Dots not evenly spaced

[tantrim (austen)]

Test Pattern (ignore blurriness, it’s a bmp file and I have to zoom in a lot):
In the screenshots below I did tests with a 169 dpi test file (top) and a 254 dpi test file (bottom)

Results:

I have 3 questions.

1. On the 169 dpi test (larger dot size) examples, why is the laser duplicating dots? Is this a software setting?
   
2. On the 169 dpi test examples, if it is duplicating the dots, why aren’t these duplicated dots aligned perfectly horizontally?
   
3. On the 254 dpi tests, why are the dots not evenly spaced horizontally as they are in the bmp file?
   

I have speed related issues as well but that’s another can of worms I’ll tackle later.

[ednisley]

@tantrim

why is the laser duplicating dots?

Assuming that is an Image layer with the BMP image imported as usual, is the layer:

• Set for Pass Through mode?
• Set for Bi-Directional scanning?

If the BMP image isn’t being passed directly through, it’s being resampled at whatever DPI value the layer calls for, which will definitely confuse the results.

Bidirectional scanning will “duplicate” dots if the Scanning Offset Adjustment isn’t set exactly to match the machine’s timing.

@tantrim

speed related issues as well

Everything is deeply intertwingled: you may have found one end of the tangle!

[tantrim (austen)]

Thanks for your help and if I have anymore issues I’ll post back

I’m using bi-directional scanning and pass-through is not enabled (it should be) so those are both problems that you’ve helped me address

I need to tune the scanning offset adjustment and enable pass-through as I’ve already have the images at the correct dpi from photoshop.

[tantrim (austen)]

So I tried running the tests and I’m getting Line Wobble.

I changed the line shift speed and y acceleration to 10.00 for both on engraving while doing fill mode and it didn’t seem to help too much.

Is it possible the machine is this unstable?

[Rick (Technical Evangelist)]

@tantrim

Line Wobble

Using your words, I found the following in our documentation. Worth review,

Scanning Offset Adjustment - LightBurn Documentation

[jkwilborn (Jack Wilborn)]

If you notice this wiggling occurs at the end/beginning of the line… this is something loose and it’s ringing as it’s trying to slow down or speed up…

If you look at your preview you can see if it’s during acceleration or deceleration… Either way it’s a mechanical issue.

[tantrim (austen)]

I read that before making the post about the line wobble. As I said above I attempted to do what it asks. Lowering the acceleration setting for your Y axis can correct this. However, in my case it did not fix it for me.

[tantrim (austen)]

the line wobble occurs after moving to a new line. It starts in the bottom left and goes right. Bi-directional scanning is on so it’s firing in both directions.

the machine’s workable area is 1600mm x 1000mm so it’s not exactly small. The head seems seems fixed rigid against the X axis rail. I’m hoping it’s not the frame the X rail is mounted too causing resonance by flexing.

How would I test this?

[ednisley]

@tantrim

• the machine’s workable area is 1600mm x 1000mm
• Is it possible the machine is this unstable?

If those lines are on 1 mm spacing, then the rigidity is (probably) about as good as it’s going to get. If they’re closer, then it’s definitely as good as it gets.

@tantrim

The head seems seems fixed rigid against the X axis rail.

The unfocused laser beam enters Mirror 3 about 200 mm over the platform, so a 0.5 mm distance on the platform comes from a rotation of 0.14°. The linear rail has bearing channels about 10 mm apart, so one side moving by 0.025 mm will suffice. The steel bracket holding the entire laser head has screws on 40 mm centers, so 0.1 mm of flex is enough.

A simple test:

• Jog the laser to the middle of the platform
• Fire a manual pulse into cardboard to mark the beam position
• Grab the bottom of the laser focus tube
• Give it a good shake in all directions

If you feel any motion, that’s what you’re up against.

Then fire another pulse and measure the distance to the previous hole. That’s an underestimate of the total backlash / mechanical slop in the whole system.

These holes in art paper should be circles:

The smaller ones are 1 and 2 mm diameter, with an actual speed much lower than the 50 mm/s layer speed. The fact that they’re so consistently distorted shows the laser head / X axis carrier / gantry shakes very predictably by a few tenths of a millimeter as the machine moves.

My laser machine is about half the size of yours, so those results may be typical of the breed.

It’s wonderful for what it does, but it definitely ain’t perfect.