Radiusing Braces - Luthier Tips du Jour Mailbag
In this episode, Robbie O’Brien demonstrates how to radius a guitar brace using a brace sander.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: How do you radius your braces before attaching them to the top or back?
Robert O'Brien: Today's Tips de Jour Mailbag question comes to us from Minnesota. "Robert, how do you radius your braces to an exact radius before attaching them to the top or back? Philip in Minnesota."
Philip, very good question. One way, is the way I show in my online guitar building courses, and that's to take the brace, put it in your radius dish, and sand it until you get the complete radius. There are other ways to do this. One way, is to use a commercially made jig, this is the brace sander jig available from LMI. It's designed to accurately and precisely sand braces to an exact radius. Let me show you how I use it here in my shop.
Using the LMI brace sander jig to radius a brace
I'm going to start by taking a roll of 80 grit sandpaper, and I got this from LMI and it's got adhesive on the back. I'm just going to place that onto the jig here and just make sure that that sticks in place [Robert applies the adhesive sandpaper to the back side of the jig]. I then place that onto a piece of plywood so I don't damage my bench, and then trim it flush, with the edge of the jig [Robert cuts off the excess sandpaper that is sticking out passed the jig]. And of course, you want to do that on both sides of the jig because it comes with two different radii.
So now that I have the sandpaper installed on the jig, let me show you how to use it to radius a brace. I'm going to take the jig, and you'll notice that the same radius that's here is also on this part of the jig, and that's called an HDPE base, and that's just some fancy lingo that means hard plastic. So I'm going to place that over the top of my brace and then just take a pencil and trace that radius on there. And what I'm going to use, is the 15 foot radius on this jig, for demonstration purposes. I'm now going to take this either to my bandsaw and trim it close to the line, or my hand plane, and use that to trim it close to the line.
[Robert uses the hand planner to trim the wood down]
Next, I'm going to take my brace sander and just put it in my bench vise and clamp it. Now, the radius I'm going to put on the brace is facing up, and I have my sandpaper installed. Next, I'm going to take my brace that I've pre-trimmed or pre-planed closer to that line that I drew. Place it on the jig and press it against the HDPE base. Remember, that's just once again a fancy word for hard plastic, and then move it back and forth. Check your progress by placing it on top of the base there, and you can see if there's any daylight you need to keep going.
Just a few passes and you have a perfectly radiused brace, and it's now ready to be installed on your top or back. Now, one of the advantages of using this, over just doing it in a radius dish, is when you're doing it in a radius dish, if you're not careful, you can roll those edges over. And instead of having a crisp edge, you can have a little rounded edge and that looks bad, and can even cause structural integrity issues when you glue it to your soundboard or to your back. With the LMI brace sander, it allows you to hold that up against the side of the base there, and it's perpendicular every time. The LMI brace sander is so easy to use that the brace will almost radius itself.
So Philip in Minnesota, thank you very much for your question. I think you'll find if you use the brace sander from LMI, you'll be able to put a perfect radius on the brace every time.
[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.]
