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Plywood will always have some variation in thickness. So woodworkers will usually overcome that by making not only rabbets/dadoes, but also tongues.

But when you're working with slotted plywood, such as the shelving in the image below, how can I deal with that? For long shelves, a single piece may have thinner and thicker sections, so different columns would have to have different slot widths. This seems a lot of work, even for someone working with CNC (which is not my case).

And coming to a subject that to me feels a lot like an urban legend: is it really a no-no to run plywood thru the thickness planer? If I am only removing wood from the outer layers and the machine is not hitting any glue, my guess is that there shouldn't be a problem. But woodworkers in most forums I've searched will advise against that, so I guessed I'd better ask again.

enter image description here Edit: the picture comes from this tutorial, and it was built with a CNC and the author did state it was necessary to sand some of the slots to get a nice fit.

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  • Not an answer, but I have run plywood through a thickness planer for some god-forsaken reason late at night, and it basically shredded the veneer off the top. Granted, this was big box cheapo ply. I'd be more comfortable making adjustments via drum sander.
    – Stephen
    Dec 4 '19 at 22:34
  • I am asking, but I have also run plywood (construction grade, softwood) through a thickness planer before and the finish was pretty good. But it was only a couple of times, not a production run. Maybe you ran the wood against the grain slope of the of the veneer (as it is not possible to know if it's right or not).
    – Eric Omine
    Dec 5 '19 at 0:11
  • This'll seem a bit like a smartass remark but buy better plywood? Some variation sheet to sheet is perfectly normal, but significant variation within the one sheet is the mark of pretty low-end ply. Obviously there are times when you want to or have to use cheaper stuff though, so then I think you just have to commit to having to customise the fit of each slot as needed with a rasp, file (vixen files would be good for this), or of course just using a sanding block.
    – Graphus
    Dec 5 '19 at 8:55
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    "is it really a no-no to run plywood thru the thickness planer?" I think advice on this front stems from a risk to the wood primarily, not so much to the equipment, at least historically. In the past you'd be advised not to do this because of the high risk of planing through the veneer in spots, which for many uses would write off that piece of ply. These days though, there are reports of grit and other contaminates in cheaper plywoods and these could cause havoc with the planer if any bit of that came into contact with the knives.
    – Graphus
    Dec 5 '19 at 9:00

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