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CNC problem?

Hello all of you, i have a problem with DIY cnc. I guess missing steps?
I would ask you to give your opinion?
On pictures you can see CNC, and problem. Circle is not closed. I try with backlash in mach and i get a bit bether result but still not perfect circle

Picture of CNC problem?
image-a9726c548bd0030703fa30ca17bcf1850ae79ead8c2afa90ddfebd533a9f1ba6-V.jpg
image-afdc8c2ca78fd54e2bfcd5d02e12ea681fd397b2581c950facdd455c235a9540-V.jpg
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skitowski10 months ago

hello! Where you able to solve this problem? I have happen to have the same exact circle! It's driving me nuts trying to fix it so far.

Also check the pulleys are tight on the stepper motors, Ive seen a fault like this before and one of the grub screws in a pulley was lose.

bciric (author)  liquidhandwash1 year ago

Hmm i will check. Thanks

Backlash that severe needs fixing mechanically, not in Mach. Check your belt tensions - they need to be HIGH for toothed belts.

bciric (author)  steveastrouk1 year ago
Hmm i strech this. How i can know when tensions is good?

How are the belts tensioned ? The best way is to have springs pulling on the idler pulley.

You need 100-150N of tension.

bciric (author)  steveastrouk1 year ago

OK, i try this with hands (i can't measure tension), in one situation i block machine , and in few other same problem :(

You have two problems with your setup:
a) the size
b) the belts

A table that size need extremly sturdy connection and drive gear!
If a belt only has 0.2mm stretch per me than yours is already pushing the mechanical limts quite hard.
What bothers me is that you say the result is the same when using a pen.
That usually means a more severe problem somewhere.
Every mechanical connection that is not 100% tight and solid will add up to the positioning error.
Since the circle is actuall round I can rule out stepping problems and I don't think the system will loose a step or two just for fun.
Considering the finer cuts look better I assume your problem can be as simple as bending mounts under load.

bciric (author)  Downunder35m1 year ago
Hello, thanks for comment.
Belts have a steal core, so i think there can't be any stretch, maybe tension is not good?
Yes, there is no differents with and without loads. I try with pen and same result is as with MDF (5mm depth). I am not sure about bendings, all is prety strong.

Check with a pen ;)
There will be no high force required to move it, if you get decent circles it means you might be missing steps, although it is quite possible that your drive system is causing it.
Belts, direct drive, screws -how does it move?

bciric (author)  Downunder35m1 year ago
Same os with pen. I use tb6600 drivers with 1/16. Also there is t5 belt and pulley for movement. Thanks