Box (Finger) joint issues needing suggestions

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Forum topic by groland posted 05-27-2017 09:19 PM 1161 views 0 times favorited 9 replies Add to Favorites Watch
View groland's profile


228 posts in 4193 days

05-27-2017 09:19 PM

Topic tags/keywords: box joints

I want to make box joints for some drawer innards. I am following the excellent video by William Ng on how to do this. But I am having some problems. I am using a SawStop table saw, a DeWalt dado set and 1/2 inch Baltic Birch plywood from Woodcraft in Cleveland, OH.

After a lot of trial and error, I got things dialed in pretty well. I’m using 1/2” box joint dimensions. I found out that if I orient the plywood so that the veneer is parallel to the saw blade, I get a lot less tear out than when cross-cutting the dado through the surface ply. I guess this ought to have been obvious! However, I am still getting tear out no matter how careful I am. Not too bad, but I’d like better. So I have some questions.

I wonder if anyone has tried cutting some strips of 1/8 inch plywood and placing them between the plywood being box jointed and the fence so that every cut has backing? Probably pretty wasteful of timber and costly.

I read here about the Forrest Box Joint saw set, which was well-regarded, but is apparently limited to 1/4 or 3/8 joints. Any thoughts on using this in 1/2 inch Baltic Birch?

Are there hardwoods less likely to tear out than Baltic Birch? Could make the boxes of pine, poplar or some other solid wood.

Thanks for your input!

9 replies so far

View mlipps's profile


122 posts in 1896 days

#1 posted 05-27-2017 09:42 PM

Could be a number of issues.

Make sure your dado stack doesn’t have a ton of pitch on it. If so clean it.
Stack may require sharpening.
Try clamping your pieces together to ensure they each support the following piece
Using a backer board for the last piece (between your miter gauge and the first piece)

View johnstoneb's profile


3145 posts in 2954 days

#2 posted 05-27-2017 09:56 PM

Try masking tape on the back side of the plywood.

-- Bruce, Boise, ID

View tmasondarnell's profile


130 posts in 2570 days

#3 posted 05-27-2017 10:03 PM

In addition to mlipps ideas, score along the cut line with a marking gauge or utility knife.

View Kirk650's profile


680 posts in 1529 days

#4 posted 05-27-2017 11:51 PM

I use a plywood backer. Works fine. Happily, I have mucho scrap plywood. I built a box joint sliding jig. Took me the second try before I got it right. Then I wrote on the jig what I needed in the way of shims to make perfect cuts, and it’s pretty simple now.

View TheFridge's profile


10859 posts in 2267 days

#5 posted 05-27-2017 11:54 PM


-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View runswithscissors's profile


3100 posts in 2806 days

#6 posted 05-28-2017 12:41 AM

Plywood, even the best quality, is very prone to tear out making that kind of cut. I prefer solid wood.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View splintergroup's profile


3804 posts in 2003 days

#7 posted 05-28-2017 01:45 PM

I have the Freud box joint set and use it for many things. The perfect 1/4 and 3/8 cuts are flat and clean.

As to your BB ply, the only solution I have found is a good backer board (I use 1/8” hardboard DS taped to my miter).

Once you have your cut dialed in, add the backer board. It will be fine for many cuts.

View groland's profile


228 posts in 4193 days

#8 posted 05-28-2017 06:56 PM

Following up on my own inquiry, I experimented with using 1/8” masonite as a backing board, and it worked very well. I have almost no tear out and the boxe joints look good.

There are some excellent ideas I shall keep in mind for future box-joint work. I know I am going to have to make another fence and I am excited to incorporate some changes there.

Thanks, Gents!

View Andybb's profile


2762 posts in 1384 days

#9 posted 05-28-2017 07:46 PM

Plywood, even the best quality, is very prone to tear out making that kind of cut. I prefer solid wood.

- runswithscissors

Yes. This was my 1st thought. Since sharpening the blades is probably the last thing you feel like doin, some ideas….
1.Tape may not hold up for plywood tear out.
2.Try clamping “backer boards” front and back to try and stabilize the sandwich. Heck, try tape and backers at the same time?
3.Plywood veneer is tough to keep from tearing out under the best of circumstances especially when the orientation is going with the grain of the wood.
4.Maybe slow the speed of the cut?

-- Andy - Seattle USA

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