In defense of notched straight edges (for the builders and fretting-folk)

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by Terry McInturff, Aug 14, 2019 at 1:20 AM.

  1. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    I think that I have read here, comments by some who disparage the utility of notched straight edges.

    I'm not sure why these are not recognized as being an invaluable tool; I certainly wish that I had thought of this idea many years ago!

    IMO, they are absolutely indispensable.

    Given the elementary rule that fret tops are sacred ground, and ideally never be modified in order to make-up for inaccuracies in the shape of the wooden surface......

    When given the chance to build from scratch, and/or the chance to reshape the fretboard surface, I'm at a loss to explain why anyone would not regard an accurate notched straightedge as being an indispensable part of a routine...a routine that's intended to result in the frets ending-up within a bare few thousandths of their original dimension... after leveling to within .001".

    I use my Newport mill to notch my own from these. The shop masters are used to check them after notching (and every 6 months thereafter). IME one out of six gets tossed after notching, the other five are good. NASA good.
    https://www.starrett.com/metrology/product-detail/385-18
     
  2. Tootone

    Tootone Member

    Messages:
    3,087
    Joined:
    Sep 24, 2016
    Not sure where you get the idea they are "disparaged".

    They are an essential tool for straightning a neck (fingerboard surface) prior to fret levelling. Any luthier worth his salt has one.
     
    Terry McInturff likes this.
  3. stratamania

    stratamania Member

    Messages:
    3,089
    Joined:
    Nov 12, 2012
    Location:
    UK and Europe
    Mainly due to comments by some that they think they are not useful. I do not share that view as they are a useful tool to have.
     
    rwijaya and Terry McInturff like this.
  4. walterw

    walterw Gold Supporting Member

    Messages:
    34,920
    Joined:
    Oct 16, 2006
    there
    probably from this thread

    i was maybe even somebody "disparaging" them for regular fret leveling as opposed to refrets, but very valid points were raised about why you'd be worrying about the fretboard wood even when you were only going to be working on the fret tops themselves.
     
  5. Moby Dick

    Moby Dick Member

    Messages:
    1,900
    Joined:
    Sep 27, 2014
    Location:
    The Motorcity
    My only reservation about using a notched straight edge is,
    It is difficult(expensive) to accurately(within .001in) all 22-24 notches so they are the exact same depth. I know this from previous experience when I once was a machinist.

    It would be easier(cheaper), to accurately machine a straight edge( called a parallel in tool and die vernacular) if there was one long “notch” which all the frets fit under and the two ends rested on the fingerboard.
    Then accurate measurements of the fingerboard straightness could be taken using feeler gauges.

    One long notch is easier to machine accurately because the machine(normally a surface grinder) doesn’t need to be move to avoid the stepped notches.
     
    Terry McInturff likes this.
  6. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    Its actually a very easy thing to do. One simply marks the fret positions for a given scale on the straightedge and mills notches that will allow any fretwire height to clear it. You then have the original precision straightedge surface resting between the frets.
    I did throw one off of spec once by absent-mindedly using an up spiral end mill to create the notches. :(
     
  7. walterw

    walterw Gold Supporting Member

    Messages:
    34,920
    Joined:
    Oct 16, 2006
    remember, notch depth is irrelevant as long as they clear the frets entirely. it’s just about maintaining the original straightedge accuracy.
     
  8. Moby Dick

    Moby Dick Member

    Messages:
    1,900
    Joined:
    Sep 27, 2014
    Location:
    The Motorcity
    Silly me!
    I was thinking there was value to the depth of the notches being exactly the same depth.
    They are just CLEARANCE!


    Thanks for correcting my
    mistake.
    :bonk
     
    Last edited: Aug 14, 2019 at 8:38 PM
  9. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    No worries valued friend!
     
    Moby Dick likes this.
  10. Harryq

    Harryq Member

    Messages:
    435
    Joined:
    Aug 12, 2007
    I guess I'm missing something. When leveling an already fretted neck, my concern is to adjust the neck as straight as possible, or at least minimize any irregularities along the fretboard, then level the frets while checking with a good straight edge. When prepping an unfretted neck, my concern is the same, except now I'm concerned with the surface of the fretboard instead of the fret tops. What am I missing? It sure won't be the first time!
     
    Terry McInturff likes this.
  11. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    Friend Harry,

    When leveling the fretboard surface yes, you'll be using standard high quality straight edges.
    After the frets are installed, and prior to leveling them, the notched straight edge comes into play; it's not unusual for the fret's wedging action to induce a very slight back bow and so the notched straight edge allows you to check your minor truss rod adjustment.
    If you did the fretboard leveling properly just a tad of loosening on the rod will return the neck to as straight as you can measure (and there will still be plenty of adjustment room tighten/loosen on the rod).
     
  12. Harryq

    Harryq Member

    Messages:
    435
    Joined:
    Aug 12, 2007
    Thanks Terry, I see your point!
     
  13. bojocatkite

    bojocatkite Member

    Messages:
    250
    Joined:
    Oct 10, 2017

    Terry, you mention an extremely important effect: the back bow often created by the fret compression (the tang being larger than the fret slot tend to compress the wood and create the back bow). You can minimize it by controlling the tang thickness using that:

    https://www.stewmac.com/Luthier_Too...tting/Pullers_nippers_sizing/Fret_Barber.html

    My question is: how do you use this back bow effect ? Do you try to minimize it as much as you can (by using the thinner tang possible, do you glue the fret then ?) ?
     
    Terry McInturff likes this.
  14. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    In the world of repair/restoration, the desired fit of the tang/slot can often be situationally dependent....regarding the exact nature of the neck, and also the working style of the person doing the work. I'm sure that most experienced fret-folk in the repair world judge each neck as an individual and often modify techniques to suit the situation.

    I would say that it would be generally correct to state that too loose of a fit is not a good idea...nor is too tight. Depends upon the situation.

    The use of intentional fret-wedging in order to stiffen/straighten a whippy neck, or one with no adjustable rod goes way back in time. In fact...back in the early 1990's when I became an authorized CF Martin repairman, that was one technique described in their official repair manual. They even supplied different sets of fretwire with tangs sized to "jack the neck back" by different amounts. In certain situations it can help as part of a complete plan to this day, but doesn't play as major a role as in the past, and thats a good thing.

    I am far luckier than repair-folk in that I build necks from raw lumber, using my proprietary design/build schedule, and so I can be in control of everything. In my case, I can manipulate the width of the slot in order to accommodate various fret wires, although 95% of what I build uses the same fret wire.

    My neck recipe calls for a slot that is exactly the same width as the tang, not counting the "barbs". My standard wire has a .023" wide tang, and so the slots for those are .023" wide. The barbs bite the wood, creating just that sort of interference-fit. The end result is a back bow ranging from zero-to-.003". The slightest loosening of the rod returns the fretboard to it's straight-to-.001" shape, as it was before the frets went in.

    From there, if the rod is loosened all of the way... with no string tension.. the neck has a built-in forward bow of .018". And so there is always tension on the rod, no chance of backbow/loose rod.

    From a stability/stiffness standpoint, it's important that the slot be filled by the un-barbed tang. And its vital that the neck always be under a controlled tension, because a cantilever that is under tension is always stiffer than one which is not. Filling the slot with the tang is one of the steps required to make a neck that acts/sounds as monolithic as possible.
     
    Last edited: Aug 15, 2019 at 5:12 PM
    Steve_U1S, walterw, Moby Dick and 2 others like this.
  15. bojocatkite

    bojocatkite Member

    Messages:
    250
    Joined:
    Oct 10, 2017

    Thanks Terry.
    Where/how do you take the measurement that you mention (.018", .003") ?
    You certainly wrote somewhere how you achieve this .018" forward bow on the neck, I need to do a search on this forum :)

    Also, any idea where I can get a hold of this old Martin Repair manual for techs?
     
    Terry McInturff likes this.
  16. Terry McInturff

    Terry McInturff 40th Anniversary of guitar building! Gold Supporting Member

    Messages:
    5,933
    Joined:
    Nov 4, 2003
    Location:
    Pittsboro NC
    1) I use the notched straightedge for any fretboard measuring after the frets are in. Backbow is measured at the nut end. The .018" spec is measured at the 7th fret.
    2) Ive never written about how the built-in forward bow is achieved, as this is a confidential matter, and I hope that you understand sir.
    3) Not sure where the old manual could be obtained, but here in 2019 it would be of mainly historical interest since the techniques described therein are mostly obsolete.
     
    bojocatkite and Moby Dick like this.
  17. Failsafe306

    Failsafe306 Member

    Messages:
    10
    Joined:
    Dec 23, 2017
    I don’t own a notched straight edge. What I do is, take 3 small blocks of maple, all the exact same height, and place one on either end of the fretboard, and 1 in the middle. When I set my regular straight edge on top of them, I adjust the neck to the point where it rests on top of all 3 equally. In theory, the neck should be as straight as it’s gonna get, regardless of what the frets are doing.
     
  18. walterw

    walterw Gold Supporting Member

    Messages:
    34,920
    Joined:
    Oct 16, 2006
    i like that idea but i'd think we would want something harder and more dimensionally stable than wood, like three pieces of identical precision-cut metal. three of the same size drill bit maybe?

    also, you might have situations where the neck profile is not ideal and those three data points aren't enough to get a clear picture; something like a bad S-curved neck where you have a bit of an upward kink where the neck meets the body and the adjustment that gives the "straightest" average profile has a slight backbow from like 5 down to the nut. three contact points wouldn't reveal any of that.
     
  19. Failsafe306

    Failsafe306 Member

    Messages:
    10
    Joined:
    Dec 23, 2017
    That’s a good point.
     
  20. Tone_Terrific

    Tone_Terrific Supporting Member

    Messages:
    27,673
    Joined:
    Dec 26, 2004
    Location:
    Canada-GTA
    Sure. Leave us to speculate.:waiting...graphite rods..of course!:idea
     
    Terry McInturff likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice