Wavy cut lines

[Ignas Kaz]

I'm struggling with my new laser cutter.
Only recently received it, had about 3 months time of theoretical learning while waited for the machine.
Now that i have the machine, and can practice, loads of problems sticking their head out.
One in particular - for the life of me i cannot get straight cuts out of it. At ANY speed. Losing steps at 250mms in Y direction, especially
when combined with X motion (drawing circles, angled straight lines).
Starting to pull my hair out (not that there is a lot left to pull).

What i tried:
1. Tightened belts (they dont ring, but tight enough),
2. Checked and tightened all the nuts/bolts/screws i could find in drive system,
3. Swapped over drivers to check if problem moves to other axis, steppers set to x32 microstepping from factory,
4. Increased current to motors from default 0.5A to 0.57A. Cant identify motors to get real specs, so dont want to increase more,
5. Cleaned bearing rails, no debris or gunk on them. Y bearing is 12mm round rod with linear bearing, X runs on block bearing,
6. After unplugging drivers checked if rails run smooth - they do,
7. Today decreased accelleration from (X) 10000 to 5000 and (Y) from 3000 to 1500 - no change, still losing steps at 250mms speed.
8. Ran loads of tests, different speeds, different patterns, resonance is always present. Slower the speed tighter the resonance.
9. Stiffened table by making sturdier mounting brackets...
10. Checked for wobbly/loose mirrors/lenses. All tight.

Look at the pics and tell me what you think... There's many more where these came from...

IMG_20190619_094155.jpg

IMG_20190619_094148.jpg

IMG_20190619_094138.jpg

IMG_20190619_094130.jpg

IMG_20190618_200627.jpg

IMG_20190618_200543.jpg

IMG_20190618_200535.jpg

IMG_20190618_185005.jpg

[Tim Mellor]

250 mm/s on your Y seems fast given you are trying to accelerate/decelerate and move the entire gantry. Even trying to do fast Vector engrave on my little toy toward 200 has seen it lose steps so I have been going slower and less power until I get a Smoothieboard fitted for better control over it and the acceleration.

I did find this reference to a Ruidia controller http://en.rd-acs.com/Private/Files/a4d9f12fe9e32eb7.pdf with some recommended figures.

Maximum Speed: it means the maximum limit of motion speed that this axis can bear. This parameter is set in accordance with the power of the stepper motor, the inertia of axis and its drive ratio. The typical value is 200~500mm/s.

Maximum Acceleration: The maximum acceleration of the axis when starting or stopping. If the acceleration is set too large, it will make the motor lose steps, jar and even squeak; if too small, it will cause the reduction of acceleration so as to reduce the running speed of the machine. For an axis with larger inertia, such as the Y, its typical setting range is 800~3000mm/s2; for the axis with smaller inertia, such as X axis, its typical setting range is 8000~20000mm/s2.

Your only other thing to test fairly easily without buying additional items would be swap you X & Y motors over if possible (unlikely it will help).

Also on a personal note can you drop your picture size to a more friendly resolution for those of us with slower internerd 1200x1k would help TIA

[Ignas Kaz]

Sadly i cannot swap motors, as X is single shaft, while Y is dual shaft.

250mms is the cut speed, not one axis alone. Also, i forget to mention that spiral starts in the centre and draws out. Meaning while its starting its losing steps for some reason, not while full swing motion is in progress. Although my factory settings suggest 500mms in X and 400mms in Y.

Also, the wobble is IRRESPECTIVE of speed. Wobles are present in all speeds i tried, from 10mms to 300mms. Losing steps at higher speeds is a cherry on top. I'd live with slowish cut if i could get the cuts to be straight...

I started my practical lasering with card (200gsm'ish), lots of small details that need be cut fast to avoid charring - thats where all this resonance its face. Cutting at 300mms very small parts loses steps and makes cuts wavy... Not what i'd expect from multi-thousand costing machine.

[Pete Cyr]

Not sure what to say - I would have recommended inspecting the laser head assembly for rigidity, the lens being snugly seated as the pictures you posted indicate something is loose or vibrating particularly when you head accelerates at a positive or negative rate.

You stated to you check all of that ...I recommend a more thorough examination - something is loose

[Jeffrey Aley]

Very interesting. You've done a great job of debugging. But that means we're left with a difficult problem.

First, I'd loosen the belts - sounds like you've got them wound up pretty tight. There's a Goldilocks setting ("this belt tension is JUST RIGHT") but you'll have to experiment to find it.

Second, shove a couple of wedges between the table (bed) and the frame so that the table can't wiggle. Not sure if you have a blade system that supports the material or what. Make sure the bed is rock-solid for your experiments.

Third, can you please post a pic at 10 mm/s? The waviness is very consistent in the pics you posted, but they're all at 100 mm/s - 200 mm/s.

Fourth, run your test WITH THE LASER OFF. I.e. turn off the power switch for the high-voltage power supply. Put your finger on the top of the head while it's moving (that's why the LASER MUST BE OFF). Do you feel any weird vibrations?

Fifth, how do you know the lens is held tightly? Suppose for a moment that the lens is thinner than expected, and that the nut is tightening down without actually clamping the lens. Could you add an o-ring or something on top & bottom of the lens to ensure it's actually being held down?

Sixth, is the head mounted securely to the gantry? Does the X-axis bearing have any side-slop?


Good luck!

-Jeff

[Jeffrey Aley]

By the way, I don't perceive that you're "losing steps". The laser seems to know exactly where it is in each of the images you showed. When losing steps, a closed figure (circle, square) won't close - the two ends won't meet.

You definitely have a problem, but we wouldn't call it "losing steps". What would we call it? Hmm. "Wavy Lines" or "Wavy cut lines" as you titled your msg.

Regards,

-Jeff

[Gene Uselman]

In addition to Jeffrey's excellent comments- if you shake the lens tube, the lens should not rattle.

[Ignas Kaz]

In addition to Jeffrey's excellent comments- if you shake the lens tube, the lens should not rattle.

And it doesnt, checked that. All mirrors as well.

1. Table has been rigidified, i made better 2 point mounted brackets, instead of flimsy factory supplied one point and too small screws to hold it. Holes drilled for m5 but mfg used m4 with oversized washers. Had to redrill access holes in the table to put second screw for new brackets. Table is definitely not vibrating - under tension from chain drive and bearings on both ends of lift rods. Will do wedge test, but i'm certain tabe is not at fault.



2. tried 10mms, cannot go lower on power for pattern to show up. Uploading 25mms i did earlier today:



3. Head is secured, no slop in block.

4. Start in this drawing is supposed to be the center of spiral, its not. i call it lost steps.. Or stalled motor.



Also, check the 100mms 20% cut, it lost steps and border is messed up. And its only 100mms, lots of char. Smaller i go more stalling/losing is coming out.



I will losen the belts tomorrow some, see what comes out of this. However right out of the box with no tweaks at all it did wavy lines, tightening a bit came after. Belts do not ring when plucked.

#EDIT# As for the test i posted, all are at 100mms as it was suggested to test for resonance in all four corners of the bed. Kept speed consitent for that, thats why its same, resonance as well...

[Pete Cyr]

Have you checked the tube tight in the mount?

[Ignas Kaz]

No, thats a first to be suggested tbh. Will have to check.