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Thread: Guitar Calculator Spreadsheet Version 1

  1. #1

    Guitar Calculator Spreadsheet Version 1

    Helpful spreadsheet I concocted for those interested in figuring up fretboard geometry. It will calculate fret locations (though you probably won't use those), fret slot depth taking radius and taper into account (i.e. it calculates the Sagitta based on the radius and widest part of the fretboard), and will calculate proper taper to maintain even spacing of the string to the edge of the fretboard. It will also take string width into account when doing that. That is important because you specify the clearance from the edge of the string to the fretboard, but most bridge manufactures specify string spread based on the CENTER of the string, so you can end up off by almost 1/16".

    It also calculates the proper taper settings for my style of taper jig. I'll take some pictures and post that later on today, but it makes for VERY simply tapering setups.

    http://www.ballofshame.com/GuitarCalculatorV1.xls

    The current setup in the spreadsheet is a sample for a reasonable spec on a 25" scale length acoustic (1.75 nut). Just change the input settings to match what you have.

    notes: you don't need to specify fingerboard length if you don't want to, but you DO have to specify the last fret. The calculation for the slot depth needs this in order to calculate the proper maximum depth as the depth gets greater the more frets you have do to the radius and the taper.

    Generally, I end the fingerboard at a fret location, so if I have 22 frets, my fingerboard ends at the 23rd fret, and where it says "Fingerboard Last Fret" I would enter 23. Some people like to extend the fingerboard longer. That's why you have a choice of specifying a last fret AND a fingerboard length. It your choice how to perform the taper. The spreadsheet will calculate both. The only place it really makes a difference is in the calculation for my taper jig. It needs to know not only the taper, which would really be specified anywhere, but also the maximum width of the fingerboard, so it needs to know how long the fingerboard will be in order to give the proper settings for the taper jig. When you see the taper jig in action, it will all become clear. The tapering part of this and the jig can also very easily be adapted to tapers on things other than guitar necks. I find the setup and calculation far simpler to get right using this technique than those traditional tapering jigs.

    Keep in mind that this is version 1. Use at your own risk. I'd like to eventually expand this to include neck angle calculations and possibly some other useful calculators as well.

    Feedback is welcome. I hope someone finds this useful.
    Last edited by John Coloccia; 09-26-2010 at 1:09 PM.

  2. #2
    Woops! Wrong Link!

    Here's the right one

    http://www.ballofshame.com/GuitarCalculatorV1.xls
    Last edited by John Coloccia; 09-26-2010 at 1:09 PM.

  3. #3
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    Is there an I-phone version ready? Just kidding. Thanks for posting that John. I'm going to take a shot at carving an archtop this winter, like a Benedetto copy but in a smaller 15" parlor size. I've never built a guitar so it should be a learning experience.

  4. #4
    Actually, I was thinking of tossing together an iPhone and Java based version of that. There's really no one place you can go that really does the entire calculation and gives you the whole geometry in one shot.

  5. #5

    Here's the taper jig

    Okay. Here's my tapering jig and how I use this. It should be pretty clear, though, that this can be adapted to just about anything. You'll notice it's similar to some other jigs that folks have made, but I use two points to index instead of a flat board. This allows you to be very precise in your indexing, and I also find it MUCH easier. Anytime I try to get a board lined up with marks, I move it at one end, and it moves at the other end, and then I go back and forth 15 times. I'm much too busy fixing mistakes to waste time aligning jigs!. The other advantage is that you can taper curved surfaces. So if you have some scroll work on one side, for example, and you need to taper the other side, it's very easy since you don't need to find or create a flat spot. You simply need to choose two points and index from there.

    This technique is also excellent when you care about keeping the piece "straight". I typically taper after slotting for the fretboard, so it's very important to me that the fret slots stay dead perpendicular to the centerline. Generally, it makes it pretty easy to take whatever pattern is in the middle of the board, and keep it aligned however you wish. The tapers on either side also need not be the same, but in my case it is always the same and the centerline always remains centered.

    Here we go. A shot of the jig. Nothing Earth shattering. Mine is precisely 6" wide because I use my table saw fence to do this. You could also use a bar in a miter slot. I happened to not have anymore bars, and anyhow I really don't like how much play I get at the beginning of the cut.


    I happen to like indexing at the 1st and 12th frets. This is just a junk fretboard I have that I made so that I could use it as a fret gauge. It's like a fretboard story stick I mark where the 1st and 12th frets are on my pieces of MDF. Pretend the MDF is a fretboard I'm preparing. In real life, it would have slots in it at this point so marking wouldn't be nescessary.


    Notice I'm marking 2. You'll see why later.


    Sorry for the blurry image. I take my "fingerboards" and mark on my jig where the 1st and 12th frets fall. I centered my stops on the 1st and 12th frets for a 25" scale length. That gives you plenty of play to do anything you may need to do. Note also the point. Those where just bandsaws from corners of 3/4" ply. Because it's a point, it can rotate quite a bit left and right and still only contact on a point. That's necessary because the locations will move a little depending on your scale length. Anyhow, mark the locations and drop a perpendicular line to the stops.


    Now go to my handy dandy spreadsheet, and pluck off the numbers for Taper 1 and Taper 2. Elsewhere in the "Inputs" section, I specified that I wanted Taper 1 at the 1st fret, and Taper 2 at the 12th fret. You can also use the ends of the fingerboard (i.e. the nut location and the very end of the board) and those numbers are given as well. It all depends on how you're comfortable specifying them, where you place your stops, and maybe even on you're mood Set a digital caliper to that setting. In this case, I'm setting up for TaperA1 (A, as in "the first cut", and 1, as is "the first location", in this case the first fret). Lock the calipers.


    Set the appropriate stop to the proper location using the caliper's depth side. Then go to the 2nd setting (TaperA2 in this case, which will be at the 12th fret) and repeat at the second stop.


    to be continued....
    Last edited by John Coloccia; 09-26-2010 at 6:42 PM.

  6. #6
    Line up the 1st and 12th fret of your fretboard with the two pointers, clamp down and you're ready to go.

    I just use my table saw set to 6", the width of my jig, but you could also use a router (precut the bulk of the waste first using the jig to mark the cut). I have to remove the guard to do this but I have some nice handles to hold on to. I stand to the right of the fence, grab base of the clamps and pass it on through, getting no where near the blade. Again, it works just as well with a router table, and I do that too sometimes.


    This puts a taper on the first side, though it's hard to see. Be sure to keep track of which side you're already tapered! With a slotted fingerboard it's easy because it will be obvious which side isn't perpendicular to the frets.

    Now set up for the second cut, cut B, and do the same thing. Be sure to put the TAPERED side against the stops this time around. You can do this one of two ways:
    1) Flip the board over so that it's upside down
    2) Flip the board around so that you're feeding it the opposite way (i.e. if you fed if 12th fret first the first time, this time put the 1st fret at that end).

    Method 1 is what I typically use because I make my own fingerboard and everything is flat at this point. If your's are pre-radiused, you can't flip them over because it will wobble and you'll have to use method 2. In that case, I suggest you move the stops so that you're indexing more towards the middle of the board. The spreadsheet will allow you to specify what frets you want to use.


    Run it through again and you'll have a perfectly tapered fingerboard...which is impossible to see here, but trust me...it's tapered.


    So why did I make two of everything? I made two jigs so I can set them up for both sides, and just slam through them. But why did I make two "fingerboard" out of MDF? I really only made one. I ran both of them through the first time, but only ONE through the second time.


    What I REALLY made where two templates. The first template will now be used to resetup the jig the next time I want to make this particular taper. Line it up with the edge of the jig. I use another board to make sure it's really flush. It's helpful to mark the template for the fence side so you know which side to flush up.


    Set the stops, and you're done. Once you have the template, it's no longer critical to line up the marks on the template with the 1st and 12th frets (or whichever) on the jig. It only matters that the STOPS are lined up with the marks on the template.


    This was very long winded, but I promise the actual process is very fast and very easy to pull off, especially once you've made you're template. The real advantage this has over other methods is that as long as you have one straight edge that's properly aligned with the frets at the start, you will end up with frets that are aligned when you're done. If you start with pre radiused board, you have the additional problem of getting the peak of the radius in the center of the board as well. You can use this jig to do that as well. It will take extra measuring and figuring, and the easiest way I know to do it is to get the board sized to the largest final dimension you need first, and then proceed as normal. That's one reason I really dislike pre-slotted/radiused boards. I haven't had very good luck getting them with even a straight edge to the frets, and then it really turns into a hairball!
    Last edited by John Coloccia; 09-26-2010 at 6:40 PM.

  7. #7
    Hi John. Nice jig. I recently made two guitars (Les Pauls) and needed to make fretboards as well. The operations were tapering the sides, cutting the fret slots, radiusing the board and then cutting the fret slots to final depth on radiused board. My approach was that I wanted to preserve the midline or centerline of the fretboard. Then I could cut the tapers by flipping the unradiused board. Also I needed a way to align the board for cutting the fret slots to depth after tapering and radiusing. It was important to keep the board's centerline perpendicular to the saw cut. When it came to radiusing the board, I wanted to do this with a pretapered board so that I had less material to remove. What I did was to make my fretboard blank oversize in length by 3/4" at each end. I marked a centerline with a pencil down the middle of the blank. Then I drilled two holes in the extra part of the fret board blank, one at each end on the centerline. I used two small screw eyes to align this to my jigs' centerlines for the three operations. I used a lever clamp as you did to keep the board from shifting during the cuts, except I used double-sided carpet tape for the radiusing operation. The reason that I needed to align the board for the final fret slot cuts was that I used a home-made fret saw made from a hacksaw blade and I needed to stabilize the saw with a small T-square guide (it was much cheaper than a conventional fret saw). When I was done with all these operations, I cut off the excess board with the guide holes. So, just wanted to mention that an alternative to using the sides of the blank as a guide is using the centerline.

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