Roller mount not tight on roller part

Hi all

I’ve finally come to the point where I’m about to enter last part of assembly. X and Y rails are not square at all. I’ve tried all hints in tips from instructions, FAQ and forums - and the only thing left is to let it run for a while to “break in”. Unfortunately, it seems like the 25mm Biltema-conduits (from Norway) are not perfectly round at all. They vary from 29.9 to 25.3 mm. Let’s see what the breaking in does - and if nothing helps, then I would get rails from a steel retailer.

Well - my question for today: The roller mount does not fit perfectly upon the roller! It wobbles a little. I watched Toms build on this part, and it seemed like he had them fit tight. For me it seems like there will be a little air between, just like with the feet. I assumed it was no probem with a little air between the feet parts, like Tom has, but the roller mount seems more vulnerable? What do I do? Should I just go ahead, or would I risk breaking things??

Edit: The whole the mount and the roller makes is 24.2-3 mm. Does the PLA shrink??? I’m very certain that I have printed the F variant.

[attachment file=“111502”]

Every part will have a small “F” embedded in it, super easy to check.

It is an interference fit, If it is not tight, something is wrong.


Try rotating the rail to see if it snugs up at any point.

Oh my oh my… I’ve come across sooo many obstacles buildning this magnificent machine!! I’m not giving up at all - but theres just sooo many things that comes up!

The rails doesn’t make an interference fit, no matter how much I rotate…

How can the roller and roller mount be too small? They’re obviously Fs. Is the rail opening supposed to be 24.3mm? I guess they must have shrunk then? How can that be, since its PLA?

If you print a 100mm cube, is it really 100mm?

I guess I have a printing job to do! Thanks for pointing out the obvious. I would have been embarrassed if I knew better…

It happens. Who cares if their Charizard is a couple % bigger or smaller? Also if you printed all your parts, they’ll fit together pretty well. It’s when you start mixing in things you didn’t print is when you start to notice sizing issues.

Now I'm both relieved and confused at the same time. Print size seems to be 100% precise! A relief when it comes to having a functioning printer, but very confusing in terms of troubleshooting the roller issue. Ryan, can I ask you about how wide the rollers are supposed to be? I'm not very familiar with measuring models digitally... I promise I won't use it to fabricate my own cnc offshoot..[attachment file=111654]

What do you mean by wide? If your printer checks out I am 99% sure the parts will as well.

What happens when you tighten the tension bolts up pretty snug?


The “F” parts are 25mm, undersized. If anything your tubes should be entirely too tight. I am getting confused. The parts can’t be perfect and tubes to big and it fit too loose. Do you have all 5 bearing on the rollers?

Confusing indeed!

I’m wondering about how wide the roller is supposed to be. Perhaps my printer has had a bad behaviour earlier and printed too small prints. I’ve fixed and tweaked many things during the whole printing process, so the parts may be too small, even if my printer now is acting well. If the roller is supposed to be 75mm wide, the print seems to be 74.8mm. I don’t see that this is enough to cause the big gap…

[attachment file=111747]

I tried to snug the tension bolts, and you still see air on both side, and definately on the belt side. It actually cracked a little, but that’s not the biggest concern right now - to say the least.

[attachment file=“20190902_135858.jpg”]
[attachment file=111746]

As long as the tubes don’t move, a little gap between these parts isn’t going to matter. They are clamps, so they need some space.