Sharpening Convex Plane Blades - Luthier Tips du Jour Mailbag
In this episode, luthier Robbie O’Brien visits with Brazilian luthier João Cassias. João demonstrates how he sharpens convex plane blades.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: How do you sharpen a small convex plane blade?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Minnesota. "Robert, I am using a small convex plane and need to sharpen it. Can you explain how this is done? Keith in Minnesota."
Keith, probably you're using the Ibex mini plane or palm plane. This is a very useful tool, especially when carving plates like in mandolins or archtop guitars. Recently, I was in Brazil visiting with Brazilian luthier, João Cassias, who happens to make archtop guitars, very beautiful archtop guitars and he uses this plane quite a bit. While I was there, I had my camera with me and he showed me a very simple technique for sharpening these plane blades. So let's drop in to João's shop and he'll show us how it's done.
Hi, I'm here in São Paulo, Brazil with João Cassias of Cassias Guitars. And João has a very interesting way of sharpening convex plane blades. And John is willing to show us how to do it. I called you John.
How to sharpen convex plane blades
João Cassias: Yeah, sure.
Robert: It's actually João, John in Portuguese. So João is going to show us how to sharpen convex plane blades.
João: The first problem I faced that doing archtop guitars and carved top guitars, is right after you receive the finger plane or whatever plane you decide to use, you have it sharp. So right after a couple hours of use, the plane is dull, so you have to resharpen it. The problem is, this is not a straight edge, it's a curved edge, it's a convex edge. And now I have developed a simple technique to aid me on the process of making this edge true and very sharp, to the point where you can shave yourself.
Well, this is the simple setup I just gathered to solve my problem with sharpening the knives. It's just a simple jig from Veritas, the honing guide, the cheapest one, a Sharpie pen, felt pen marker, the plane blade and the body and the blade holders. The first step is to score the plane knife with the felt marker, so it will aid me throughout the process. This way I'll know if I am making it right or wrong, as far as matching the angle of the sole of the plane. The next step is just to find an adjustment that will suit the amount of material that will be taken off.
Just before we start, I am using a Veritas guide, but you can use anything really. It's just a simple jig with the roller bearing and a homemade, hand made honing guide will do just as well. Right now, I just made a few tryouts here. And after a couple passes, the felt mark was gone, so now I know my angle is right. I'm going to continue. I'm going to just start with the 800 Grit Japanese Waterstone. And right after, I'm going to go for the 4,000. Right after, the 8,000 to finish up and polish it. The trick is not to stay in the same place for a long time. So right after a few shots here, I move it around. I curve it around three times, curve it a little bit more three times. And what you are going to have, is a surface that's not perfectly convex, but it will sure do a perfect job maintaining the angle that you need for a sharp edge.
Just to have a better idea of what I'm talking about. The movement that I do, is just pushing a little bit left or right, according to the angle you can achieve with my thumbs here. So this way, you get a very nice convex edge instead of a flat one. Three times, skew it a little bit with my thumbs, you get the idea. So at this stage I made all the process with the 800, the 4,000, which is the underweight in the underside here. And now I'm going to finish it up with the 8,000 Grit Norton Combination Waterstone. Well, after a little bit of work, that's all it is. Let's put it back to together and see if it works. It's approved.
[João makes a few passes with the convex plane on a demo guitar body]
How to sharpen scrapers
Robert: All right, so there you have a very easy way to sharpen a convex blade. Now, while we're on the subject of sharpening, João also has a very interesting technique that he does for his scrapers. João, can you tell us a little bit about that?
João: Yeah, of course. Well, it's very simple. Most scrapers come in a rectangular format and mine isn't. The reason behind that, is that my first time, my first guitars came out really scratched, because of the sharp corners. Now, I just round them over so I prevent digging in the sides while I'm working with it. The process is quite simple. I just take it to the grinder or sander or files, if you have the time to do it, and cut the corners off, round them over really smooth to prevent that. Simple.
[João works the hand scraper across the demo guitar body]
See? As it's rounded on the sides with this way of sharpening and making it curvy, I don't dig in the sides and scratch the wood when I'm working.
Robert: So there you have it folks. Ways to sharpen a scraper and ways to sharpen the convex plane blade. João, thank you very much-
João: You're welcome.
Robert: For allowing me to visit you here in your shop in São Paulo Brazil.
João: My pleasure.
Robert: And I look forward to working with you here next week. We're going to do our guitar building course.
João: Yeah, sure. It's going to be fun.
Robert: All right.
So Keith in Minnesota, I hope you found this information useful. And remember, always work sharp 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.]
