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Reinforcing a miter joint

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Forum topic by Joe posted 07-13-2011 03:40 PM 3971 views 0 times favorited 24 replies Add to Favorites Watch
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Joe

16 posts in 1976 days


07-13-2011 03:40 PM

Topic tags/keywords: mitered edge reinforce spline question joining

I am about to start a new project that incorporates several mitered joints like the one pictured below.

The project is cabinetry and will be made from 3/4” birch plywood and poplar. My question is: What is the best way to reinforce this joint while maintaining precision?

The two methods I have considered are a spline and biscuits. I hesitate to use biscuits because I don’t think I can get perfect alignment of the pieces using the fence on my biscuit joiner (I could be wrong about this, I have not tried a test yet). On the other hand, I am not sure how to cut the slot for the spline safely. It seems like I have to stand the pieces on their mitered edges to rip them on my table saw. Otherwise, the blade would have to be tipped to 67.5 degrees. I would like to avoid having to support the pieces by hand on their edges or building a jig that will do it for me.

What about cutting the slot before I bevel the edges?

Any suggestions would be appreciated, thanks.


24 replies so far

View Lee Barker's profile

Lee Barker

2170 posts in 2310 days


#1 posted 07-13-2011 04:42 PM

I’d like to know more about how this fits into the overall project and whether there is any stress on the joints. It is possible they don’t need anything beyond glue.

Biscuits would be a poor choice, both for precision and the difficulty of pulling the joints together.

To get precision in a spline cut, you’d probably end up making some kind of purpose-built sled.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

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Joe

16 posts in 1976 days


#2 posted 07-13-2011 04:56 PM

Here is a model of the overall project:

You mention a related concern that I have, which is how to clamp the pieces and draw them tightly together when gluing. I don’t think stress on the joint is much of an issue. Since this is going to be painted, and these pieces are sandwiched between the top and bottom of the case, a third idea I have is to just screw through the top and the bottom of the case and then plug the holes. Then the miters would not be reinforced. This solution is easy and would work well for this painted project, but I have another project in mind that will be stained, so I am still curious if there is a better way.

Thanks.

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Gregn

1642 posts in 2443 days


#3 posted 07-13-2011 06:07 PM

I agree with Lee on the spline joint as well. A sled would be the way to go to get your cuts accurate, although I don’t know why making one would be a problem, but understand. As for clamping you could use strap/band clamps to clamp with. Another suggestion might be to use pocket hole joinery with glue, since you only would need to drill pocket holes in one piece eliminating alignment problems. My first choice would be a spline joint though.

-- I don't make mistakes, I have great learning lessons, Greg

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DLCW

530 posts in 2113 days


#4 posted 07-13-2011 06:42 PM

Personally I would attack this with biscuits and pocket screws.

You can adjust the fence on the biscuit jointer to accurately align both pieces of the joint. The biscuits will help keep things lined up and the pocket screws will be your clamps.

If you’re not comfortable at first with this, cut some scrap pieces and play with it till you are comfortable and ready to attack the production piece.

-- Don, Diamond Lake Custom Woodworks - http://www.dlwoodworks.com - "If you make something idiot proof, all they do is make a better idiot"

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Loren

8293 posts in 3107 days


#5 posted 07-13-2011 06:52 PM

The easy way to do it is just glue joints and use pinch dogs
to clamp. Hammer a few wire nails into each edge and clip off
the heads. When the clipped nail shanks press into the other
edge, the alignment becomes pretty well fixed – they function
as tiny steel self-drilling dowels.

I wouldn’t mess with biscuits or splines unless the material was
weak, the joint stressed or the joint involved end grain.

I think you can get barbed biscuits that will hold long grain
joints together while the glue sets.

Another easy method is to either permanently or temporarily
affix blocks to the back that will make it easy to clamp the
work or drive screws at the most helpful angles.

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ChefHDAN

805 posts in 2309 days


#6 posted 07-13-2011 06:58 PM

Pocket hole screws would do the trick NICELY without any fuss and clamps would not be needed

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

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helluvawreck

23111 posts in 2326 days


#7 posted 07-13-2011 06:59 PM

I recently built two corner cabinets for our living room and the front face frame was made in such a way that the stiles for the face frame had two surfaces each at 45 degrees to each other These two piece stiles were put together with a 22-1/2 angles on each part. I built a jig out of 2×4’s that insured that the clamping would hold the angle accurate until the joints dried. I used biscuits in the joint. I kept each pair in the fixture for 45 minutes to an hour before removing them to insure the glue had dried and then let sit for 24 hours. Of course it was very important that the angle was exactly 22-1/2 degrees on each part. By previous planning I had plenty of things to do on the project while these parts were assembled in the fixture and drying. With these two parts complete the whole face frame was glued up. The face frames fit the top, bottom and middle shelf perfectly and everything went well with the rest of the cabinets. These corner cabinets were approximately 36 in wide and 72 in high and were installed as built ins in each of two corners of the living room.

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

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GregD

783 posts in 2595 days


#8 posted 07-13-2011 08:24 PM

Unlike Loren, I would have no luck gluing up joints that long unless there was something to keep them aligned. My biscuit jointer doesn’t always help enough.

With pocket screws I would be inclined to extend the pilot hole into the mating piece before driving the screw. Usually the screw tries to push the joint apart before it digs into the mating piece and pulls the joint together. Very aggravating when you are trying to keep tight alignment on parts that are difficult to clamp together.

If I were going to use splines I think I would cut the slots with a slot cutter in my router, and 22.5 degree wedges on either the router base or the router table to get the correct orientation.

I bet this 22.5 degree lock miter set would work well.

Another idea is hard to describe. Imagine setting up your dado for the thickness of your stock, and then cutting the dado at a 45 degree bevel (to the table). Now imagine setting the depth of the dado so that the deepest edge just severs the top piece of the work. You end up with a “rabbit”, but the bottom is oriented at 45 degrees to the surface of the work and is exactly as wide as the thickness. If you do this on both sides of your thin pieces, then the wider panels will butt up into the bottom of the rabbit. I wouldn’t actually make the cut as described – it would probably make a ratty edge. I’d probably use my normal blade set for a 45 degree bevel and cut what would be the bottom of the rabbit (running the work good side down, blade angled toward the work) to get a clean edge. Then run the work good side up and nibble out the rabbit from the edge to the shoulder (otherwise the waste would be trapped). Or just stick with the dado angled toward the work and run the work good side down so the chippers of the dado cut the shoulder of the rabbit. Not sure how practical this is.

-- Greg D.

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Loren

8293 posts in 3107 days


#9 posted 07-13-2011 08:38 PM

Oh – the trick with the pinch dogs is to make your pieces overlong and
joint your joints with a slight belly so when you clamp the ends together
the rest of the joint is clamped firm too.

View Lee Barker's profile

Lee Barker

2170 posts in 2310 days


#10 posted 07-13-2011 08:54 PM

I don’t see how the pocket screws would work if you’re going from one facet into another. If they went deep enough to bite, they’d protrude. And if one entered slightly off, you’d have no easy corrective measure.

The potential for misalignment with splines, and the inability to pull a biscuit joint together, preclude my using either of these.

So here’s what I’d do, since it’s paint grade. I’d use MDF (perhaps just for this part) and cut the parts and lay them out right side up and tape them together with masking tape. Turn the tambour over carefully, apply glue (best with an acid brush here) and fold it together. You can get amazingly good joints with this technique.

Clamp the construction with more tape and let it sit.

Cutting it overlong, as Loren suggested, is a great idea—that way you don’t have to concern yourself with endo as you’re glueing and clamping.

Any irregularities could be easily sanded out.

I have done this same trick with even plywood, but you have to be sooooo careful because the veneer is so thin that you have no grace—the facets have to meet perfectly.

Cut some scrap to your angles, widest piece you can get on your chop saw, and try all the methods that you’re pondering. It’s worth converting the shop to a “test laborrrrrr a tory” when you’re faced with this kind of a challenge.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View Joe's profile

Joe

16 posts in 1976 days


#11 posted 07-13-2011 09:08 PM

I am a big fan of pocket screws, but unfortunately they will not work for this application. I think you are right, Lee. The screw would exit the face of the opposing piece. There is another problem because I am trying to connect narrow stiles; some of them are only 1.5” wide, so no room for a pocket hole.

I am thinking that I can align the joint with tape and then shoot in some 5/8” 18 gauge brads. This could even be feasible, although maybe not perfect, for a stained project. It would be nice if the brads are uneccessary.

Hey, Helluvawreck, do you happen to have a picture of the clamping jig you made? Or could you describe it a little?

I will definitely be experimenting with different methods to see how tight I can get this joint. Just in case, does anyone know where I can get famowood by the gallon?

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helluvawreck

23111 posts in 2326 days


#12 posted 07-13-2011 09:55 PM

Joe, it’s hanging on the wall in my shop for the next time that I need it. All you need is a good flat piece of ply wood and some 2×4’s. It also has it’s own built in clamping system. I ordered 6 1-1/2 inch long 3/8 socket set screw with swivel feet. These screws go into t-nuts on the edge of a board. from the opposite edge an allen wrench applies the pressure along the length of the board and there are plattens behind the board. You can build the jig easily in an hour with a Kreggs jig and a chop saw. The pressure is applied exactly the way that you want it to be and the 2×4’s form a perfect bed. You placed wax paper under the parts to keep any renegade glue from sticking to the jig. The length of the joints were 48 and 36 inches. With this jig it might be fine not to use the biscuits; however, it doesn’t take that long obviously to put the biscuits in – even in an angled edge so I figured what the hell – put em in. I’ll see about getting a picture of it and the cabinets.

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

View shipwright's profile

shipwright

7161 posts in 2257 days


#13 posted 07-13-2011 10:46 PM

Lee has it.
I’ve done lots of glue ups with tape alone (check my blogs) where alignment was extremely crucial and had great and very strong results.
Clear packing tape actually lets you visually check the joint for alignment after assembly.
As for clamping, the tape alone will do even with PVA glue but the best strength will be achieved with the least pressure in the shortest time with hide glue.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

View Cosmicsniper's profile

Cosmicsniper

2202 posts in 2618 days


#14 posted 07-13-2011 11:47 PM

Glue it up like Lee said, using tape as your clamp. It works fine. Then brad it together. Nothing wrong with using brads, especially when you can cover it over with paint.

-- jay, www.allaboutastro.com

View Lee Barker's profile

Lee Barker

2170 posts in 2310 days


#15 posted 07-14-2011 04:32 AM

Thanks for the affirmation on the tape system. It sounds funky, but works so well.

I can’t go along with the brads. Too much potential for problem, and they won’t add a bit of strength. The ugly possibilities include a brad hitting a hard spot and blowing out the side, not being set all the way (how do you pound on that?) and just the putty issue.

If you are unsure of the strength of this joint, consider what forces would have to be present for it to be driven apart. I think you’ll find it’s all downward. Brads won’t make a difference. They’re a waste of your valuable time!

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

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