Starmill - Axis pulley slip

[NylonAdmiral]

I hope this is in the right place, I wanted to put this under "General" rather than in the "Machines->Starmill" section as my question is open to anyone really.

I recently replaced the stepper motors for the X and Y axis on my Starmill. I tried to also replace the pulleys that are fitted to the shaft on the stepper motor. Unfortunately these have since been discontinued by Denford and I can't find replacements with the correct dimensions anywhere else.

The pulleys and the original stepper shaft have a grub screw to secure them in place but also a through hole, through which a split dowel pin can be pressed to prevent the pulley slipping around the stepper shaft. Unfortunately this through hole looks like it was done by hand and isn't in the center of the shaft making it pretty hard to drill the hole in the same place on the new stepper shaft. This is why I was trying to buy new pulleys so that I could drill new centralised holes in both the stepper shaft and a fresh pulley.

Out of interest I placed the old pulley on the new shaft and did up the grub screw. It does seem to hold it in place rather well and considering that there isn't actually a huge amount of torque being transmitted I wondered whether or not the through pin was absolutely necessary. Considering it looked like it had been drilled roughly by hand I wondered if this was a modification done by a previous owner of the mill that isn't usually featured on these kind of machines.

My question really is, does anyone else (on any machine) know if they have a similar stepper motor/pulley setup where they aren't using a pin to prevent the pulley from slipping? Is this unnecessary or is it risking accuracy problems to not do it?

Thanks in advance!

[Denford Admin]

Hi - I've put it into the Machines section, but not under any particular machine section...seems the most logical place for it.

I think if it were me, I'd add another grub screw to the pulleys (if possible)

Durability studies show that the cup point offers superior resistance to wear while maintaining a strong grip
https://en.wikipedia.org/wiki/Set_screw

[Martin]

It was most likely pinned at Denfords.

As Admin says put a second grub screw in it or file a flat on the shaft for the first grub screw.

[NylonAdmiral]

Thanks, that is a much more logical place to put it!

I think I will probably opt for the second grub screw and keep a close eye on it. I would imagine it will probably be ok but I think I will continue to look for new pulleys anyway, although this is proving to be fruitless so far.

Thanks again for the replies.

[Denford Admin]

It was most likely pinned at Denfords.

Who by ?

[Martin]

One of the fitters!

we did have a couple of instances where the shafts broke due to the pins fitted. The hole for the sellock pin was nearly as wide as the shaft. I think they may have been 1/8" sellock pins.