For those betas out there, what did you use for your x rails?
23.5, 25 or 25.4?
Just wondering if 25.4 is still optimum for a 48/49" wide capacity, or if the extra rigidity of the very cool looking “bridge” makes the whole difference moot.
Also for those that built a full width machine, am I looking at a 63" wide table - As if I can’t wait for the calculator to be updated… 
I used a 1" for the X rails.
If you look at my building thread, you will see that my table has a wider X, I follow the directions, so can cut 48.5" on X axis as it is.
I could easily stretch it to 50" if I need to, just need to get longer X rails
I’m not home right now to measure my table but, You will be fine with a 63" wide table.
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I have a 24" span. I am still using the 1/2" EMT. It is much more rigid than my 25.4mm LR1 was (using completely unscientific hand push tests).
Also, the main strut is the only part that changes. The core is the same for all sizes.
My advice would be to use whichever you have. If you are buying new, then use 3/4" EMT. If for some reason that doesn’t work, it won’t be a huge trouble to change it.
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I’m using 1" DOM steel, but really, I don’t think that the 1/2" conduit from the very first beta release was a problem. Keep in mind that I work for a company that sells wholesale structural steel, and can therefore get it for a pretty steep discount.
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I used 1" SS on my full-sheet capable LR3. Some of us had some concerns with twist in the gantry using the original 1/2" emt, so we wanted to try other options. I had the 1" SS from my now disassembled LR2, so it was an easy choice. I originally chose the SS for the LR2 due to the high humidity where I live.
Huge credit to Ryan that he designed a machine where only one part (the brace) needs to be changed in order to change the diameter of your gantry metal. Core rides happily on any of the choices.
I kept the 1/2" emt for my Y rail. It works fine and it’s cheap.
63" table width is more than enough. My table is 64" wide, but that is due to the components I used to build it. It looks like anything over 61" would work.
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Thanks guys for all the input.
It sounds like 3/4" conduit if starting from scratch, 1" DOM or SS if you have on hand, unless that size puts too much stress on the pla due to reduced material.
Since I have (2) 62" sticks of 1" DOM I might as well just start printing 25p4 unless…
And 1/2" conduit for the Y rail, since there doesn’t seem to be a reason for that to be bigger, better, stronger.
And it seems my beloved Openbuilds black box will be staying on the PBurly (burly with all the primo parts printed but not yet installed), as that is strictly a four axis controller, and I can see the need for the 5th axis. It’s one thing to try and save a few bucks, it’s another to compromise the integrity of the build.
Last question, other than the bearing wheel brackets, any difference between using bearings and XX mm wheels? IOW, if I decide to switch one way vs other, it’s just a matter of printing those brackets, no?
I’m trying to visualize the geometry changes in my head, but it’s Sunday morning and I haven’t had enough caffeine yet…
Most of us are using the wheels from the LR2. I did print the parts to use the bearings wheels but haven’t have the time to install it yet.
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We thought hard about the differences in bearings and wheels. The roller wheels are meant for grown people to stand on, so I don’t think they will deform enough to matter with 15 lbs on them.
The diameter is maybe the only difference. If you have a crack or screw head where the wheels track, the smaller diameter will sink in more (and it isn’t linear). When you hit a chip, both wheels will rise up the same amount, but the larger wheels will rise a bit earlier and later, and they are less likely to get stuck. But I doubt you would want to ride over a chip that would block the bearing.
IMHO, they are very close to equal.
It was sort of an afterthought, but it should help self sourcers who are having trouble finding 60mm wheels. I think Ryan still has a bunch of roller wheels in stock, so they will be supported for a long time.
Since the lateral motion is now constrained by the rail, the stickyness of the rubber doesn’t matter anymore. So printing wheels is another option.
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There were a couple concerns during beta testing that the bearings as wheels addressed.
One was that, going forward, this particular size of skate wheel is getting harder to find.
Two, and most importantly, was the possible difference in Z from one side to the other. As designed, the bearing-wheel side (X-) will have the exact same Z as the side that runs on the rail. I like this because I have not yet installed any endstops, and would like to avoid it. I want my machine to be mechanically as "square " as possible.
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Dam you guys are killing it with these answers. I might have to start the FAQ’a using this. #1 FAQ so far, why only one rail, two is much better… HAHAHA
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Jeffe & Jonathan,
That clears things up greatly. I have some 60mm wheels and bearings so I can go either way. I know it the past with the LR2 it was suggested by many to route a shallow groove for the wheel to rest in, to aid in tracking. I assume that is no longer needed.
I do wonder/worry about a chip or even sawdust mucking up a small bearing, something the much larger wheel might just as well roll over. I have plenty of time before I have to decide which way to go…
I have to admit, this morning I was actually wondering that. Only because I read that someone 
used 1/4" aluminum side plates. I thought aw heck, if we’re getting that precise, why not run a 2nd rail and lock the sucker down. But that would be harder to make it dance like I saw in the video.
Of course, this morning I also realized that there were only (2) x-axis rails and not (3). I kept seeing 3 rails, which kind of made sense, in a triangulated way. I even studied the braces, thinking what the 3rd rail just tucks in there? When in fact I was seeing the same front side of the LR3 from both ends, not the backside where the control is very nicely mounted, I might add…
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It would be a horrible idea now. No good, same as a rail on both sides.
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Same here. It wasn’t until I read your post that I realized it was only two…
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Ok, so now I don’t feel so stupid. Well, at least not as much as before.
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I don’t know what it would take to block the bearing. I think the Y drive would just push most stuff out of the way if the bearing won’t just roll over it.
I have been considering reprinting with the.bearing wheels, but it hasn’t been an issue yet, so the skate wheels stay for now
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Could a air assist blower be setup to clear the area?
Hello from Austria, can you tell me the wall thickness of the emt tube, which is the best choise, or should i make the lr3 with aluminium tubes.
Thanks for your help
Christian
Internet tables indicate that US EMT has a wall thickness of 1.2 or 1.3mm or 0.049 inches. I took a quick measurement of a chunk I have here, and it came it at 1.5mm, though the rough-cut end of the tubing probably accounts for the extra 0.2mm.
As for aluminum, generally it is a bad idea since the steel bearings will cut/gouge/deform the aluminum tubing over time.
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This topic has some posts about rail options and suppliers @ My own take on the spirit of the MPCNC - #132 by azab2c
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