Considering applying a compound radius to my One And Only

I have made one F5, which I am currently learning to play on. It has a flat fingerboard.

I am currently making three F5s, which I plan to give away to musician friends and ask for their feedback. One of my friends is a professional guitarist, and he told me he prefers a compound radius on his fingerboards. In doing my research, I became intrigued by the concept, and I began to think I'd like a compound radius on my own fingerboard. It would also give me good practice in preparing the mandolin I'm building for my friend.

Is this commonly done--applying a compound radius to an existing, flat fingerboard already on an instrument? I assume the frets would have to be removed and new frets then applied... It may be more common, I imagine, to start with a new fingerboard, apply the compound radius then replace the old one...but I'm afraid I didn't use hide glue on the original build. So removing the old fingerboard my be difficult.

Thanks for any advice you can provide.

-Mark

I had a radius and a refret done to my Gibson Fern. Not uncommon and not necessary to remove the fingerboard.

It can be done while the fingerboard is on the instrument.
It's a good idea to protect the peghead and body with some thick cardboard.

You will have to pull the frets, then get to work with the tools of your choice. I've used flat sanding blocks with coarse paper, radiused blocks, and files. I do not recommend conventional planes- it is too easy to chip the fret slots. The next one I do, I might try roughing out with a surform plane [a Stanley product].

Keep checking your work as you go along. It's easier to make minor corrections along the way than it is to wait until the end and have to make major corrections. Be careful not to create any unintentional drop-off at the nut end or the bridge end of the board.

You need a very good straightedge. If you're building, you should have one anyway. After you have roughed it out, you will have to find and dispose of any unintentional bumps. 2", 3", and 6" straightedges can be useful for locating bumps. Small sanding blocks can be useful for levelling them.

Important: the process will take most of the depth out of the fret slots at the edges of the fingerboard. If the board is un-bound, the depth can be restored with a slotting saw. If the board is bound, a Dremel with a router base and a jeweler's burr will work. It's better to not let the slots get too shallow before you re-cut them. You might have to interrupt the radiusing operation once or twice and deepen the slots a couple of times. Be careful not to wallow them out.

When you re-fret, make sure your board is true. It is best to wait a day before you re-fret-- you might find spots that you missed that will need to be trued up. Remember to bevel the edge of the fingerboard before you re-fret.

Be prepared for a lot of work and tired muscles.

Personally, I've never felt that radiused boards were of any great advantage to me on a mandolin. But each player has their own needs for comfort. I do think that radiused boards are essential on steel string guitars. I have occasionally played instruments that I thought had too much radius to be comfortable.

I am not building an instrument, but that was interesting.
Thank you for the detailed instructions.

I have a Stanley Surform. I got it out to take a closer look.
It seems like a rather coarse tool for working on a mandolin.
Would you care to describe that part in more detail?


Thanks,
sounds_good

Are there standard radii used along the neck for the compound profile? I wouldn't expect much variation as short as the mandolin neck is. Do many just use a constant radius? It would seem to simplify the process a little.

Putting a radius on a fretboard involves pulling the frets, sanding the radius and re-installing the frets with a level, crown, etc. A compound radius is the same except it is more complicated to form a compound radius. Many guitarists like compound radius because they allow a radius that is comfortable for fingering chords in the first few positions while transitioning to a radius that makes string bends easier in the upper frets. String bending is not nearly as common on the mandolin. Unless your style of playing includes using bends on upper frets, I don't see any advantage to having a compound radius on a mandolin.

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Originally Posted by Nevin

Putting a radius on a fretboard involves pulling the frets, sanding the radius and re-installing the frets with a level, crown, etc. A compound radius is the same except it is more complicated to form a compound radius. Many guitarists like compound radius because they allow a radius that is comfortable for fingering chords in the first few positions while transitioning to a radius that makes string bends easier in the upper frets. String bending is not nearly as common on the mandolin. Unless your style of playing includes using bends on upper frets, I don't see any advantage to having a compound radius on a mandolin.

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Thanks, Nevin. I had not thought about that. I am going to ask my friend his opinion and preference. While he has owned and played a couple of mandolins before he is primarily a guitarist, and that's where his expressed preference for a compound radius came from. Maybe after explaining to him this way he will prefer a plain radius. Thank you.

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A follow-up question: With a radiused fretboard, are the nut and also the bridge also radiused? That would seem to make sense to me, but I wasn't sure. Or perhaps this is different between plain and compound radiuses?

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Originally Posted by putnamm

A follow-up question: With a radiused fretboard, are the nut and also the bridge also radiused? That would seem to make sense to me, but I wasn't sure. Or perhaps this is different between plain and compound radiuses?

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Yes. Nut slots and bridge should be radiused.

Quote:

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Originally Posted by sounds_good

I have a Stanley Surform. I got it out to take a closer look.
It seems like a rather coarse tool for working on a mandolin.
Would you care to describe that part in more detail?


Thanks,
sounds_good

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Yes, it is a coarse tool. To radius a flat fretboard requires the removal of quite a bit of wood, especially at the outer edges of the board. A surform might come in useful, but only for the initial "roughing out" of the process. I would have to work in the same direction as the grain. It might not work; it might chip the fret slots. It would have to be followed up with tools with a finer cut.

I have yet to try it. In the past, I have started with coarse sandpaper on a block. Even with coarse sandpaper, it takes a lot of time and elbow grease. I'm considering the use of a surform to save time and muscle. I'm going to try it on an upcoming job on an instrument that is not valuable. If I see any signs of chipping at the fret slots, I will cease and desist and switch to the slower tools.

@sounds_good. I’ve used these things for wood and bondo (where they’re called ‘cheese graters’) and yes, very aggressive. I’d expect tear out at each fret slot. Plus, a 12” radius on a narrow thing like a fretboard involves very little material, which is why hand sanding with a concave block should work, unless you’re in production!
For major wood removal with less chance of ripped pieces, abrasives are safer. For power tools, an air disk sander is a good roughing tool, but not for this. I have a (now obsolete) 2 1/2 X 16 belt sander that’s light and controllable. The nose end can be used for some concave areas. I also use a large variety of sleeve drums on 1/4” shafts, And of course, I really like hand planes and drawknives, but they also are inappropriate here.
The half-round Surform, though, is just the thing for hogging out your concave sanding block in a hurry.

Radiusing a fingerboard is quite simple thing. But it's not just sanding along with radiused blocks of your choice. If you start with one circular arc and end with another and connect them along strings with straight lines you won't get circular arc in the center of the board uness the taper of the fingerboard matches perfectly the ratio of the two radiuses.
For this reason the ultimete method is just use straight flat sanding block along string direction and wobble it to sides to create erched crossection. I would mark edges of he board with pencil 1/32" or so (depending on your target radius) below top level of flat board and remove wood till I'm close to the line (while watching/checking the radius at nut). This will result in nice even sides of fretboard and "compound radius" (the curve at the end of board will not be circluar arc but will be "less curved" than at nut).
From my personal use I liked most slight radius at nut vanishing towards bridge - the bridge can be flat (or almost) if you do the math and work methodically. That worked best for me both for left and right hand.
You can also check frets.com. There is lots of info on fingerboard work and Frank Ford is mostly using flat sanding board as well.

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Originally Posted by Walt

Yes. Nut slots and bridge should be radiused.

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My current bridge is not radiused. Being that I'm inexperienced, is the best thing to drop the money on one, like those from CA or other makers? Or is there some way to radius the saddle of the bridge myself? If so, I'd like the chance to learn. It's not a fancy bridge. I think I just ordered it from StewMac or LMI.

Radiusing a bridge saddle is about 20 minutes work. You have to adjust the string compensation; the lengths will be altered slightly by the radiusing process.

If you want to learn, don't be afraid to mess up. It's part of the learning process. If you ruin a saddle, you can buy another. www.axinc.net will sell the CA saddle alone without the base. Or, if you really want to learn, you can make a saddle yourself. If you do, use very sharp drill bits and drill your holes before you thin the saddle blank. If you use dull bits or drill after you thin the saddle, you'll find out why.

Radiusing a fingerboard is slow work, is much more difficult, and requires a high degree of precision. In the past, I've always done most of it with flat sanding blocks. A couple of radiused blocks with different radii cocked over towards the edges can be useful for the first couple minutes of rough cutting. Then, it's flat block, straightedge, correct any errors, flat block, straightedge, correct errors, over and over until you've got it done.

The process is slow and painstaking enough that I'm willing to take a risk and try a stroke or two with the surform on the next one to see whether or not it will work without tear-out. The instrument is not valuable and I've only got 200 bucks in it. If I'm wrong and have to replace the fingerboard, I don't mind.

I'll try only a few strokes on the edges right at the beginning of the process. I'll take a gamble that if it does tear, there should be enough wood left that the standard sanding process will correct the tears. But it is a risk, I could be wrong, and I might change my mind. I don't recommend anyone else try it unless they consider the work to be expendable.

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Originally Posted by rcc56

Radiusing a bridge saddle is about 20 minutes work. You have to adjust the string compensation; the lengths will be altered slightly by the radiusing process.

If you want to learn, don't be afraid to mess up. It's part of the learning process. If you ruin a saddle, you can buy another.

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Thanks, rcc56. I'm not afraid to try, learn or mess up. My only issue is figuring out how it's done... Do you actually sand or cut a radius in to the saddle itself? Or is it just about changing the string slots? I've looked for video tutorials online but can't find any. Thanks again for the suggestions and guidance.

I sand a radius into the top of the saddle. You can do this by eye, or with a radiused sanding block.

Usually, I rough it out by knocking a little off starting at the ends and tapering to just beyond the 1st and 4th strings, and file the string slots until the action is close to correct all the way across. Then I take any excess material off the top and create a nice arc, do a final slotting, adjust the compensation, and make it pretty. It's pretty much all hand work. It's too easy to take too much wood off with a belt sander. If you're really good with a disc sander you can give it a try, but it's easy to slip and mess up the work or one of your fingers.

I do both saddle and nut the same way... First adjust string slots to correct depth and then remove wood so I'm left with just abot correct depth of slots. I adjust nut slots according to clearance over first fret when string held at second and I adjust saddle slots measuring string height over 12th fret so all strings have correct action (of course after adjusting bridge so I won't have to cut deep into saddle, just bare minimum).
I would not use surepform rasps or anything such on fingerboard, chipout is guaranteed. Starting 60-80 grit on straight block will give you the radius in less than 5 minutes (including checking with templates), then few finer grits to smooth out. finish with 360-400 or so.

Thanks very much as always. This is all very helpful.

I'm with Nevin, a compound radius is unnecessary. All five of my mandos have a straight 12" radius, I find it to be a comfortable compromise and several of my guitars have that radius too. I did spring for an aluminum radiused sanding beam. Just roll some stickyback sandpaper on it and go to town. Because the beam is longer than the fretboard, it's very easy to get a perfectly true fretboard. For roughing out, I usually get it close on a benchtop beltsander and true and finish with the sanding beam. A healthier approach would be to use a freshly sharpened handplane. Ebony actually planes beautifully if the iron is fresh (warning: you're going to lose the two pearl dots at the octave fret either way, be prepared to replace them). You can also use the sanding beam to radius the top of the bridge and nut.