What Are These "Jigsaw Piece" Shaped Patches Plywood?

I always thought they were to fill in knot holes from branches and such.

Drew K

That would also be my guess. The uniformity doesn't mean much as the wood panels are manufactured in such a way that you are likely seeing a different part of the same knot.

There was a really good discovery channel documentary on the subject (Modern Marvels I think it was called).

Correct. Plywood veneer is made by shaving thin slices off large 8 foot long logs as they turn in a lathe like machine. So many of the same knots will be in one piece of veneer.

They turn the logs down to a diameter that allows two 2x4's to be made from the remaining core. (2x4 being an out dated term, I realize)

The machine then trims good pieces to plywood size, or smaller, depending on the defects, that are sensed by optical sensors. Smaller pieces are used to make the internal cores by combining slices.

2x4 being an out dated term

Oh really. First I heard of it. What is the new term, then?

http://answers.yahoo.com/question/index?qid=1006041925967

Exactly that... patches where the veneer has an imperfection.

These veneer imperfections are caused by pitch pockets, holes from boring insects, branches, knots, bark... these are cut away with a die, and the patch is glued in.

Patches like that are not found in appearance grade wood.

Very common around here is the 'boat' or 'football' patch:

Plugs to replace inperfections

Wow, the image of Batman!

It's the Cape of Chiroptera.

I would put those on eBay right away.

And... don't forget oriented strandboard.

Strandboard...oh, I thought you said sandboard and was thinking it must be related to this sandstone.

I was lucky to visit at the right time to get to handle some and bend it when I was visiting Penn State University in Pennsylvania USA.

Drew K

They are signs that Batman works night at the plywood factory.

Or maybe, just maybe they are patches to fill where manky knots are. They are regularly spaced because the veneers are peeled off the log in a continuous sheet round and round the log. Nah, that's just too far fethed... I'd go with the Batman explanation
Del

Thanks to everyone who replied especially SolarEagle for such a complete answer.

My original search of google images for "plywood patches" did not bring up anything which satisfactorily explained what was going on.

Now, however, and, quite surprising to me: the same search brings up the picture I took and a link to this thread. So idiots like me will not need to trouble you all again.

http://www.google.co.uk/search?hl=en&site=imghp&tbm=isch&source=hp&biw=1354&bih=872&q=plywood+patches&oq=plywood+patches&gs_l=img.12...4234.10515.0.13969.15.9.0.6.6.0.125.1045.0j9.9.0...0.0...1ac.1.8.img.Frj6zLKH6q4

We are building the information highway.....carry on

One other thought is they are center markers for nailing.

Clearly they are ghosts......

"You know, there are more things in heaven and earth, and clearly plywood, than are dreamt of in your philosophy Horatio!"

Or maybe they are simply plywood patches. But why ghost shaped instead of the usual oval? Who knows?

No really...why would they use ghosts instead of ovals?

Less likely to come apart?

I can see from the OT's picture that the grain pattern surrounding each patch is the same, supporting the repetitive knot that appears as the veneer is peeled off the log. I also question why a "ghost" shape instead of the "football" shape? Maybe it's just a preference in the UK.

They are in fact repair patches. That particular shape is what the mill making the sheet uses. They have a matching punch for the defect. The even spacing is from the production of the top layer. It is peeled off the log like unrolling a paper towel, as are all the plys. Being that close together means a very small core being peeled.