How to Create a Scarf Joint like a Pro with Robin

Robin loves a scarf joint and in this video, he shows you how to create a strong joint using his Hikoki 36v cordless circular saw.

This is part of our top tips with Hikoki series, there’s more to come!

We’ll have more woodworking tips and hacks from Robin Clevett soon.

Roger & Robin also have an epic fight, see who wins this battle.

Video transcript:

Welcome to Skill Builder. I’m Robin Clevett, and I’m just going to show you, and talk to you, a little bit about the new 36 volt, 185 mil, brushless circular saw. It’s a cordless circular saw. What’s significant about that, all my career I’ve used a circular saw just like this. This is a lot bigger. It’s a lot heavier and, of course, it has a cord. With the advent of cordless tools, and precision cordless tools, this is actually solving a lot of problems for me. You can see, I’m out on site now. Let’s say, I don’t have any power, which sometimes the case. This is perfect. I’m going to do a simple joint for you. The joint is called, a scarf joint. It’s something I use all the time. It’s for extending timbers and making them super long. The principle of the joint is quite simple.

You’ve got a length of timber, and you’ve got to join another section onto it. What you do is, the height of the timber times three. Three times height is the length for the joint. What we’re going to do, we’re going to form a scarf, which is basically … I’ll just draw it out for you. It’s something like this. There’s one part, there, there’s another part. What we do is we put a set of folding wedges in there. When we drive the folding wedges together it pushes this one this way, it pushes this one this way, and then we finish it with a mechanical fixing there and there. The joint will hold without a mechanical fixing. In fact, I often use them without mechanical fixing. There’s no glue involved. Quite often if it’s a hip rafter, for example, which is where I use them all the time, or a ridge. Because of the length of the joint, you might have a jack rafter fixing right over it, sometimes in a couple of places, and that actually clamps it. It’s a beautiful job.

Let’s take a look at the saw. Compact, lightweight, and mechanically very well built. For example, it’s so simple there’s a lot of easy movement to get your degrees of pitch. Obviously, you’ve got your fence screw there, which is quite sturdy as well. It’s got a lovely spring on the guard, super important, that, for safety reasons. Why I talk about that, as well, for the experts out there, one thing you’ll notice this doesn’t have a riving knife. And, for me, that’s quite a good thing, because I do a lot of plunge cutting, which I’ll show you in a minute.

The other thing to say about riving knife, if you’re cutting a lot of sheet material, make sure your sheet material is well supported, because as you’re going through, if it gives you a little bind, whereas the riving knife would hold that bind, this isn’t going to do that. It’s likely to kick back, so you got to avoid that. Make sure your work’s well supported. The battery, again, 36 volts, this one’s fully charged, just come off charge. Take’s about 25 minutes, it’s really good. It’s quite a high output battery as well, that. It’s got your indicator on the back, which shows you how much life it’s got. This will run until it’s finished. There’s no dullness. It will run, run, run, and just go boom, finished.

Let’s mark up the simple scarf joint. We just need a couple of bits here. This is the length of timber I’m going to put the scarf joint on. We only have to mark it out once. Even though it’s two pairs, it’s two parts to it, we only have to mark it out once. Let’s just that bit of shake off there. The joint principle is three times … the length of the joint is three times the height of the timber that you’re joining. I’m going to round this up, just simply, to make it a little bit easier. I’m going to hold it 180, so it’s 300 plus 240. It’s 540. That’s the length of the joint. That’s three times the height. I’ve just got another shoulder line there, over to the other side.

I’ve got a section of timber, which is exactly the same thickness that way. I’m going to take the outside to the outside, and I’m going to mark here, and I’m going to mark on the opposite side, here. Then what I’m going to use is my speed square to run a couple of shoulders in. So, basically, my shoulder, here, runs down. It’s a 90-degree shoulder, to there. All right. That’s 90 degrees there. And the same on the other end, coming back there 90 degrees, there. And then all we need to do is put one in the middle, same principle. Now, that is effectively the joint. This is the bit I’m taking off. That’s the bit that stays. All right?

We’re going to cut that out now. Just going to check this is square out of in and out of the box. Pretty nice. This is where the magic begins. This usually happens on a customer’s drive, or anywhere I can find the space. As you know, timber isn’t an exact science. A natural product, it moves, it bends, it bows, and we got to go with that sometimes. You’ve got a stack of timber, you pick out the straightest ones for the most important components, a little bit like this. What I need to do is add this whole length onto the end of there, so I need a bit of space for that. Find a nice flat spot on the drive. I’m going to run it over here, there. We get our piece we’re joining on, make sure the best end of it is going to be joined with that joint. If there’s any cup in the timber, that’s when the timbers go like that. Try to marry the cups up, don’t have the opposites.

Sometimes, just by looking at the end grain, you can see, that if you match the end grain, the chances are the cup’s going to be in the right place. But this particular structural timber is beats the stuff, haven’t really had a problem with it. I’m going to lay that on the ground, and we’re going to lay that over the top, here, crush it off. But the most important thing now is know which is the top of your timber. So, if this is the top of my timber here, for example, I’m going to give it a little bit of bow. So when the joint goes in, and it goes into compression, it goes straight. It can only go straight. It doesn’t sink. I’m going to look down that now, make sure it’s nice and true and straight. You can do a string line as well, but I know, from experience, where it needs to be, to be straight, and that’s it.

Now, it’s a matter of marking the male to the female with a pencil, and you can’t get better than that. If you try to mark the joint out to two separate bits and put them together, chances are you’ll have a few gaps, or it won’t exactly fit. Now, there’s one more bit we need to cut, which is here, and the same there. You see, I’m just roughing it in. That’s 18 millimetres, roughly. That’s for a pair of folding wedges. I’ll put that back up on here. And we just make sure we’re going to cut off the bit we want to cut off, to repeat the process. I’m going to mark my extra shoulder and cut that as I do it. The joint’s nearly ready, just got to adjust this one. The last bit to make is a pair of folding wedges, and we can just take that off of another cut.

Okay, now. We’ll demonstrate how strong this joint is. There are our folding wedges, will go in there. What I like to do is attach one, so when I push the other one, it doesn’t move. All right. We’re just going to tack that in there now. It’s heartbreaking to see that. When I started putting this joint together, I used that to mark it, which is the same thickness. The only reason I do that is so when I make my folding wedges, it’s the right thickness. And it’s just years, and years, of trying them, practice. You just think of the quickest way. It’s just an off cut. It’s all it is. Now, we need to demonstrate the strength of this, so we need a couple of bits of timber supported, and we’ll walk across it once it’s wedged together.

Get more wedge, pull that one over. The principle of this joint, I’m just going to mark an arrow on it in two places. That’s what’s happening as we bang the wedges in, a gentle tap. You can see, it’s pulling up now to the shoulder. What do you think about a joint like that, straight off a circular saw? I mean, it’s what you want. This joint isn’t designed … It’s not for a floor joist, so don’t span big areas and do it for floor joists. It’s ideal for a hip rafter, side rail for a ridge, so the ridge will stop it from pulling apart. Hip rafter’s got lots of support by jack rafters, but I’m just going to demonstrate. I’m only 65 odd kilos. I’m going to have a little walk across this, just-

That is 10 and a half stone. I’m a bit of a lightweight. I’m just going to stroll across it, just to show you. And Dillon is going to try to get a closeup, see if there’s any flex in it.

A little bit of balance is needed. It’s a bit wobbly, but that’s nothing to do with the joint, that’s the timber. I’m on the tight rope. And he makes it.

There you saw me making the scarf joint with this brushless 36-volt cordless saw. You can see how easy it coped with it. This timber is fantastic structural timber. It’s been dried out for ages inside, and it cut with no problem. Now, if you want to see some more tips and tricks, just keep checking back to the channel. I made you a scarf joint, and in return for the scarf joint, I want you to subscribe. If you’re not a subscriber, it’s got a ring to it, saw, scarf joint, subscribe. Are you getting it now? Thank you.


About Dylan Garton

Dylan Garton
Dylan Garton is a freelance video producer, camera operator, animator and editor. He also writes scripts, articles and develops websites. Cofounder of Skill Builder.

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