Symptoms of Belts too tight

New Home Forum Mostly Printed CNC – MPCNC Troubleshooting – MPCNC Symptoms of Belts too tight

This topic contains 49 replies, has 8 voices, and was last updated by  P3DCNC 2 years, 9 months ago.

Viewing 20 posts - 31 through 50 (of 50 total)
  • Author
  • #27558


    Glad to hear it’s not a common problem. Will get you that info tonight. To answer some of the questions:

    1-My height is reduced to the point where only 1.5″ of tubing is showing on the feet.
    2-Will post pics tonight.
    3-I am using your mount with the router bolted to it. It’s solid. Will post a pic and the stl for it tonight.
    4-Same, tonight.

    I realize you are busy and really do appreciate the help @vicious1.



    So jerk is a setting that did not even work correctly in the firmware until RC7 (if I remember correctly). It could be a jerk issue but I doubt it. Who knows maybe the jerk setting is the problem as I have never tuned it other than the first time and set it for Milling, not printing. Low Jerk settings just mean more movements will use acceleration, High jerk means small movements will change speeds with no accel. (simplified) For cnc low settings means the bit will linger in a corner longer but not wobble, as a printer this means you could get bulging corners from lingering too long.

    All you have to do is increase the number and try it.

    This should be a fun project, get your hands dirty try some things if it doesn’t work flash it back. That should be part of the fun of having an inexpensive machine we are free to experiment.

    My Guess to your problem is over tight hardware, but it could also 100% be software/firmware related. At this point in the MPCNC life I am fairly confident software and firmware issues and limitations a have been discovered. There are thousands of these machines out there, tons of videos of smooth drawings large and small.



    1-Your machines are both double the recommended size in foot print but neither of you specificity the most important one of height. and what material are you using stainless or conduit.

    24″x36″ is the workable area (34.4″x46.4 is the footprint). EMT 3/4″ standard US Home Depot conduit.

    2-Picture of your machine So I can spot an obvious errors. A picture is literally worth thousands of words in this case.

    3-That jagged drawing I need to see how it was set up, what tool mount, what pen, what surface were you drawing on, how big is the actual drawing?

    Using your pen mount with a gel pen, barely touching an 8.5″x11″ standard copy paper.

    4-Screenshots of all the speeds you were using in whatever software.

    Image 1

    Pen mount

    letter size

    letter close up


    Whole setup

    X axis



    My machine is ~120mm of Z travel… way more then I need that I know. Not sure if that matters at all when it just moving with nothing on the Z.

    1″ Stainless closet rails. 60″ long.

    I printed and configured and bought all my own components. Tuned as per the specs you have listed through out the site.

    Most of the time I am using a 6 watt laser with a small chinese heatsink and 40mm fan. no appreciable weight compared to a router. Yes it hangs down several inches when engraving but like i said the problem occurs with 0 weight.

    speeds i use are typically 600-1200 mm/min. My problem happens regardless of directional travel. Happens in X, Y and diagonal movement.

    The only thing I cannot spin by hand is the long 5″ tension bolt down thru the xyz axis. the hole is kinda tight. All bolts on the rollers, and x y center pieces I can spin by hand.

    I do believe that it may have something to do with over all size. as it seems that when it starts the vibrating that the rails are bending slightly but the could be an optical illusion from the vibrating itself. But just straight rolling with no load should be smooth.

    I have my self pretty well convinced it has to be a couple bad bearings.


    Sergey Kovalyov

    Let me suggest the following experiment to separate physical origin from logical origin:
    1) create a sample job, e.g. a drawing
    2) remove any zeroing from the gcode, if any
    3) run the job
    4) shift the logical zero a few millimeters by manualy moving the gantry and issuing G92 (or just restarting arduino)
    5) rerun the same job and compare the artifact positions
    If the artifacts stays with physical origin, the problem is attached to the frame – rails, bearings, etc. If the artifacts move to the new origin and stays in the same place relative to the job, the problem is attached to the firmware



    I would believe it if was firmware the problem would be more wide spread as I am using the stock RC7 image from here just changed my sizes to fit my machine and steps per mm because I switched to 1/8 stepping.



    1/8th stepping means curves will have a stair step. you should use at least 16th.



    When I first built this I tested this, I made as large a circle as would fit in my machine and drew it. Then kept lowering the steps until I could see an issue, at 1.8th I saw stair stepping.



    Hmmmm……does it seem better?

    Better print



    1-25.4mm SS Tubing. Leg height 40mm of tubing exposed. Scratch board to bottom of XYZ assembly 85mm.

    2-Picture of your machine attached.

    3-gcode file of what I was cutting (not drawing) is attached.

    4-Screenshots attached.

    Plus more videos and pics… MPCNC Jittering Diagonal Issue

    Did I miss anything?

    …Files are uploading at the moment. May take some time.



    Jason- let me know if that fixed it when you get some free time (world’s most valuable commodity).

    Zeenon – looks like that is pretty good, could just be the texture underneath showing through, what did you change?

    P3D- Attaching the drag chain to the z motor mounts could really be doing some/most of this, plus you have a very large machine which makes it more susceptible to these sorts of issues. That drag chain is acting like a breaker bar and pulling on your entire middle assembly. Nothing should ever touch this. It also looks like you are attaching a vac hose to your router, making it even worse. You really can’t have it all buddy. Giant machine, tall z axis, drag chain, vac hose, and super precision. I use a small machine, hold my vac, no drag chain for a reason.



    The drag chain doesn’t affect X only or Y only motion. Only diags and circles are affected. When the pics upload, you can see one of the cuts has a Y only clean cut (to the right of the pic) and a chopy diag and circle (center and left). My issue is only on diags and circles. I would think the drag chain would affect all of them no ?

    I want my cake and I want to eat it too! 🙂

    In some of the videos where I lowered the speeds to F50 you can hear the alternating X Y motor dance. They do not move simultaneously. Is that normal ?

    If you watch the little white wire at the top of the Z you can see it only shakes on diags and circles. Pure X and Y it doesn’t move.



    My Guess to your problem is over tight hardware

    I think my biggest issue was the bearings on the XY outside axis were gripping the conduit too tight. I loosened the bolts until I could spin the bearings, but yet, they still made contact with the conduit. Too loose, and the bearing would not come in contact with the conduit. Too tight, and spinning the bearings (if you could), would move the axis.




    Got more pics to send but having an issue with getting on my PC.

    Did a few things. Redid the zip ties on all belts. Also moved the GT2 16T pulleys in a bit. Also loosened some more bolts. Seems quite a bit smoother. Still has repeating patterns but definitely much better. Will post pics as soon as I can. Time for some sleep.



    @vicious1 I started out at 1/32 stepping and the problem happened then as well. Really the only thing that changed when going to 1/8 was the motors seem a little cooler. I was have issues attaining higher speeds while lasering 1/8 helped speed that up as well a little. Other then that anything I have tried has not changed anything. I will have time tomorrow to play… I am going attempt loosening the bolts off a bit on the 8 bearings in x/y that are held in with 1″ bolts. I have those tightened up pretty good. Perhaps they are not tracking 100% straight causing a wobble.



    @jason I redid my belt tension, loosened the bolts on the xy that I could get to, and also redid the GT2 pulley. See the pics I just added (dated feb 16). You can see an improvement in the jittering although it is still there and notice the repeating patterns.

    20170216_001143 – shows two cuts in different areas of the stock material with identical patterns. The more pronounced one is the plunge location.
    20170216_001025 – shows the difference after redoing belt tension and loosening some of the bolts.
    20170216_001008 – same as above.
    20170215_235329 – shows the location of the GT2 pulley before.
    20170215_235436 – and after.

    I’m going to dismantle my xyz and redo it. See if that changes things.



    Just an update.

    I remixed my XYZ pieces, the spacer and nut trap so that the Z bearings aren’t spreading as much and my MPCNC is square at rest now (see attached photo). Was not able to square it before. I think the torsion on the center assembly was part of the cause of the issue.

    I tightened all the corners of the frame and added mid span supports on the X axis (see attached photo). That stiffened the frame quite a bit.

    I can now cut circles at 1100mm/min pretty cleanly (see attached photo). I can even cut at 7200mm/min but it’s rough looking, but the bit and setup can handle it just fine. Impressive. 3mm per pass on an 1/8 bit at 20000RPM.

    All in all, much happier with the results.



    I dont quite understand what you mean about the z bearing spreading.

    I do not have any mid span supports perhaps i should.

    Your results are impressive. Good work.



    When I had the original XYZ parts, the moment I inserted the Z tubes it would force my X and Y axis out of square by 5/8 of an in inch. So I remixed the XYZ parts so that the bearings were backed off a bit by placing the holes for the bearings so the bearings would just touch the tubes. Now when I insert the Z tubes, everything stays square.

    The mid span supports are a huge benefit. I might even add more.. I’ll post the stl’s tonight on thingiverse and add a link here. They just mount to the standard MPCNC corner mounts. No use in re-inventing the wheel.



    Here are the span support and nut trap that you stack on the stock mpcnc foot corner pieces.

Viewing 20 posts - 31 through 50 (of 50 total)

You must be logged in to reply to this topic.