Compound radius/conical fretboard advice

[lamanoditrento]

Hi there,

I am building a short scale classical (604mm) and would like to put a compound radius/conical fretboard on. I am intending on doing this by hand with different radii sanding blocks but am just trying to work this through my head and any advice help understanding the process would be greatly appreciated. Width at the nut will be 47mm, 58mm at the 12th, so calculating a 16' at the nut will give me 20' at the 12th and practically flat(?) at the saddle.

So am I correct that as the radius at the nut is smaller that at the 12 than the 18th fret that to get an even fretboard thickness along the side of the whole board the the centre of the fretboard at the nut will be higher than at the 18th? Does this change how I treat my neck angle? (building on a solera but haven't assembled yet).

Any help/tips/advice with this would be greatly appreciated!

Cheers
Trent

[lamanoditrento]

Having written that all out, I think I have figured out that if the edges of the fretboard are even along their length the angle should not change. It is just the centre of the fretboard at the nut end, but as that diminishes to 0 at the saddle.

[kiwigeo]

Having written that all out, I think I have figured out that if the edges of the fretboard are even along their length the angle should not change. It is just the centre of the fretboard at the nut end, but as that diminishes to 0 at the saddle.

When I'm hand radiusing my fretboards (fixed radius) the crest of the fretboard remains unsanded (ie pencil centreline remains). Without drawing myself fancy diagrams in my mind I see the angle at which crest of the fretboard meets upper bout as remaining as set and the angle changing slightly as you move out towards fretboard edge

[Allen]

A conical fret board will have a constant side depth. If it was a constant radius, then that side profile depth would change.

So on mine, while they are made on the CNC the end result can be achieved with sanding blocks etc. The side is a constant 3mm, and it's 12" radius at the nut and 16" at the the soundhole end.

[simso]

I have a swing arm over my belt sander that allows each end of. Afretboard to be sanded to a different radii or the same, can take photos if you want

Steve

[lamanoditrento]

I have a swing arm over my belt sander that allows each end of. Afretboard to be sanded to a different radii or the same, can take photos if you want

Steve

That would be great thanks Steve

[simso]

Over top of belt sander

Pivots

Adjustable arcs

[simso]

A conical fret board will have a constant side depth. If it was a constant radius, then that side profile depth would change.

So on mine, while they are made on the CNC the end result can be achieved with sanding blocks etc. The side is a constant 3mm, and it's 12" radius at the nut and 16" at the the soundhole end.

Very correct, its hard to achieve a consistant side width with a compound radius

Steve

[lamanoditrento]

Thanks Steve, well put together jig! Unfortunately I will have to wait until I have long enough linisher before I could have a go at that.

Ok, so after quite a bit of youtube/google research I think I have my head around the process and I now have a plan to proceed. As I often find years old threads really useful, for posterity I thought I would post what I had found:

I found this this http://www.jemsite.com/forums/f21/compo ... 19627.html on another forum and in particular the following comment from ol'mate Frank Falbo really helped me understand:

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.

I can now see how you can keep the side depth consistent because you set that with your first radius along the whole board. It will then give you a guide for you next one as you will never reduce the side depth from then on in.

This vid https://www.youtube.com/watch?v=I2QAWZ-5uL0 gave me the idea that I need a map of the graduation, so using the the stewmac fret calculator and radius formulas http://www.stewmac.com/How-To/Online_Re ... ained.html , I made a spreadsheet to map the radii on this fretboard for any given radius at the nut so I know when to transition to another radius block.

Compound Radii.JPG (91.68 KiB) Viewed 11077 times

Of course now I have got that straight in my head, I'm thinking how on earth am I going to bend and increasing radius in the fretwire...

[Allen]

You shouldn't have to change the radius of the bend in the fret wire. It's so subltle that once it's hammered / pressed in they all sit down fine.

[lamanoditrento]

Hmmm so I might have been over thinking this is bit. It turned out to no where near as difficult as I thought it was going to be

[simso]

Always the way isn't it, we dilly dally and think and think and sometimes it's just a case of do it.

Looks good

Steve