Grub screw fell out during cutting - can't find out from where!

Was cutting a profile when I noticed something fall into a previously cut pocket. On pausing the cut I noticed the item was a grub screw. I cancelled the cut and checked the grub screws on the Z,X and Y motors but they seem to be all there. ( Put allen key in hole - also tried putting the screw into the holes but doesnt go very far confirming existing screw is already there.

I think it came from the Z axis area but with the dust extractor I cant be sure where it really came from. Here’s a poor phone photo of the screw that tried to run away…

Is there somewhere else where this grub screw might belong to?



Ah yes I had this happen as well and I believe we determined it’s from the idler pulley behind the zaxis plate. I never put mine back on and it runs fine. Next time I have it apart I’ll threadlock them in.

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Thank You for the swift reply!

I’ll keep it on hand… ( somewhere safe that no doubt i wont remember where when I need it)

Appreciate the quick reply - its put me at ease - I’ll get on with the cutting!

Lots of topics on this, search pulley screws and read all about it. There’s probably two on the pulley, one on the flat and one not, hopefully that one is not the one that holds against the flat on the shaft. Good luck, Jude

I agree with @ItsDan, mine just shed one of those last week and it came from there. The cool thing is because the belt is locked by its teeth in there it probably doesn’t make any big difference. I found mine after running a longish cut and the Z never skipped. I had zero loctite on the one I found, but it does now😉


Thanks everyone for their replies/advice. Indeed machine is working o.k. without it - so will leave it till when ever I need to take the Z axis apart and refit.