“Curtains” in engravings

after finding it I was reminded it was spotting throughout the engraving, not the banding you are seeing. Laser glitching around text

Frankly, I’m quite surprised you are seeing the same results at fast(200+ mm/s) and at slow(~50mm/s) speeds. Seeing the same period/spacing of the bands at different speeds, AND when you had the belt inverted just doesn’t sound right.

The spacing of the bands does change with different speeds. You can see that in the image I posted above (quoted below), apologies if I was not clear on that. Now what does not seem to change anything is inverting the belt. I did at one point have the GRBL controller connected to the big laser, it was displaying the same symptoms as the FluidNC controller. I swapped them because the guys developing the FluidNC software had a devastating bug with the Espresiff SDK and I was suspicious.

When I look at the picture below, all I see is a reflection of the GT2 belt pattern. It is damn near identical…

Somehow I must have missed the important fact that the pattern does change when you change speed. When I mentioned running at different speeds I thought you just said it still does the banding and nothing more.

Did you measure the spacing of the bands at different speeds to try and determine a correlation between speed and banding period? And I’m sure you know that as you change speed you also have to change power so that you’re getting the same amount of power dumped into each pixel.

It would also be helpful to provide the link to the post with the image instead of creating a low resolution image of a previous post.

I did not provide explanation. It’s not your fault, its mine. I did say “it still does the banding”. It does seem like the banding changes with speed, besides the images I have provided, I have no empirical evidence that shows the actual speed associated with the images I have posted. I will make a few burns tonight and associate them with speed and power settings. I will then make another post so I can provide more concrete evidence of what is happening and at what speeds and powers.

Here is a link to the post so you can see the high quality image:“Curtains” in engravings - #11 by James_Harding

Varying with speed makes me wonder about how you are managing laser power. I don’t think you have shared a schematic with us?

Are you using an analog pot to set the max power, so that you can use the full range of digital PWM? If you aren’t, then you are using only a small portion of the 8 bits of PWM duty cycle, and I think you could end up with aliasing like this. This would be a difference from the K40 where you would be using a larger proportion of the digital range, and thus see less of an aliasing effect. I’m just listing one thing that could be related here, could be something else.

In any case, it’s worth listing all the components you used in the big laser with a schematic of how they are connected.

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Judging by these comments, and my own experience, I would check the idler wheels riding the aluminum extrusion for nicks or out-of-round. I built a custom laser machine myself and had the same problems. Turned out it was the delrin wheels. Some were out-of-round, which would cause an oscillating pattern length equal to the circumference of the wheels. Also, when you load the gantries on to the extrusions, the sharp edges of the aluminum can pit the face of the wheels causing a repetitive disturbance in the motion.

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No, I am not using a pot. The K40 is also not using a pot.

Parts:
Laser Power Supply: Cloudray
Laser: Cloudray
Lens: TEN-HIGH
Mirrors: Amazon
Laser Head: CloudRay
Laser Mount: Amazon
Y-Stepper: Amazon NEMA 17
X and Z Steppers: Stepper Online NEMA 17
24v Power Supply: MeanWell
Z-End Stop (Auto Focus): CloudRay
Z-End Stop Relay: Amazon
Power Strip Relay (exhaust, water pump, air assist): Solid State
V-Slot Wheel: Amazon
Smooth Idler Pully (x and y axis): OpenBuilds
Nut Block for Z Axis: OpenBuilds
Lead Screw for Z Axis: OpenBuilds
X Axis Belt: Amazon 9mm w/ 16tooth pulley
Y and Z Axis Belts: Amazon
Shielded Cables for Stepper Motors: Amazon
Exhaust Blower: Amazon
Water Pump: Amazon
5v Output Module FluidNC: Bart Dring
FluidNC Controller: Bart Dring

Nuts Bolts and miscellaneous hardware all came from Openbuilds

Surely there is more, if you have something in particular, just ask and I’ll find where it came from.

Here is a schematic of the current setup:

So then maybe you put an analog meter on the laser and adjusted a POT inside the LPS to set your maximum power output?

Normally( DIY, K40, everything but Ruida ) uses a voltage set on the LPS-IN input(usually using a pot across 5V and the wiper going to LPS-IN) which sets the avg max power output and then you set your firmware so 100% PWM equates to this “max power”.

@jkwilborn on the LightBurn forum dug into this and found that the LPS still sends 100% power in a pulsed fashion(much higher freq ) even when the LPS-IN is set lower. So he has opened his LPS and adjusted the onboard POT(dangerous if you don’t know what HV is and how it can kill you) to limit the LPS from outputting more than the tube is rated for.

Well, I was wrong. Apparently it’s exactly the same at every speed. I don’t know how the image with pine in it had the lines so close together. This is essentially what I’m battling, a seemingly completely inconsistent result. Some days I swear I come out to the garage and it works for a few burns, and then the next day, or ten minutes later, it’s not working.

In this image, each row has 1 speed and power. I have it this way because as you can see the pattern appears differently across each 40mm x 20mm square. Each square was engraved individually.


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Edit:Fixed grammar and tried to clarify engraving.

I don’t know that the problem is electrical, but I’ll explain why I asked…

To get the same effective power from your 90W tube as you do from the probably ~30W tube in your K40, the max duty cycle for the 90W tube will be about 1/3 as long. This means that if you have the same PWM resolution on both lasers, you have fewer discrete values for PWM on the more powerful laser.

By contrast, if you use a pot to set the maximum power, and PWM for power relative to that maximum, you can use all the resolution of however many bits of PWM are available and get finer gradations of output.

I see that your speed map goes only to 50% power; if you used a potentiometer to set the max, you could make your power settings relative to your max setting on the potentiometer. (I also don’t know whether stopping at 50% in your speed map actually limits you to 50% power.)

Have you tried changing the pwm_hz Laser config setting to see whether it has any impact on the pattern? Try 50000 and see if it looks any different.

Edit: Oh, that was written before I saw that you were seeing the same thing at every speed.

To me, that points in the direction of mechanical and not resonance. Bad bearings, bad belt, wrong pulley (an MXL pulley with a GT belt will do this because MXL pitch is 2.032mm and GT2 is 2mm pitch and their tooth profile is different — but very close and so sometimes confused. I know that what you ordered was GT2 so that seems unlikely, but wanted to mention it because we have seen results that looked something like this, so trying to be complete).

I’m wondering why you are running StealthChop on y vs. CoolStep on x?

I cleaned up the X-Axis wheels and inspected them. I didn’t see any physical damage to the wheels. As I glide the gantry back and forth, I don’t feel an odd acceleration or wobble that might be caused by an oblong wheel. Do you have a better way to check for roundness?

Here are some videos of the actual X-Axis after I cleaned up the wheels…

To answer your question, the configuration file was given to me by Bart Dring himself. I’ve had multiple issues with the file I was given. I should have reviewed it more thoroughly. Doing a walk of shame to my laser to see if this is the issue…

This is 250mm/s 40% power 4% over scan with stealthchop enabled on the x axis. The x axis sound completely and entirely different running in this mode.

sounds like you identified it as curtains…

:smiley_cat:

I have tried upto 7800 and didn’t see any differences. Never thought to go up to 50,000. Trying now…

Here is 50,000 hz with at least two different stepper modes. I don’t think FluidNC supports spreadcycle, but it didn’t throw an error when I loaded it into the config so I ran it.

The harmonics on stealthchop and spreadcycle are so much different than coolstep its wild. Crazy what software can do.

Overall though it seems like 50,000hz is what is making the big difference. Not calling this solved until I burn at least 50 ornaments without seeing this pattern re-emerge.

Is there a guide out there for the pot tuning. I would like to have the full spread of values for power. Then my LightBurn power settings could stay the same from machine to machine (or at least closer to the same)

Edit: Not solved. Got trigger happy. Pattern is still emerging from the depths of my engravings.

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I have a couple of 3D printers made with 3D printed parts, in PLA, and one of them was a dickens and sent me threw the slicer and the controller for a couple of months. Turned out to be thermal expansion and contraction of the 3D printed parts in the carriage. On cold evenings things would get too tight and in certain spots a stepper would skip a step and then on warm days there’d be too much play/wiggle and parts wouldn’t be sized as was once calibrated. I ended up replacing the 3D printed carriages with 400mm long linear rails and things were so much better.

For a laser cutter like you have, some parts might be better off laser cut from acrylic if there’s any chance of thermal expansion and contraction causing changes in how well things track on the extrusions. ABS might not have the same properties at the temperature ranges we are talking about 60F to 90F for my setup before I upgraded to whole house forced hot air and AC.

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First off, I don’t think this is going to fix your pattern, it’s just information for once that is solved. Whether it’s mechanical or electrical, it seems that after your system rests for a while it gets better, and then after some use seems to get worse?

I know that we’ve had plenty of discussions about them here. @donkjr do you have a blog post focusing on the potentiometer?

First, though, if you haven’t read it yet, this comment might be helpful:

You might start from this comment and read forward:

@donkjr you have actual knowledge here of lots of LPSs, do you mind checking this and commenting?

I think there are two ways.

The general idea is that you hook a 1K or 10K linear potentiometer across signal ground / input control signal / output power 5V

Then I think I’ve seen two ways to connect PWM:

  1. connect an open drain control signal to the input control signal
  2. connect the PWM control signal to the appropriate switch laser control line, either high or low

I would trust @donkjr to know which is appropriate here and why. :smiling_face:

Here’s the labelled connections for this particular LPS:

Ive built the MPCNC and its 36"x32", quite a bit larger than my big laser and the 3D printed parts are put through hell and back on that machine. Lulzbot is known for 3d printing the majority of their parts for their printers, those printers make astounding parts. I’m not saying its not the 3D printer parts, but I don’t think the forces that are being exerted on the 3D printed parts, nor the temperature changes are what is causing these patterns. My mounting plates and axes remain tight over the course of my runtimes.

That being said, I’m taking the advice I get here seriously, and don’t want to write off any observations and recommendations as not applicable.

I’m starting to think that there are certain parts of the bed/axes that are more susceptible to vibrations. That’s why when I said it works one day and not the next, it’s really because one day I was working in one area and the next day I was working in another area.

Edit: also electrical. Not sure my previous problems have been fully alleviated: CO2 Laser Interfering with stepper motors - #48 by James_Harding

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You missed my point… I was not discussing the strength of the 3D printed parts. I was talking about thermal expansion and contraction affecting mechanical parts which require stable dimensions so there is a constant force on other parts which have different thermal expansion coefficients.