Tough spots in cutting plywood

My wife and I are still new to the laser business and Lightburn (still working full-time for “the man”, instead of our part-time venture).

Early on, while experimenting with cutting 1/4" birch plywood, we experienced areas which didn’t cut all the way through, which we later read might be patches of glue in the inner plies of the sheet. After removing the sheet, we had to cut through with a razor knife.

I’m wondering if Lightburn has a feature (which I haven’t seen) where, if using the camera, the user could freehand circle or otherwise enclose an area on the on-screen artwork where it is known the cut hasn’t gone all the way through (although sometimes this probably isn’t known until after the sheet is moved or removed from the bed), and have Lightburn re-run ONLY what is encircled, at the same settings as the current layer, rather than recut the entire job?
I ask because we have seen areas where it was pretty clear the wood was still not cut through, and it would have been helpful to be able to have somehow select the small area (about 2" of the entire cut job) and rerun just that.

Thanks!

Thanks for the feedback and good idea. This has been suggested previously, so you can add your support for adding this to LightBurn by visiting, signing up and add your vote here:

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If this request becomes a feature, it would save a tremendous amount of post-cut editing. Currently, when I have non-contiguous cuts due to mother nature’s work in creating wood, I attempt to identify on the cut plan, then break it up with the node editing tool and select only those portions to reburn, making use of the “selected items only” feature.

It’s got my vote!

This feature request already had my vote but implementing it like highlighter tool where you click and drag with your mouse along vector lines to highlight the portion of the lines to indicate where you want them recut would be awesome.

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I added my vote for this as well. I see this problem on some cuts but don’t usually see it until I’ve taken the piece from the bed. Do most of you use jigs or other exact placement methods that would allow you to run the second pass easily? I don’t do production type work so just thinking about how I could really use this tool.

I test it by wiggling the parts while the sheet they were cut from is still on the table. Parts that bind are fairly easy to spot. If there’s a big spot that didn’t cut I set all the other objects as “don’t cut” and recut just that piece.

Fair enough, I usually try to do that as well but was wondering if there was something I was missing, maybe shining a light through the cut would show up a bad spot? Thanks!

I cut a lot of 1/4" birch plywood and discovered a few things:

  • The board should have even plies. Some have thin outer plies of birch, and inner plies of some mystery wood. Even plies will generally use the same wood throughout.
  • The board shouldn’t have any voids. None at all. Check all the edges of the sheet. Proper “Baltic Birch” is engineered from the factory to not have any voids.
  • Don’t use sheets that have brown glue joining the layers. It doesn’t cut very well, and burns leaving a black char. Ideally it should cut leaving a medium to dark brown edge.
  • One side will be perfect, and the other side might have football-shaped patches. This is okay as long as the patches are seamless. You shouldn’t feel the patches at all when running your hand across them. The patches are areas where knots were. These knots are where the laser has problems because the knot is much denser.
  • Cost doesn’t mean much. The plywood I ended up using is from a chain hardware store (but not a big-box store), and towards the lower price range. It also has a Russian stamp on it and is sold in 5x5ft sheets ($20 per sheet) so is “the real thing” (although good stuff is made across Northern Europe and in the US). The very expensive European stuff from a specialty lumber store was crap for laser cutting. I also found a local plywood distributor who had good stuff and could get anything I wanted, but only in pallet quantities.

When I found the plywood I use now my cutting problems almost completely went away. There sometimes is a small problem (maybe a mm or two long) but it’s easily fixed with a razor.

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What laser are you using? I have a 10 watt diode laser trying to find out what’s a good starting point for 1/32-1/16 plywood sense I know I can’t really cut anything much thicker than that to be remotely efficient at least, I’m looking for good website for plywood laser plywood I was told to get for the best results but I’m having trouble finding reasonable cost laser plywood. Thanks :blush:

There is an easy approach to doing what you wish…

Anytime you create a job, frame your entire job in a box. Size the box accordingly so that it frames your project exactly (or sometimes you may want the frame to be set exactly to the size of your material to help you with nesting considerations). Set this box layer to Show / no output.

Anytime you run your job, select everything in the project file and utilize the functionality of LB to output only the selected objects / use selection origin.

Now if after you complete the job you find anything has not cut to your expectation, you can rework any layer / grouping individually. To do this, you just run the job again making sure you always include your frame. The frame maintains your origin.

Even more flexibility is created by such proactive framing:

For example, after your job is done, you can select all, copy, paste into an empty area of your workspace, selectively delete objects, add elements if you’d like, and when done just select the frame and framed elements and run job.

This is also how you can create a secure spoil board index. For example:

I precut 3/4” solid oak plaque blanks on my CNC mill. Using that cad file, I use this plaque outline as my frame.

Then on LB, use this outline to cut a spoilboard inlay alignment jig on my laser work table using coroplast.

With the spoilboard inlay securely fastened to the work table (using rare earth magnets, tape, weights, or whatever works for you) I can process engraving jobs on any number of plaques always placing the plaque into the exact position on the work bed of the laser by subsequently disabling output of this frame but still including it on every engraving job.

Honestly, I have never quite understood the allure of a bed camera. Call me old school if you want, but nothing works as good as or as accurately as a frame (such as what I described).

There’s so much you can do with Innovative CAD “tricks” (that’s what I call it). Also, you should be building an arsenal of indexing jigs for your machines if you are aiming to go commercial.