Installing Reverse Kerfing Without Breaking - Luthier Tips du Jour Mailbag
In this episode, luthier Robbie O’Brien provides insight on how to install reverse kerfing without breaking it.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: I'm struggling to install reverse kerfing without it breaking. Do you have any tips to prevent this?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Nebraska. "Robert, I'm having trouble installing reverse kerfing without it breaking. Can you offer any tips to help keep this from happening? Matt in Nebraska."
Two types of kerfing
Basically, Matt, there's two types of kerfing; other than solid linings, you're looking at your normal kerfing and your reverse kerfing. And reverse kerfing, the one that I like to use, is the one that's the problem when you're trying to install it. So, let's step over to the bench, and I'll show you a couple of tips.
So Matt, other than solid linings, like I mentioned, here's basically your two types of kerfing. This is normal kerfing. In other words, the kerf is facing inside the guitar. So, when you go to glue it up, you put the glue on this side and it goes in like this. And it usually doesn't break, because the solid lining is against the edge and the kerf is on the inside, so it flexes really good. If it does break, then you just leave a small gap, and keep right on gluing. And no harm, no foul, you can't even see the gap. You can't even see the break.
So, reverse kerfing is the problem. The kerf is where the glue goes, and it goes against the side. And usually in the upper bout, here's where your problem is. As you put it in, you pull it up, it likes to break. So, when you piece it back together, you can usually see the seam where the break is.
Now, I like to use the reverse kerfing, even though it's harder to install. I do that for tonal reasons. Now, I know what you guys are thinking. "Hey, my guitar sounds great, and I use just the regular kerfing." That's fine. There's some great sounding guitars out there that have regular kerfing in them. However, I made the decision years ago to go with the reverse kerfing, and I'm a big proponent of stiff sides, and I think this helps me get a little stiffer side. Of course, there's a lot of other things that need to go right in that guitar to make it sound good. However, this could be one of the good things that helps you get a great guitar. So, let me show you a couple tricks to install a reverse kerfing without it breaking.
Tips for installing reverse kerfing without breaking it
So Matt, here's your first tip. What I've done is taken a piece of my reverse kerfing, and I've got it wet. I just spritzed it with a spray bottle. I'm going to come in, I'm going to start on this end [Robert points to the upper bout], because this is where I want to start installing, and I'm just going to clamp it to the outside of the form. Now, I know what you're thinking. "This guy's a nut. What's he doing, clamping to the outside of the form?" When I get back here, break off the excess, clamp it up. What I'm doing is pre-shaping or pre-molding this kerfing. It's wet right now. You can go ahead and do both sides, clamp it on the outside, go have a cup of coffee, have lunch, come back, and it's dry, and you're ready to install it on the inside, and it's been pre-formed. Now, if you're in a hurry, like I usually am, a hairdryer or a heat gun dries this off real quick. Don't heat the rubber bands, they don't like that.
So, here's the other side. Let's go ahead and install it [Robert sets the kerfing on the outside and starts clamping it with clothes line pins]. The reason why I'm starting on the heel block end is because if there's any gaps, you want them back here in the back end of the guitar, where nobody can see them. So, always start on the heel block end. Now, I know you're thinking. "Hey, he just cut that off too short." But once it comes into the inside, I've got excess on there. So, hit it with a hairdryer, and we can install on the inside. So, now I've hit it with my hairdryer real quick, I can pull it off. It still will go back flat, but it's got somewhat of a memory there, and the fibers have been stretched. Now I'm going to apply a little bit of glue, and put it inside the rims.
All right, Matt, here's your second tip. When you're putting your glue on, put a little dab in here. We're going to use this as a lubricant instead of an adhesive. When you come in and place it, don't just put it in here and pull it up tight. It's going to want to break right here, right in that area. So, what you want to do is place it in here like this [Robert starts the kerfing at the waist on the inside], flat, and then just slide it into place. There you go. Make sure you slide it all the way up against your block. Put your super high-tech, lutherie fastening devices on there [Robert fastens down the kerfing using basic clothes line pins].
And in this area is a little tighter radius, especially on your OMs or your steel string type guitars. And so I like to put a little more horsepower in here. So, I'm just going to use these clamps that have just a little bit more oomph to them. And then once you get past that area, you can go back to your regular scheduled programming, which is just the Amazon clamps. Make sure that you keep your kerfing just a scooch proud. That way, you don't have to radius your side down to it, you can radius your kerfing down to your sides. I had a friend once that did that.
And back here, if you've been living right, like apparently I have been, it just slides right into place there. Now, in order for that to happen, you need to have been driving the speed limit, paying your taxes on time. If you don't do that, it never works out just right, and you have to come in and cut that off. So, there you go, Matt. Hopefully that will keep you from breaking your reverse kerfing as you install it. And if you work fast enough, you can go ahead and do the other side, and the other side of the guitar as well, before you have to clean out the squeeze out. And we all know that you have very little squeeze out, because you didn't use much glue.
So, Matt in Nebraska, thank you for your question, and good luck installing that kerfing. Happy building.
[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com. Private and small group guitar building and finishing instruction available.]
