plywood and box joints? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 06-07-2012, 10:51 PM Thread Starter
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plywood and box joints?

I just tried out my newly made box joint jig with 1/2" plywood. I noticed an extreme amout of chatter when making the cuts. The plywood really seemed to fall apart in about half of the fingers. I was using a 1/4" straight cut bit with a 1/4" shank. Am I using the wrong bit, or is plywood just a really bad choice of wood for this application. I have lots of plywood scraps lying around, a need for little storage boxes. I would hate to trash all that wood.
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post #2 of 10 Old 06-07-2012, 11:24 PM
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youre getting tearout. since youre using plywood im gonna assume your making drawers ???

try :
going slower with a spiral bit

make them with your table saw

using solid wood

build it right or not at all
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post #3 of 10 Old 06-07-2012, 11:25 PM
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Quote:
Originally Posted by mlewis View Post
I just tried out my newly made box joint jig with 1/2" plywood. I noticed an extreme amout of chatter when making the cuts. The plywood really seemed to fall apart in about half of the fingers. I was using a 1/4" straight cut bit with a 1/4" shank. Am I using the wrong bit, or is plywood just a really bad choice of wood for this application. I have lots of plywood scraps lying around, a need for little storage boxes. I would hate to trash all that wood.
Plywood isn't the best choice for box joints or dovetails, especially small ones. You may have better luck with 1/2 joints. Also better grades of plywood. Baltic birch, with few or no voids, will usually work pretty well. Home depots version is tuff to get a groove in without disintigrating. A spiral bit will always work better also.
Since you are trying to use up scraps you probably don't want to buy more wood. Depending or your major objective, make the boxes or tune up the jig. If it's to make boxes, I'd suggest going with lock rabbet joints and just get 'er done. If to tune up the jig, pick up a spiral bit and switch to wider fingers.

John

If I strive for perfection, I can generally achieve good'nuff, If I strive for good'nuff, I generally achieve firewood
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post #4 of 10 Old 06-08-2012, 06:46 AM
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There are a few different reasons for the problem you are having. One is, it's possible the plywood is defective. In recent years they are using less and cheaper glues when making plywood and it just falls apart especially if it is Chinese. The Russian birch plywood is much better however I'm seeing more and more of it delaminate also. Incidentally the glue line in plywood is very abrasive and hard on router bits. If you are going to use plywood you might look for a good sale on router bits so you have some to use while others are being sharpened. Another thing that will help routing the box joint is if you can sandwich the drawer member between two other pieces of wood. This should stop the tear out even if the plywood is bad.
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post #5 of 10 Old 06-08-2012, 05:22 PM Thread Starter
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Thanks for your imput. The plywood I'm using is the really cheap sheathing stuff with lots of voids. I won't use it again in this application. Are the fingers suposed to be the thickness of the stock your using? ie 1/2" fingers in 1/2" stock
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post #6 of 10 Old 06-08-2012, 06:08 PM
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Most of the dovetail router bits have a 1/2" cutting surface so normally you use 1/2" stock and make the fingers 1/2" long. You can though if you don't want to see the end of the fingers on the back of the drawer make the fingers 7/16" long so it has a little wood covering it. Then the drawer fronts are normally 3/4" thick and you mortise into it 1/2" so there is 1/4" of wood in front of the fingers. It's just a matter of preference. You just need to make the fingers match the depth of what you've mortised for.
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post #7 of 10 Old 07-28-2012, 02:23 PM
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I make box joints all the time with 1/4" thick baltic birch plywood on the table saw. I found the 1/2 joint works best. I could never get the multiple joints to fit and reduce the tear out. Might help to put a piece of scrap wood behind the joint your cutting to not tear out your work piece, or wrap masking tape around the joint.







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post #8 of 10 Old 07-29-2012, 02:59 PM
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Those are nice boxes
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post #9 of 10 Old 07-29-2012, 08:32 PM
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Why the nylon screws in the boxes?
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post #10 of 10 Old 07-30-2012, 09:51 AM
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Thanks,,,, they are 1/4" x 2"H for model boat propellers.



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