Box Joints in Plywood

[Greg Hines, MD]

Does anyone have tips for cutting box joints in MDO plywood? I am attempting to build a couple of large, utilitarian, storage drawers for the router table, and wanted to use box joints.

I built a jig for the router table miter gauge, set it up for 1/2" box joints, and used a new sharp spiral bit. The tear out was incredible on the front face of the workpieces. I did try using masking tape on the cutlines, and that, if anything, made it worse. Is it the MDO layer that is the problem? I know that Norm has used box joints in the past in plywood (or so I think he did).

I did use the box joint jig on some scrap pine before I tried the plywood, and it worked great.

I think that the photos attached ok of the test work.

What did I do wrong with this?

Doc

[Jim Dunn]

I'll bet the MDO layer is not as good as you'd expect and that is causing the problem.

That said though, his Normness cuts box joints on the table saw with a dado blade set up. That would score the cut with the outside blades and "may" eliminate tear out. I say may because I still suspect your material.

As an aside how much a sheet was your MDO? Locally it sells for about $80 a sheet for 3/4". Pretty pricey, I think.

[Mike Malott]

Not to hijack, but here in Cincinnati, I just priced 3/4" MDO at $50 & change per sheet.

Mike

[Peter Quinn]

When I use the router table for box joints in qrt white oak I got chip out. I made a 'backer' from scrap to go in front of the stock and this eliminated chip out an the face.

[Greg Hines, MD]

I'll bet the MDO layer is not as good as you'd expect and that is causing the problem.

That said though, his Normness cuts box joints on the table saw with a dado blade set up. That would score the cut with the outside blades and "may" eliminate tear out. I say may because I still suspect your material.

As an aside how much a sheet was your MDO? Locally it sells for about $80 a sheet for 3/4". Pretty pricey, I think.

Here they call it "Sign Makers Plywood" and I bought a sheet of 1/2" about two years ago. At that time, I think it was about $40, but I haven't priced it lately. Table saw is my next option, and I have also considered building a sled to give it better support.

That said, I am trying to figure out a way to hold a backing piece onto the front of the workpiece. Carpet tape would work on the holding-it-on part, but I am worried that it will remove the overlay on the taking-it-apart part.

Doc

[tim harris]

Hi Greg, I would bet that you could get a good cut on that plywood with a high speed on the bit and a backer board on BOTH sides of the cut, the only problem is that you will tear up as much backer as the plywood.

Good luck, I would enjoy seeing more pics of your set-ups and jigs for the router table!

[Jim Becker]

I agree with Tim...backer on both sides to help keep the chip-out away.

[Ellen Benkin]

I've done box joints on a table saw with a dado blade (and a backer board) with no problems.

[glenn bradley]

Sandwich the piece to be cut between tightly clamped scrap. This creates a entrance and backer board to protect your veneers. That being said, the method is only a cure for when you absolutely have to box joint or DT veneers. Normally I avoid it if at all possible.