compound radius for fingerboard and frets?

SilverSurfer2 · #1 06-06-2003, 08:59 PM

I've got some flat fingerboards that i want to put a compound radius in for lower action.

What is the proper process to creating the compound radius on the fingerboard and the frets?

I've got radius's from 9.5-20 .........and want to use them to create the compound radius on fingerboard and frets.

Any advice would be helpful.

frankfalbo · #2 06-06-2003, 09:36 PM

I've always done mine by hand, and it allows me to make the transition more dramatic at the higher frets. I like to start with 9.5" and go to 16". Finishing off at 20" could be okay too, I just like the feel of a 16" on top. I like some arc because it's natural to the way your fingers move treble to bass. So think of your transition as exponential.

The way to do it is to start with a 9.5" radius all the way through. Then, as you transition to the other blocks, you'll notice that you aren't fully transitioned to that radius until the block is just touching the outer edges of the fretboard. Slowly move up the neck to the highest fret. Each time you switch to a new block, radius the fretboard with it from your starting point all the way to the highest fret. In other words, you'll keep re-radiusing the higher frets each time so that you know you are maintaining flatness across the radius changes. That's about it.

The real way to do it is to have a long, perfectly flat beltsander, and hang the neck with 9.5" of chain or pipe on the 1st fret and 16" of chain or pipe on the 22nd, set so that as you swing it like a pendulum, it applies the radius to the board. You still need to hand finish it, though. A friend of mine also has saw blades behind it so it cuts all the fret slots in the same swoop.

SilverSurfer2 · #3 06-06-2003, 10:44 PM

Frank, how many frets cover what radius.....before switching to another radius......and how many frets of that radius and so forth?? Does it make a difference whether 3, 4, or 5 frets are with a 10" radius before transitioning to a 12" radius for 3,4, or 5 frets as you move up the neck??

And when all is done.....isnt the fingerboard at the nut going to be higher/thicker than the 22nd fret? And isn't a straight edge going to show that it slopes/tapers down from the nut to the last fret.....because if the 22nd was 9.5" and you flatten it to a 16", the top of the curvature will end up lower than what it was when it was 9.5".............or is this not the case?
I'd have to see a pic of that chain apparatus you are talking about.....to really understand how you do it........
Sounds kinda complicated

frankfalbo · #4 06-07-2003, 01:59 AM

If you did it eliptically, like with a belt sander or a CNC shaper, the change would be perfect and gradual, technically beginning even before the first fret, with your nut slot or nut end of the fretboard at 9.5". I like the first three frets to be at 9.5 and then begin to flatten. Conversely, I don't like to be at my final radius until the last fret. That is to say, don't make the top 5 frets all 16", because the most dramatic effect of a compound radius is in the bending of those last frets. But to make it simple, you can figure about four frets per radius. Of course there will only be one fret that is actually that radius, because the rest will be a transition. But about every four frets you should begin to use another block. Again, remember, 1-24 are 9.5", then transition to 4-24 10.5" or 11", then 8-24 at 12", etc.

The slope phenomenon you're talking about isn't a curved slope at all. It is the very essence of a compond radius. Think about it. Your fretboard will either be thinner in the middle on the high frets, or if you did it in reverse, thinner on the outsides of the low frets. What the straight edge should show is actually a straight line IF you follow in the direction of the strings. Yes, on a blueprint type drawing the G and D strings would get closer to the plane of the outer E's. That is what is supposed to happen. And the bridge will be set for a 16"-20" radius for proper action. Most Floyds are pretty flat, and just about everything else besides tune-o-matics are adjustable.

There's no pics of that machine, at least you can't see it in any of the pics of the shop. Picture a playground swing where one of the cables is shorter than the other. It will swing ****eyed. Back and to the left, then forward and to the left. I think you'd have to use pipe or something else solid like he does, so it didn't pivot on the axis where it was attatched.

SilverSurfer2 · #5 06-07-2003, 08:22 AM

Frank, that makes more sense to me now. Cuz when it is a straight radius throughout the fretboard....then checking with the straight edge in line with center from treble to bass would read as "flat" (if done right)......and for a compound radius, following the line of strings will and should read "flat". I think i'll stop at 16" at 22nd.......and switch every 4 frets....like you said. I understand how the transition should be.....like you said.

What about the radius of the nut.....like a floyd nut for a double action tremolo(or regular bone nut), should that be 9.5?

frankfalbo · #6 06-08-2003, 01:18 AM

The nut radius should always match the first fret. Remember, once you fret a note, the nut is no longer in the equation. So how your radius changes after the first fret means nothing.