Incorrect Sizing

I have calibrated the machine over and over
when I calibrate the X & Y
I do it over a long ruler with a and I can get it to travel the distance and be completely accurate.
after calibrating if i cut a 1" square it ends up not being the right size

If i base my calibration on cutting and i compensate the Steps then sizing changes on different materials
I increased the pots in case I was skipping steps. its often too large which doesnt make me think its not missing steps
I tightened the pulleys (i assume missing steps would make this smaller then normal)

Im running Gt3 belts which are snug

not sure what to do at this point.

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Is it off by a lot? It could be due to run out in your spindle or incorrect bit size. Measure your bits as they are generally slightly different than the nominal stated size.

I meaure the bit with a digital caliper for it was .123"
some items im off 1/4" - 1/2" over a 15" distance.
running a Dewall 611
X and Y have been reinforced

Feeds/Speeds 60in/min .06" cut depth
1/8" two flute endmill
cutting 1/2" birch and 1/4" PVC

Adam - I assume when you changed to GT3 you also updated the $100 and $101 (iirc) Grbl values?

yes for sure. I have been tweaking the $100 & $101 to get it as accurate as possible.
but sizing under load and without load is different.

To me it sounds like something is slipping. Check your pulleys, I find the set screws like to back out and the pulley will slip on the stepper shaft.

Yes i adjusted them with a meter, but that didnt seam to help as it seems like needed voltage was arbitrary
I basically started to use my hand to see how much force was needed to stop the gantry, once i felt a decent amount of tension I stopped increasing the pots.

Belts are tight, But i have no good way to measure this tension.

I just checked the pulley set screws and they seem fine… I will even be putting locktite on them.

I will try and readjust the pots again… and hope it helps
when you guys calibrate your xy steps… do you do it under load? and measure a cut piece or do you use a ruler and see distance moved unloaded

Write down your $100 and $101 numbers, and then set them back to the default steps/mm (I’m not sure what the default is for the GT3 belting, GT2 was 40steps/mm). Make a test cut and measure how much it is off from your target dimension. Is the amount your cuts are off by greater or less than the amount you were off by with your calibrated steps/mm?

-If the difference is closer to your goal with the default steps/mm than with your adjusted steps/mm, you might have your equation upside down and need to make your adjustment of steps/mm in the opposite direction.

-If the difference is greater with the default steps/mm vs your adjusted steps/mm, keep adjusting the steps/mm in the same direction you were going.

I learned that the hard way and couldn’t figure out why my calibration seemed to be getting worse. I still use the GT2 belts on my machine, and was never off by more than a couple mm over a 500mm travel distance, no load. Robert’s method for setting the pots for your axes is a good way to go. I calibrate my steps in a no-load situation, with a ruler and the smallest tip v-bit or engraving bit I’ve got available.

Stupid question. If you’re using Easel to cut the square, is it set to cut outside the line instead of on the line?

Another stupid question: You’re not using a ruler that measures in 1/10 increments of an inch and mistaking them for 1/8", are you? Theoretically, it would be easy to use one of those stupid things and assume that something like 10.3 inches is actually 10-3/8", which is .075" off. Of course, someone like me would never make a mistake like that in front of coworkers. Twice. :tired_face:

What length ruler/scale are you using to calibrate? It’s best to try to use the longest and most detailed scale that you can find, like a 600mm scale. If you’re using a small one, like 6", than any error due to readability or other reasons would double at twice the calibration distance. So using a 6" scale and being off by .020" could add up to a .100" error across a 1000x1000 machine.

If you want to check whether the error is due to runout/wobble, try to cut a 3" line that’s .050" deep (in Easel you can just make a square that’s .001" tall and cut on the line). Do the cut, then measure the line width with your calipers. If it’s effectively the same as your bit diameter, then it’s not runout.

If you’ve checked the easy stuff like V-wheels, pulley screws (use loc-tite!), and belt tension, then you may want to make a more quantitative adjustment to your potentiometers. I really like the idea behind your method, but I’m not sure how well it would relate to the high and low voltage settings.

When I calibrate, I don’t do it under load. I still do it the way I showed in the video I posted in the maintenance video thread (X-Carve Maintenance/Troubleshooting Videos - Add Your Own!), except I now turn the V-bit 90 degrees and try to read across the flat instead of using the point. It helps to cut down on the parallax error.

One word of caution on the calibration, either flatten your wasteboard before calibrating or make sure your bit is high enough that it won’t jam into the board. I almost did that once, and would likely have broken the tip off of the bit. It’s bad enough that I’ve accidentally tried to drive two of them through my aluminum touch plate…


Just another thought, make sure your frame is square and tight.

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When cutting square . Cut path is set to outside

I use a 900mm steel ruler. With individual mm markings. I usually do 600mm movements to check position.

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