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Fretboard Radius Problem?


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Hi Folks,

I am hoping some of the more experienced luthiers out there can help me in understanding a conundrum!

I like to radius my own FB blanks as it allows me to use a much wider variety of timbers, scales etc.....I do however have a problem with my technique and I just don't understand how to fix it.

OK, picture a FB blank, that has been slotted, bound, inlayed and TAPERED....43mm width at nut and say 54mm at the 12th with 6mm even depth across the FB, no twists, dead perfect flat, square etc..... Seeking a 12" radius......using a Stew Mac 12" radius block (I have a 2 foot long one also).......the 43mm thin end begins to take the radius first as the edges drop away and you start to get towards the centre being sanded......however, despite how EVEN and CONSISTENT one does this......due to the wider end being wider.....the wide end still has MILES to go......it starts to drop at the edges but still flat across centre of the fb with heaps more to take off........now if I kept going to get the correct 12" radius at the wide end, I would be left with a much THINNER FB at the wide end (as in 4mm at the centre or so and 6mm at the narrow end which leaves little room for side dots at the wide end) in as it would require much more sanding to take away the excess..........I have done this on all my builds so far and managed to get away with it by leaving the last 6 or so frets a bit flat in the middle, but I thought, I must be missing something here and want to get this issue sorted out.......I want it 6mm thick end to end, centre to centre.....then if I CHOOSE fall away. that's up to me, not forced because of this problem.

I know a little bit of run off (fall away) at the wide end can be ok for low action etc, but this just doesn't seem right to me. I am not sure that I have explained this very well but I hope someone out there reads this and goes AHA (lightbulb)....I know what this aussie is on about :D

Any help would be greatly appreciated. Thank you for reading my post. :D

Edited by AprilEthereal777
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Thanks Jammy.....just saw a post from a few days ago where this topic was also touched on....please contribute though if there are other thoughts ideas such as tips on how to achieve say a 12" to 16" radius on a tapered FB........I have actually started doing this manually.....constant checking with a straight edge and radius guages and only a LITTLE bit of sanding then check again.....no rocket science in this method.....any other tips anyone?

Also, if I radius then taper........how do I get bindings on such a thin (4mm approx) surface.....hard enough with 6mm thin strips to do it......accurately!

Also, to radius before tapering would totally change my build process as I glue the tapered, slotted, bound fretboard to the neck, then use it as a template to rout the neck flush to on a flat surface...can't do that if the taper isn't done etc....back to templates for necks etc which I'd like to avoid.

For those wondering, YES I did research this topic on PG 8/11/08 (that's 8th November for US folk)........and could not find this exact issue, although it may be buried in an unrelated topic........

New thread title and a sticky perhaps mods?

Edited by AprilEthereal777
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I simply continue to sand my entire board - with less wood to take away, the nut end of the board does start to get get radiused first, but by continuing to sand the whole board evenly, until the entire thing is radiused, I end up taking the same amount off the middle of the board all the way down. I continue to measure the board with calipers as I'm sanding it to make sure I've removed an equal amount.

Starting with a slightly thicker fretboard allows me more room when the whole thing is finished for side dots if I'm doing a particularly wide fret board.

Sanding more thickness of the wide end (bridge side) of the board shouldn't be an issue if you've got a flat plane along the string path. However, if you don't take the fact that the front and the back of the neck are no longer perfectly perpendicular into consideration when setting your neck, this slight difference will manifest as fall away, as you mention dealing with.

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Starting with a slightly thicker fretboard allows me more room when the whole thing is finished for side dots if I'm doing a particularly wide fret board.

I think j. pierce has the answer for you if you want to use a straight radius. There is nothing you can do to eliminate the edge difference unless the board has a compound radius. Since you want to use larger pieces and cut them to size or use non standard woods make sure you find pieces thick enough.

You can also remove some of the wood with a small block plane to make the sanding easier at the upper frets.

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Sanding before tapering might sound like it will get you an even edge thickness, but in the end you get the same result either way. It is just an unchangable geometric issue. When using a straight radius, the narrower end is going to be thinner. Draw it out on paper and see where different widths lie. I am not really sure what the big companies do to compensate for it, if they do anything.

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Also, to radius before tapering would totally change my build process as I glue the tapered, slotted, bound fretboard to the neck, then use it as a template to rout the neck flush to on a flat surface...can't do that if the taper isn't done etc....back to templates for necks etc which I'd like to avoid.

I always taper the neck first (yes using a template - not sure why you want to avoid them), then glue the radiused, slotted, inlayed, untapered fingerboard to it, then taper the fingerboard using the the neck as the 'template'. Then I put the frets in, and lastly shape the back of the neck.

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  • 6 months later...
I always taper the neck first (yes using a template - not sure why you want to avoid them), then glue the radiused, slotted, inlayed, untapered fingerboard to it, then taper the fingerboard using the the neck as the 'template'. Then I put the frets in, and lastly shape the back of the neck.

I am radiusing after having attached the FB to the neck. Just seemed easier to work with once attached to something more substantial. Otherwise, that is the order I am proceeding in as well, so you have given me some reassurance. (My first build obviously.)

Now I don;t mean to hijack this thread, but I have a related question and this is the closest topic I could find. I am in the process of radiusing said fretboard (rosewood) and it is taking a loong time. Maybe I am impatient, because I am only used to working with softwoods, but still, it seems excessive.

So, my question is: is it reasonably safe to use some coarser grit sandpaper to get things close to shape? I would have thought the obvious answer was yes, but nowhere I read do I see anyone mention grits less than about 300. I am being pretty adventurous already using 120, but it's still taking hours and hours to do this.

And what I am actually working with is a 12" radius I am trying to flatten a bit to 14", so it really shouldn't be that bad. Was using coarser grits just too obvious for anybody to have mentioned, or am I missing some technique, or does it really take like 10 hours to radius a fretboard?

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My fingerboards tend to be tapered by the time I attach them to the neck as I like use templating bits to transfer the profile, after which I radius by hand using short blocks as you do. The radius "cuts it's own path" as I remember somebody saying (Spoke?) but as long as whatever path it is following "meets" the centreline of the fingerboard consistently, then you're not far off the mark. Straightness is essential to this.

As for grits, I cut the initial rough radius using 80 grit (with most woods) and then fine tune it flat using a straightedged bar at 120 and keep it in radius with higher grits from thereonin. My reasoning is that 80 grit will cause at worst <1mm scratches which higher grits can take out easily. As long as you're hitting your radius within a ~1mm tolerance initially, all you're doing is improving the target. As long as you have a way of checking any inconsistencies you're good.

Addendum - I used to radius boards before attaching them to the neck using my router radiusing jig, but I find that only useful for especially hard woods that won't sand easily by hand, like ebony or bloodwood. Hand sanding is slower, but by the same coin much more steady and allows constant checkups on progress.

Edited by Prostheta
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So, my question is: is it reasonably safe to use some coarser grit sandpaper to get things close to shape?

By all means, yes! I use 80 grit for rough shaping. Use good quality coated paper. It sands faster, loads less, and leaves a more consistent scratch pattern. I sand with 80-grit until the fretboard ever-so-slightly not done, then switch to 120 to finish the shaping. If the fret slots need to be deepened, I'll do it after the 120-grit. Otherwise, I just keep sanding up through the grits. Of course, frequent checking with an accurate straightedge and radius gauges is a given. Also, it's best to have some kind of guide for the radius block so that you're always sanding exactly parallel to the centerline of the neck. The one I use is dead simple: just a piece of plywood, 2 feet of 2" angle iron, and a flat board.

Radiusing by hand is definitely a chore, but it shouldn't really take that long to go from 14" to 12" radius.

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