Help getting correct measurements on cuts

When I have a test pocket cut of 20mmx20mm pocket/fill cut and an outside cut of 40mmx40mm I get 3-4mm short in each direction. my 20x20 is around 16x16 to 18x18, havent hit 20 yet. my 40mm square is 36x36 or something like that. I have run calibration as many times as I’ve tested… ~9-10. I have remeasured the other settings and run again. I have done some at ridiculously low speeds (150mm/min) and insanely fast for maslow (750) something that remains constant is cuts being short. I have a 1/4" bit and I put 6.35 in for it every time. I have included my GCode file as well. not sure what else to do at this point. if someone else could run the gcode to compare it would be much appreciated, maybe that’s a big part of the issue? Not sure where to go to now. My last calibration and test did worse than before.

test (2).nc (5.0 KB)

Image included just as an illustration of how many times I’ve been trying to work through this. I have things generally working well but if Im going to move on from cutting generic signs and get to things where pieces fit together then measurements matter.

thanks in advance.


@Jay_Settle is in the same boat. Maybe he can try your gcode.

Have you tried @Joshua ‘s holey calibration? Have you gone through the List of sources of error thread?

Right now in the sweet spot im getting ~0” - 1/4” error. I’m still working through the variables.

yes Ive gone through the list. I’m not familiar with Joshua Holey Calibration

This may be relevant:


May '18

I think I know what’s going on. The issue has to do with the default resolution of MakerCAM not matching the resolution of the file saved from inkscape. Changing the import resolution to 96 in MakerCAM fixed the issue for me.

I’ve created a pull request here to propose updating the file resolution to import into MakerCAM the correct size.

This earlier sled design is actually a little smaller than the new 18 inch sled (I think it’s 400mm?) so don’t be concerned if it comes out a little smaller.
I hope the above paste is a link for you to check out.

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So let’s go through it. What are you using to CAD? What are you using to CAM? What OS are you on?

Thank you

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CAD: Easel
CAM: Ground Control

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Unfortunately GC is not CAM as it does not produce g-code. I have not used Easel, but my understanding is that it is CAD/CAM. The fact that you are getting squares and not rectangles speaks to a scaling issue and not a calibration issue. I think @TheMerryYeoman’s suggestion has merit.


ok, you got me… I generated the gcode in Easel. I attached it to this post as well. I also generated gcode in easel for an xcarve and it came out perfect, no scaling issues. I can try the scaling adjustment, but really don’t think it’s addressing the issue and if Im correct will manifest in issues in other ways.

I might get etslcam just because it’s supposed to be nice for planning paths etc. I can also try cutting the large calibration pattern in ground control.

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I ran through the first segment of g-code, and you are correct, it is certainly specifying a 20x20 mm square cut if you are using a 1/4" bit. I’d be happy to take a look at it on my machine, but I probably wouldn’t be able to get to it until the weekend.


thanks a lot, Im in no rush

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I guess you didnt have time to mess with it?

Hi Anthony. No, sorry, I completely forgot to run your code. Sorry about that. I will get back to you once I’ve had a chance to play with it.

Anthony, did you figure out what caused it? - I’m experiencing the same issue. Generated an 18" circle (guess what for…) in Fusion 360 and it comes out at 17 3/4" in Maslow CNC. I posted this question on FB user group and someone printed my .nc file and he got an 18" circle. There has got to be something with settings, but i have no clue what… Thanks for sharing, if you solved it.

what is happening is that in the CAM step you are telling Fusion360 that you
want the bit to follow the line you drafted. But since a 1/4" bit will cut 1/8"
outside the line and 1/8" inside the line, you end up with a circle that is 1/4"
smaller than what you designed.

look for where it says ‘cut on line’ and look at the other options, that will
direct it to move the bit to one side or the other of the line, depending on
what you choose you will either get the size you want, or a circle 1/2" smaller
than you want.

David Lang

This setting- Compensation Type- is set to Computer. it means that the toolpath is offset from the feature geometry by the radius of the bit. i need to see if Ground Control is skipping this part of the g code… I’ve been seeing g94, g17, g28, g54 missing, and have no idea why GC is not reading them… G41 that per the article is responsible for the compensation wasn’t among the missing commands in GC. I’m a complete novice, so please cut me some slack for naming things incorrectly. Link

cut on line is separate from compensation type. you can have compensation type
set to computer and still have it cut on the line instead of offset.

in gc, does it show the toolpath outside the line or on the line?

GC does not skip any g-code

David Lang

I didn’t know GC is developed enough to display tool path separately from the feature geometry… so to answer your question it shows ON the geometry line. Now, what setting in Fusion 360 exactly is responsible for outside offset of the tool path from geometry?

GC doesn’t know anything about your feature geometery, it just knows where it
has been told to move the cutter.

I have only seen Fusion 360 once, but the guy had it set for computer generated
offset, but in some other setting, he had it set to cut on the line.

David Lang

I haven’t found anywhere in Fusion nor on the web this “additional setting” that you’re referring to. GC cuts along the path generated in CAM software, path that includes information including drill bit offset from the geometry lines. And GC ignores commands: 94, 17, 28 and 54. (“command xyz unsupported and ignored”) Attached is the .nc file. Since i can’t interpret it, maybe someone else can. 18 Test (285 Bytes)

FIGURED IT OUT: It was indeed a Fusion 360 setting: “In Computer”. It’s late, but i’ll narrow down the correct settings tomorrow and will post here. my 18" circle now cuts at 18" as it should.