I can’t seem to get my gantry square.

I can’t seem to get my gantry square. That’s the only reason I can think of, that is causing my router to shudder and miss steps. My X & Y axes are belt driven. I’m beginning to think I’ll have to convert it to all lead screws…I’m so frustrated!!

What driver are you using?

I have a TinyG v8 controller with 4 Nema 23 motors. 2 on Y axis…belt driven with GT3 6mm belts.

Try loosening the eccentrics on the guide wheels that support the gantry. Too much resistance will cause missed steps.

Hey George,

Do you have a way to move your gantry manually so you can pull one end square to the x axis…place a large square against the y axis and maneuver the gantry until it is square. Check square on the other y axis rail. BTW, those two rails need to be parallel to start with.

I have experienced shutter and missed steps from the motors not having enough power. This can be set by carefully turning the pot for each motor on the tinyg board.

Just loosen the belts and manually square up your frame. Then drive the gantry against the end until both motors make that noise of losing steps. They are now both at the same position along the rail and square to the other axis

Don’t blame the belt drive. Belt drive is not inherently bad. I’ve built dozens of belt drive machines without the problems you are seeing, so it’s not a problem with the design, but with something specific in your setup.

It’s possible that the ends of your X axis beams are not square and/or different lengths. Also, if the 20x40 brace is a different length it may cause the gantry to rack.

As Julius said, just run the gantry up against the end stops (assuming they are square) and it should automatically square up the gantry. Also check your bed by measuring corner to corner to see if it is square.

And, as Jim said, readjust your eccentrics. You should just be able to turn the top wheels with your fingers if they are properly adjusted. If you can’t turn them, the eccentrics are too tight, if they spin easily, your eccentrics are too loose.

Also, check your belt tension and tighten the setscrews on the motor pulleys. They are famous for coming loose. I replace the setscrews with button head machine screws, becasue they have a bigger hex in the head and you can get them tighter. Loktite also helps immensely.

Having said all that, those problems should not cause what you are seeing - shuddering and missed steps. Make sure your motor currents are set properly, and the TinyG has heatsinks on the chips and a fan blowing on them. Overheating of the drivers can cause current limiting and missed steps. IMHO, the TinyG is not robust enough to properly drive NEMA 23’s to their full potential.

Check motor wiring for loose wires.


Ok. I’ll look at the set up. I’d rather not have to change anyway. I was milling oak, which is a hardwood. That shouldn’t make a difference? That is what you are saying.

I’ve thought about the eccentrics and I just began looking at those yesterday. I have noticed that the x-axis doesn’t move smoothly as I manually push it across the x-axis.

It is possible that your feed speeds are just too high, your bit is dull, or your depth increments are too much. Oak is typically a very hard wood, you may have to reduce feed speeds and depth of cut and increase router RPM.

But, your original post said your problem was the gantry is not square, it didn’t mention anything about cutting.


@George_Allen This could be due to a couple of things. If the power is off, and you move the axis, the motor acts as a generator and puts voltage back on the driver. At some threshold, the diodes on the driver will start conducting and partially short the motor windings, causing the motor to “chug” or “stutter”. This is normal, and is a function of the driver, not the mechanicals. If you move it very slowly, it shouldn’t do this.

With the power on, assuming you have partial motor current when it is disabled (not moving), the motors should be locked. Grab your Z axis and try to move it side to side and forward and back. If there is any slop or play, it is likely that your wheels are too loose, or something else has come loose. These machines vibrate a lot, and screws come loose all the time. I can’t recall how many times I have been routering away and a random screw drops onto the table… You need to go over the machine and tighten everything up on a regular basis, and keep it CLEAN.


I had the exact same problem and found that it was my wheels were WAY too tight (mine is a 1500mmx1500mm Ox). I live just outside of Phoenix and built the thing in the house on the kitchen table last winter (76 degree house). It is mounted on the wall of my garage on a piano hinge so that it folds up out of the way when I need the space.

The temp difference in the summer was huge, 110-115 degrees outside when I finally got to play with it and the heat expansion of the rails bound it up fiercly. Once I loosened the wheels so that they didn’t allow any unwanted movement, but still allowed the gantries to move very smoothly, all my problems went away and I was able to drop the motor power outputs (cncXPro controller) to minimum again.

I also did replace the set screws on all motor pullies with M3 socket head screws to be able to tighten them well and used locktite blue.