fretboard radius question

[darylcrisp]

will be starting a build soon, the fretboard is cut out already and is flat so I want to put a radius on it.

1)what do most of you find you prefer for 13 7/8"scale mandolin?

2)Do you find it easier to radius the FB before its attached to the neck, or easier to radius after its glued on the neck.

3)what is your method of doing the radius(I'm looking at the aluminum radius sanding beams at stewmac:
http://www.stewmac.com/Luthier_Tools...640_B_20170714

thank you
d

[Oliver A.]

Daryl, I think you'll find that the degree of fretboard radius is largely a personal preference. For what it's worth, I use as standard, a 7 1/2" radius. It is fairly pronounced but I wouldn't characterize it as radical. I suspect that the most common radii are from 10" to 12".

I have put the radius on fingerboards both before and after gluing to the neck. Either way is fine. Currently I radius the board before gluing. I use a wooden block that I made myself by rubbing a block of mahogany back and forth over the drum on my thickness sander which has a 15" diameter. You can do the same by taping some sandpaper to a cylindrical object that has the radius you prefer.
Before sanding the radius into the fingerboard, I use a colored pencil to rub lines crosswise over the entire board. This allows me to "see" my progress as I sand and is a great help in keeping things even.

One of the down sides of radiussing the board off of the mandolin is that you will need to make a special clamping caul that fits the radius. For that reason, you may want to do the procedure after the board is glued to the neck.

Here's one of my cauls in action on an A-model.

[sunburst]

I use a 7 1/4" radius for mandolins. As Oliver says, it's fairly pronounced, but many people don't even notice it, or they'll ask me if I can do a radiused fingerboard while they are playing the mandolin(!), so it's obviously not radical.
I like to radius the fingerboard before gluing it to the neck and before cutting the profile. In other words, I like to work with a rectangular slotted fingerboard. It is easier for me to keep the arch centered and consistent from one of the 'board to the other.
I don't like radiused sanding blocks. They must be stroked absolutely straight and parallel to the fingerboard center line with no twisting of the block. The only way to do that is to slide the block along a straight edge aligned with the fingerboard center line. Also, each successive grade of sandpaper is thinner than the grade before, so each time the sand paper is changed on the sanding block, the radius changes. 50 grit sandpaper is quite a bit thicker than 320 grit sandpaper. It's a minor thing, but it means more work having to sand the center of the board down to the edges each time.

I start with a sharp block plane, and depending on how well the fingerboard material cuts with the plane (some ebony is much more chip-prone than other), I'll either completely establish the arch using the plane and a radius gauge or I'll switch to course sandpaper on a flat block and establish the arch with that. I continue to check the arch with the radius gauge as I go through the grades of sandpaper until it is sanded to 320 grit.

I use radiused clamping cauls too, but the caul can be "over-radiused". In fact, some folks use cauls that only clamp the edges of the 'board because the moisture from the glue (unless you use epoxy as some do) tends to "cup" the 'board so that the center part is clamped tight as long as the edges are well clamped.

[Graham McDonald]

I take around .5mm/.020" off the edges along the length of the fretboard and round off the rest to fit, ending up with a compound radius. I use a piece of 16mm melamine faced mdf the size of half a sheet of 80grit aluminium oxide paper to put the basic shape on the fretboard already tapered to finished size. A small jig with tapered edges holds the board to a work board for sanding first with the 80 grit and then up to 400 great before fretting. I have no idea what the radius the fretboard ends up, but I really don't think it matters, even if the profile is not perfectly part of an arc. The important thing is that the fretboard is straight along the line of each course of strings. The board is fretted, leaving out the 2nd and the 10th for locating pins, before being glued to the neck.

[Tavy]

I take around .5mm/.020" off the edges along the length of the fretboard and round off the rest to fit, ending up with a compound radius. I use a piece of 16mm melamine faced mdf the size of half a sheet of 80grit aluminium oxide paper to put the basic shape on the fretboard already tapered to finished size. A small jig with tapered edges holds the board to a work board for sanding first with the 80 grit and then up to 400 great before fretting. I have no idea what the radius the fretboard ends up, but I really don't think it matters, even if the profile is not perfectly part of an arc. The important thing is that the fretboard is straight along the line of each course of strings. The board is fretted, leaving out the 2nd and the 10th for locating pins, before being glued to the neck.

+1.

However, by way of experiment, the next pair I'm gluing to the neck before final levelling and fretting, just to see if there are any improvements that way, in particular if it results in flatter/straighter boards before the frets go in. Yes, I know it should make no difference, but you only have to be a fraction out on the board or neck or both, and those fractions add up..

[darylcrisp]

wow, thank you all highly for all this information.
and Graham, thank you for including the thought of the compound radius, I was thinking of asking regarding that also.

every method sounds good, now to decide which way(or chicken out and leave it flat-lol).

thanks again folks, this was all excellent
d

[Rob Roy]

Hi Daryl,
I found my personal preference lies with a straight 12 inch radius. I tried a compound radius on one build but found I had a harder time noting cleanly on the E string on the lower frets with a tighter radius. I'm convinced now that compound radii work best on electrics where string bending is an issue. I splurged on the stewmac aluminum sanding beam, pricy but exceedingly reliable. I like to bind the board, rough in the radius on the stationary belt sander, then finish with the sanding beam. It's so consistent, I take it all the way out to 220 grit on the beam. It was a lot of $$$, but I work on guitars, acoustic and electric, a lot and a 12" radius seems to show up regularly. I also bought their plated steel square channel with machine-ground surfaces for leveling frets (along with diamond crowning files). The older I get, the more I realize it's worth it to spend more for good tools and save my poor fingers and joints for playing. Enjoy your build!

[Jonathan Ward]

For whatever it's worth, Stew-Mac is currently running a deal on their aluminum radius beams. (Not cheap, but strong and accurate.) I mounted one on a modified straight-line (i.e. autobody) air sander, and with a couple of grits of self-adhesive sandpaper it will grind fingerboard radii all day long.

If you get one of their 18" beams, you can cut it in half. One piece mounts to the sander, and the other end becomes a fingerboard clamping caul.

[Tom Haywood]

1) 10" radius, but thinking of going back to flat. I don't see the need for a compound radius.
2) Prefer doing radius with fret board attached to the neck, if the neck is raised above the top plate. Have done it both ways. Requires a solid support underneath the neck.
3) I use the 6" wooden Stew Mac concave sanding block. It does require paying close attention and having a good touch and steady hand Takes me about 20 minutes. The block is also useful to radius the saddle and nut.

[darylcrisp]

For whatever it's worth, Stew-Mac is currently running a deal on their aluminum radius beams. (Not cheap, but strong and accurate.) I mounted one on a modified straight-line (i.e. autobody) air sander, and with a couple of grits of self-adhesive sandpaper it will grind fingerboard radii all day long.

If you get one of their 18" beams, you can cut it in half. One piece mounts to the sander, and the other end becomes a fingerboard clamping caul.

thanks Jonathan,
that's exactly what I've been looking at. I have some of the flat beams and have found a lot of uses for them.
I'm probably going to get one once I decide the radius I want. I love the F9 fit and such I picked up a few months ago, and I like Weber necks/specs a lot, so I think i'll measure the F9 radius and go with that.

thanks again to everyone, excellent info being given
d

[amowry]

I like using a compound radius because you end up with edges of the fretboard that are the same thickness the whole length, but it's not a big deal on mandolins. On larger instruments it's more noticeable, and more necessary in terms of playability. When you dress the frets later you're putting a compound radius onto the fret tops even if it's not in the board. I use CNC for the radius now, but before that I used a rocking jig on the belt sander-- it's not hard to make and worth it if you're making more than a few boards.

[sunburst]

I like using a compound radius because you end up with edges of the fretboard that are the same thickness the whole length...

From the guitar world, I am used to and have come to like the look of the tapered fingerboard edge that results from a simple radius arch.