Issue engraving numbers

I’m just starting to explore engraving with my custom built machine with a Cohesion3D/Smoothieboard and have encountered an odd issue where letters engrave just fine, but numbers are slightly skewed. This can be seen in the attached image, (compare the angle of 1 vs. B), and associated LightBurn file. The text is one item using default Sans Serif font on Ubuntu and I engrave it from bottom to top. If it was happening on both lines of text I’d definitely be looking at my machine as it’s still a work in progress, but perfect letters and skewed numbers doesn’t make sense to me. Any ideas?

Test file: test2.lbrn (26.7 KB)

… and of course you have tried other fonts?

I haven’t done any exhaustive testing beyond what you see. While I can certainly try different fonts, reversing the direction of engraving / order of characters, etc. it doesn’t change the fact that the 6 different tests that I did run all showed the exact same issue so it’s not random.

I’ll try again with some different fonts and see what I get but I’m not sure what that will tell me. I should add that the preview in LightBurn shows exactly what you would expect. I’m going to review the G-Code, but doubt I’ll see anything obvious. I’ll post this issue on the Cohesion3D forum in case it’s controller related, but if the G-Code is good then I can’t see why the controller might be at fault. That leaves the mechanics of my machine, but if it was the machine/setup I wouldn’t expect perfect letters and skewed numbers every time. Definitely a mystery to me.

Here’s an updated image with different tests / fonts showing the same issue.

From bottom to top, left to right

  1. Sans Serif but with origin set at top left instead of bottom left. I thought this would cause it to engrave from the top down, but it did not. Still engraved from bottom up. Maybe I’ve misunderstood this option, or maybe I’m missing a setting somewhere.

  2. Sans Serif but numbers followed by letters. Still all a single text object.

  3. Bitstream Charter True Type.

  4. Courier 10 Pitch True Type.

  5. Single line of numbers in Sans Serif.

  6. Single line of letters in Sans Serif.

Try ‘convert to path’ on your text - numbers and letters - and see if you still have the same problem.

If it is a mechanical problem it should also be reconstructed with lines and shapes, it will be interesting to see what the cause of the problem is - good luck

I’ve had no problems cutting shapes, and the examples I’ve done have been on different locations on the bed of the machine so I don’t think it’s mechanical. I’m going to try Bo’s suggestion later today and see where that gets me. I’ve also written a quick Java program to preview the cuts similar to what happens in LightBurn’s preview, but independently. That just needs a little debugging and then I’ll be able to rule out the gcode. If the gcode is good and I think the mechanics are OK that just leaves the controller doing something weird.

OK, so I’ve confirmed that the gcode is OK - no real surprise there. I’m still going to do the convert to path test suggested by Bo, and I would like to do a test where the engraving is done top to bottom. My first attempt at this didn’t work. Can someone point me in the direction of how to achieve this? I’m also going to switch off bidirectional and see what that does.

on the right side you can determine the direction

You can also change the ‘Scan Angle’ to 180º to change the fill direction for that layer.

Scan angle, in the layer settings

Screen Shot 2021-02-27 at 11.40.28 AM Screen Shot 2021-02-27 at 11.40.19 AM Screen Shot 2021-02-27 at 11.40.10 AM

Well I’ve done some more tests and I’m reasonably confident the culprit is my X-axis. What still puzzles me though is why it’s not effecting the whole scan evenly. Even when I did the numbers followed by the letters it effected the numbers and not the letters. That just doesn’t make any sense to me. If you look at the following image I think it becomes clear that it’s an X-axis issue though.

From bottom to top:

  1. Default text and settings showing original issue.

  2. Bi-directional scanning switched off. Much worse and also effecting letters.

  3. Scan from top to bottom, (scan angle set to 180). Letters OK, numbers skewed opposite direction.

  4. Scan angle set to 90 degrees, i.e. now burning along Y-axis instead of X-axis. Looks about perfect to me.

  5. Scan angle still 90 and text also at 90 degrees. Again a perfect result.

  6. Mixed letters and numbers with scan angle back at 0 degrees. This is weird to me. The top line shows both letters and numbers skewed, but the bottom line shows both looking OK. Makes no sense!

  7. Convert to path test still shows original issue.

So despite the weirdness I have to conclude that it’s an X-axis issue. I do have the acceleration dialed right down but even then it is creeping in one direction or another. I don’t really understand why the direction changes between test 1 and 3 which are both scanning bidirectionally. And I don’t understand why it seemingly only effects one line of text and not both, or as in the case of yesterdays test a single line of numbers but not a single line of letters. That’s why I originally thought it wasn’t a machine issue.

So until I get the machine out of prototype stage and get a more sturdy frame built such that I can fine tune the axes I’ve got a good workaround in scanning at a 90 degree angle. Thanks all for your help!

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