Making Square Joints

[dennisvogel]

I need to make some 14 x 14 x 8 inch cubes (no front or back). Material is 3/4 inch melamine coated MDF. I was going to use simple lap joints with biscuits to hold. Experimenting with some smaller pieces shows biscuit placement can easily be a little off in either direction and the sides aren't square or flush at the front and back.

I'm wondering if a Kreg jig would make it easier to join these as it is a sort-of clamp that should make it easier to align the pieces before drilling?

Any opinions? These cubes don't need to bear a lot of weight so I'm guessing a few pocket screws at each joint will do. (I don't have a Kreg but, hey, if you can't buy a new tool for a project what use is there doing it?) Will the Kreg jig really help hold these pieces (with some extra support, I'm sure) so I can get them square and aligned?

Dennis Vogel

[JackD]

I thought cubes had six sides and length width and height are equal.

This is a glue up problem, not inherent to biscuits. Build them face down on a flat surface (that way the fronts will be aligned). Use spare piece of the mdf (cut perfectly square at 12 1/2" x 12 1/2") as a jig to keep the pieces square. There are countless other jigs/clamps you can dream up to do this. I'd use glue and biscuits myself.

-Jack

[Doug Bell]

I've seen some pretty nice joints made in melamine using a lock miter bit in a (table mounted) router. Makes a strong joint, pretty much self aligning to make it all come out square and mitered corners all in one pass.

Doug

[George]

Lock miters are expensive bits and fussy to set. I'd go with a combination joint, formed by a 3/8 straight bit. Rabbet one, groove the other if open MDF won't offend. Strong and self-aligning joint made with a relatively cheap bit.

This assumes that your "lap joint" is really a butt joint at the corners.

[Kim Whitmyre]

If you always use the same (flat) reference surface to rest the biscuit joiner and stock on, you should have no problems.

Kim

[lonestar1]

I've had great luck with the Kreg jig, after a little trial and error practice. The joints are extremely strong when you use glue and screws. I got the little one with a single bit guide for just under $20 at Lowes. (Add another $3.50 for the screw drivers and another $3.50 for screws) There are more expensive options and I'll probably spring for the full kit when I need that level of sophistication. The key to a square joint is making a simple square jig that you can clamp the pieces to when you do the drilling as well as the assembly.

[dennisvogel]

That's part of the problem. Bench top isn't as flat as I'd like. Holding 12" long pieces on end is tricky. That's why I'm considering the Kreg since it holds both pieces.

Dennis Vogel