Miter Bench Joint Strength Test

[james golob]

Hello everyone,

I am looking for some advice on testing the strength of these miter joints. Can anyone help with testing these to simulate real life without building a complete bench. See attached pics. Bench is appx 60" in length and 16" wide, by 18" tall. Material is about 1.75" thick alder. My thoughts are if the joint is going to open, it would open from inner out over time with use. I have currently made a few with 7 10-50 dominos spanning the joint. I have been reading more and more, and this method might fail over time. My goal is to make a repeatable test to check several ways of connecting these joints, (spline, my current domino method, using more smaller dominos, epoxy, and a rabbeted miter) video it, and post it. I figure that I could just make half the joint for the bench making a 16"x 16" miter using the same material of each joint. Then secure that to my shop wall upside down to put the stress on the inside of the joint by placing weights on it until it fails. Is this a good way? Any suggestions? My goal is to determine how much weight can sit on my bench without failing(with people sitting on it) I would really appreciate any input.

Thanks
James
"what's your next build made of"

[Lee Schierer]

When I make mitered joints. I apply an equal amount of glue to each side of the joint. You are essentially gluing end grain which will absorb a lot of glue. Miter joint failure IMO is usually due to glue starvation.

Try this experiment. Make two small samples of your joint. Glue one by applying glue to only one side. Clamp it up and let it dry for at least 24 hours. On the second sample apply glue to both sides before assembly. Again clamp it and let it dry at least 24 hours. The try to break the joints first with your hands and then with more forceful means. See which one is stronger.

[Mike Wilkins]

Fine Woodworking magazine had a past article on joining corners and mitered corners. The author utilized some L-shaped connectors made of wood and some made of metal to glue the miters together I will check my stack of magazines later and post again with the issue number.

[james golob]

Thank you mike. I would appreciate it.

[james golob]

Lee i started my trails today. I will post results soon.

[Jamie Buxton]

When I'm making a mitered case joint like that, I use a technique I've never seen anywhere else. It is a mortise & tenon, with loose tenons. A key feature is that the tenons all have facegrain-to-facegrain glue faces. (Facegrain glue faces are stronger than endgrain ones.) A second useful feature is that the template for making the joint is easy to make in the shop.

Here is a pic of cutting the joint. The router has a template guide, and a simple straight bit. It just slides in and out to cut the slots you see in the workpiece.

Not seen in this photo are the tenons. They're simple squares of wood, milled to whatever thickness is needed by the slots.

The template is just a piece of plywood. I cut the slots in it with a stacked dado on the table saw, with the template stock standing on edge against the miter gauge. There is only one template. It just flips over to do the other side of the joint. Because there's only one template, the slots in the two halves of the joint line up perfectly. You can put as many tenons in a joint as you think is necessary. In the pic, the case is 18" deep, and there's a tenon every three inches or so.

This technique works even better in thicker lumber, like you're using for your table; there's more glue area on each tenon.

miterpic2.jpg


miterpic1.jpg

[andy bessette]

Biscuits or splines (with the proper grain orientation) and glued with WEST epoxy, thoroughly saturated, would be very strong. Letting the splines show wouldn't hurt aesthetics.

[Brian W Evans]

Fine Woodworking magazine had a past article on joining corners and mitered corners. The author utilized some L-shaped connectors made of wood and some made of metal to glue the miters together I will check my stack of magazines later and post again with the issue number.

I immediately thought of this as well. It is an article called "Add Muscle to your Miters" and is found in #254–May/June 2016 Issue. The author laminates aluminum angle and wood to make L-shaped tenons. I imagine you could pin these tenons from underneath using metal rods to help avoid glue/epoxy failure.

[Tom Bender]

Your test method seems sound.

I like splines. These can be in a contrasting wood or the same wood but with definition because the end grain will absorb more finish. They can also be wide enough to show under the bench. Much stronger that way and adds interest to the piece.

A box joint would also be strong.

Taper the legs (thicker at the top). This will add interest and strength.

[David Utterback]

I am interested to learn more about your energy source used to attempt to break that joint when glued with multiple loose tenons.

[Kevin Jenness]

You are overthinking this in my opinion. I applaud you doing some testing, but I would be surprised if you are able to dismantle a well glued 16" wide miter joint including 7 10mm x 50mm dominos without a very large commander.

As you know, clamping those joints requires some serious effort, and the more dominos you put in (see post #5) the more pressure required to close up the joint. Jamie Buxton's spline technique (post #6) or multiple biscuits similarly oriented in slightly thicker material allows for folding the joint up with tape at the corner. The grain orientation makes for a stronger glue bond than the domino joints you are currently using.

Have the benches you made up to now been through a year of seasonal movement and stress? Any failures?