I have a problem with prominent lines showing up in an engraved image and after many tests i am stuck with what might be causing the problem.
I have the omtech polar 50 watt
its minimum dot is 0.165 mm
the lowest power to fire is 18%
My best test is at 50 mm sec @ 20% power at 600 dpi with a scan angle of 2 degrees.
This gives a shallow etch and a relative bright etch on acrylic.
My query is what may be causing the brighter lines in the engraving (as in the attached image)
The 600 DPI = 0.043 mm line interval is much too small for a 0.17 mm spot: each scan line gets hit four times.
The Y axis motor step size is on the order of 0.02 mm, which means it cannot step precisely at a 0.043 mm Line Interval. That will result in doubled passes when the next commanded Y axis position falls less than half a motor step from the current one.
Ruida controller firmware / hardware handles 0° and 90° scan angles, with all other angles implemented in software by LightBurn.
Because the scan lines are not parallel to the X axis, successive points will have tiny differences in the Y axis that the motor cannot resolve. A 2° angle means the Y axis will change by 0.035 mm for each millimeter of X axis motion, but the Y axis must move 0.02 mm per step (or whatever the stepper driver is set for), so the scan line will have about one Y axis step per millimeter.
IMO, the irregularities in the image come from the combination of:
Too-small Line Interval
Angled scan
Clash with hardware capabilities
Software simulation of a hardware / firmware function
Although you may like the results you’re getting, the combination of settings operates the machine in a region where it isn’t doing what you expect.
Run a Material Test from 200 to 500 mm/s and power from 18% to 30% to find the sweet region. Use a Line Interval of 0.15 mm and a scan angle of 0°.
Then run another Material Test varying the Line Interval from 0.1 to 0.4 mm, again at 0°, to measure the actual spot size. The lines will become obvious at the larger intervals, but you won’t see much difference at the low end: pick the largest interval with the best results.
A bonus of a larger Line Interval will be a dramatic reduction in overall job time, because the machine is not plowing the same trench four times.
Thank you for your quick reply.
I read your post with care and realised that the machine has restrictions on the movement of the y axis.
This become clear when I calculated the overlap of the scan lines.
All is now a much better result and your post certainly helped in achieving a better result.
Thanks again.
There isn’t that I know of. As far as I can tell it’s only good for changing which axes is really working using a 180 deg scan angle. You know what you loose using something other than the X axes to work a lot.
Hi contributers,
I am following the discussion with interest and I thought I would pass on my reasons for (incorectly) using a low scan angle.
My original test showed bright lines in the resulting image.That was fixed after reading the original reply. I hadnt reasised that the y axis movement was 0.02 and had too many overlapping lines. I thought (incorrect again) that if I travelled on a slight angle the overlapping lines would counteract each other and leave a smooth etched surface. Wrong.
Resetting the paramaters to acceptable values has fixed my images and taught me a valuable lesson.
Thanks for your interest and replys.
I attach an image of a simple edge lit piece that I have made for a friend.
The only benefit I have seen is when you stop in the middle of an image. You hit the 180 button so it burns from the top down, and you stop it when the burns connect. Beats the heck out of trying to use the Preview and State Here button.
My laser is not that fast.