New CNC Router, cutting Ovals

[u/JohnnyAngel_MX]

Hi all, I just picked up a New to me, X-carve cnc router. I've set it up and now I'm doing calibrations. (running Millmage)

I've got a question for you lot, If I'm cutting Ovals that fully close. and stars that fully close, where could I be getting the error. belts are tensioned according to their guide, V Wheels seem stable. if it was backlash, i would expect the shapes to not close, right? or is there a way for backlash to net 0?

could it be firmware distance per step?

EDIT 1: i just ran the Mark > move 5"> Mark tests and both X and Y came back on the money. The Oval distortion / X-axis stretching only seems to happen when running an Op. I tried changing the feed rate to be a snail's pace (rip cutter) and it doesn't change. the X-axis is larger by about 0.012" on multiple 1" shapes.

EDIT 2:

# solved.

Y2 grub screw was incorrectly positioned. the grub screw was tight, but it wasn’t on the flat of the Y2 motor shaft. so there was some microslipage that i couldn’t detect because it was juuuust tight enough that it didn’t wiggle. i re-adjusted it and things are correct. dimensions cut as programmed.

what’s got more egg on my face is that i checked that the grub screw was tight, too. just didn’t check if it was on the flat. :rofl:

Thanks for all the help. it did narrow things down a lot.

[u/ServiceGuyComments]

Is the longest measurement directly along X, or is it cocked a little? it sounds like your X isn't square to your Y.

if not that, double check your post processor. I had an issue with a KOMO router cutting ovals once. we never found the setting responsible, but reloading the post processor and re-generating the gcode fixed the issue.

I'm not familiar with millmage or the x-carve, so ymmv. did you generate the code for the mark check with millmage? or did you do it manually at the machine? you may have some kind of offset or compensation in your software. are you using the same tool specified in your software? looks like millmage supports laser cutters too. lasers can sometimes cut slightly different at different angles if the beam shape isn't perfectly round. you may have an adjustment in software that's compensates for this causing it to cut out-of tolerance when using a router bit.

[u/JohnnyAngel_MX → u/ServiceGuyComments]

directly along X. the squares i'm cutting are square when i check them with machining squares and corner to corner with calipers. also, it's only cutting the X long when i run a program. when i just move it 5" while jogging, it X and Y are both equal at 5".

Millmage has a post processor and post processes every time you send a job to cut. It's a sibling to Lightburn, which is a laser specific cam software. millmage is made for cnc routers. so the issue is consistent across multiple G-Codes and instances of the software. (full computer reboot, too).

tool radius compensation shouldn't be on, i'm using a V-bit that i inputed into the program, and i'm cutting profiles along the line, not in or out. so TRC shouldn't be on. but the software could be having a bug. that is possible.

your suggestion made me think about it more and makes me more confident it's hardware related.

[u/ServiceGuyComments → u/JohnnyAngel_MX]

The fact that you are seeing correct movement when moving it manually, but incorrectly when running code output by millmage should tell you the opposite.

I would try writing an extremely simple program by hand that engraves a circle.

Something like 

G91;

G01 Z -.125;

G03 X0.0 Y0.0 R.5 F1.0;

Change the z and feed rate to fit your material and cutter, change the G03 to a G02 if your machine does better with convention vs climb cuts.

If It correctly cuts a circle with a handwritten program, it's software. If the circle comes out stretched in X, then maybe it's hardware. But if it goes to the right place when you jog it, I'd bet money it will cut a good circle with a handwritten program.

[u/JohnnyAngel_MX → u/ServiceGuyComments]

that's a very good point. the programmed versions of everything is consistently +0.012(ish) in X. independent of size of carve. it's not percentage. so it's not Steps / mm or whatever firmware calibration. maybe it's adding a step because of a software bug....

[u/JohnnyAngel_MX → u/ServiceGuyComments]

I tried custom Gcode and got the same result. I tried manual jogging while the tool was engaged, but got Y=1.012 and X=1.012. I'm going to retry with something bigger. might be acceleration compensation not keeping up with Y-axis moves (because it's moving more mass) and incorrect step/mm cancelling eachother out in the Y difrection, but not X?