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How accurate should fret slots be?

Discussion in 'Tele Home Depot' started by Slowtwitch, Jan 10, 2021.

  1. Hobs

    Hobs Tele-Meister

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    A 25.5" scale shifted up a fret is 24.069", which is plenty close to 24. I've only measured the scale on one 24" Fender (a 66 Mustang), but I'm pretty sure that was the actual scale length. Nut to 12th fret was about 1/32 more than 12". So, they were probably using existing saw bars with the nut slot cutter moved to the first fret position.
    Edit: What Crazydave said. :)
     
  2. beanluc

    beanluc Tele-Holic

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    Nah, you'd want 96.96% and then you'd only be 3.030303/100ths off. Going with 96.97% you'd be off by 96.969696/100ths.
     
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  3. beanluc

    beanluc Tele-Holic

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    ROUNDING, baby! :cool::cool::cool::cool:
     
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  4. Jimclarke100

    Jimclarke100 Tele-Afflicted

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    Last couple I’ve done by hand using a pull saw.
    I cut before trimming the board with one side of the board used as a datum edge and the centre line parallel to that.
    Measure each fret direct from the nut as accurately as possible.
    Then I use a set square and run the blade on the saw carefully along the rule to start the cut to get a straight cut.
    Is it perfect? - unlikely.
    Is it accurate enough? Yes. I hear no issues and, using a clip on tuner I see no difference from guitars made with pre cut slots.
     
  5. crazydave911

    crazydave911 Doctor of Teleocity

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    Nice to have honest backup :)
    My main method, check any of my bigger build threads especially old Build Challenge threads

    Dave
     
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  6. old wrench

    old wrench Friend of Leo's

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    Good question @Slowtwitch :)

    When you are in the habit of doing accurate work, and depending on what you are working on, 1/64" can be a huge error and way too much for a tolerance. 1/64" is very visible to the naked eye.

    I don't know it for a fact, but I'd think that Fender's gang saw was set up with spacers and shim stock between the blades to a achieve a tolerance much smaller than 1/64", very similar to the picture that Peegoo posted. When your companies reputation is at stake you sure don't want to sacrifice it with a sloppy set up on the gang saw.

    Precision measuring tools have been around for a long time. Old companies with a reputation for producing accurate measuring tools like Starret and Brown & Sharp capitalized on that by charging and getting high prices for very accurate measuring tools.

    Believe it or not, the best trim carpenters work to an accuracy of 1/64" or less. Just because my tape measure or ruler measures in 1/32" or even 1/16" doesn't mean I can't subdivide the gradations and work to a higher degree of accuracy. With trim carpentry it has to look right, with fret work it has to look right and also sound right.



    I guess @Slowtwitch's question is how close is close enough?

    What is the amount of difference that the human ear and brain can register as the change between being "right on" and flat or sharp?

    We could no doubt come up with a formula that would express the amount of deviation or error as a percentage.




    The problem with tolerances is that if you are not careful they will compound themselves.

    If your tolerance is 1/64" and you carry that tolerance in 3 or 4 measurements, before you know it, you have a fret that might be off 1/16" - and I'd reckon that much is noticeable even to my old abused ears, it's going to sound either sharp or flat.

    A better way to measure is to calculate the distance to each individual fret from a solid reference point, like the nut, instead of measuring from fret to fret.




    I don't have a clue as to the accuracy of copy machines. I trust them for replicating a copy of, for instance, a Tele body shape, but beyond that I don't know.



    That brings up another question - how accurate are the home shop CNC machines?

    Does anyone check theirs, or do you just assume they are "accurate enough" ?
    .
     
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  7. guitarbuilder

    guitarbuilder Telefied Ad Free Member

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    Home Cnc accuracy depends on machine flexibility, router runout, whether it has lead screws or belts.... I think mine is in the ballpark of +/- 008 or so on a good day.


    This is a comparison of my scribed by a cnc slot / cut on a miter box sawn fretboard compared to a stewmac fretboard. I scribe the positions on the board with a dremel tool in the router and then take the board to the stewmac miter box to cut them.


    f6.jpg
     
    Last edited: Jan 11, 2021
  8. Meteorman

    Meteorman Tele-Afflicted

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    wfret will print out a spatial fret map which can then be transferred directly (albeit carefully) to your fretboard.
    wfret can be downloaded from here
    you would of course check it with your micrometer first to make sure your printer hasn't boogered up the scaling - mine never has.
     
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  9. Freeman Keller

    Freeman Keller Poster Extraordinaire

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    My two cents. The very first instrument that I built a long long time ago was a mountain dulcimer. I measured and hand slotted the board, and got a couple of frets in the wrong place. The instrument never played in tune, I hated it. Last summer as part of Brother Dave's challenge I reslotted it and now I enjoy playing it.

    That taught me just how important the fretboard really is. I can't tell you what the accuracy should be, but it should be accurate. For my first couple of guitars I bought preslotted fretboards - those guitars all turned out well, play in tune and I kind of got hooked. Over the years I have built everything from 17 inch mandolin to 26.5 baritone, and each case I simply call up LMII and tell them what radius and scale I want. The boards cost an average of thirty bucks (for comparison a rosewood blank is 10 to 20) - every one of those boards has been much better than I could do.

    When I built the fir classical I put together a quick and dirty miter box and hand slotted the board to 650 mm using a Starrett rule borrowed from a machinist friend. Fretboard is fine, guitar plays nicely in tune.

    I guess if I was only making one scale or was in some kind of production situation I would put together an accurate fret slotting rig, but for the few guitars I build I'll stick with buying the boards.

    ps - I've always said that if I was going to let a cnc into my shop one of the first tasks I would assign to it would be slotting fretboards. But I can buy a lot of preslotted ones for the cost of that mill.

    pps - Gibson, like Fender, has used a gang saw for their fretboard slotting. There is some story about changing it as their scales have changed over the years.
     
    Last edited: Jan 11, 2021
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  10. pavel

    pavel Tele-Meister Ad Free Member

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    As a data point, consider that the much treasured 59 LP bursts used the "rule of 18" slot spacing with an actual value of 18 - it's 17.817 when done "correctly" (and even Leo knew better in the 50s). The resulting scale is off by as much as 0.7 mm on some frets compared to the more accepted modern spacing in a comparable scale. But folks still seem to be happy listening to Jimmy, Peter Green or Eric the God wailing on one of these out of tune bursts.
     
  11. Newbcaster

    Newbcaster Tele-Holic

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    Loudness at a concert fixes a lot of sins. and since all of those notes are equally out of tune, no one would notice.

    Its when only a couple are abysmal that people notice.
     
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  12. pavel

    pavel Tele-Meister Ad Free Member

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    So if you are someone like Buzz Feiten, what volume will it take for you to enjoy listening to LZ II and not cringe? :);)
     
  13. wadeeinkauf

    wadeeinkauf Tele-Afflicted

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    When I was working with multi-scale I printed out my fretboard layout from www.ekips.org on card stock paper. If you use regular typing paper and a glue the paper can stretch. I secure it to the neck with double sided tape. I just use a small square with sandpaper taped to one side to keep it from sliding and cut by hand carefully. You must have a saw with around the thickness of just under the thickness of the fretwire tangs. It is around .023 inches. These saws are not cheap. For those of you reading this if you are just making one guitar as a hobby and cannot justify buying the saw and box then you can use a standard hacksaw blade. It is around .019 inches thick and will work.
    4.jpg 9.jpg
     
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  14. Jupiter

    Jupiter Telefied Ad Free Member

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    I've done this twice now, once with a Fender-scale FB and once with a Gibby one. Just cut the end off a pre-slotted FB and put the nut where the 1st fret used to be. EASY PEASY! :)
     
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  15. Newbcaster

    Newbcaster Tele-Holic

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    Actually cardstock is a MAGNIFICENT IDEA. ekips/wfret is fine as long as you print it and the printer isnt jacked up. I will do this for my 24 inch scale. Thanks for the tip!!
     
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  16. Newbcaster

    Newbcaster Tele-Holic

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    Well done!! Still, thats some strange, sy gogglin redneck math. Its true for sure, but thats some country math if I've ever seen it. :)

    I love out of the box thinking.
     
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  17. 017_017

    017_017 Friend of Leo's

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    This is where the frets are meant to me:

    [​IMG]

    So don't fret it. (pun intended)

    LMII make them. Click on the link below, then click the "Pre-made Slotting Template Choices" tab:
    https://www.lmii.com/tools/22413-mix-n-match-slotting-templates-start-at-2365-ea.html
     
  18. Slowtwitch

    Slowtwitch Tele-Holic

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    I'm still wondering why I never was able to print out frets accurately (enough). And for the record I worked in an engineering design office with many CAD operators, so I do understand scales, tolerances, etc

    Hence me going with the CNC scribe the miter box saw route.
    I guess I'll stick to the CNC, I don't trust myself so much as to measure and mark after reading everyone's opinion here :)
     
  19. wadeeinkauf

    wadeeinkauf Tele-Afflicted

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    Just as a test go to www.ekips.org print out a scale to a guitar you have now and compare it to your guitar. It will print as a pdf. Be sure and click the box "do not scale".
     
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  20. crazydave911

    crazydave911 Doctor of Teleocity

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    You're making this way harder than it is
     
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