I have a BP Series 1 was Boss 3-5 controlled, have Gecko G210's and would eventually like to replace the Sigma stepper motors.
My understanding about the Sigma #026744 motors is:
-6 wires
-5/8" keyed shaft

I need to know:
-NEMA size?

What I am looking for is a bolt in replacement bipolar with about 1750"oz torque. I can probably add the keyway using my other mill.
The Y axis has a size limitation of about 8.5" body length. X & Z are not a length problem.
It needs to be the same flange and shaft size though.

When I solve this puzzle I will have 3 good Sigma motors available.

Regards, Chrissi

Look at http://www.kelinginc.net at their Nema 42 stepper motor. The shaft is smaller than the spec sheet says (the spec sheet size would have matched your pulleys) but only needs a new Taperlock bush to mount the pulley. I know it works for the Y axis. I don't recall whether the X and Z use the same type pulleys. The bolt holes match up but the new motor doesn't have threaded holes like the Sigma/Superior so you may have to use nuts and bolts.

A friend was having issues with table jerkiness. The Y and Z were both Sigma and the X was Superior. He swapped in a kelinginc motor on the Y and resolved his issues. The Z is still a little jerky but he is living with it. The Superior motor is smooth. I tried his old Sigma motor on a unipolar HobbyCNC board with various step settings and it was jerky on it also. It would only smooth out if the current setting was set so low it stalled too easily. He has Gecko 201s on his mill.

Chrissi-
The Sigmas (and Superiors) are 8 wire motors. The original BPT wiring had 6 leads with two jumpers at the motors. I have tested my Sigmas on my BOSS 5 conversion (underway) and would love to know how your Geckos are wired to them. Mine works great unipolar, but I had a problem when I tried them wired in parallel.

Mike-
You're right about the shaft size...Keling's info page says 3/4 shaft, but the spec sheet pdf shows 16mm. Taperlock sounds like the best way.

If the bolt pattern is the same, (Keling vs Sigma), how about inserting 5/16-18 Helicoils on the motor...the 8.5mm holes (.335) are just right for the Helicoil tap drill size.

Rob

Thanks guys, sounds like the Keling motors with Taperlok and helicoils would be the way to go. Will have to save my pennies for them =)
The best way would probably put the existing ones up for sale?
Regards, Chrissi