Help

[Terho]

Hello I have a problem. My new machine is weird. When I mill out a square of 50x50x16 mm with 2 mm in depth at a time, the outer dimensions get bigger and bigger the further down I go in both x and y what's wrong? from 50x50 to 50.3x50.3

[sebba]

spindle out of tram?

some info here (you can do it with a single dial)
https://www.servomagazine.com/magazine/ ... cnc-router

and other nice way to do it
https://www.youtube.com/watch?v=L0tiNUSMYow

[Terho]

spindle out of tram?

some info here (you can do it with a single dial)
https://www.servomagazine.com/magazine/ ... cnc-router

and other nice way to do it
https://www.youtube.com/watch?v=L0tiNUSMYow

No, checked it, have the same error on all four work planes

[sebba]

No, checked it, have the same error on all four work planes

what do you mean? you said 16mm final depth of the pocket and 2mm depth of cut for each pass, so you should have 8 passes, right?
you are saying you have 50.3 instead 50 even for the first pass? and 50.3 will be even after last pass?
if yes, check the tool, could be bigger than you think (let's say 3.175mm instead of 3mm)
or could be too long and/or unbalanced
or the calibration (pulses per unit)

[meena]

Hello Everyone,
I'm having a similar issue where the dimensions keep getting bigger with each pass. Could it be a problem with the stepper motors or calibration settings? I’ve checked the spindle and tool size but still not sure. Anyone else have this problem?

Regards,
Meena.

[bhdavis]

My guess is you have a calibration error on the steppers. For example if you program in a 10 cm move and it moves 10.1 cm, and the calibration error is identical in both x and y, each pass in each directions is going to take you .1cm further and further away from your intended 10 cm location, and add .1cm to the size of the square you are cutting.

If you were machine a 10cm square recess, instead of it being 10cm x 10cm after the first pass, it would be 10.1cm x 10.1cm. Since the second pass is now starting .1cm outside of the original x0,y0 then the next pass around the perimeter is going to be at 10.2cm x 10.2cm.

So I'd suggest taking a look at your calibration settings and adjusting accordingly to bring it down to a more precise setting. Easy to do. Mark out the longest distance you can on your work surface and put a pointed bit in the router. Bring the bit over the first mark and call it 0 in that axis. The tell the machine to move the distance to the 2nd mark. If it isn't dead on then you have a calibration error. Assuming the same steppers on both x and y, and the same calibration settings in the software, then whatever you come up with in x will be the same in y.

The other issue that comes into play is backlash in your axis drive system. Backlash though should give you a trapezoid shape instead of an square when making repeated cuts, and should result in a smaller rather than larger cutout.

All of this is rather assuming you have the same steppers and drive setup on both x and y. That of course would make resolving the problem a good deal simpler than if the two axes were driven differently, and this facing different calibration settings and potential backlash issues.


BH

[RsX]

It could be backlash, tool deflection, machine deflection... a photo of the setup may help
Also the square is a pocket? a cut-out? an emboss?

p3.png (91.75 KiB) Viewed 3140 times

[cncdrive]

I think it is possible that your Z axis (tool) is not perpendicular to the XY plane.

[bhdavis]

If the Z-axis is not square to the table then one side of your 2mm deep recess will not be perpendicular to the bottom cut surface. Have you checked this?

BH