Sunday, February 1, 2009

Maching ACME threaded rod

ACME threaded rod, cut to 1150mm long, first end machined.

The 0.5 inch ACME was turned down to 10mm to match the inner diameter of the bearing. It was then threaded to M10 for ~ 30mm to allow for the lock nuts to go on, and then turned down to 4.75mm for the last 10mm to match the coupling for the motor shaft.

The metal was a serious pain to machine. Owing to the length (> 1 meter) I was running the lathe at fairly low speed. The steel work hardened VERY easily, and it's very flexible steel. This meant that it was just as easily bent away from the lathe cutting tool as cut. And it was threaded to boot, which mean highly variable loads on the initial cuts...

I ended up using the live center to attempt to hold it in place which improved matters a little, but not much.

Eventually, I used a handful of skate bearing to make up a jig to support the other end, which let me run the lathe much faster, which made the whole thing easier to do. I was initially turning it at 220 rpm with HSS cutting tool. Running it at ~ 480 rpm was dramatically easier.

The threading was done with a 60degree lathe tool, mounted upside down, with the lathe running backwards. I threaded it in until it "looked done", and then cleaned up by running an M10 x 1.5 die over it. Worked very nicely as I didn't need to try to fight workhardening steel with the die getting an initial thread.

Now to make the bearing brackets...

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