Shopsmith Forums

I need to make a bunch of window screens, about 3 feet wide by 5 feet tall. I was going to use 1x2 stock and miter the corners. I've done an acceptable job before, but I thought the biscuit joiner (now on sale) might make things easier and a bit stronger. In this second round of screen-making I was going to add a stretcher halfway up, which would also be biscuited.

Am I asking for trouble introducing biscuits into miters?

davebodner wrote:I need to make a bunch of window screens, about 3 feet wide by 5 feet tall. I was going to use 1x2 stock and miter the corners. I've done an acceptable job before, but I thought the biscuit joiner (now on sale) might make things easier and a bit stronger. In this second round of screen-making I was going to add a stretcher halfway up, which would also be biscuited.

Am I asking for trouble introducing biscuits into miters?

For window screens, I would be more inclined to half lap with mitered face.

I agree. I would probably use a mitered half lap for the corners BUT biscuits will work well.

If the windows get changed out seasonally, however, I would recommend the mitered half lap because the joint is IMO stronger.

Good mitered half lap joints are more difficult (time consuming) to make than biscuited miter corners. Decisions, decisions. Life is full of decisions.

Other than aesthetics, why miter? A plain ol' half lap will be plenty strong.

Gene Howe wrote:Other than aesthetics, why miter? A plain ol' half lap will be plenty strong.

Ditto! Take a look at other doors in your neighborhood.

I hadn't thought of half-laps. Ok, you all convinced me.

The one time I tried a half-lap I had a hard time cutting away exactly half the depth. But for this, close enough is good enough.

You've got a good horizontal boring machine, why not butt joints with two dowels in each joint? Along with a waterproof glue that would be quite strong.

Or, an open through mortise/tenon bridle joint.

I have a Shopsmith biscuit joiner, and find setting it up and using it to be quick and easy. As long as you make sure to keep the workpiece pressed flat against the table, it's hard to go wrong.

So far, I've only used mine to help align board edges for panel glue-ups. Just last weekend, I decided to use two bowed poplar boards to make a crude shelf in my garage. The boards were junk for most purposes, but OK for that. I cut biscuit slots in the edges, with the convex side of the board down against the table. At glue-up, the biscuits did a fine job of pulling the bowed edges into alignment, and I would up with a nicely joined (but still bowed) 12" wide shelf.

Your post got me wondering about the limits of using biscuits for structural joinery. I recalled having read about using double-biscuit joints for structural joints, but didn't know how they compared, strength-wise, to more traditional joints.

Google turned up this excellent article from Fine Woodworking. They used controlled laboratory testing to compare traditional M&T, loose M&T, and double-biscuit joints. The double-biscuit joint turned out to have about half the strength of a traditional M&T. I would think that should be ample strength for your application.

I also like the half-lap suggestions, and especially the bridle-joint idea, for the corners. But at the stretcher, a half-lap would seriously weaken the stile, and the bridle joint would become a traditional M&T. Double-biscuits would be a lot quicker.

I have been told (perhaps incorrectly) that biscuits don't really add much structural strength (mostly alignment). In the past I have used other joinery for strength like dowel and bridle joints. But lately I've switched to pocket hole screws (where they won't show).

I made new storm windows a couple of years ago and they were much faster, easier, and with plenty of structural integrity.

anmius wrote:I have been told (perhaps incorrectly) that biscuits don't really add much structural strength (mostly alignment). In the past I have used other joinery for strength like dowel and bridle joints. But lately I've switched to pocket hole screws (where they won't show).

I made new storm windows a couple of years ago and they were much faster, easier, and with plenty of structural integrity.

Matthias at woodgears.ca did some controlled joint-strength tests as well, here. He didn't test biscuits, but he did test pocket screws. Interestingly, he found that they also begin to fail at about 1/2 the load of a traditional mortise and tenon.

So either pocket screws or double-biscuit joints should be fine for applications that are not severely loaded. I like pocket screws for utilitarian applications, and biscuits where they aid in assembly alignment, or where I don't want the pocket holes visible.