Primo: 1" tube vs 3/4" conduit?

I built my Primo several years ago, right after the design was published. At the time, the only US design was using 1" tubing, which I did. It was DOM tubing, purchased locally, and unusually thick walled… maybe even 0.125"? Because it was not stainless, I primed and painted it.

That Primo build did NOT use the dual end stops, which I have come to really appreciate in my LR3 build. In addition, painting the tubing has not really worked very well… the bearings have worn tracks in the paint, badly degrading the appearance and possibly affecting performance, even though the tubing has been rotated occasionally.

On the other hand, the accuracy seems to be decent: a few days ago I used it to cut out a rectangular hole in a piece of hardboard. Over 16 inches, it was apparently out of square by about 0.050", which for that purpose was adequate. I’ve also been able to do a small amount of aluminum milling, which is also nice.

However, because of wanting to switch to the dual endstop configuration, and, to address the damaged tubing paint issue, I’m toying with rebuilding this Primo, which is primarily re-wiring, but could include new tubing. (My controller can handle the dual endstops, so that just requires uploading a new firmware version. )

But, I’ve noticed that after I built my unit, a new design was added that used the 3/4" conduit instead of 1" steel tubing. Obviously, from the cost and convenience standpoint, the conduit version is desirable. However, it’s clearly not as robust as 1" steel tubing.

So, my question is, are there significant compromises inherent in using the 3/4" conduit design? I realize that all the 3D printed parts would be new, but that cost/time is not a big deal for me. Or, is the 1" tubing enough stiffer that it is still the preferable solution?

My Primo has a work area of about 24" x 24" and I would not be changing that. Thus, all the belts, motors and bearings would be re-used in either case.

Any insights into these tradeoffs would be greatly appreciated.

The 1" OD tubing is going to be a more rigid solution. Especially because you can purchase different wall thickness. You can get .120" thick wall tubing if you want. Even the .065 wall is plenty strong for a 24" x 24" I believe.

I went with .083" wall on my 24" x 36" Primo and I haven’t noticed any issues over the years. If you have the funds to go with stainless tubing then I would suggest to do so.

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