Jobs Shifting Mid Operation - Results Consistently Inconsistent

I ran into a weird issue today that I’ve never seen before where the laser ends up offsetting paths mid-way through an operation, I’ll start with pictures then provide setup details:

I’m trying to cut this - blue lines are vector engrave (2 passes), the black lines are vector cut (2 passes).

I cut this 5 times without any changes in Lightburn and got 5 different results, with the fifth being correct:

First attempt, notice that the top left 2 squares started in the correct position, the 3rd one started rendering correctly then shifted down the y axis:

Second attempt:
Y shift again, but this time it almost finished the first row before it shfited:

Third attempt:
X shift this time, everything was right until the second vector cut:

Forgot to photograph the 4th attempt but it was another Y shift halfway after the first row.

Fifth was money.

Machine: Snapmaker Ray 40W
Source file type: Adobe Illustrator
Blue Lines: 60% 8000mm/min 2 passes
Black Lines: 100% 720mm/min 2 passes
Material: 3mm MDF covered with blue masking tape (for spray painting later)

I made no changes to the file for the initial 5 cuts, my only interaction was to run the job again.

2 passes for the cut and engrave because the tape seemed to inconsistently “diffuse” the burn - the lines weren’t showing up as well in the wood and the cuts would unintentionally leave “tabs”. Even at higher powers/slower speeds it was happening so I just did a second pass. Not sure why the masking tape is having that much of an impact on penetration, but it is so I just went with the simplest solution. MDF be crazy yo.

The file was designed in Illustrator except for the long curved engrave line. I tried a sixth cut without the curved line and it worked perfectly then I just engraved the curved line as a completely separate job and it worked fine. I did not try any attempts where I ungrouped the Illustrator object and re-grouped it with the curved line.

I’ve cut this project before (without the curved line) and had no problems so my biggest suspicion is the additional line is somehow throwing things off but the inconsistency of the results is concerning - usually if something is wrong with the project the error is consistent, like I’d keep seeing the first result over and over.

Fortunately the piece was small so I was willing to experiment - at first I was more interested in root causing the problem than getting a good cut.

Lightburn version?

All testing was done on 1.5.04 but I’ll get latest and try tomorrow to see if it repros. Fortunately the most consistently problematic piece is small so I don’t have to waste a lot of material trying to cut it, though from the patch notes it doesn’t sound like my Snapmaker will be impacted.

I decided to cut another copy of the project and I had the same problem with each piece, even the pieces that cut successfully on the first try yesterday and the problematic piece from yesterday was still problematic. Total cut and engrave time for this project should be closer to 15-20 minutes and I probably burned 3 hours of my life away just tonight trying to troubleshoot before I finally gave up and just went back to Luban (Snapmakers software) which ended up printing all the parts successfully on the first try.

if i had to guess, i would say you have a rapid movement shift
Where the Y and X axis moves to do the 2nd outer part of the cut you lose steps

You would try to optimize the path to make sure the rapids are done as slow as possible
And slow down the white space travel (Edit > device settings) as a diagnostic

Seems definitely mechanical and NOT software

Agreed, Gil. I would expect a software bug, design error, etc to be consistent and repeatable. That’s not to say a settings change won’t fix it if it’s lost steps due to acceleration or something.

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My vote is for loose set screws…

If the laser emits blue-ish light, then blue-ish tape reflects nearly all of it, letting very little of the energy through to the material you want to cut.

Any other tape color would be better. :grin:

I thought it might be a mechanical error but considering I had never seen this in the Snapmaker software and I’ve only used Lightburn for this specific project I decided to try to repro in the Snapmaker software: 20 cuts of the same small part with the same work and jog settings and I had no issues.

My next test is going to be using Lightburn on a machine with a direct USB connection - I’m going to try to remove network traffic as a variable.

@ednisley: yeah that occured to me after the fact but I have spools of blue tape for my CNC/wood working so the two pass solution seems pretty sufficient for now: first pass for making it through the tape then the second pass to “finish” the cut.

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