# Undersized plywood bits



## Davisjr70 (Apr 14, 2012)

I have been searching undersized plywood. Why for 1/2" plywood bits are sold as 31/64" and not 15/32"?

Just curious.


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## DaninVan (Jan 1, 2012)

Hey, William; you realize you just caused hyperventilation amongst the metrically inclined... lol
(1/2" = 32/64")
(15/32 = 30/64)
So, William is asking why the bits are 1/64" under rather than 2/64" under(?).
Just spit-balling here, but if the _plywood_ is 15/64" it isn't going to fit a 15/64" _slot_. You need a bit of room for 'fit' and humidity expansion.


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## Phil P (Jul 25, 2010)

DaninVan said:


> Hey, William; you realize you just caused hyperventilation amongst the metrically inclined...


Oh no he hasn't, Dan, 18mm MDF is just that......... :dance3:

Although having said that in the USA it would need to be 17.6mm to fit the pattern set by plywood :lol:

Regards

Phil


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## billg71 (Mar 25, 2011)

Interesting observation, never noticed. Freud sells all the plywood bits 1/32 undersized, Amana offers a 1/64 and a 1/32 undersize in 1/4" only, the rest are -1/32, Whiteside is -1/64 only for 1/2 ply, all others are -1/32.

I usually go 1/16-1/8 under on my dadoes and rabbets then take a rabbet pass on the edge of the piece to be fitted down to match the dado. Plywood thickness is all over the place, I occasionally see a piece that's exactly 1/32 under, never seen 1/64. At least in hardwood ply. I've seen Baltic/Russian Birch vary by almost a 1/16.

Thanks for the info!

Bill


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## Cherryville Chuck (Sep 28, 2010)

I read or was told once that finish plywood starts out at the correct thickness and then is sanded to a satisfactory smoothness and it doesn't seem to be perfectly consistent. As for the fit, you never want to have to force the parts together. There has to be some room for the glue or the joint will be glue starved and not as strong.


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