How smooth should rollers move?

Forgive me as this is my first build. I have just now started constructing my frame. When I put my rollers on the tubing and try moving them, they seem stiff. Not stuck, but for sure not butter smooth. I have no reference/experience for this, but it seems common sense that stiff is not good. All the roller assemblies seem the same.

Hence the question is, when you push on the a roller assembly, how much friction should there be?

In trying to search the forum, it appears that all EMT is not created equal and some people polish it (

I think i will try to search for a different type. Mine might be galvanized (not 100% sure). Its not rough per say, but it does not have a “smooth” looking finish (see

Finally I have a cheap digital micrometer, it reads something like 23.7 mm (not 23.5) and this is the first EMT I have tried.



If your tension bolts are as loose as they can be you are fine, give it some time to break in. If you tightened them, don’t, until/if you ever need to. My Red and black build doesn’t even have nuts on some of the roller tension bolts and it is old.

Just to be 100% clear. These two bolts (uninstalled in the picture below) are considered the tension bolts on the rollers or is every bolt on the roller considered to be a tension bolt?



The bearings will also wear down the galvanized surface pretty quickly. If you decide to polish them, make sure you don’t breath the dust.

Basically any bolt that goes through a bearing that has plastic on both sides, are tension bolts.

For the sake of completeness I provide an update. Since my original post, I did end up creating an working MPCNC. In other words, I got to the Crown test without issue (have not tried to progress past that yet). I made no special considerations, I just continued along the build following the advice given above.

I still have some sinking feeling that the grade of my EMT is still “too big”, but that is hopefully just paranoia and lack of experience.

Having said that here are a few observations with noting:

  1. When I made my original posting, I only had one length (10 ft) of conduit. This was intentional because it was actually the very first thing I bought for construction. I wanted to print a part (like a foot) to actually see that things would generally fit. As such, I had to go buy another couple 10ft lengths. I went to (in Edmonton, Alberta, Canada) the following stores: Home Hardware, Rona, Lowes, and Home Depot. Here is what was slightly interesting: A) They all sold the same conduit Columbia (see screen shot) and B) every piece in every rack measured slightly differently and they were all slightly larger than 23.5. Again, the surprising thing was not one of the stores I visited sold a different brand.
  2. I would describe my movement as "firm" as opposed to "stiff or binding". However, it is for sure NOT as smooth as this one (Making Stuff Video Clip). A little concerning for me still.
  3. Finally, every single part I printed fit without issue and in fact I was shocked at how well everything fit. Except one set (see pic). The Z-Lower and Z-Motor brackets. The motor and the bearing fit perfect, bit the rails where crazy tight to start with. I had to pry the mount apart with a screwdriver to have a chance (a small hammer may have been involved). After the rails where in they seemed okay, but I am still suspicious.
P.S. As of this posting, my MPCNC is nowhere close to broken in obviously.


I’ve seen that too. I think there are regional providers for the stuff. Maybe it’s because of code or because they are shaviing shipping costs or something.

I’m hoping it works out ok. How much bigger than 23.5mm was it?

It was all over the map. I took the cheap digital caliper I had. I did not write down each measurement but mostly 23.6 to 23.8 if I recall. I even think it varied of the length of tube. So one end was 23.7mm and the other 23.6mm. Once I saw that, and the same supplier at each store, I kinda gave up trying to stumble across something better than was I bought the first time. I though I would just try the build. If it was a disaster I would just go source stainless or something.

Time will tell.