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You need to know how far the arc drops for the width and radius of your fingerboard. There are a number of ways to calculate this using the "versine" function, but the EASIEST is to go here:

http://liutaiomottola.com/formulae/sag.htm

and use the calculator. That will tell you how much the fingerboard drops at the edges. You add that amount to the depth you want the slots to be, and that will give you the total depth you need in order to clear all the fret tangs all the way down the board.

Soooooo.....

If you use a 12" radius and the fingerboard is 2.25" at the widest point, the "sagitta" that arc is .053. Typical fret tangs are about .050" to .060" deep. You don't want to bottom out so you add .010"....maybe .020". Add it all up, and it's no mistake that default fret slot depth for many is 1/8" (.125")....which, on a typical 1/4" guitar fingerboard is just about halfway down

I hope that helps.

Author:	Spyder [ Fri Feb 08, 2013 12:15 am ]
Post subject:	Fret slots
I have begun work on the fret boards for my first two. I will be using a radiused board, and bought a sanding block from Stew Mac to make the radius. So, a couple of general questions on the order of doing things. My drawing (Antes parlor) says to make the fret board .19 inches thick. From looking at the drawing, after applying the radius this will make it .19 in the center, tapering to slightly less at the edges. My question is, what is the best way to cut my fret slots to the proper depth? I am using the Compiano book as a reference. If I remember right, the procedure is to square the blank, mark centerline, cut taper, glue on the neck, radius the board, then make the slots deeper if necessary. Is this the best way? Or is it better to cut them slightly deeper to begin with?

Author:	meddlingfool [ Fri Feb 08, 2013 2:22 am ]
Post subject:	Re: Fret slots
I cut mine about halfway deep and it works fine....

Author:	theguitarwhisperer [ Fri Feb 08, 2013 2:25 am ]
Post subject:	Re: Fret slots
You can get one of those saws that has the depth stop and measure the tang.

Author:	nyazzip [ Fri Feb 08, 2013 2:49 am ]
Post subject:	Re: Fret slots
or, you can epoxy on a strip of wood, to the side of the saw as your own "depth governor"...i did, works fine- but NOT in a mitre box! just for final freeform depth slotting. i cut about 2/3s into the blank initially(counting on a 9.5" radius), then radius, then finish the slots free-form, using above setup shallow slots cause big problems. deep slots look ugly, but thats about it

Author:	Tai Fu [ Fri Feb 08, 2013 5:40 am ]
Post subject:	Re: Fret slots
If you have the Stewmac Fret Saw, they sell pieces of plexiglas that goes into the hole in the blade to act as depth governor. The problem is the saw seems somewhat dull.

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Author:	John Coloccia [ Fri Feb 08, 2013 10:36 am ]
Post subject:	Re: Fret slots
You need to know how far the arc drops for the width and radius of your fingerboard. There are a number of ways to calculate this using the "versine" function, but the EASIEST is to go here: http://liutaiomottola.com/formulae/sag.htm and use the calculator. That will tell you how much the fingerboard drops at the edges. You add that amount to the depth you want the slots to be, and that will give you the total depth you need in order to clear all the fret tangs all the way down the board. Soooooo..... If you use a 12" radius and the fingerboard is 2.25" at the widest point, the "sagitta" that arc is .053. Typical fret tangs are about .050" to .060" deep. You don't want to bottom out so you add .010"....maybe .020". Add it all up, and it's no mistake that default fret slot depth for many is 1/8" (.125")....which, on a typical 1/4" guitar fingerboard is just about halfway down I hope that helps.

Author:	Spyder [ Fri Feb 08, 2013 11:29 am ]
Post subject:	Re: Fret slots
Thanks everyone. I supppose I should have mentioned that I already have the Stew Mac miter saw with detachable stop (the plexiglass one), and their fret cutting miter box. So I think you've given me what I need, thanks! That web site link was good, surprising how simple that formula is now that I think about it.

Author:	Pmaj7 [ Fri Feb 08, 2013 2:17 pm ]
Post subject:	Re: Fret slots
I saw to .080 first, radius, resaw with plexi depth stop. Kind of a pitb but seems like you would lose a lot of hardwood meat right down the center of the neck right where you want the most strength if you don't. I'm working on rigging up my mitre box to cut a radius.

Author:	SteveSmith [ Fri Feb 08, 2013 3:53 pm ]
Post subject:	Re: Fret slots
pat macaluso wrote: I saw to .080 first, radius, resaw with plexi depth stop. Kind of a pitb but seems like you would lose a lot of hardwood meat right down the center of the neck right where you want the most strength if you don't. I'm working on rigging up my mitre box to cut a radius. I don't worry too much about strength in the fretboard since it's going to be glued to a much thicker neck. So I cut mine straight on the table saw before tapering or radiusing.

Author:	Tom West [ Fri Feb 08, 2013 5:58 pm ]
Post subject:	Re: Fret slots
Make yourself a depth gauge. Take a 3" piece of fretwire and at the 1" mark file a notch in the tang to its full depth. Then bend the wire to look like a hockey stick. File the barbs off the tang of the 1" section until it easily fits your fret slots. Check the full lenght of fret slot before fretting to insure tang will sink to it's full depth. Tom

Author:	John Coloccia [ Fri Feb 08, 2013 6:47 pm ]
Post subject:	Re: Fret slots
Ideally, the fret tangs fit well enough that it doesn't matter much. If you've ever worked on an old guitar with loose fret tangs, it's always got a big forward bow that you need to fix. It really depends on the tangs fitting well. The material in the middle hardly matters. The edges matter because that's where all the stress is. The stuff in the middle has very little stress on it and contributes very little to the stiffness, so that's why tubes are not appreciably less stiff than solid rods.

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