Strongest 90 degree joint

[Burt Alcantara]

I'm going to make a steady rest for my lathe. I'd prefer to do it with a square frame as opposed to a circular frame. The frame won't take that much stress but I'd still like to make the joints as strong as possible.

I'd like to use MDF because I've got tons of it but if ply is better then so be it. What's the best way to make this frame? The left side would be open so the frame would resemble a square J with a serif on the top.

--------
|
|
|
------------

(The "shape" is reversed, but that doesn't matter)

Burt

[Jamie Buxton]

I'd bricklay the MDF. That is, use three pieces of MDF perhaps 2" wide to form a C, meeting as a butt joint. Then use three more pieces to make another C, laying on top of the first C. The joints are also butt joints, but they are set up so that the seams in the first C don't line up with the seams in the second C. Then I'd add another C like the first one. Continue until you get an assembly as wide as you want.

The joint, technically, might be called a finger joint.

[Lee Schierer]

You probably want to use a bridle joint which is two half laps back to back if you are using multiple thicknessts of material. If it will be single thickness use a haf lap joint. You could also use a mortice and tenon joint, but it may not be as strong as the half lap or bridle joint. A butt joint would be about the weakest joint.

I'm not a fan of MDF so I would use the plywood or solid wood.

[Anthony Whitesell]

A magazine asked and tested that question. It turns out the strongest joint is the box joint. According to the article, it maximizes glueable surface and contact area and also has the most material involved with making the corner. With that said, the test was done on solid wood so grain and grain direction played a role in the effectiveness. There is no grain in MDF and the grain alternates in plywood, and I don't know how that effects the strength of the joint.

[Prashun Patel]

If yr goal is a strong joint, then go with plywood instead of mdf. Any well glued joint other than a butt will be reasonably strong. I'd go with dowels - but only bkz I have a Dowelmax.

[Burt Alcantara]

A lot of good ideas here. Sounds like ply or solid wood is the way to go.

Thanks for the help.
Burt