Square/Acme/Trapezoidal thread milling?

[jamesgates1000]

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.

[m_c]

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.

[jamesgates1000]

How small is the smaller diameter?

These are the smallest I could find...

http://www.cutwel.co.uk/thread-makin...rs-screw-clamp

http://www.cutwel.co.uk/threading/in...reading-insert

[m_c]

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.