HELP Can't make square cuts

This topic contains 71 replies, has 7 voices, and was last updated by Profile photo of Jason Christman Jason Christman 7 months, 2 weeks ago.

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  • #11753
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Hello,

    I finally have my MPCNC assembled and working, but I can’t seem to get square cuts out of it. I printed everything myself (no scaling) in PETG, and had no fitment issues while assembling. I bought the bundle from the vicious webshop. I have no endstops, and the total rail length is 31″x31″.

    I spent a few days last week trying to square up the frame unsuccessfully, but I printed the updated corners, and I’m now confident my frame is square (I used dowels cut to length to ensure the rails were the same distance apart, and the diagonals are within 1/32″). My squares are still coming out parallelograms, and circles aren’t perfectly round. See attached photos. Both sides of the square are the same distance apart and parallel, but the diagonals are about .5mm off on this ~20mm square. You can also see with a ruler that the corners aren’t 90 deg.

    I pulled the 4 3″ bolts from the center assembly, and then reassembled while it was all on the rails, but that didn’t seem to help. I’m not sure what to try next, and am starting to get frustrated…any suggestions?

    Thanks,
    Jason

    #11766
    Profile photo of vicious1
    vicious1
    Keymaster

    So what usually happens is when you drag the tool around the rails get tweaked one way or another usually worse when you start in a corner. I am sorry I need to do a little guide for this but the answer is usually pretty easy. To try and describe what is happening if you have the tool all the way on the left side and pull it towards you, the right side will follow behind and give you crooked cuts.

    Get the tool where you want to start then measure all 4 rollers and set each side equal (x and x, y and y). I measure from the corner block to the roller and check and set each side, and I usually double check.

    Let me know if that isn’t clear enough.

    #11795
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Thanks! That makes sense and seems simple enough, I’ll give it a try.

    Jason

    #11906
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Okay, so I had some time to look at this over the weekend. The rollers are definitely not square to the corners, there is almost a 1/4″ difference between each side (roller to corner). I don’t see how I can adjust this though. I try manually moving each side; with the steppers both engaged and disengaged, but it just moves back into the original position as soon as I let go. Am I missing something?

    #11907
    Profile photo of vicious1
    vicious1
    Keymaster

    Try loosening up your 4 long bolts in the center assembly. Sometimes they got tightened down so much you need to take them all the way out and put them back in being careful not to over tighten them.

    #11908
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Thanks! I actually already pulled these guys out at one point, but maybe I’m over tightening them (wouldn’t be the first time).

    #11916
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Nope, no luck. I removed all 4 long bolts and re-installed them, being careful not to over-tighten them. The gantry is still off square by pretty much the same dimensions it was before. Ugh. Where else can I adjust it?

    #11917
    Profile photo of vicious1
    vicious1
    Keymaster

    Maybe tighter? Is your frame square?

    #11920
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Tightened everything down a little more. Still off, although it seems closer than it was. I tried cutting a 4cm square, and as you can see in the photo it’s still a little off.

    I spent a ton of time getting the frame square. Diagonals are within 1/32″ of each other and so are the side rails.

    Attachments:
    #11922
    Profile photo of vicious1
    vicious1
    Keymaster

    Are you setting the rollers before you start the cut, like I described in the second post? It should easily be squared that way if your rollers are only off by 1/4″ when relaxed.

    #11923
    Profile photo of vicious1
    vicious1
    Keymaster

    Are you cutting really fast and over torquing the frame? Are your tubes bent?

    I’m not really sure whats going on if you can’t set them by hand before the cut, usually it can be pretty far off and still work that way.

    #11924
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Yeah, I’m trying to set them by hand before the cut, but it always goes back to how it is now. Maybe I’m not understanding the process of settings the rollers correctly.

    I’m cutting with your recommended settings, feedrate is 15mm/s and only a .1mm cut depth in super soft wood. Hmmm…I’ll check for bent conduit, that’s possible I suppose.

    #11936
    Profile photo of vicious1
    vicious1
    Keymaster

    I have been stuck thinking about your problem, what is the exact outside diameter of your rails, are they pretty round or are they oval? Also the middle end and joiner tension bolts can have an effect on squareness.

    #11938
    Profile photo of vicious1
    vicious1
    Keymaster

    Copied from the other thread.

    Not to many people seem to have this problems but when I try and replicate it it is because something isn’t “balanced” I guess is a good way to word it. I would say loosen up all the tension bolts including the 4 long ones and as you start to snug things up check the rails with a carpenters square, if don’t have one they are about $5 at the hardware store. This is how I have been checking on the new middle assemblies I have been making. If they aren’t square when it is completely loose something else is wrong, either with the rails being bent or your roller f’s are tweaked. The roller f are very strong and should hold it very square by themselves.

    #11958
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Thanks for the quick help! I’ll try these suggestions tonight and let you know what I find.

    Thanks,
    Jason

    #11983
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Ugh…I suspect all these problems are mostly or entirely user error!

    I went through a bunch of the these suggestions, short of completely dissembling the middle section, and was still coming out with the same measurements (about a 1/4″ off with the steppers relaxed.) However, just as I was getting frustrated, I figured I’d see if I could manually park the tool as you originally suggested. I plugged everything in, powered it up, and low and behold, when I manually moved the tool it would stay where I set it! Aha! Then, just as I was getting it close to square, the steppers stopped holding again. I think the whole problem is the steppers disengaging while I’m trying to set the gantry square for the cuts.

    Here’s what I’m doing.

    1. I plug in my laptop to the board, connect Repetier Host.
    2. I move the tool with the manual controls in RH. Everything is working.
    3. I try to set the tool square to the corners. The steppers are engaged for a minute or two, then disengage. Is that normal behavior? I feel like I’m probably missing something really simple here.

    #11990
    Profile photo of xanicel
    xanicel
    Participant

    a) Maybe your stepper drivers get to hot after some time and power off?

    b) There is a setting in your marlin firmware:

    // Disables axis when it's not being used.
    // WARNING: When motors turn off there is a chance of losing position accuracy!
    #define DISABLE_X false
    #define DISABLE_Y false
    #define DISABLE_Z false

    I don’t know the exact behaviour of the disableing process, because I never set this value to true. Could it be possible that you set this value to true and after some idle time the steppers turn off?

    #11992
    Profile photo of ShaneEEEE
    ShaneEEEE
    Participant

    You may have seen my other thread stating the exact same problem (I didn’t see yours before I resurrected mine otherwise I would have just posted here).

    Viscous made mention about the outer diameter of my conduit, since I am using the international version (Australia) which is designed for 25mm conduit but the conduit I got was actually 25.4mm. Doesn’t sound like a lot but it means everything is a tight fit and things get bent out of shape. In addition my conduit is aluminium which is not strong enough and is soft enough for it to be bent out of shape quite easily with the forces involved.

    So I am currently printing out the new corner pieces, and tomorrow will be getting 25mm OD galvanised steel conduit to replace all the aluminium rubbish.

    I am pretty confident this is going to solve a lot of the issues I have been having so once I have it done I shall comment here with the results.

    #12016
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Hey Shane,

    I saw your thread; it does sound like we’re having the same symptoms.

    I’m using the 23.5mm edition, and my tubes measure around 23.4-23.45 and seem pretty round, so unfortunately I don’t think that’s my issue. That’s not to say one or more of my tubes didn’t get bent for other reasons.

    The new corners do wonders in getting the frame squared up! I did the same thing when I first starting troubleshooting this, and they are so much easier.

    I’ll be looking forward to the outcome of your part replacements.

    #12017
    Profile photo of Jason Christman
    Jason Christman
    Participant

    My conduit is 23.4-23.45 and is round. I can’t see any bends putting a straight edge against it, but I can’t be sure it’s not slightly bent somewhere.

    I loosened the middle joiner bolts a little, but not all the way as I don’t think I can get those bolts out without disassembling the whole middle. I have my machine in an enclosure, and removing the gantry is going to require taking the whole machine out (and unscrewing and re-squaring the frame) so I’m trying to leave that until the last option.

    I’m hoping getting the steppers to stay engaged so I can set the start position resolves most of my issues. Is it normal for the gantry to be a little out of square when relaxed, or is still a symptom of something else wrong?

    #12020
    Profile photo of ShaneEEEE
    ShaneEEEE
    Participant

    I got some chrome rod which is almost spot on 25mm, was the only thing close to 25mm I could find at the hardware store. Still waiting on the new corner pieces to finish so while I was waiting I thought I would try a test fit of the rods in all the pieces. They all fit except for the middle carriage, pulled that all apart and it fits in to all pieces except for the middle end pieces. Could I have printed the 23.5mm versions instead of the 25mm versions? Surely I can’t be that stupid lol

    I wonder if that’s my not square problem right there, didn’t notice it with the aluminium because the aluminium just got squashed…

    #12021
    Profile photo of vicious1
    vicious1
    Keymaster

    It happens all the time. The new parts are marked with letters for the different versions for this reasons.

    #12034
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Tests today looked much better. In fact, this 20mm square looks pretty good to me. The diagonals were only about .1mm off (with cheapo calipers that probably aren’t even that accurate) and it looks square against a drafting triangle.

    The steppers still disengage, but I feel like I’m doing something stupid. I didn’t change the firmware setting and got my board from the vicious1 store, so I don’t think that would be set.

    Do I need to start the print first before the steppers will stay energized? If that’s the case, I can put a pause at the start of the gcode and manually set the tool position then, but I’m not sure I should have to do that.

    I appreciate all the help!

    Jason

    Attachments:
    #12040
    Profile photo of ShaneEEEE
    ShaneEEEE
    Participant

    My understanding and experience is the motors are only active during a print, they are disabled after the print is complete. At the end of the GCODE there will likely be an M84 command which is the command to disable idle hold. It could also be an M18 which just disables all stepper drivers. You could delete that from the GCODE if you don’t want it to turn them off after a print.

    Sending an M17 should enable all stepper motors, so you could send that before setting the tool position.

    I believe however that if you need to manually move one or both of the axis to get it square there is an underlying issue somewhere else. That might just be mine though, as I pulled the middle carriage apart on mine and noted the middle joiner pieces weren’t square to each other so I suspect there may have been a printing flaw when I printed mine.

    Hope that information helps!

    #12049
    Profile photo of vicious1
    vicious1
    Keymaster

    I am able to set mine without having them powered up. If you cant set yours this way you should make sure you have the correct center parts printed.

    #12054
    Profile photo of Jason Christman
    Jason Christman
    Participant

    Thanks Shane, that’s exactly the clarification I was looking for, even though it still sounds like my machine has issues.

    Thanks vicious, I definitely have the correct center parts printed. The only thing I haven’t done yet is remove all the bolts from the middle assembly and re-tighten everything, just because for me that will involve taking the whole machine apart, re-squaring the frame, etc. I guess I’m going to have to do that, though I’m not very optimistic that will fix matters.

    I am considering if the problem could be at the rollers. There’s a little bump/print blemish near the top edge (see photo. It’s barely visible in the circled area). It didn’t seem like much, but if it’s at the same location on both sides is it possible that over the span of the whole gantry it could add up to the ~ 1/4″ misalignment I’m seeing?

    Attachments:
    #12057
    Profile photo of vicious1
    vicious1
    Keymaster

    That could be it, it would be on opposite sides and could be pushing the tubes. Razor blade or a file should make quick work of it and at least eliminate that possibility.

    #12085
    Profile photo of Jason Christman
    Jason Christman
    Participant

    That didn’t seem to help. 🙁 I thought it might have improved matters, as I was able to set the tool to what seemed like equal distance to the corners (maybe 1/32 off) without the steppers locked, but the cut square was still crooked. I guess I’m taking the whole thing apart, but honestly I’m not very optimistic that’s going to help anything, and I’m pretty discouraged at this point.

    #12092
    Profile photo of vicious1
    vicious1
    Keymaster

    What are you using for a spindle, what kind of bit, and what speed and depth are you cutting?

    #12104
    Profile photo of Gannicus
    Gannicus
    Participant

    Forgive me here, as I’ve never used a CNC before, just 3D printing knowledge…but why would you need to square up the gantry before each cut?

    Once the unit is assembled, you shouldn’t need to touch anything again. It should remain square. Or am I missing something here?

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