Reinforcing Mitered Box Corners

[Andy Compton]

Hi All,

I'm a beginner to woodworking and am making my first box to hold our ever growing Cards Against Humanity set. It's a maple box with a sliding walnut lid and a baltic birch bottom in a dado. In my complete "newb-ness" I decided to miter the corner of the box. Is there an easy way to reinforce the corners? My understanding is that the end-grain to end-grain glue-up likely will not last.

Thanks in advance!

[Pat Barry]

Rubber binders

[Bade Millsap]

I typically use hardwood spline like pictured in this link ...https://picasaweb.google.com/lh/photo/e40-7K0SqvL8CKHa2iCBIdMTjNZETYmyPJy0liipFm0?feat=direc tlink

[Jamie Buxton]

Bade's splines are a good solution. You cut the slot for the spline on a table saw. You make a cradle that stands the box on its corner. It runs along the rip fence.

[Jim Andrew]

I use biscuits. If you have a biscuit joiner, it is easy to put them in miter joints. About the best use of a biscuit joiner.

[Bade Millsap]

I should have been more explicit ... check out this google image link and you'll see lottsa examples https://www.google.com/search?q=miter+spline+jig&espv=2&biw=1770&bih=955&tbm=isch&tbo=u&source=univ&sa=X&ei=O7TaVI22GcmMyAS4uoCgDw&ved=0CCsQsAQ#imgdii=_

[Art Mann]

Here is a photo of a keepsake box I built for my daughter-in-law. The sides of the box are 3/8" thick. The keys (also called splines) are the thickness of my table saw blade. I have built several of these and the corners are extremely strong. The box is black walnut and the keys and inlay are soft maple.

Click to zoom

306639

[Jeffrey Martel]

Glued up mitered corners are still stronger than the surrounding wood. Putting splines in helps, but isn't really necessary. It's more for decoration than anything else.

[roger wiegand]

Either biscuits (hidden) or a splined miter (exposed). Have done the keys for decorative purposes as well. The spline running the length of the joint or a biscuit helps keep things from slipping during glue up, though tape on the outside of the miter is also great for that.

[Art Mann]

I don't agree with that assessment. Gluing mitered corners is almost the same as gluing end grain to end grain. You need a lot of surface area to get a strong joint in end grain. You don't get that with 3/8" stock I use. 3/4" material might be more successful. I make my boxes and then cut and install the keys. I have dropped a box on the concrete floor before the keys were installed and it came apart due to glue joint failure. The keys are decorative for sure but they are also structural.

There are other ways to make strong mitered corners. One method I have used is a lock miter bit. With this method, the gluing surface area is greatly increased and you get some long grain to long grain contact. Another way is the old familiar finger joint. Lots of surface area and it is all long grain to long grain. Still a third way is to cut a groove along the length of each beveled face and then install a true spline the length of the joint. Unfortunately, these methods aren't available on the OP's current project.

[Jeffrey Martel]

I don't agree with that assessment. Gluing mitered corners is almost the same as gluing end grain to end grain. You need a lot of surface area to get a strong joint in end grain. You don't get that with 3/8" stock I use. 3/4" material might be more successful. I make my boxes and then cut and install the keys. I have dropped a box on the concrete floor before the keys were installed and it came apart due to glue joint failure. The keys are decorative for sure but they are also structural.

There are other ways to make strong mitered corners. One method I have used is a lock miter bit. With this method, the gluing surface area is greatly increased and you get some long grain to long grain contact. Another way is the old familiar finger joint. Lots of surface area and it is all long grain to long grain. Still a third way is to cut a groove along the length of each beveled face and then install a true spline the length of the joint. Unfortunately, these methods aren't available on the OP's current project.

Try it for yourself and see. In practice, as long as you achieve a glue joint that is stronger than the surrounding wood, that's about as good as you can hope for. There is no real structural benefit to it. Especially in a small box application, there is no need for anything additional. Vertical splines help with alignment, but that's about it.

Cut a 45 deg miter, put glue on, let the end grain soak it up and add more, then clamp it together. After a couple of hours, see if you can break it. If it breaks along the glue line, then you know you will need to add something extra to it. If it breaks out the wood, you are good. So far, when I've tested it, there's been no need for additional splines.

EDIT: Also keep in mind that we're talking about a box to hold cards. Strength isn't needed in this case. If I was doing a box for something that would see hard use, but sure I would do something else or add splines. For this case though, you don't need it. I've built many, some with splines and some without. None have failed yet.

[glenn bradley]

I too use miter keys.

306666 . 306665 . 306667

[Jerry Olexa]

splines or biscuits.....

[John Sincerbeaux]

Try it for yourself and see. In practice, as long as you achieve a glue joint that is stronger than the surrounding wood, that's about as good as you can hope for. There is no real structural benefit to it. Especially in a small box application, there is no need for anything additional. Vertical splines help with alignment, but that's about it.

Cut a 45 deg miter, put glue on, let the end grain soak it up and add more, then clamp it together. After a couple of hours, see if you can break it. If it breaks along the glue line, then you know you will need to add something extra to it. If it breaks out the wood, you are good. So far, when I've tested it, there's been no need for additional splines.

EDIT: Also keep in mind that we're talking about a box to hold cards. Strength isn't needed in this case. If I was doing a box for something that would see hard use, but sure I would do something else or add splines. For this case though, you don't need it. I've built many, some with splines and some without. None have failed yet.

Ive been making and selling decorative boxes for a long time. I would not sleep well at night knowing I sold a box that had any joinery that was not "mechanically" joined. Many of my boxes have small trays that also get mechanically joined. I mostly use blind tendons cut with a multi-router.
The OP stated he was new to woodworking. Might as well learn by challenging himself to be a "craftsman". A Craftsman cares that his joinery will last not a few years, but...lifetimes.

Sincerbeaux.com

[Prashun Patel]

I've been experimenting with glue sizing and that really helps to improve the strength of mitered joints. A lot of the glue in a butt or miter joint wicks into the surface of the wood before it can dry. Pre-wetting the joint with thinned glue, waiting an hour, then sanding any nibs and re-gluing seems to result in a stronger joint than just gluing them outright. When I say 'seems', I mean, after a week, it takes a little more force for me to break apart than an unsized miter glue up. That ain't science, so take it FWIW.

I prefer to domino (or biscuit) my miters if for no other reason than it makes clamping a lot easier.

depending on the thickness of your sides, you can also pin them from the outside with 1/4" dowels. There are ways to make those pins decorative with spacing or staggering them between the front and side.

you can also spline the joint by running slots along the length of the miter. I personally find this harder than keys, but keys do require a jig.

[Jeffrey Martel]

Ive been making and selling decorative boxes for a long time. I would not sleep well at night knowing I sold a box that had any joinery that was not "mechanically" joined. Many of my boxes have small trays that also get mechanically joined. I mostly use blind tendons cut with a multi-router.
The OP stated he was new to woodworking. Might as well learn by challenging himself to be a "craftsman". A Craftsman cares that his joinery will last not a few years, but...lifetimes.

Sincerbeaux.com

And if I was selling then I would probably add splines for a) decoration primarily and b) a belt and suspenders approach backup. However, I was posting to clear up misconceptions that a plain miter joint will fall apart on its own as that is not the case. Structurally speaking, in a small box they are not necessary. If one doesn't believe me, test it out on some scraps. Usually the problems come from a glue starved joint as the end grain sucks the glue up. The fix to that is to apply glue, let it soak most of it up, and then apply some more. If strength were a big issue, then we would all use nothing but finger joints as they are the strongest corner joint due to the glue area.

Regardless, everyone should do it how they see fit. It's more of a personal preference thing.

[Prashun Patel]

I agree with Jeffrey. In relative terms, a miter may not be as strong a joint as its bigger brothers, but that doesn't mean it'll fall apart if you look at it the wrong way. Remember too that box corners have relatively long joints and don't suffer from the same type of cantilevered stresses that, say, rails and stretchers and aprons may face. For certain, more delicate applications, it can work just fine.

I think a craftsman knows his joints and deploys them deliberately.

[Art Mann]

Try it for yourself and see. In practice, as long as you achieve a glue joint that is stronger than the surrounding wood, that's about as good as you can hope for. There is no real structural benefit to it. Especially in a small box application, there is no need for anything additional. Vertical splines help with alignment, but that's about it.

Cut a 45 deg miter, put glue on, let the end grain soak it up and add more, then clamp it together. After a couple of hours, see if you can break it. If it breaks along the glue line, then you know you will need to add something extra to it. If it breaks out the wood, you are good. So far, when I've tested it, there's been no need for additional splines.

EDIT: Also keep in mind that we're talking about a box to hold cards. Strength isn't needed in this case. If I was doing a box for something that would see hard use, but sure I would do something else or add splines. For this case though, you don't need it. I've built many, some with splines and some without. None have failed yet.

I have been building boxes for 40 years and pretty much know what I'm talking about. How about you? Some of my boxes are high value and I can't afford for them to break if they are dropped or abused. Therefore, I do destructive testing to verify every new design concept. Do you do that too?

[Jeffrey Martel]

I have been building boxes for 40 years and pretty much know what I'm talking about. How about you? Some of my boxes are high value and I can't afford for them to break if they are dropped or abused. Therefore, I do destructive testing to verify every new design concept. Do you do that too?

Yes I do perform destructive testing. Thus far, plain miters have held up just fine for applications such as this. Again, we are not talking about a high value box in this instance. It's a box to hold playing cards. For that purpose, a plain miter joint is acceptable.

Again, for your application in high value boxes, it is not an appropriate joint. That is not what I am making a point about.

Apparently offering a difference of opinion based off of what the application is, is not acceptable on this forum. We are talking about a little to no stress joint here. Not a high value project that is sold with a lifetime warranty. Be realistic with the actual requirements for what was posted. Not what you are selling. What works for you is not the 100% solution for everyone.

[Ralph Y Thorne]

The OP stated he was new to woodworking. Might as well learn by challenging himself to be a "craftsman". A Craftsman cares that his joinery will last not a few years, but...lifetimes.

Sincerbeaux.com

Well said John. I just looked at your website... WOW! Your boxes are absolutely beautiful. You are truly a craftsman.

[Mike Henderson]

I use an ff biscuit in the corners. In addition to reinforcing the corners, it makes it much easier to keep everything aligned when doing the glue up. You can see how I cut the slots for the biscuits here (http://www.mikes-woodwork.com/RectangularTray6.htm)(bottom of page).

My joinery preference is not to show joinery. The biscuit is hidden in the joint so all you see is the junction of the two pieces of wood at the corner. And as an aside, it's nice to cut the sides so that the grain is continuous around the corner.

Mike

Mike

[Jim Matthews]

+1 on this. The joint is plenty strong.

Unless you drop it from some height, right on the corner it should be fine.

[Phil Thien]

Have to agree w/ Jeffrey here, all the boxes I've ever made with simple mitered corners are still going strong.

I spread some glue, wait 1-2 minutes, add some more, and clamp.

[Mike Sniedze]

Another trick that you may want to try is to spread a bit of glue on the mitre, and then , using an exacto or razor blade, push/scrape the glue into the grain. Wait about 5 minutes and then add a regular thin coat of glue to both sides. I usually add splines as well, but for very small or light duty uses, mitres alone done this way appear plenty strong. Mitres are somewhat of a hybrid grain. If you're unsure, spline away! Can't hurt by any means. My two cents, although in Canada we got rid of the penny, so I guess I have no " cents".

[Tom Giacomo]

I have made a few small boxes over the years and have found a mitered joint very good for small boxes. I use primarily birch ply but you must be very fussy about the joint. It have to be exactly square and it must have no voids in the joint and sanded smooth before gluing. A drop will not break it. I cover my birch ply boxes with veneer. One example.

[Andy Compton]

Thanks for all the great advice. I ended up drilling two holes in each corner and driving walnut dowels w/ glue. It looks great and will hopefully add some strength. I'll post some pictures once I've finished. A spline jig is on the to-do list for my next box project. Thanks!

[Jim Finn]

I make a lot of small boxes with mitered corners. Never had one fail in the seven years I have been making and selling them. The top and bottoms are glued on so they help to hold the miter joint in place. I have also make about fifty larger trunks with mitered corners. (24"x15"x15") I glue gussets to the inside of these mitered joints. I once knocked one of these cedar trunks off of a table to a concrete floor and did not damage the trunk in any way. (Surprised me) I have done splined corners on small boxes but just for appearance.