How to check a populated gantry for square


I can not easily measure the gantry with a measuring tape to see if it is square on the diagonal because there are a lot of stuff mounted on the gantry.

Is there any smart way of doing this?

/ Oskar

I did a gcode for cut 4 dots at 400 mm distance in a square.
than I mounted a Vbit and wit the MPCNC cutted the 4 dots 1mm deep.
Than I took the diagonal measure for check the squareness.
This was enough for my wish, I hope it can be helpfull for you.

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Ah okey, so no measuring of gantry needed then.

I will try that too! Did you every have that 400x400 square being not square, if so, did you change anything to make it square?

If the diagonal of the cutted square results equal, than you are fine.
If not than you need to move the feets (see the annex pdf)
Annex also a 400 mm square dxf: (39.3 KB)

In order for this test to be accurate, you first need to have the axes what you believe to be square. Said another way, your feet could be perfectly square, but if your axes are not square with the feet, then this test would display a parallelogram. Getting the axes square means using either calibrated physical endstops or electronic endstops. If in your tests you are close to square but not exactly on square, you can make the finer adjustment to get square by 1) adjusting the endstops or 2) adjusting the firmware. See the Testing and Calibration section of this page for firmware adjustment.

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So I jogged the machine in a 40x40cm square in the middle of the table with a pen now and got this result:

So I guess I need to adjust my physical end stops?

Tweak one endstop. did you double check that all 4 sides are actually 40cm?


No, X axis was 40cm (or maybe 39.8), but Y axis was almost 39.5cm everytime.

I have tweaked one endstop since!

But this is the result I get:

After one 40x40 it becomes a line gets offset when it starts to draw the square the second time.

Tweaking the endstop didn’t make it more or less square then before.

Have you checked the grub screws on your Y pulleys? If the configuration for steps per mm is the same on both axes but the actual length moved is different from the commanded move on Y, then there’s most likely something mechanical wrong on that axis. Grub screws has been the culprit multiple times.

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Y is my short axis, and I did check the grub screws on that pulley a couple of days ago. I unscrewed it and screwed it back. Seem to have been OKEY before and after.

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I am quite lost in why this is happening.

  • I’ve checked grub screws.
  • The pipes are square with the plastic parts holding them and so on.
  • Gantry pipes is square to the Z-axis pipes
  • Wheels are tightened perfectly so they have no wiggle room side to side.
  • It doesn’t rub against the table
  • Machine feels quite solid in all directions when trying to move it by hand with steppers on.

Actually the X-belts (my long axis) are rubbing against Z-pipes. But I guess that is not that big of a issue. Will fix this with some shims in the belt holders.

Looks like a solid machine. Is the double line caused by the wheels slipping to the side?

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I don’t know! But I did some measuring now since you asked! So now I know :smiley:

  • I ran the machine 40x40cm like before.
  • I measured the left wheel at the end of each square
  • Made 5 squares

Measured like this:

This are the results at the end of each square:

  1. 53.68
  2. 53.84 (+0.16)
  3. 54.39 (+0.55)
  4. 55.34 (+0.95)
  5. 56.01 (+0.67)

And this is how the lines look hehehe

I had this trouble, and I installed 3/4"x3/4" plywood tracks just inside the wheels. The wheels drag on it a little, but it has consistent position in X.

Some other people have used 3/4" aluminum angle brackets, or routed a small groove in the table for the wheels to ride in.

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Yes, I’ve seen that… But I didn’t know if it was a good idea. But since you tell me this I will start sketching up my version of it! Thanks!

Questions about it:

  • Will the friction caused by the wheels dragging on the guide rail affect the cut?
  • Is it enough to set up a guide rail for just one side and let the other side run with a guide rail?

I like the small groove also… Seems easier to achieve, but harder to tweak if it goes wrong.

Also, is this the reason why it does draw a 90 degree square?

If you overdo it, I am sure it will. I just used a nail gun to tack them down, using the gantry as a guide, making sure the first one was square to the table. I will say that you can make this bind. You don’t want that. It should travel straight on its own. This is just to cut off the worst offense. If you get it within a fraction of a mm or just touching, it will be more precise than that fraction of a mm.

IDK. You could try that but I would guess whatever force causes it to go to one side is reversed when travelling back. Your numbers went up and then down, so that kind of strengthens that argument.

Thanks Jeffe!

I also just noticed this…

Between these points I get following measurement… It is the center point of the wheel axis:

Outside: 308mm
Inside: 304.5mm

So they bow in a bit. That will surely cause problem I guess. The sides are 12mm MDF.

I will try to make a metal part that brings the wheels axis to square in the inside. If that makes sense.

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little off topic: are you using custom belt tensioners? Can you share them? :smiley:


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Here buddy:

Excellent! Thanks :smiley: