Support bracket for Y idler on ToM

by tomlombardi, published

Support bracket for Y idler on ToM by tomlombardi Mar 13, 2011
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Unlike the X axis, the Y axis idler is supported on one end to the acrylic middle plate. This arrangement places a pretty good load on the acrylic and I noticed some flex as the Y axis would change direction. I designed the bracket to fit over the head of the Y axis idler bolt and attach to the two top screws of the rod cover.

Please note, this part is dimensioned for a stock ToM. My ToM Y axis rods a slightly longer than the body and make the body bow out. I've seen others comment on this so I know I'm not alone.

Also, I'm not implying that this is a defect in MBIs design, the acrylic may be happy with this for years without problems.


Print the part and drill out the holes. The hole for the idler bolt is 9/32", work your way up to this so you don't change the location of the hole. The two rod cover bolt holes are 1/8"

To install just remove the two top rod cover screws, slide the part over the idler bolt head, run the screws back into the part. The screws are just long enough to work.

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You mentioned your Y rods are to long. Ths could be because you are using the Z rods in place of the Y rods as they are very close in size.

I'll check that out, thanks!

9/32" and 1/8" ?

Last time I cheacked the TOM used metric parts there and it's 7mm for the head of the idler bolt

and M3=3mm for the rod cover bolts.

Sorry to confuse you, here in the US we use SAE drill sizes and it would be difficult to find a metric drill set at a local hardware store.

I usually have bolts cut their thread through the plastic. That would work for the M3 holes.

The 7mm one can then be slightly conic to press-fit and self-center the bolt-head.

If the skeinforge-profile is calibrated correctly (especially perimeter-with-over-layer-thickness and if required the strech plugin) this should work without drilling.

Ok, I just made my own copy.

Some improvements:

  • make the 7mm hole 1-2mm larger.

  • the bolts are not long enough to still have the nuts on the inside.

  • So make the 3mm holes 3.5mm and allow for a trapped M3 nut.

  • tapper the edges of the nut-hole and the m3-holes on the other side by 1mm equidistant

  • tapper the 7mm hole by 2mm equidistant

This should make the part fit instantly with no drilling and the nut-less M3 bolts can never come loose as they have their bolts attached to them.

If you provide the original design-file, I could do these changes myself and post the result.
(I'm not sure what software you work with.)

I use Solidworks 2010, here's the file.

sorry, "bolt-less", not "nut-less"

I printed this out and was surprised to discover that my idler was further away from the rod than the bracket I printed, by 3mm. I modified it and printed a new one, will see how it works.

I also found my idler further away. TOM 4542 (5/6-6/6 2011) so perhaps they moved it? I used a dremel to widen the slots and install it. Otherwise great!

Wow, I feel honored, I've implemented a lot of stuff on your page, good work.


Thanks for making this thing. I printed it thinking it wasn't really going to do much. But when i put it on, I actually had to loosen the stepper. So obviously my Y idler pulley was already leaning somewhat. This will ensure that it stays straight. I don't think I would have ever thought of this.

And that piece of acrylic thanks you too! :)

I was going to model up the same thing, but now I can just print it. Thanks!

This is awsome! I have thought the mounting was a problem and the cause of a lot of noise from my T-O-M. Printing this ASAP. I was going to fab one from aluminum- but now I will just print it!

I found this actually is causing more noise on Y movement. It seems to conduct the vibrations into the body more. So much so that I'm thinking of sanding it down so I can put a gasket between the body and the plastic part.

I my case it didn't increase the buzz, and it didn't help either. I originally designing this to get the load off the acrylic. Using a gasket might work. The problem is when things start to resonate with the source of the buzz. We used handle bar end weights on our motorcycles to stop the buzz in the mirrors, perhaps adding a larger fender washer to the bottom of the bolt under the acrylic would be enough? Be careful, acrylic likes to crack so don't make it too tight. Keep me posted on what happens. Thanks.

maybe a little bathroom (silicone) caulking? between plastic and bot and maybe bolt too?