Making a strong edge miter

[David Costa]

Hello All! First post after being a long-time spectator.

I am building a credenza/sideboard/buffet, and it has some rather large top/bottom (18” x 80”) and side panels (18” x 20”), all made from 7/8” thick hard maple. I would like to create edge miters at the four corners, thus I need to make four 18” edge miters.

What is my best option to make the miter strong?

I do not want any joinery showing at the front edge nor on the mitered edge, so miter keys are out.

I had toyed with the idea of sawing off a strip at the front edge, using a lock miter joint, and then re-attaching the front strip, in order to hide the lock miter.

I have also thought about a blind internal spline, but making this will require some fancy jiggery, as merely flipping the fence and board after the miter is only good for a through spline. Also, doing this with an 18” x 80” board would be a bit cumbersome at the router table. I am not opposed to pursuing this avenue of thinking, however.

Any thoughts or suggestions would be welcome!

Thanks in advance.

[Brian Holcombe]

Perhaps a blind version of this;

[Jeff Ramsey]

I would still consider a spline; they're quite strong.

[Frank Martin]

I just did this for a shoe cabinet I have been working on and used 5mm dominos. If you have a Festool Domino it is piece of cake, perfect alignment and super easy to do the joinery. Although, I precisely calibrated my sliding saw to make sure all four boards are perfectly square, as there is very little room to hide any imperfections in this type of joinery.

[David Costa]

Frank, I do have access to a Domino, although I have only used it a few times. I don't have access to a sliding saw, and realize that these miters will take some precision to get right on my conventional table saw.

Is this merely a matter of setting the fence on the domino at 45 degrees?

[Steve Jenkins]

So you are joining the ends to the top with miters? I use biscuits to reinforce that joint. On an 18" wide top I'd probably use 3 biscuits.

[Larry Fox]

I'm with Frank on this one - Domino. I have made a few cabinets with long miters (one floor-to-ceiling in a bathroom) and put Dominos in the joint and they have been rock solid and showing no sign of failing for years now. The trick (if you can call it that) I have found is that you want to get the reinforcement as close to the outside of the join as is practical. This means that you can't really go very deep with the Domino slot. It takes some time to find the sweet-spot (practice on scrap) and once you find it put more Dominos in than you think you need. Be VERY careful and precise with the marking and cutting of the slots and things will line up. In things involving a lot of Dominos, if you are using the narrowest setting errors in alignment propagate so I like to give myself a bit of wiggle room by running the edge of each side of the dominos over a block plane. Given the shallow depth of the mortise you also have to cut the Domino but that is no big deal.

This is a really tough joint to glue so I tend to do it in 2 halves. I glue Dominos in the "up" side of the join a day ahead. I do the "up" side first because if you do the "down" side first you could get glue drips when you are trying to fit the "up" and align the joint.

This goes without saying but very accurate saw setup and dry fitting are very important here. A well fit miter is a thing of beauty - a poorly fitting one is a hag and there is very little room for error. It would be really difficult to correct for poor machine setup on an 8' miter.

[David Costa]

I am leaning towards the Domino, for sure.

I can see how a row of 12+ dominoes could be extremely sensitive to alignment errors. Would it be advisable to make one side of the miter with a series of tight-fitting domino mortises, and do the mating side with a series of slightly wider slots? Front edge alignment would not be indexed perfectly, but the long edge would be unaffected, and this would effectively solve the bigger issue, while eliminating the need to trim each domino. Thoughts?

[David Costa]

you want to get the reinforcement as close to the outside of the join as is practical. This means that you can't really go very deep with the Domino slot.

I am curious as to why this would be better than going towards the inside, where it is possible to have a much deeper mortise/domino?

[Frank Martin]

I am leaning towards the Domino, for sure.

I can see how a row of 12+ dominoes could be extremely sensitive to alignment errors. Would it be advisable to make one side of the miter with a series of tight-fitting domino mortises, and do the mating side with a series of slightly wider slots? Front edge alignment would not be indexed perfectly, but the long edge would be unaffected, and this would effectively solve the bigger issue, while eliminating the need to trim each domino. Thoughts?

I used the middle setting (some wiggle room) for the Domino in all of them, as the strength mainly comes from the long grain side of the domino. I cut the domino slots closer to the interior corner as there is more wood there allowing better reinforcement. I did the entire glue up in one shot using long setting epoxy. I used band / strap clamps with corner protectors in addition to some parallel clamps.

Regarding ability to cut the miters, I don't see why you can't do it with an accurately set-up table saw. I had a Unisaw before that I am sure I could do the same with. Not as easily, but definitely doable. Just test the whole process with scrap to dial things in and you should be fine.

[Larry Fox]

I am curious as to why this would be better than going towards the inside, where it is possible to have a much deeper mortise/domino?

David - I should have said "I want to get the reinforcement..." instead of making a general statement. My reasoning was that is the part of the join that shows, and for the piece I was making the miters were the very first step and would be moved, twisted, flopped around during construction and I thought having the reinforcement close to the front would help. I honestly don't know if it is based on any sound principles of physics but, in my mind at least, if you stress the joint in a way that would force the joint to open having a reinforcement closer to the front would help counteract this leveraging effect.

As I said though - based on no science other than the "makes sense to me" logic that I employed at the time of making the joint.

[Brian Holcombe]

This is made much simpler with a shooting board and a plane. Get it close, then fine tune the fit....use feeler gauges to see how much must be removed.

[David Costa]

I would not have thought to make an edge miter shooting board, but that could be just the ticket to a perfect joint. I am, however, striving to get it right with a meticulously set-up table saw. Thanks for the idea. If my dry fit isn't "perfect", I'll make a shooting board.

I would have used straps for this--just seems easier than clamps to apply even pressure to each corner. Epoxy is not something I have worked with on wood-to-wood joints. Is cleanup terrible/impossible!?

Any thoughts on staggering the dominoes, such that half would be longer (towards the inside of the miter), and half would be shorter (closer to the outside)? Am I adding extra work for a marginal (if any) increase in strength?

[pat warner]

No planted top? Would hide the joinery, mistakes and all.

[Frank Martin]

I would not have thought to make an edge miter shooting board, but that could be just the ticket to a perfect joint. I am, however, striving to get it right with a meticulously set-up table saw. Thanks for the idea. If my dry fit isn't "perfect", I'll make a shooting board.

I would have used straps for this--just seems easier than clamps to apply even pressure to each corner. Epoxy is not something I have worked with on wood-to-wood joints. Is cleanup terrible/impossible!?

Any thoughts on staggering the dominoes, such that half would be longer (towards the inside of the miter), and half would be shorter (closer to the outside)? Am I adding extra work for a marginal (if any) increase in strength?

I am sure the traditional way is a shooting board, but if you setup your table saw well, no need for it. The other critical item is to use stops to make sure opposite members are exactly the same length, so no measuring mistakes...

I always use long setting epoxy for complicated glue-ups. I learned not to use too much and deal with the cleanup using chisels and sanding.

I did not and would not stagger the dominoes. Unnecessary complication in my opinion with no value added.