Compound Radius Fretboard - Luthier Tips du Jour Mailbag
In this episode, luthier Robbie O’Brien shows how to put a compound radius on a fretboard.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: Whats your preferred method for doing a compound radius on a fingerboard?
Robert O'Brien: Today's Tips du Jour mailbag question comes to us from Canada. "Robert, do you have a method for doing a compound radius on a fingerboard that uses common Luthier tools? Felder from Saskatchewan Canada."
Whats a compound radius
Felder as a matter of fact I do. The first thing we're going to do is talk about what a compound radius is. A normally radius fretboard, if there is such a thing, has just one singular radius all the way along there. Now, depending on the taste and perhaps your style of music, that would depend what size radius you have. On my acoustic guitars, for example, I like to put a 16-inch radius, sometimes a 14-inch.
Now a compound radius would have one radius here that blends into perhaps another radius here and then perhaps a third radius here on the end. And the reason for that is the flatter radius usually goes down here and the guys can distort the strings or the notes and do their bending and pulling up here on a flatter surface, and it's usually a little bit easier. Down here, a little tighter radius matches the natural curvature of the finger when you're doing your bar chords.
Common tools used to radius a fingerboard
So now that we've explained what it is, let me show you how to do it. So Felder, let me show you some common luthier tools I use to do this. First of all, you need a fretboard and normally I would have the fretboard already glued to the neck, which has been carved. To put the radius on there, I'm going to use radius blocks that I got from LMI. These come with one radius on one side and one on the other, and you can get them in a variety of different radii. I have a couple of those.
I also have sticky back sandpaper that I got from LMI in various grits to put onto the sanding blocks. To check my radius, I have a radius gauge that I got from LMI, comes with various radii so you can check your precision once you're done. I also have a leveling bar made out of some bar stock that I got from my local luthier supply big box store. And I'm going to use this to blend the radii together.
So I'm going to start by just putting some Double-stick Tape on the back of my fretboard and attaching it to my bench here so I can show you how to do this in the video. So for the purposes of this video, I'm going to start with a 10-inch radius in this area, blend it into a 12-inch radius and then finish with a 14-inch radius. I have my appropriate sanding blocks here from LMI ready to go. I've got 80 grit sticky back paper on them.
Compound radius options
I'm going to start with the flattest radius, which is 14-inch and just do the whole board. There's a couple ways you can do it. You can do the whole board and then come in with your next radius, which is a little tighter here, and then come in with your final radius, which is very tight and do here. If you go ahead and just do the whole board, you're going to wind up doing this anyway, so you might as well just save yourself a little time and go ahead and begin to knock that down.
Another way to do this other than just radius block is with a hand plane. If you want to come in and knock off a little bit of the edge with the hand plane to get it started so you don't always have as much elbow grease to do, you can. A word of caution though. If you have a bound fretboard, sometimes the binding wood chips, sometimes the edges of the fretboard would chip. If you have inlay, you've got a lot of things to worry about. So if you don't have a lot of finesse with your hand tools, you're not used to it, just use your sanding blocks.
Sanding the 14-inch radius
So I'm going to start with the 14-inch. And here we go. When you do this, you don't want to wind up doing this or lean in a little heavy on one side, then on the other, you want it all to be even. So you get right over the top of the board and just come down it like this [Robert sets the fretboard down on his workbench vertically, then works the sanding block up and down the entire length of the fretboard]. If you want to put some chalk on it to check your progress, you can [Robert applies pink chalk to the entire fretboard]. I recommend pink. It helps the mid-range. I'm kidding, guys. It doesn't matter what color you have.
[Robert starts working the sanding block up and down the entire length of the fretboard]
And you can already begin to see very quickly that I'm knocking off the edges here. I want to keep going until I get all the way to the middle. That usually happens right before your arm falls off. I do also recommend using a dust mask because you're going to put up a lot of dust into the air. Obviously that's not good for your lungs, so protect your lungs.
Now as you work, you'll notice that this area being wider needs a little bit more attention than the narrow end. The narrow end goes much quicker. And you can see my chalk is almost gone. It's getting really close to the middle here. I'm almost ready to go here. So after spending some quality time here, I've got the fretboard completely radiused up to a 14-inch radius.
Sanding the 12-inch radius
I'm now going to jump over to 12-inch and work just this area right here. Let's chalk it up again in this area. And it shouldn't take very much. Just get yourself a little tighter radius right there. If you want to take the 12-inch all the way out into the board, you can. It's just giving you a head start because in a minute I'm going to come in and do a 10-inch radius there.
Sanding the 10-inch radius
The important thing right now though is to blend your 12-inch into your 14-inch. And it looks like I've done that. I now can chalk up the end of the board, use my 10-inch radius side [Robert points to the 10-inch radius side of his sanding block] and finish it up right here on the end. [Robert works the sanding block up and down the end of the fingerboard] There we go.
So just to check my progress, I'm going to take my LMI radius gauge, check it out here in the end. There's no daylight under there. I've got a perfectly radiused, 10-inch radius on that end of the fretboard. Then bumps up into 12, and then finally back here at 14.
Leveling the fretboard
Now, there is a problem using these shorter blocks like this. I don't know if I'm level, I like to keep the fretboard level. That's where this guy comes in. Notice that he is the length of the fretboard. I can do the whole fretboard at once. I want to blend the 10-inch radius into the 12-inch and the 12-inch into the 14-inch. If I just come in and go across the board, that's what I would normally do for a normal radius, not a compound radius.
This one has to be a conical shape. So as I'm doing this, I'm doing it like this [Robert works the fingerboard leveler up and down while working it left and right], in the shape of a cone. And once again, I'm going to chalk it up. Make sure you use pink chalk, guys. That's the secret. Start with my 80 grit sticky back paper from LMI and work like this. Notice I'm just running across the board like this. Maintaining that shape, the conical shape that you put in there, back and forth like this, almost like you're skiing or surfing. Now notice I had to concentrate a little bit more here. I'm already good at the ends, but I must have concentrated more in the middle. So that's a little low spot. So let's take care of that.
As you're doing this, be very careful you don't roll over the edge of the fretboard. You want the edge of the fretboard to be nice and crisp now. When you come in and install your frets later, then we'll do some sanding and stuff, we'll knock that crispness off. But right now it needs to stay crisp.
Okay, all my chalks gone away. I should be level. However, this is only with 80 grit. I want to rinse and repeat the process all the way up to about 320. That's what I like from my fretboards, maybe even 400, perhaps even 600 depending on what day of the week it is. So now I'm just going to peel off my sticky back paper, bump the grit up to 120 and rinse and repeat. All right, here's my 120. Concentrate down here.
Go into your 12-inch radius [Robert switches sanding blocks] and then finally into your 10-inch radius [Robert switches sanding blocks]. Now, I've already put the radius in there. All I'm doing now is getting the sanding marks out. I also want to do that again with 120 with the leveling bar. So once I get it up to about 220, I then come in with just a regular sanding block and just hit it with that and take it as high as you want go. If you're that kind of guy that likes to take it all the way up to 2,000 and have it shiny, that's fine. Like I said, mine goes to 320, 400, 600 depending on what day of the week it is.
Now, I know what you guys are thinking. You're thinking, "Hey, isn't he going to screw up the radius or take it out of level just by using a small hardback sanding block and 320 grit paper?" Well, as Kent Everett likes to say, "You'd have to be a real idiot to screw it up at this point. 320 grit paper is not very coarse. So just run it along the fretboard like that. Blend everything together and life's good. If you want to check it with your radius gauge again, 10, 12 and 14, then you should be ready to go, and that's how you do a compound radius.
So Felder in Saskatchewan, Canada. Thank you very much for your question. I think now you know how to do a compound radius. If you want to take it further, go a little bit more in detail on how to do the compound radius and other aspects of electric guitar building, check out Mike Snider's online Electric Guitar building course on my website. I think you'll find it very useful and 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.]
