Okay, I have bought an electric motor, it has a 14mm bore, unfortunately the part I need to affix has an internal diameter of 16mm (5/8"). So, to fix this problem I call upon your experience and expertise. Is their a way to perhaps sleeve the bore with a (tiny) grub screw holding it in position? Or perhaps a better alternative that will not create vibration at around 2800 rpm? I should let you know that I do not have a milling machine or metal lathe at my disposal unfortunate as that is, but if I did I wouldn't be asking this most likely. I probably should mention that this project is an abrasive belt sander, of which I have already built fromantic scratch. This is in fact the last hurdle. Thank you for your time, Regards, Peter

  • $\begingroup$ Could you add some pictures or diagrams of the two parts you want to connect? It might help people understand your problem better and lead to better answers $\endgroup$ Commented Jun 5, 2017 at 15:17

1 Answer 1


Brass shim should do the trick.

Basically you need a strip of 1mm thick shim stock and wrap it most of the way around the motor shaft. It may help to make some sort of simple former to help get it the right shape and indeed maybe wrap it with 1.5 turns and trim off the excess as the ends tend to be harder to bend.

Shim stock has pretty accurate dimensions so it should end up being adequately concentric.

For the grub screw, it sounds like this is a moderately high torque application so I would suggest a decent sized screw, maybe M8 with a pointed tip. If you drill through the mounting bore with the shaft in place and carry on a bit so you make a small dimple in the shaft maybe a couple of mm deep that will provide a more positive grab for the screw and reduce the risk that it will slip and chew up the shaft and/or wear the shim. Then tap the hole and use loctite on the grub screw to stop it vibrating loose.

You want the grub screw to locate in the gap between the ends of the shim (hence not wrapping it all the way around the shaft). The reason for this is that brass can creep a bit so you may find it starts to get slack after a while if the screw is bearing on the brass.

I have used exactly this solution to fit a polishing mop holder to a motor shaft (about 900W) and it has worked for years with no problems.

  • $\begingroup$ Thank you for your help, this seems to be a good option for me, I will try it and let you know how it goes, best wishes and once again, thank you. $\endgroup$ Commented Jun 6, 2017 at 9:18
  • $\begingroup$ Maybe experiment with cutting the ends of the shim at an angle and dove-tailing the ends rather than butting the ends together. $\endgroup$ Commented Aug 5, 2017 at 19:08

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