Problem with 3/16 birch plywood box joint - Router Forums
 
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post #1 of 9 (permalink) Old 10-22-2011, 04:05 PM Thread Starter
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Default Problem with 3/16 birch plywood box joint

I cut some 3/8" box joints in 3/4 inch popular and got clean cuts trying my OP jig. Then I put some 3/16" birch plywood in to make a small box. It seemed to tear on both sides and I even had it clamped to backing board. When I move the board for 2nd and subsequent cuts, it does not sit down all the way on the jig because the guide on the jig is deeper than the cut in the board.
Is the problem with birch plywood? Or maybe much thinner plywood than bit diameter? Or, that uneven-ness sitting on jig? Or, something I'm doing wrong or just missing??

I do have the backing board against a fence riding on the jig guide. Good tight fit but, ugly tear outs.

Appreciate any tips.
Regis
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post #2 of 9 (permalink) Old 10-23-2011, 06:23 AM
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Yuo'r asking rather a lot trying to work with ply that thin, if you have to have very thin material then use solid timber to avoid this mess.



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post #3 of 9 (permalink) Old 10-23-2011, 06:57 AM Thread Starter
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Originally Posted by derek willis View Post
Yuo'r asking rather a lot trying to work with ply that thin, if you have to have very thin material then use solid timber to avoid this mess.
Derek,
I did a little more with the birch and it didn't work out. I'll take your advice and consider this a lesson learned. I'll reserve the thin birch for dividers and such that slide in narrow dado slots.

Thank you,
Regis
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post #4 of 9 (permalink) Old 10-23-2011, 08:53 AM
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HI Regis

It can be done and I'm sure you can do it, the key is to clamp all 4 parts for the box and it's best to add one more part so you do all 5 parts at one time, the one in the front will be trash but the others should be just fine, it's best to use some DST on all the parts ,you don't want the parts to slip out or move in the sandwich , note don't pull the stock back over the bit once the slot is in place,power down and reset for a new pass..

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Derek,
I did a little more with the birch and it didn't work out. I'll take your advice and consider this a lesson learned. I'll reserve the thin birch for dividers and such that slide in narrow dado slots.

Thank you,
Regis



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post #5 of 9 (permalink) Old 10-23-2011, 02:21 PM
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Regis,
I've had 'some' luck routing box joints in Luaun and Birch ply, but not much.

Normally, to get a clean cut I have to put a good heavy coat of Poly on the pieces where the cut is going to be and then back it fore and aft with a layer of softwood as a sacrificial offering to the joint Gods.
I also have to move a bit slower than usual... not hard for me, I only have two speeds, one is granny gear and if that's too slow, you won't like the other one!

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post #6 of 9 (permalink) Old 10-27-2011, 08:59 PM
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Last thing I do with ply is box joints. Always a problem.
When you make a box joint cut, raise the bit to make a taller one. Allow for that height in your design. Sand the excess after glue-up.

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post #7 of 9 (permalink) Old 10-28-2011, 12:20 PM
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When I cut plywood whether it be with a router or saw I use cellophane packing tape on both sides of where I will be making the cut. If it is a straight line cut I sometimes score the ply with a knife at the cut line as well as using the tape. I learned that little trick from a scroll saw magazine where you cover your pattern with cellophane tape to help lubricate the saw blade and reduce tear out, so I tried it with the router and circular saw and it works.

As per Bob's suggestion of sandwiching and also using the tape should make for a nice clean cut.

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post #8 of 9 (permalink) Old 10-28-2011, 12:39 PM Thread Starter
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All these are helpfull and I appreciate it. I was also looking at the clear tape that is used in scroll sawing but, never thought about it for use at router.

Thanks all,
Regis
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post #9 of 9 (permalink) Old 10-31-2011, 10:29 AM
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Use a tsable saw.

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