# Box joints using plywood



## asrubin (Jan 1, 2008)

I am trying to make box joints using 1/2" plywood. I am using a straight bit 1/2" with 1/4 shaft. All joints are tear outs....should I use a spiral bit instead of the straight bit? All on test wood...nothing but sawdust.....This is being done on a router table. Thanks for all help....


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## Titus A Duxass (Jan 6, 2010)

Plywood can be a bugger for tear outs.
You need to place a sacrificial block of wood after your work piece to prevent tear out.


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## lpret (Apr 28, 2010)

*How to do multiple passes*

I cannot post the URL, but if you search for 'using a lock miter' on google videos, the very first link should be: 'Pool Table Build - Part 1 - Using the lock miter bit to create the leg columns'. He uses plywood and explains how to prevent tearout. 

Hope it helps.


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## LexB (Apr 12, 2010)

I made box joints with 3/4-inch ply a few months ago. I used a 3/8-inch spiral cutter with the sacrificial fence acting as a backer board. I had minimal tearout that was easily sanded. Because this was a paint finish project, I used Bondo to smooth out the box joints and when sanded, it looked like the box was made from one piece of wood. You could try wrapping the edges of the plywood with painter's masking tape before cutting the box joints. That might help reduce tearout too.


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## Gene Howe (Jul 10, 2007)

Adding to previous posters.....Baltic Birch ply will help, also.


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## jschaben (Jun 21, 2009)

lpret said:


> I cannot post the URL, but if you search for 'using a lock miter' on google videos, the very first link should be: 'Pool Table Build - Part 1 - Using the lock miter bit to create the leg columns'. He uses plywood and explains how to prevent tearout.
> 
> Hope it helps.


I just went and watched that video. Two details shown on the video but not pointed out via audio.
1. When the guy cut out the pieces, the grain of the face layer of the plywood was laid out so it was parallel to the direction of cut with the lock mitre. Making the vertical cut cross grain on plywood with the LM is gonna give you tearout you can't believe. Don't ask me how I know this:wacko:
2. Stop the video and look carefully at about 3:35 into the video and he did get significant tearout on the video but it was on the inside. Those legs were also substantial enought that it could deal with some tearout with little adverse effect from a strength standpoint. Using 1/2 or 3/8 ply, it would be significant.

Just one other point. Any tearout with the lock mitre will likely occur on the inside of the joint so on a closed component; ie. boxed leg or something like that, there would be no cosmetic impact.


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## asrubin (Jan 1, 2008)

Thanks to all...I never thought using the lock miter bit....that is much better than box joints....


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