My Lowrider not very rigid

Well, i was expecting my lowrider to be quite rigid at this smaller size (30x50 desk, inches, lol).
Some of the parts were the end of some Petg I had handy, and on the roll after I finished printing this, I had some underextrusion I traced back to a broken piece on the extruder assembly, so it’s possible that some of my parts were a little light, too.
At any rate, wifey is interested in some cnc furniture, and I’ve probably just got the bug, but it looks like it’s time for a larger cnc. Probably half sheet for now.

Anyway, check this out. Looks like a lot of the looseness might be back to the wheels, but just everything seems sloppy.

I’d hate to go reprint everything and only make marginal gains, but I’m not sure I’ve seen anything else at that size that would let me reuse the pricey parts.

I’d really like to hit 80ipm at 0.25" DOC or better. Am I out of my mind? I ruined two really long jobs after losing steps on the short axis (with only one stepper) and I was nowhere near that. Maybe 50 ipm at 1/8"(edit, I did some figgerin and see that this is over twice the speed Ryan recommends for lowridering, but that’s at the depth I want, soooo).
I know I could hit that on my old mpcnc, and I don’t think the teeny tiny would even blink.
Does this look as bad as I think it does? Are my expectations just way out of line? Both?


It is impossible to tell how hard you are pushing on it, but it looks too rubbery to me anyway a couple things to keep in mind:

  1. Petg is harder to break, but less rigid than pla.
  2. The higher the Z is, the less rigid it will be. 2x farther is about 4x less rigid.
  3. The voltage gives you a speed limit. Deeper is easier than faster for the steppers.

80ipm/0.25" is 34mm/s, 6mm DOC. That is really fast and already pretty deep. Those numbers are, of course, not the only variables, but I think it will be really hard to get to those numbers. If you get there, more power to you.

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From what can see it definitely looks like your wheel is wobbling. Did you use the wheel spacer between the bearings? also is that the correct diameter bolt?

You have a cracked XZ_Side_Belt print. While from the video it doesnt look like prints are making it flex that much. If something else is cracked it could possibly be that. If you’re cracking PETG youre tightening the screws way way too much.

If you had to tighten that screw so much to get it to snug up Im wondering if you may have neglected to put the J_Spacer in there. I did that on my MPCNC and had to tighten the corner caps so hard I cracked one. There’s supposed to be a gap between the XZ /XZ_Side_Belt pieces and the XZ_Main.

If you had under extrusion problems that would likely make holes over sized which would possibly manifest as slop between the bearings and tubes, and loose bolt holes. Some of the bearing slop can be taken out by tightening the tension bolts but those can only do so much. Loose bolt holes will eventually lead to misalignment and off the top of my head im not sure much could be done other than drilling out the holes and sleeving them.

Other than that its hard to tell but it looks like your belts might be loose, I can see a decent amount of bounce in the X axis.

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It does seem to me that a lot of the flex is coming to the wheels, both wobbling ever so slightly on the bolts and actually compressing on the rubber (stole them from an on scooter instead of hockey skates).
It also seems like a lot of movement of the tubes in the y plate parts rather than the xz (where I had to use petg).
Not a ton of force, just by my fingertips, certainly less than 10 pounds, probably more than 5.
I know 80 is really fast for these things, just kinda hoping it wasn’t TOO fast. I think my spoilboard being so thick isn’t helping, since you reminded me about height. I could probably get away with raising the wheels up.

Thanks for the detailed breakdown. Pretty much confirms everything I suspected. Like I mentioned, I’ve built a couple mpcncs, so I’m familiar with the V1 style and assembly quirks, just not so much with how the lowrider OUGHT to look/behave.
I didn’t crack anything while assembling, all spacers are there. I do think the underextrusion issue was around for a while before I found it, and maybe those parts are weak. Must have broken at some point between then and now.
The spacers also came from the scooter, so I think that’s the big problem there with the bolts.
So now, the big decision. Reprint everything and rebuild? Or try something different just because. I mean, it seems like everyone else around here has built five or six different machines. I gotta catch up! I’ll still have all the LR hard parts so I can always come back to it.

Might be worth it to do a couple sanity checks first. Maybe take off a few of the bearing carriers and see if the hole for the tubes has the same diameter as the model.

Something I think I might be seeing on the wheels. It’s hard to be sure but it looks like the bearings may be slipping in and out in the scooter wheel hub. Would be easy to pull the wheel off and see if the bearings are easy to pull out or if the wheel hub is out of round. Would be an easy replacement and could explain a lot of the flex if all the wheels have play on their bearings.

Good point. 20 dollar fix, 20 minutes of wrenching.

Well, i started talking it apart, and woodenchano?

Geez, muscles. Take it easy :slight_smile:

Honestly, my first thought was, PETG. I reviewed the thread and that’s what you’re using alright. That’s clearly more than just flex. My PETG projects end up like that though. Like they aren’t adhering to themselves well enough.

Well, at least you found it.

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Yeah. I had even considered just waiting for more PLA to show up, but the thought in my head was “Meh, the fact that people argue about it means it’s probably good enough for a SMALL lowrider.” And who knows, maybe the extruder WAS broken back then and it SHOULD have been good enough.
Anyway, knowing what the problem was, I’m likely in for a reprint. But first, I’ve got all these plastic things laying around from failed/abandoned projects. Gotta see if I can do anything with them, and then back to the CNC.

I’ve done lots of PETG printing and although it might be more flexible on high infills is really sturdy too…but for once I stuck to what V1 said and did mine on PLA with 40-60% infill and so far they look quite rigid.
PETG needs really high temps to adhere properly, and honestly unless the project demands it I stick to HD870 PLA which I’ve been using lately with great success…HD stands for High Resistance…as a test I printed same 2 parts with normal PLA (amazon) and this new HD870PLA and it makes a difference…you could always cook it in the oven to gain higher resistance too…but too much hazle I guess :rofl: better do some cakes in the oven !!!

Reprint them and give it another try…and that wheel looks really woooobbbllyyy (spelling)

Àlex