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Thanks David,
To answer your question, the ends are exactly even with each other. I talked to Edward this morning about this jig, and he knew exactly what you were trying to do. This jig will not do a compound radius in relation to the fretboard taper, but he also said that it is such a small difference, that you usually sand that much out when you glue the fretboard on. It will incrementally increase the radius as it goes from the nut end to the bridge end of the fretboard. So if you had a 16" radius at the nut and you had a 20" radius at the last fret, somewhere in between you should have an 18" radius. Mathematically this may not work out as you mentioned, as it may be 2/3 up the fretboard when the radius starts to incrementally change. But then again, I really don't think a player can notice this.

You or Fillipo had asked if the end pieces take into consideration the string spacing, and the answer is no it does not. It cannot calculate the fret spacing and radius incrementally based on fret spacing either. This jig will do a compound radius from one end to the other, and that is it. To me that is a true compound radius. But maybe mathematically it is not. There is very little play in the 2 radiused ends, so you will not be able to move one end a whole lot more than the other end to get the string spacing/fretboard taper issue resolved.

I think there is a lot of theory being thrown around about compound radius', but I'm not so sure this all really matters in praticality. For example, there are very few factory guitars that have a compound radius on the fretboard. And this is mostly electrics. I know of no modern factory acoustics that have a compound radius(Old acoustics did have compound radius'). And maybe this is a stupid question, but why does anyone want a compound radius on an acoustic? Most acoustic players don't play with very low action and slinky strings, so bending past the 12th fret is not really a problem. I'm not trying to be argumentative, just trying to understand the practicality of a compound radius on an acoustic.

Also, there was question about deflection, and yes, we did run into this problem. The middle of the fretboard deflected about 20 thousandths of an inch under the pressure of the drum. So to resolve this issue, we imbedded 2 steel bars in the fretboard rest. After retesting, it was about 7 thousandths deflection, which is about the thickness of a piece of masking tape. That was perfectly acceptable to Edward, as he said this much will be sanded after the fretboard is glued on. Hope this helps answer all your questions about this jig. Hope none of you take my comments as argumentative, as they are not meant to be.
Regards,

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Tracy
http://www.luthiersuppliers.com

if you're still sanding after gluing, re-think your adhesive.

yes, many acoustic player have to run action higher than electric players, but that's all the MORE reason to help them out by having a truer fretboard, so that they may run their action lower than they have in the past.

Collings, for one modern factory, does a compound.... You go tell Bill he's wasting his time. And go tell my clients that they're action would have been .007" higher had I not 'bothered', and see what their responses are.

It's always the same; those who say we don't need a compound radius are always those that don't understand them, don't play them, or can't make them. Or all of the above...

This is the drawing we're talking some pretty small differences.
12" to 20" is .011"
12" to 16" is .004
12" to 20" is .007
This drawing is scale twice actual size

That's fine...just don't dare touch that thing with sandpaper!

This cone geometry that is often referred to and used in making compound radius boards is actually a bit off from an ideal compound radius board, where you want the surface of the frets to form a straight level under each string. the perfect cone will actually only work in very particular circumstances, where the radius increases in direct proportion to the width of the string spacing. When these circumstances are not met, the further you move out from center, the further the line would be from pointing to the peak of the cone. This results in a parabolic line, rather than a straight one.

In the perfect cone example the radius will infinitely approach a straight line. In the ideal example I think of (in which under each string lies a straight line on the board) the curve would eventually pass beyond straight and invert at some point past the bridge if you continue the lines.

It's more of an interesting math riddle than anything of significant practical usage though. When it comes down the the few thousandths (if it's evan that much) between the cone and whatever parabolic form it is I'm talking about, it's probably inconsequential. Any small difference is probably less than the tolerances achieved in shaping the board, and would be wiped out anyway when leveling the frets. Still, I like riddles, and sick as it may be, I actually enjoy math....

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Eschew obfuscation, espouse elucidation.

Mario,
I laughed when I read this last line, how true! I understand where you are coming from, and do agree that I like a compound board on an acoustic. I was just saying that the majority of the public playing Martins, Gibson, etc. don't even know what a compound radius is.

About the fretboard leveling, that will open another can of worms that I don't want to go there because of so many factors involved(seasoned wood, adhesive, twist in the wood, fret slot width, clamping pressure, etc). But I will say this, the 7 thousands deflection can be overcome by simply applying some masking tape under the fretboard before using the jig. If you want to sand in your relief while using this jig, you can do that too by just adding more masking tape in the right place. So all issues can be resolved fairly easy. This jig is designed more for the home builder who doesn't have the time to make a jig like yours, and already has a thickness sander, and they are trying to save time. I've talked to some builders who are using sanding cauls to radius their fretboards, and they are wasting about an hour or more doing this, and it is not that accurate after they are done. There are so many ways to do this, and this jig is just another way of doing it.

Pls53, thanks for that informative drawing. It really helps to illustrate the small amounts we are talking about.

Oh yea, and David, I think you are mathematically correct, and Edward was alluding to this when I talked to him this morning. I like riddles too, and trying to solve these problems is always fun for me.

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Tracy
http://www.luthiersuppliers.com

Tracy your solution looks seductively simple and usable by most having drum sanders. Keep us posted on its availability.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

OK...the math.

You can't fit a cone through two arcs of different radii if they're parallel to one another. ie: Your 20" radius arc would have to be four inches higher than your 16" arc. So, if you wanted to cut a conical radius using a jig the inserts at each end would not be arcs, but rather ellipses. Put another way: if your ends are both arcs, then your fretboard doesn't have a cone cut into it.

Now, I'm not saying that's a bad thing and in fact I don't use a conical radius on the boards I make for people. I use a lofted surface between the two end arcs. So, essentially, you stretch a piece of rubber between the two curves. The interesting thing is that the intermediate curves aren't arcs at all (ie: at the 12th fret on a board meant to go from a 12" nut to a 20" saddle, the cross-section isn't an arc at all). This accounts for string spread (flattening of the radius compensates for the spread of the strings) well enough and it means that your arc-shaped nut and saddle are going to 'fit' the board geometry right.

The 'ideal' board for an absolutely constant string height from end to end is a cone section which is matched precisely to the starting radius on your fretboard as well as the string spread. The more string spread, the flatter the saddle radius. On a board with a 1.75" nut and a 2.125" string spread, the ideal radius at the saddle is almost exactly double the radius at the nut. It's a quadratic relationship.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

And it would be useful, if it were accurate. At around the 10th fret or so on the E strings, the differences between a 12" radius and a 16" and 20" are 0.01" and 0.017", which are both things a good/picky player would notice.

I'm looking forward to using some of the same ideas Mario has been for super-consistent fretting (since I made the cauls, I have an idea of the process ) combined with super-accurate control of fretboard geometry to see what I can do in terms of getting the perfect action on an acoustic. For me having the CNC isn't so I can make 200 guitars in a year (though I could), it's so I can do some <i>real</i> R&D on my instruments (when I finally get to build stuff for -me- again )

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

the majority of the public playing Martins, Gibson, etc. don't even know what a compound radius is

So, are they the uppermost target? Don't think so... And? Are we running factories? Is your target buyer the same fella who's shopping for a Martin or Gibson? If so, sorry to say, but they're buying a brand, not an instrument.

Our place in the marketplace is to reach higher than the mass produced items. Our place is to actually care for that last .007" of perfection. If we think otherwise, then we're wasting our time here, or at least, I am.

What Bob's referring to with the things we made is a whole system that I thought up and he CNC'd the jigs for. It works. But it's still a bit quirky, so until I have it 100% foolproofed, I can't let all the fools of the world know about it yet.

Here is my take on a similar jig for doing compound radi. It is similar to Mario's design except that the router table is stationary and the fingerboard swings under it. I got this idea from Bo Walker of "LINT", one of Steve Kinnairds buddies.
You can use any bit that has a flat bottom. I use a cam clamp to hold the swing arm steady and adjust it for each pass. It works very nicely and It take just a little sanding to true it up and get rid of the router marks. I don't do that until it is glued to the neck and after trueing, it is ready for frets.

The fingerboard is held on with double sided tape. If you wanted to get fancy, you could use vaccum.

I used to use a dovetail bit with a flat bottom but that went into another jig I use for routing purflings and bindings flush with the top and back. So now I use this bit.

Sure is nice to have that edit button back, even if it is only for a moment.
Thanks Lance & Brock!

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Tickle your guitar daily, and it'll tickle you back.

Tracy, can't wait to see your new jig in production.
-j.

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“If God dwells inside us like some people say, I sure hope He likes enchiladas, because that's what He's getting”
-jack handy

Nicely made jig John! It would appear that one really doesn't need the spherical bearings. Are you concerned about slop/wear in the wooden bearings?

On the issue of these jigs and newcomers to lutherie, aren't newbies far more likely to own a router than a drum sander? I would have thought so. I would rather spend a few minutes with my router to produce a super-accurate surface (and perhaps have to spend another minute vacuuming a little - the process actually makes very little mess because such a small amount of material is being removed) than spend what I guess would be about 3 times as long (10 second pass with the router vs. 30 second pass with the drum sander) running the fretboard profiling jig through my drum sander which has nowhere near the setting accuracy that I can attain on my router.

I can't wait to see what Mario and Bob have cooked up for the ultimate jig for fretboard profiling......

Cheers,
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"

Good points David & Bob...a little more homework, and I realize now that a plane intersecting (at 90 degrees) the surface defined by the string courses (or any conical surface) will actually be an ellipse rather than a circle (or parabola). But as you say, the deviation from a circular arc is not large one.

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The member formerly known as erikbojerik....

Thanks Dave, yes bearings would be better and the more slop you remove, the better. I will no doubt refine it if/when I rebuild the thing.

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Tickle your guitar daily, and it'll tickle you back.

I'm quite public about my 'jig', but you guys just think $40000 is too much to pay for one! With jigs there's a tradeoff between cost, accuracy, and versatility. I want the second two, so I paid a lot of cash. If you're going low cost then you've got to pick accuracy or versatility. Mario's deal should be deadly accurate when the bugs are worked out, but it's also specific to his boards.

That balance is there all through the business. Taylor got special tooling made so they can make their bridges -really- fast, but that tooling's no good for any other bridge design.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Dave:

Looking at the jig, I was wondering why the "axle" between the arc centers would be necessary. Couldn't there just be rotation bearings supported by the plywood frame at these points to further simplify the jig? Or would this "rack" the jig in operation? Just asking, as it looks good to me. thanks for sharing

Danny R. Little

Sorry, I posted without going back and seeing John's post, without the "axle"

Nevermind

Danny R. Little

I built mine based on the Grizzly jig over a belt sander. Only difference is it works on a router table. It works great!

http://www.mikrovisions.com/jig/

I haven't finished the second part of the tutorial build so also look at the prototype section. If you have questions please ask.

Mike

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I'm outside looking in, just farther from the window than most.

Looks good Mike! Seems like another fine way to do it.

My first fretboard came out perfectly. After gluing to the neck, fretting, and getting the neck set right, it looks to me like I won't need to do any fret leveling at all, but time will tell when I get the final nut and bridge/saddle done in a week or two.....I'll let y'all know....



Sorry about the focus on this picture - I'm still getting used to my new camera (Olympus E-3) - the next lot will be much better, I promise!

As far as whether the shaft is necessary or not, I don't think it is absolutely needed, but it sure makes life easy, being as how it forms a very stable, no-slop center of swing action.

Cheers,
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"

THx Dave,
Just another way of getting there,
Mike

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I'm outside looking in, just farther from the window than most.

[quote="Bob Garrish"]
I'm looking forward to using some of the same ideas Mario has been for super-consistent fretting (since I made the cauls, I have an idea of the process [quote]

I'm a bit of a nube here. Could you point me in the direction of this thread. I'm not turning up much info on this. Thanks.

Hi Sheldon,

There isn't any more information on what Mario and Bob are cooking up just yet! We have to be patient and wait until they have gotten thier new process just right, and even then, they have the right to keep their ideas to themselves and/or license it and/or produce a jig/machine to sell. Or not.

HTH,
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"

With all the discussions lately on compound radius fretboards, I was curious what you're using to press your frets in?

Those who do no leveling (Mario and others) must obviously be using fret presses, but do you use a "graduated" caul - start at 14 at the nut, do a few, then switch to the next caul, etc...?

I suppose if you have used this jig to route the fretboard, you could simply place a piece of brass or aluminum at each slot position and use a small bit to make perfect graduated cauls. Would take time to switch out each caul. but you would get perfectly pressed frets.

Am I over thinking this?
Steve