Grub screws and Allen key tolerance - new builders take note

Having just completed my first build I thought I should share a problem I had.

While mounting the X and Y belt pulleys, I had a lot of trouble with the grub screws. The 1.5mm allen key would just not grip. I blamed the crews, thinking their sockets not deep enough, or that they were not well made. I got them as tight as I could by angling the allen key and pressing hard, then I swore eternal hatred of grub screws and got on with the build.

First print and X and Y are slipping. I expected a little backlash on Y as I thought I may not have had the belt quite tight enough, but had expected better results on X - axis.

Anyway, while adjusting the Y belt I checked the pulleys. The grub screws are no longer aligned with the flat part of the motor shaft, they are slipping. Sure enough, the screws are loose. Both X and Y pulleys.

In the meantime I had bought a new set of allen keys (the short ones I had were fine until I got to mounting the power supply - you really need the long reach there)!

I try the new 1.5mm allen key on the grub screw, and it fits perfectly, sits deep in the socket, and I can get them really tight. So I realign the screw with the flat of the shaft (you can do this without removing the whole assembly - it's what Ian would refer to as "fiddly - especially the X pulley, but it can be done)

So I get out the digital calipers. The old "1.5mm" allen key measures 1.75 mm - too big for the grub screws,. The new one measures 1.49mm.

Lesson learned, not all tools are made well and the grub screws are obviously made to very tight tolerance.

I will print again tonight and hopefully should see great improvement.

James

Hi James

Thanks for the note! I have to occasionally describe things as 'fiddly'; unfortunately it's the engineers here that design them that ways!

Ian
RepRapPro tech support

LOL Ian

Most of the things you call "fiddly" I call suicide inducing! But the PSU mounting was the worst (even with a long reach Allen key)! Surprisingly, getting the nut onto the screw in the spool holder went faster than I expected. I may write up my method as contribution to your intructions ;-) (which are excellent by the way)!

Haha, perhaps I just have rather nimble fingers! Any feedback gratefully received.

Ian
RepRapPro tech support

It's also a generally good idea to use loc-tite (or any generic non-permanent thread-locking fluid) to secure all screws that are threaded into metal and subject to movement. On the Ormerod that would be things such as the pulley grub screws and the M3 screws that hold the motors in place.

jstck, I was actually thinking exactly the same thing. Not going to take a chance with them working loose again.