Mapping BB ply interiors

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Eh, figured I’d mention this in case anyone found it useful: I’ve had decent (not flawless!!) luck mapping BB plywood for interior inconsistencies.

Right now I just set a cut line (using whatever settings I’m going with) a little bit in from each edge of the piece (~0.25" in), and cut. This trims the piece into a smaller square (which is unfortunate) but more importantly it shows me spots where a single pass is not going to get through.

I then transfer the boundaries of those areas to the top side of the plywood using a pen or pencil and, in conjunction with looking at the grain of the top & bottom (knowing, then, that the interior pieces will be going in different directions), I can make a reasonable stab at choosing spots on the piece where I’ll be able to cut through without hitting an obstruction.

…now, this is not perfect; it’s entirely possible/likely that you can hit a knot or void that has no trace at the edges of the plywood panel, but I believe I’ve improved my odds.

I started doing this because Woodpeckers BB ply seems to have formaldehyde glue in it, which I’d really rather not vaporize if I can avoid it.

For certain pieces where visual appearance is irrelevant, I’m starting to try to put together a test grid of tiny (tiny!) holes, and lasering that first. That will substantially improve the resolution of obstruction-mapping, and in many cases I don’t really care if the end result has a scattering of pinprick holes in it.

(if I had access to nigh-infinite quantities of BB ply and time, I wonder if it wouldn’t be possible to develop a model of imperfections such that, given the test-grid result, you could mathematically analyze a given panel?)

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I believe you can spot a lot of them non-destructively by shining a strong flashlight through it. It picks up the knots and voids. :slightly_smiling_face:

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I find that keeping a fret saw around is just as quick and easy :slight_smile:

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An illustration of what @jules said:

https://community.glowforge.com/t/trick-for-inspecting-plywood/15168

Your method definitely works but requires a lot more fiddling. You can scan a full sheet in seconds using bright light. I tend to use a plain bare bulb lamp in a darkened room, can scan a whole sheet of ply in 5 seconds.

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…how powerful? I mean, do I need one of those “these will blind you and everyone standing nearby” kind? Genuine question – I’ve got a fair stack of 1/4" and it’d be nice to be able to just sit down and sort out the crappy ones in a speedy fashion.

Turns out, incidentally, that the grid method works really darn well. Albeit destructively! Takes about 4-5min for a 26x26 grid, and one thing you learn is that the motion planner gives up and more or less goes randomly when confronted with this type of arrangement. Sort of fun to watch, in a very dry humor kind of way.

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:grinning: For quarter inch, I’d go with the blinding kind. I just use a little LED one on the 1/8".

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Rather than a hand light, since we have lasers making a lightbox with a blinding (or two-stage) light inside and a frosted acrylic lid would work for batch work - drop the piece on the box, mark the bad areas and swap out another sheet of plywood.

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Not a half bad idea! :slightly_smiling_face: