Tips for Clamping Miters with Increased Pressure
George VondriskaEven veteran woodworkers can find it challenging to establish solid clamping pressure when gluing up mitered projects such as picture frames or mitered face frames. Clamping miters is tricky because if you use any traditional clamping approach, the clamping pressure that you apply will immediately force the miters to slide out of alignment. Therefore, if you want to learn how to make strong mitered corners, you’ll have to use an approach for clamping miters that aligns the clamping pressure in a direction that is perpendicular to the joint line, so that the clamps are working for you, rather than against you.
George demonstrates an approach for clamping miters that can produce a perfect result every time by providing an approach for clamping miters that enables standard bar clamps to pull the joints closed effortlessly. To utilize this approach, you will want to do the following:
Build a prototype jig. First you’ll build a jig for clamping miters using the instructions provided, sizing for your project and your specific clamps.
Test on your actual project. Then test your prototype with your project to ensure that it will work with your clamps and direct the clamping pressure right where you want it. Make any necessary modifications to ensure that the jig works perfectly for your situation.
Make the remainder of the clamps necessary for your project. You’ll need 8 jigs for each project that you want to glue up simultaneously. Don’t be shy about stocking up on these because they’re cheap and quick to build and come in extremely handy.
Once you have these jigs in your tool arsenal, you’ll find tons of opportunities to use them and you’ll never feel the frustration of clamping miters without them. If you find this useful, WWGOA has lots more tips on gluing and clamping.
When you're bringing together miter joints, challenge is getting clamps on here so that you can really draw those joints closed, hold 'em close 'til the glue dries. So my solution for this is really simple. So this shop-made block. This is just a piece of 3/4 inch BC plywood. And the key to this is it's got this bird's mouth cut out of it.
Now, the key to that bird's mouth, is that when this goes on here, look at how this cut lines up with the end grain of the miter. And that's critical, because what I wanna be able to do is put a clamp here so I can get pressure right on those miters. So making these, they're an 1 1/4" wide, the bird's mouth was laid out. It's just a 90 degree cut. So 45 and 45, made that cut on the band saw, tested its location and then made a bunch more.
A bunch more because we wanna have one of these on the end of every board in our frame that we're gonna clamp together. Now lemme get a clamp on here, and then we'll look at a dry-fit, just so you can see how this whole thing is gonna work. The key to the clamp blocks, is that we have to secure those to the frame pieces. So that's what these clamps are doing here. Then, when I'm ready to go, I put glue on every corner, and then come to the corner I'm ready to start with, bring my miters together.
And then simply, bridge those corner blocks with my clamp. Line up the miter, clamp that corner closed. Now, because of our configuration here, that's why this set of clamps is pointing out, this set of clamps, the handles are pointing in, so that I have clearance here and I can get this clamp on. And then it's just second verse, same as the first. We're gonna repeat this process all the way around.
Line up your parts. Clamp pressure. Now, what'll happen is, if you don't get this clamp tight enough, if you don't get the clamp that's securing us to the frame tight enough, when we start putting pressure on the miter clamp, this piece is gonna start to creep on you. So you do wanna make sure this is nice and secure. Do a dry-fit like I'm doing here and make sure everything is working for ya.
Take it back apart, apply glue, and you'll be ready to go. It's a great way to get good, solid pressure across those miters and make sure they close up for ya.
You mention the possibility of creep if the clamp holding the tail is not tight enough. How about cutting the ends above the bird's mouth so it sticks out a distance equal to the width of the clamping pieces. This could be improved by cutting these ends so that they'll interlock.