Radiused fret board

[bullrun6]

After playing a Collings that has a radiused fret board I decided that I want to try one on my current project. I have a 9 1/2" radius sanding block, do I just sand the FB until it's rounded? How about the fret slots? Do I cut them before or after the sanding is done and how do I get a uniform depth? I assume that I also use the sanding block to get the same radius for the nut and bridge...am I on the right track here, none of the 3 books I have mention this. Any guidance from you more experienced guys would be greatly appreciated. Thanks,


Patrick

[sunburst]

I'm not fond of the radius sanding blocks, and here's why.
Unless you have a way to maintain absolutely straight strokes with the block without the block turning at all, the edges of the radius will "fall off". In other words, even if the center part has the right radius, the edges of the board will be sanded to more of a curve.
Also, as you change sandpaper grits from coarser to finer, the paper and the coating of abrasive on the paper get thicker. Because of this, the radius you are sanding is a little flatter with each successive grit, so that more sanding is required than would be necessary if the radius of the sanding block could be maintained the same.

I use a sharp block plane to establish my radius, then regular flat sanding blocks, checking frequently with a radius gauge.

The fret slots can be cut before or after the radius, I cut mine first, deep enough that they have enough depth at the edges. If they aren't deep enough at the edges, a few strokes with a small back saw will take care of them.

For the nut and bridge, I cut string notches 'til the action is correct, then file and sand the top of the nut and bridge 'til half a string is in the notch.

[bobz]

Hello Patrick
I would`nt say this is the right way to do it but this is how I done mine. Fist the board was fret slotted in the stewmac fret slotting tool. Then I used the radius jig I purchased with my adjustable radius sander to scribe the radius on each end of the board. Then I planed off the bulk of the wood with a jack plane using the scribed ends as a guide. A yellow pencil line was then drawn down the centre of the board and the radius sanded until the yellow pencil line disapeared. You can see the radius sander in photo bottom left. Then I used a fret saw with an adjustable depth stop to bring the slots parallel to the radius. Hope this has been of help to you.

[Bandersnatch Reverb]

9-1/2 radius is sort of severe on a mandolin isn't it?

I mean... its all a matter of taste but I thought the radiused boards were more like 12 to 16 inch radius.

If this was a guitar, you could slot the board first, but be aware that you're better off with only the amount of slot you actually need. If its slotted deep enough to still be ok after radiused, the center is much deeper than it need be. An adjustable depth saw will keep the fret slot depth uniform across the width of the board.

If the board is a new one, not already on the instrument, you could easily make a fixture to keep your sanding block straight and unwavering.

[sunburst]

9-1/2 radius is sort of severe on a mandolin isn't it?
I don't think so. I use a 7 1/4" radius, and sometimes people play the mandolins and don't even notice the radius.
Keep in mind that as the board gets narrower the radius needs to be tighter in order for the edges of the board to be the same amount lower than the center.
A lot of Fender guitars have a 7 1/4" radius.

[John Flynn]

I am not a luthier, but I have looked into building and will probably do so at some point and when I do I will want to do the raduis thing also. One thing I discovered is that Stewmac sells ebony 12" radiused fingerboards, already slotted, for $25. I guess it depends on how far into DIY you are, but that is a lot of precision work already done for $25.

[sunburst]

Stewmac sells ebony 12" radiused fingerboards, already slotted, for $25. I guess it depends on how far into DIY you are, but that is a lot of precision work already done for $25.
Right you are! Especially if you're just making a few instruments.

I started making my own fingerboards so that I could choose the wood, the number of frets, the radius, and be assured of accurate fret placement. It was more frustration with what I could or couldn't buy than a DIY desire that got me making my own. It's actually pretty expensive in terms of tools bought and in terms of time in tools made, but now I've got the fingerboards I want.

[Jim Hilburn]

The Stew-Mac boards are temping, but if you want less than 29 frets, your out of luck. They won't do custom work. Maybe some of you guys could go into the specialty components biz like Steve Smith.
Here's a couple of shots of what I do. I start by knocking off the edges on the drum sander. That ruler gives just about the right amount of rise, and I can use the inch marks to make sure I get the same results on each side. This pic is a set-up, and since I don't have any blanks cut up, that's a scrap piece for the demo.

[Jim Hilburn]

Next, I double sticky the board to this jig to get a 12" radius. The table on the sander flexes too much, so I have to apply hand pressure to the back of the swinging board to get an even cut.

[Jim Hilburn]

Then it's on to luthiers elbow as I hand sand in a compound radius.
However, during all this posting, I got to thinking a compound may be as easy as proping up one end of my jig and sanding from the center to the edge, then reversing it for the other side. Time to go experiment.

[sunburst]

a compound may be as easy as proping up one end of my jig and sanding from the center to the edge, then reversing it for the other side.
Seems to me all you need is two different length arms on the swinging part of the jig.
For example if you want your radius to go from 10 to 16, one arm should be 10" long and the other 16". I'd have to try it to be sure you could get the sander at the right tilt, and the board would sort of "arc" past the sander, but it might work.

At the risk of further complicating the jig, I might suggest some triangles. If you were to brace the upright part to the level part with some diagonal braces, the jig would be stiffer and might not require as much hand preasure for stability.

[Jim Hilburn]

I know what your saying about triangle supports, but that table on the sander will actually flex so I don't gain anything.
LMI sold a compound radius jig for a while that was quite expensive, but I never figured out exacty how it worked, but I thought it was swinging across the sander at an angle.

[amowry]

Yes, I know some folks who use a similar jig with arms of different lengths for compound radii.

[Mario Proulx]

Yes, I do compound radius fretboards(for guitars, but the concept is the same for mandolins) using a similar jig. The two arms are different lengths, causing the swing at each end to be different, thus cutting the compound radius.

Build the jig(or modify yours), then shim it on the table until the fretboard blank sits flat to the sanding belt, and secure it there. Procede as you did previously, and enjoy!

I now use a similar jig, but run a router to cut the radius instead of the sander; comes out a little more accurate, but not by much. Mostly, it doesn't tie up the sander as much(which is the second most used tool in the shop).

BTW, all you need to do if you don't want 29 frets from the SM board is to cut off the ones you don't want. What am I missing, here?

[sunburst]

all you need to do if you don't want 29 frets from the SM board is to cut off the ones you don't want. What am I missing, here?
Speaking for myself only, my design goes a little past the next fret slot and I don't want to see an empty or a filled slot.

I used to send boards to a couple of different places for slotting, but because I didn't want 29 slots, I had to pay for a custom set-up. If they can't use their gang saw, it's a custom set-up, and a chance for errors. If I compared the boards I was getting back, the frets were never in the same places.
You know what they say, if you want it done right.......

[Jim Hilburn]

Mario, I had one of your guitars pass through my house once, and it was one of the best I've ever heard.
I vividly have the picture in my head now of what has to happen to do compounds on the sander. I think I'll give it a try.
Some folks like this look even though it makes no sense except for the look.

[Bill Snyder]

Mr. Hilburn,
The photos of your mandolins make them appear to be as beautiful as any I have seen. I would imagine anyone that takes the time to make them look so fine would also build an instrument with wonderful tone.

[Jim Hilburn]

Anyone in the Denver area can hear that one on stage at the Arvada Center tonight.
Here's the quickly modified jig, and on a test piece, I got a 7.25 to 12" radius. It needs a little more precision work done to it and adjustability would be a nice touch.
But not tonight. I'm going to get a beer.

[Mario Proulx]

That's the ticket, Jim.

Here's a trick: For testing and fine tuning of the jig, as you're going to need to do, I like to use 1/4" multi-ply birch. Cut and taper a few pieces to the same shape as your fretboards will be. You can tell if your radius is even across the width and along the length by looking at the ply layers as they sand through. Way easier than measuring all the time.

Sunburst, that looks like it could be done by cutting out at the next slot. It may be a tad shorter, but not a whole lot. I do know what you mean about cutting your own, though; same reason I do.

[sunburst]

Jim, no sense in wasting time huh? I'm not usually done with the mental part of jig making or modification for at least a couple of days.

Mario, yeah, I thought the same thing as soon as I saw the picture post, it looks shorter than it is. I tried to shorten the board enough to keep from having that next slot be a problem, but I just couldn't get it to look right in context with the rest of the instrument.
Good idea about the plywood, by the way.

[bullrun6]

Thanks everyone for the replys, unfortunately this discussion quickly got over my head! I don't have the most of the tooling mentioned so I quess I'll just have to muddle on by hand. How does this sound? If I sand the fret board blank before I cut it to shape won't that eliminate or reduce the "falling off" at the edges that sunburst mentioned? I'm tempted to buy the pre-made FB from StewMac but I really do like the idea of doing it all myself. I quess I'll try it on my own and if that doesn't work out I'll spend the extra $25. Thanks for the help. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif

Patrick

[sunburst]

Yes, that helps. I radius mine while still rectangular anyway because it's easier to keep my center line so that the radius centers on the board.

[JiminRussia]

I visited the Collings factory a few days ago and there I saw one of their ingenious shop built jigs. Although they have several that greatly simplify their work, this one in particular really caught my eye. It was a very simple jig for radiusing fretboards.
Before I get started with a description, please remember that I don't know if this has been patented. In fact the tour guide "thought that it was" but didn't know for sure. Remember that inventions can be patented, but concepts cannot. It's up to the courts to decide the fine line between patent violation and concept integration, so be careful in how you follow through with this.
The whole thing stars out with a "T" shaped piece of metal a little bit longer than a standard fretboard. Actually it's two flatbars that are joined together on edge to form a long "T" shaped piece that is like one half of an "I" beam. On the ends of this are two semi-circular pieces of aluminum, about 3/8" thick with a slot cut into them in the middle that is perpendicular to the flat edge of the semi-circle. The semi circle of one end is at (I think this is what he said) a 9 1/2" raius and the semicile on the oher end is at (again, I think)a 22" radius.
Now in practice the fretboard is placed on the top of the fixture and the screws (remember that slot in the simi-cirle?) are adjusted so that the top of the fret board is tangent to the center of the arc at both ends. In other words you slide the "T" shaped piece up and down so that the exact center of fretboard ends are just at the top of the center of the half round aluminum things on the end and then tighten the screws. What holds the fret board in place? Well, I don't remember, but it was prabably vaccuum. Thy use a lot of that around there, but a couple of drops of glue would probably work. Maybe hot glue? you could latter heat the metal and break the glue joint pretty easily. Ater all, they are on the bottom of the fretboard so who would know anyway.
So now what to you do with this modern marvel? Simply place this device on top of your bench-top oe stand alone horizontal belt sander with the round side of the jig down and the center line of the fretboard along the centerline of the belt and then rock it back and forth (the jig, not the belt sander). As long as the jig is longer thatn the belt in the sander, the aluminum will never be touched and only the fretboard will be ut away by the sanding belt. The end rersult is that you end up with a fretboard that is perfectly raidused from 9 1/2" on one end and 22" on he other (more or less depending on how much longer the jig is than the belt) and it takes about ten minutes total from start to finish.
It's simple, fool proof, adjustable, and cheap to make. You could make up several diferent semi-circular pieces for just about any radius that a person could want. A litle bit of experimentation can get all of your dimensions right, but I'll bet that it will save you a bunch of time on a new build. With a little ingenuity you could modify the conept to allow you to radus a fretboard on an already built instrument too.

[Jim Hilburn]

I've put the radius jig on the back burner for now, but the whole thing is clear as mud to me.
I just got the Grizzly Luthiers catalog, and they're offering a radiusing jig for only $450, but it only fits their sander. But that's not important, how it works is. With this one and the one LMI offered, it appears to me the length of the horizontal arms determines the compound. The sanding table doesn't appear to tilt to accept different lengths of the vertical hangers. So it appears that the angle the board sweeps across the sander is what determines the compound. That's what I had in mind when I said I just needed to raise one end of the platform on my jig.
Who understands the principles of this? I would like to have a little better idea of what I'm doing before moving forward.

[Jim Hilburn]

Here's the other shot from the catalog.
I'll be away the rest of the weekend so I'll be looking forward to your responses.
I should also get a kick-back from Griz.

[Mario Proulx]

Jim, in the first photo of the Grizzly jig, you see the pivot point for each arm, about 2/3 of the way down. What you would do is adjust each arm to the pivot you want(say, 8" and 16"). Now, that will leave you with unequal length arms, so at the top of the jig, you can see that the arm's lengths are also adjustable. Ajust each of the arms until the fretboard is parallel to the sanding belt.

Tah-dah!

BTW, with such a jig, if you want a 10"-20" compound, you'll also have to account for the length of the jig, thus you'll need to add a bit more at each end. That's where my little plywood tip comes in: nothing beats good 'ol trial and error(or as my Dad would have said, trial by error).

[JiminRussia]

Sorry, but I guess that I didn't describe that jig very well. It really is a pretty simple operation that will work on any sander. I wish now that I had a couple of photos of it. Try to envision a very tiny baby crib, the kind that rocks from side to side. Now, if the rocker at the head is smaller than the rocker at the foot and the fretboard is clamped between the rockers so that just the edges of the fretboard are sticking out because of the arc in the rockers, you could set this on top of the sander and just rock it back and forth to get the compound radius. Changing rockers would change the readius and the distance between the rockers could be made adjustable to acommodate different fretboard lengths. I'd bet that you could make one up in just a couple of hours for just a few dollars in materials.

[Luthier Vandross]

Yeah Jim, that's how we radius, built a jig just like that, but not infinitely adjustable, just to the ones we use.

-click-

M

[Jim Hilburn]

I'm with you so far, Mario, but why is it held at an angle over the sander?

[Mario Proulx]

Jim, the photo was likely just staged, rather quickly.

[Mario Proulx]

On looking at it again, I see what you mean. No, that's not a fluke; The reason for the angle to the table is to use the entire belt's 6" width to do the sanding, thus extending wear. This isn't absolutely necessary, but it's nice. It's the arc of the arms that will invoke the proper radius, and this doesn't affect that part of it.

I thought you meant that it looked like it wasn't parallel to the belt.