Do I need a keyway?

[GEOFFREY]

3mm, no shaft flats or dimples, but the grub screws are tightly screwed in. G.

[Jonathan]

3mm, no shaft flats or dimples, but the grub screws are tightly screwed in. G.

Which reminds me, if you've got no flats or dimples on your shaft, then put a small piece of brass bar under the grubscrew, such that the brass presses onto the shaft and not the screw. That way the shaft wont be marked, since brass is much softer than the steel, so if you need to remove the pulleys there wont be an annoying burr to stop them sliding off easily...

[GEOFFREY]

I agree with Jonathans comment about the bur making it a little more difficult to remove the pulley (hopefully you will not need to), but doubt if there will be room for any insert (my grub screws are about 4mm long and need as much grip in the ally pulley as possible) and I do feel that a slight burr will help to stop the pulley from slipping. G.

[kingcreaky]

what he said....

[birchy]

Fair play Jonathon, you always impress me with your facts and figures. I'm more of an "over engineer it, guarantee it'll work" type person. But then again I used to make parts for massive steel bridges when I was an apprentice!

I have to admit that I'm VERY surprised the load is so small when converted to Nm via the ball screw and pulleys. Obviously I'll have to be a bit careful with the acceleration/deceleration but I'm more interested in accuracy than speed and would rather err on the side of caution than bollock the machine flat out and end up wearing it out prematurely.

Thanks everyone for your replies. Not needing keyways is one less headache to worry about. Just for the record, I'll be using M4 or M5 grub screws at 90 degrees, dimpling the shaft slightly and applying a little Loctite for the final fit.