a acme tipped tool and single point thread cut. You could use a single point lathe tool with acme tip to thread mill.

21-04-2017, 11:52 PM
The problem is I can't even find a single point lathe tool that will work in the smaller diameters.

One option I had forgotten about was a tapping head mounted in a drill press with the work piece mounted high up to give enough room for the tap to pass through, although I'd have to make sure the drill has got enough travel.

22-04-2017, 10:04 AM
How small is the smaller diameter?

These are the smallest I could find...



22-04-2017, 12:07 PM
For the commonly available 12x3 or 14x3, the minor diameter is 10 or 11mm.

The more I look at this, the more standard metric thread seems to make sense.