Official Luthiers Forum!

why don't you radius the nut end of the fretboard,
and radius the other end of the fretboard,
and straighten it out from those two points?
then adjust the strings so they work.
ain't rocket scientry.

Believe it or not, when I've done a compound radius I've just drawn the radius on each end of the fingerboard, divided the arc into segments, connected the intersection of each radius end to end, then faceted the surface of the fingerboard accordingly, then refined the surface.

Often as not, my tool of choice was an angle grinder, but if your plane is set up well enough it would work better. I've worked with an angle grinder for fine shaping for countless hours, its not the first tool that I would recommend for others.

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Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

You need to read his post again Filippo. That dang sawdust affects all our brains.
I've never done a compound radius Fretboard but I know some Fiddle makers use a small block plane and check the curve by simply using a template and a straightedge. For a compound radiused Fretboard you may need 3 or 4 such templates. The other method is to buy the various shaped sanding blocks that Stewmac sells: http://www.stewmac.com/shopby/item/0410

Rick's jig is great for a single radius and I am very happy with mine but despite what is claimed I have found it is not able to cut a 'compound' radius. To do this the platen would need to twist in order to allow each bearing carriage to follow it's radius insert and that just can't happen. That said the jig 'can' be used to cut a number of blanks to very accurate single radii which can then be used to sand a profile into a set of templates to check your progress as you make a board by hand. Use the jig again to cut a slotted board to the least acute radii of the compound, then work toward the nut end with a plane, the templates and abrasives.

Using my version of Mario Proulx's jig - here

Dave F.

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Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

That's how I do it, basically. I'm not sure what you mean by "adjust the strings so they work.", though? The way I do it, there is no special adjustment of the strings involved.

I use my SM fretting cauls, typically the 12' one as a radius template for the nut end, and the 20' one for the other end, and plane the board to connect the two radii (sp?). Next, I sand with a rigid, flat block (#5 plane body a la Frank Ford) to even things out, and the board is ready for fretting. I check frequently with a straightedge while planing, to make sure the fingerboard surface is straight under each string, imagining a normal string tapering.




Why would you need 3 or 4 radius templates? The way I see it, more radius cauls (or concave sanding blocks) will only serve to mess up this process.

As the others have menitoned, there are several mechanized methods, involving routers and sanders and more or less elaborate jigs, to produce these, but I find it is quite easy to make them sufficiently precise with hand tools, so I don't bother. I suspect that if you count set up time etc with some of these jigs, my methods is not much slower.

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Rian Gitar og Mandolin

I think if you had several differing radius sanding blocks each with the increased radius you desire, radius the entire lenghth of the board to the shallowest radius then you could start at one end and work your way down switching radius blocks along the way . jody

I just radius both ends of the board with a radius block, then connect the dots with a straight block useing pencil marks between to check the progress until done.Not really that hard to do by hand. I'm sure that there are machines to do the same thing though.

One of these days when I make more money on my guitars that I spend in tools I will get one of these.

http://www.grizzly.com/products/Radiusing-Sander/G0574

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John Thiessen
http://www.iszacguitars.com

hey filippo, what i meant was to radius at the nut end, for example a 12" radius,
then at the other end radius, say 15", then just connect the two working with a straightedge a plane, or sanding blocks,
or, we could have chris p. make a jig!

Filippo, I built a jig similar to what Dave has shown. Works great and almost needs no sanding after routing.

Chuck

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I was planning to build something similar to the Grizzly rig, shown above. After doing some trial runs, I decided against it. The swing arms would have to be very rigid to resist the tendency to follow the belt & take material off evenly. My rough trial fingerboards were not straight along the sanded surface.
Also... Unless the belt is very tight, it tends to form a slight "wave" at the leading edge of the fingerboard, resulting in excessive thinning for the first inch or so.
I abandoned the idea after playing with it for a couple of hours.
Just my own experience. Maybe others have had better results?

I begin by getting it close on the belt sander; hand guided, no jigs. Then I sand it by hand and eye, using a set of radius gauges, a straightedge, and a couple of (non radiused) sanding blocks. Takes 15 minutes more or less, depending on how it goes.

Another overly mystified building process. An individual builder doesn't need to be jigged up like a factory.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Doug, why don't you just leave the nice little facets? Then each string will have it's own fretboard.
Just kidding.

EDIT: Actually I've found Howard's method above to work well.
I do use a radiused sanding block, however, to finish sand.
Nelson

I've pondered this as well. Here's a method I thought up for doing it with no radius blocks at all, but otherwise similar to Alan's.

First, you decide what height difference you want between the center and the edges (this defines the two radii). Then mark a line along each side of the fingerboard at that height. Then plane a smooth curve, following the taper, until you get down to the marks on the sides. Never touch the center line. Otherwise the height difference between it and the reference lines on the sides would be reduced, thus creating a larger radius.

You could draw a curve onto the ends of the board as well, but I suspect it would be easier to just look at it and judge. Nobody said a perfectly circular arc is the best fit for a human finger anyway

It would still be tricky since you can't just do continuous runs of the plane the whole way down the board. The plane cuts a constant thickness shaving, which makes a bigger difference to the tighter radius on the nut end than it does at the wide end. So you'd have to start with shorter plane runs and check with a straightedge frequently, and only do full length runs at the end. It would be easier to start by sanding it down close to the reference lines with a radius block, so you could get away with full runs from the start.

By my calculations, a 12" radius at the nut means an edge height difference of about 1/32", which corresponds to a radius of about 20" on the wide end (for nut width 1.75" and wide end 2.25"). 16" nut radius is 1/42" edge height.

You could also slant the bass side reference line just a bit to provide more clearance for the larger vibrating arcs of the low strings. Definitely not a true circular arc then.

I use a low angle block plane and a well tuned scraper.
Then sanding blocks .
I check it all just like Howard does .

Mike

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Mike Collins

DennisK, you should stop thinking about it and just try it! Neither the geometry of the compound fingerboard, nor the process to create is as complicated as you make it sound. I'm no wiz with the hand plane or sanding block, believe me, but I can produce a FB the way I described it about as fast as Howard, its really not that difficult once you get the feel of it.




Actually, a cross section of the compound FB taken anywhere should be "...perfectly circular..." as you say, or have a constant radius, if done the normal way (Imagine it as a section of a cone). This ensures that the surface of the fingerboard under each string is a straight line. This makes it easier to set the instrument up for good action all the way up the fingerboard, and it is their main advantage over FB's with a constant radius, IMO.

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Rian Gitar og Mandolin

Me too. I made an adjustable jig that used a router, but found I could radius the board quicker than I could set everything up.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

That alone would not ensure a straight surface under each string. Each cross section could be a section of a circle, and the board could curve along its length. For example, a single radius all along the board could be part of the surface of a torus. With a compound radius, all cross sections could be circular and the board be a surface section of a curved cone (like a saxophone).

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Well OK, but I said in my previous post that "...I check frequently with a straightedge while planing, to make sure the fingerboard surface is straight under each string, imagining a normal string tapering". I also understand that a cone can be curved (like a saxophone), but when I said "...section of a cone...", I meant a straight one. Was that unclear?

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Rian Gitar og Mandolin

I made a jig that I use to shape compound radius on my jointer. I don't have pictures though.
Basically it involves two semicircular plywood boards screwed to a sturdy cross member that holds the neck face down. The neck is placed on the holder with a 7 or 8 inch radius plywood disc on one end and a 12 or 20 on the other. With the planer off, I set the depth of cut by zeroing the neck on the outfeed table so the fingerboard face touches the outfeed table at the nut and end. The large radius disc is still on the infeed table. And tighten the discs to the holder.

To plane the radius I first run a light pass in the center and there should be NO planing. As I run a pass on each side of the center there is a slight amount of wood removed outside of this there will be more passes reqiured to bottom the radius followers.

Edit, The leading radius disc gets set on the outfeed bed and doesn't touch the bed. The other radius disc stays on the infield bed and doesn't get touched by the blade.

I am not sure how well it works yet. I just made it up yesterday and assembled it, tried it once and it made a nice radius but at the time I didn't figure out yet how to set the depth of cut.

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Ken

Arnt, I think a conical section makes a good compound radius shape, but there are an infinite number of other possible shapes that would give straight line string paths, and some of these are practical also. Really, you can chose any cross section you want at two points on the fret board. Connect those points with straight lines, and that defines the shape. An extreme example would be a finger board with a 7" radius at the nut, and dead flat at the 12th fret. Beyond the 12th fret, the fret board would be concave in cross section, and the saddle would be a big smiley face. I doubt many players would prefer this shape, but the string paths would all be straight lines. With that in mind, you can play around with whatever cross sections you like, and see how they play out. Elliptical sections, and irregular curves are completely viable cross sections.
I think a very interesting discussion would be about the advantages and disadvantages of different contours for different playing styles. We usually think of the tight radius at the nut (easier barre chords, and partial barres), flattening out as you go up the neck (clean string bends), but I could make a case for the opposite approach for a player who just wanted to play Freddie Green style rhythm guitar.

I don't need no STINKIN' Jig!!!

But, seriously-I am in the 6 X 48 belt sander camp...

It's hard to explain (but easy to do) Basically I gently roll the fretboard on the sander and it just sort of "automatically" makes a compound radius.

It just seems the end toward the bridge gets less of a radius than than the nut end.

Of course I finish it up with a block and sandpaper checking with radius gauges and a straight edge as I takes something around 30 minutes.

Here is a drawing of my double bass fingerboard, just for the sake of discussion and to illustrate an extreme approach.

My bass fingerboards are planed by hand to get this shape which is a parabola. Fingerboards on violin family instruments usually cited to be in mm radius but in reality some luthiers will create more of a radius with flat ends, or a flatter radius on the edges and more radius in the center (parabola). This way the fingers don't feel like they are sliding off the fingerboard, yet there is sufficient bow clearance as not to hit double strings.

Take a look at the drawing and see there is a lot going on in the set up that seems simple yet creates ease of playing that can't be described easily.

I believe this is true for the guitar but in a much different way. Of course it is player specific.

Anyway, I thought this might be a little interesting, but not really specific to this topic.

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Ken