Offset Fill Corners

I am attempting to engrave a 1/8" wide border around a piece of MDF. For time savings, I am using offset fill. I notice that, after making all of the passes clockwise, the laser moves to each corner and pulses once or twice before running the passes counterclockwise. Because of the pulses, I end up with pin holes in the corners which are visible from the back side of the material.

I assume that dialing back the power will alleviate the pin holes, but I am trying to keep the border as dark as possible. Is there a setting in offset fill that will eliminate the corner pulses?
Base

If you check the Preview, you’ll (almost certainly) see those little spots tucked in the corners.

Offset Fill traces inside the outline using the specified Line Interval, so the traces are exactly that far apart on their centers. Those little dots are exactly what’s needed to fill in the last little bit of space: LightBurn is doing exactly what you asked it to do.

The other problem you’ll run into is when the distance between two parallel parts of the outline are juuuust slightly more than a multiple of the line interval, in which case you get an unsightly gap down the middle where there’s not quite enough space for another line.

In both cases, there are no options to override that behavior, which is why the doc says “Raster fill is preferred for general use”

Please attach your .lbrn2 file so we can take a closer look thanks.

To darken the engrave, you can de-focus the laser a few mm at a time. I have found 10-20mm out of focus gives the darkest result on my Ortur 10w dual laser. It does have a long focal length, so your laser may need different amount of out of optimal focus.

File is attached.
Stand.lbrn2 (20.1 KB)

I can eliminate the problem by using flood fill, but that increases the completion time.

Thanks

I had never tried zooming in on the preview mode but you are correct.
Thanks!

Yes, as you zoom in on the preview it is easy to see what is happening:

Another option (if you don’t mind micro-managing the results to sub mm level) is to take the outside shape, and offset it inwards by the same amount as the ‘Line Interval’ then change the mode for those shapes from ‘Offset Fill’ to ‘Line’:

image

It’s a little tedious, but as long as you have ‘Select resulting objects’ enabled, you can use ‘Alt+O’ followed by ‘Enter’ in pretty quick succession.

Although the results (below) are tidy and efficient, this method is only suitable in select circumstances, where you want the result to be like a thick line of uniform width, and I’m not sure if that is what you want (notice the inside radius becomes smaller). But it does at least stop the laser from needing to fill small isolated pockets.

2 Likes

Preview reveals many hidden secrets! :grin:

The top preview shown by @NicholasL shows how the line spacing in the corner causes the gaps other folks kvetch about, where the distance between the outlines gets slightly too large.

Looking closely at the parallel sections away from the corner, you’ll see the two traces down the midline are (much) closer than the line spacing calls for, because the offsets start from the perimeter. Folks kvetch about the not-quite “overlap”, too.

It’s complexity all the way down!

I sometimes adjust the Line Interval for an offset fill until I’m happy with the preview. Increasing or decreasing the value very slightly will make the pattern the laser cuts change slightly. In the attached examples I used 0.080 (the lasers suggestion), 0.100, 0.090, and 0.091.

Thanks to all for the tips. I’ll give them a try.

Follow up:
Creating multiple lines, offset as suggested, worked perfectly. In fact, I’m now wondering why the Offset Fill tool doesn’t work this way. I suppose in some situations it might be preferable to have the single continuous line provided by Offset Fill over this process, but the savings in print time is about the same either way. I just had to reduce the minimum power setting by 25% to eliminate problems at the corners.

Thanks again for all the suggestions.