Neck Reset Formula

Is this the widely accepted formula for determining how much material to take off at the heel?

1) (the difference between the action you want & the action you have) X 2 X distance from bottom of fingerboard to bottom of heelcap

2) Take resulting number above and divide by the distance from the 14th fret to the saddle.

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Thank you sir.

Paul, i'm digging up a bit of an old topic here, but I wondered if you or anyone else can complete part of this neck reset equation for me.  How would you use the mathematics if the saddle has undergone its maximum amount of lowering?  Would you temporarily shim it up to the proper height (about 3/16 above the bridge per one of Frank's articles), take the measurements, do the reset, and then create a new saddle?

Brian,

The purpose of a neck reset is to restore the proper neck angle to counteract the lowering of the saddle (as well as the usual causation stresses & movement) that developed over the years. A new saddle is always indicated as part of a neck reset. A neck reset's purpose is not exclusively limited to lowering the action. It corrects all geometric issue caused by the stress induced 'shifting'.

I just want to make sure you understand the true purpose of a reset as many folks mistakenly think it has one purpose.. lowering the action.  I apologize in advance if I misunderstood your request.

I was going over a post from a different Paul, Paul Breen, after reviewing this link...

http://www.liutaiomottola.com/formulae/Reset.htm

All i'm getting at is that a modified saddle skews the 12 fret reading from what actually is happening. The equation seems to favor a guitar that still has proper saddle height, but improper neck angle in need of a reset.  I'm just getting my feet wet on neck resets and gathering a few lower end instruments with both standard dovetail construction and non standard for practice.  I want to better understand the measurements involved as opposed to making multiple adjustments and checking alignment at the top ledge of the bridge.  It will probably still be a trial and error process at first no matter how prepared I try and be.  Any insight is welcomed.

I know that you were asking Paul Breen. :) I just replied with my own set of comments & questions.

However, I believe you should read more about "HOW" to do a reset. I think if you further investigate the 'why & when' a reset is needed (commonly over-prescribed by novices nowadays), my next statement will make more sense.

Math formulas and algebraic algorithms may help getting it into the ballpark but math will never allow you to beat the straightedge method for getting it 'just right'. It's a lot of extremely detailed work that's reflected in its price.

Again, I'm sorry if I can't get a read on your skill level and have given you too basic of a reply.

Best of luck with your practice.

you are correct, I went through this too when I first looked at it.  Normally when you get a guitar in that needs a reset, the saddle has already been lowered as much as possible so using the formula with the "too low" saddle will do you no good at all.  Figure it using a "normal" saddle height.

I've never heard of the "widely accepted formula"

I simply just start removing a few thousands of an inch at a time from the heel,  continually checking the change in neck angle, until it's where I want it. Where I want it is, when the straightedge is above the center of the bridge about 1/32" or slightly more, it's about right. Also, always checking how the neck lines up with bridge pin holes, as too much, or not enough, can get removed from either the treble or bass side of heel, throwing off string alignment on the fretboard.

I don't use any mathematical formula for this. Actually math was one of my worst subjects.

Jim

Same here - never occurred to me to try to calculate the amount to take off the base of the heel.  Even if I did know exactly how much to remove, how would I achieve that measurement, except by trial and error.  Better to trial fit the neck and work a bit at a time.  After all, that's why I drag sandpaper through the joint - to go slowly with control, trying the fit as I go. . .

The math has been a real time saver for me.  After I determine how much to remove at the heel cap, I scribe a line using a stack of feeler gauges as a spacer between the binding (or a block clamped to the back on flush heel "caps" as on gibsons) and my razor blade or marking knife.  Then it's a matter of cutting just shy of the line to leave room for lateral adjustment and a few swipes of sandpaper between the heel and the sides.

The math I use is here, check out photo 7 (I plug the measurements into a spreadsheet):

http://fingerlakesguitarrepair.com/taylor-neck-reset/

Scribing the heel cap is pictured in photo 3 here:

http://fingerlakesguitarrepair.com/martin-dovetail-neck-reset/

The math is more accurate and faster because it compensates for a rubbery neck or a top that rises more than normal with string tension.  Kind of like doing fretwork under simulated string tension.  Using math also factors in the current saddle height, whatever it may be.

*If you plan on doing a refret after the reset, it is important to factor in how the fretboard, fret height and neck relief will change after the refret while doing the reset math.

I was aware of this link and posted it when Brian asked for a math formula but I have to admit that I have never used it. My method is a bit more seat of the pants and doesn't require my poor math skills to be involved.

Once the neck is off and I start sanding the neck heel using the pulled sand paper method, I just use a straight edge to monitor progress. Once it's close to having the straight edge land on top of the bridge, I put it in a jig I made to hold the neck heel down and I string it to pitch.

The top will come up a bit and require that I do a bit more sanding on the neck heel. I pull it back apart, sand, put it back in the jig, string it to pitch, check with the straight edge and see where it lands. This is repeated until I see the straight edge just touch the top of the bridge.

The jig is nice for glue up too. I clamp and string to pitch when I do this. Maybe a bit over kill but nothing is left to chance when your this far along.

The cord in the sound hole goes to a light bulb to heat things up from the inside.

I first saw this type of jig concept on Brian Kimsey's web site and came up with my own version.