# Routing Baltic birch plywood (noob warning)



## dan_house (Feb 18, 2009)

I build most prototypes out of 1/2 inch baltic birch plywood.

To date, Ive not done anything all that complicated with the router that couldnt be cleaned up with some sandpaper.

But this weekend I'm starting my most ambitious build, and sucess will depend on how well my routing goes.

2 questions: is routing plywood any different than working regular wood?

Is ther a chart/list somewhere on the forum for dealing the uniqueness of commonly used materials?

tia

dan


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## Gene Howe (Jul 10, 2007)

Routing BB doesn't seem to be any different than routing solid. Maybe a little fuzziness with other than a straight bit. I'm not sure, but it seems to dull my bits faster.


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## Drew Eckhardt (Aug 2, 2008)

dan_house said:


> 2 questions: is routing plywood any different than working regular wood?


Every cut is both with and accross the grain so there are more situations where you want to back cuts up with a sacrificial piece to prevent tear out.

Low quality plywood introduces additional problems. With really thin face veneers (the home stores sell really bad plywood with .010" veneers versus .050" for a nice piece of 18mm Baltic birch) you have to worry about using a bit with the right shear angle when cutting accross the face ply grain. Cuts may expose voids that you need to fill if you need an air-tight seal as in a rabbet for a flush-mounted speaker driver.

Plywood has glue between layers which is harder than wood and saw dust is produced instead of shavings which can carry away more heat. So plywood is probably harder on bits than solid wood but not as bad as MDF which is mostly glue, becomes wood flour when cut, and eats router bits even with recreational levels of use.

If you're using joinery bits like lock miters you need to be careful on glue up. There seems to be some spring-back in plywood so you get tighter joints than with solid wood. PVA sets up when it looses moisture which tight joints make happen quicker. Things can setup nearly instantly even with Titebond Extend. Consider a different glue here (I switched to epoxy) or adding moisture to one side of the joint (I didn't try that; it would make for finer glue lines if it worked).


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## bobj3 (Jan 17, 2006)

Hi Dan

Routing plywood is tricky ,it can be just normal plywood or birch or veneer ,, this is when you need to use the right bit  for the job...
MOst router bits nail/hammer the plywood and it chips and rips out the layers,,upcut and down cut bits work well but if you use one that does both jobs at same time you will get a real nice cut.. 
And you plywood edge will not look like you used a axe on it.. 


Compression Up/Down Spiral Router Bit

http://www.mlcswoodworking.com/shop...pages/bt_solid.html#compression_updown_anchor

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dan_house said:


> I build most prototypes out of 1/2 inch baltic birch plywood.
> 
> To date, Ive not done anything all that complicated with the router that couldnt be cleaned up with some sandpaper.
> 
> ...


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## dan_house (Feb 18, 2009)

Drew Eckhardt;101918.... There seems to be some spring-back in plywood so you get tighter joints than with solid wood.....
PVA sets up when it looses moisture which tight joints make happen quicker. Things can setup nearly instantly even with Titebond Extend. Consider a different glue here (I switched to epoxy) or adding moisture to one side of the joint (I didn't try that; it would make for finer glue lines if it worked).[/QUOTE said:


> Spring back? Like poking a balloon? Soon as you move your finger away it comes back? That would explain some stuff...
> 
> I was not aware of plywood sucking moisture out of glue. Maybe cuz Ive been over doing it.....
> 
> Thanx for the info guys


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## Drew Eckhardt (Aug 2, 2008)

dan_house said:


> Spring back? Like poking a balloon? Soon as you move your finger away it comes back? That would explain some stuff...


Lock-miter joints cut in solid wood end-grain join with a slip fit. The lock-miter joints I cut in birch plywood took a few mallet taps to close which felt a lot like a slight interference fit in a slightly undersized dado. I could pickup my boxes by one side and needed my dead blow mallet to separate them after the dry fit.

I speculated that the wood moved aside a few thousandths when being cut and moved back once the cutter passed.

I was not amused when my glue with an alleged 15 minute open time hardened before I got all four sides together and square.

Other people on sawmillcreek.org reported the same thing; I just wish I'd known that before I applied glue so I could use clamping squares or something.



> I was not aware of plywood sucking moisture out of glue. Maybe cuz Ive been over doing it.....


You need pressure for that to happen. Interference fits do the trick.


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