novice neck reset numbers- please advise

[stoneaxe]

Onward with my novice neck replacement project...
The dovetail on my Gallagher replacement neck is cut and fits fine.

I am ready to commit to the angle of the neck set but wanted some advice from the experts.

With the new neck seated in the dovetail, the fingerboard laid on the neck, and two .037 thick shims to simulate frets- a straight edge shows 3/64" above the bridge. The straightedge is between 3/8" off the soundboard.

The bridge is quite thin, at 5/16". The old saddle was 1/8"" above the bridge.
The old neck/fingerboard/fret straightedge test would touch the top of the bridge, unstrung.

I did notice, with the old warped neck, that adjusting the truss rod to lower the action resulted in a noticeable loss of tone.

These conditions seem to indicate the 3/64" above the bridge, although a slight bit higher than recommended for a new neck, may be OK because of the thin bridge and low saddle of the original set up. Is this OK?

Your professional advise will be appreciated! Thanks, stoneaxe.

[stoneaxe]

Empty post here by mistake..

[stoneaxe]

Kicking this around, If it was a normal thickness Martin bridge, .375", the measurements would be on the low side for a new neck, with the straight edge touching the top of the bridge.

Since the Gallagher bridge is thin, and the saddle had .125" height, I am going to add another 1/16th or so of set to the neck.
That should bring the straight edge to about 1/8" over the bridge.

[John Arnold]

The standard Martin bridge thickness is 11/32". 5/16" is the thin bridge, and 3/8" is the thick bridge.
IMHO, there is nothing wrong with having the straightedge at 3/64" above the bridge, provided you don't want high action.
On new builds I use a 11/32" (0.344") thick bridge, and set the neck for a 0.390" straightedge measurement. This measurement is taken unstrung on top of the frets in the center of the fretboard.
My normal action setup is 7/5 64ths (medium gauge strings). This is with a long through saddle, which IMHO is not as compatible with taller saddles as a short saddle in a routed slot. As a result, my saddle height is usually between 1/8" and 9/64".

[stoneaxe]

John, thank you for the advice!
Since it was beyond my power of will to leave things well enough alone, , before I read your post, I went and changed the set up so the straight edge is 7/64" off the bridge, and 7/16" off the soundboard just in front of the bridge.

It could be brought back to where it was, no problem- or I could split the difference .Do you think that would be wise? The bridge is a stopped slot, the action will be medium in height.

[Hot Vibrato]

Originally Posted by stoneaxe

Onward with my novice neck replacement project...
The dovetail on my Gallagher replacement neck is cut and fits fine.

I am ready to commit to the angle of the neck set but wanted some advice from the experts.

With the new neck seated in the dovetail, the fingerboard laid on the neck, and two .037 thick shims to simulate frets- a straight edge shows 3/64" above the bridge. The straightedge is between 3/8" off the soundboard.

The bridge is quite thin, at 5/16". The old saddle was 1/8"" above the bridge.
The old neck/fingerboard/fret straightedge test would touch the top of the bridge, unstrung.

I did notice, with the old warped neck, that adjusting the truss rod to lower the action resulted in a noticeable loss of tone. .

Adjusting the rod will change string height, but the purpose of the rod is not to raise or lower the action. It's there to counteract the bow that is induced by string tension. The proper way to adjust it is so that the neck is almost straight, with just a small amount of forward bow. If you over-tighten the rod, the neck will back-bow, which will indeed cause a noticeable loss of tone. If you lose tone by merely straightening the neck, then the saddle is too low.

I'm curious - why didn't you just plane the fingerboard of the old neck and refret it? I've never seen an acoustic guitar neck warped so badly that it couldn't be made perfect with a plane and refret.

Regarding your original question, when doing a neck reset or replacement, I want the saddle exposure to be 1/8" above the top of the bridge. It's hard to predict how much the top and neck will bow under string tension, so I always string the guitar up several times while I'm adjusting the neck angle.That way, I know for sure it'll be right once it's glued on.

[stoneaxe]

"I'm curious - why didn't you just plane the fingerboard of the old neck and refret it? I've never seen an acoustic guitar neck warped so badly that it couldn't be made perfect with a plane and refret."

The neck was made narrow at 1 5/8", a very thin sharp V, and had a compression rod in it anchored at the nut end that had pulled through about 1/2" inch of end grain and was bottomed out. The fingerboard was badly worn and thin also. The neck has a bow, but also a definite twist.


I dropped this guitar off at a highly respected luthier and she was going to do as you suggested, but after looking it over and consulting with some other luthiers she also recommended a new neck, or at the minimum a reset, new board, etc- no matter how that is sliced I was going to be looking north of $1000. Since I am not a pro, and money seems to be getting scarcer, I elected to make the new neck myself. The woodwork is not the hard part, it is knowing what the objective is, AKA, knowing what to do.
The folks here have been most helpful!

Although a fine sounding instrument, and a handmade one, it seems to have little collector value, but great sentimental value to me, as I bought it new from JW Gallagher in 1973.

[stoneaxe]

Originally Posted by stoneaxe

John, thank you for the advice!
Since it was beyond my power of will to leave things well enough alone, , before I read your post, I went and changed the set up so the straight edge is 7/64" off the bridge, and 7/16" off the soundboard just in front of the bridge.

It could be brought back to where it was, no problem- or I could split the difference .Do you think that would be wise? The bridge is a stopped slot, the action will be medium in height.

I went ahead and returned the angle to where it was, at 3/64" off the bridge and a fraction under 3/8" off the soundboard.
To get a better grasp of the situation, I used some shims on top of the "fret shims", to approximate the actual string height. This showed clearly the 7/64" off the bridge would result in a very high saddle.

[Hot Vibrato]

Originally Posted by stoneaxe

I went ahead and returned the angle to where it was, at 3/64" off the bridge and a fraction under 3/8" off the soundboard.
To get a better grasp of the situation, I used some shims on top of the "fret shims", to approximate the actual string height. This showed clearly the 7/64" off the bridge would result in a very high saddle.

Keep in mind that the neck will pull up some and the top will bow under string tension. The exact amount these variables affect the final bridge height will remain unknown until you can put strings on the instrument.

I've never built an acoustic guitar neck from scratch, but I've done dozens of neck resets, and a one complete acoustic neck replacement. While adjusting neck angle, I like to periodically string the guitar up (at least with some of the strings) so I can eliminate these unknown factors. That way I know for a fact it's right before I commit to gluing it in.

The fact that you're installing a neck that doesn't have frets, and possibly doesn't even have the fingerboard or rod installed complicates the procedure, simply because stringing up the guitar is at this point not an option, not to mention that truing up the fingerboard will slightly reduce its thickness. Since my experience lies mainly in repair and restoration, I'm unsure of how to further advise you for the most part.

However, since in your OP, you requested specific numbers, I'll say this regarding your "fret shims": If you consider the height of the nut (specifically the bottom of your nut slot), which is only slightly higher than a fret - no more than .005 higher, so add that to your fret height (approx .040"+.005"=.045"), an make a shim that thickness and set it at the nut end of the fingerboard. Then consider the string action at the 12th fret, which is probably around .080" at the D and G strings, and add that to the height of the fret (.040"+.080"=120"). Make a shim that thickness, and lay that on the fingerboard right where the 12th fret goes. If you lay a long straight edge across these two shims, projecting over the bridge, it should very closely simulate the actual height of the strings above the bridge with the action set to an average height. The ideal amount of saddle height above the bridge once it's strung up and adjusted should be around 1/8" (.125").

[stoneaxe]

After all my monkeying around, I had to glue a couple of shims to the dovetail, but the fit seems fine.

With .040" Fret spacers, there is 3/64" off the bridge.
With a .045" spacer at the nut, and a .125" at the 12th fret, there is 7/32" off the bridge, and 17/32" off the soundboard.
These measurements are with a straight neck, no relief, no tension on the guitar.

The neck surface is sitting about .002"-.004" proud of the soundboard, dry fit on the dovetail. My guess is, it will pull up flush when the glue lubes the joint and there is a clamp on it. Is that a safe bet?

Hopefully tomorrow I will cut the neck and headstock outline, and glue in the truss rod and spacer, glue on the headstock overlay and find or grind a 7mm drill bit for FB mop dots.
I have done a fair amount of pearl work in the past, but I want to get this done and playing, so no fancy work.

[Hot Vibrato]

Originally Posted by stoneaxe

The neck surface is sitting about .002"-.004" proud of the soundboard, dry fit on the dovetail. My guess is, it will pull up flush when the glue lubes the joint and there is a clamp on it. Is that a safe bet?

Put it in clamps! It should probably close up once you clamp it, but you shouldn't wait until you're gluing it to find out. Do several dry runs to rehearse the procedure, and make sure everything closes up and looks the same each time.

If the fingerboard doesn't sit flush when dry clamping, it surely won't when the moisture from the glue swells the wood, especially if you're using Titebond, which has a very fast initial grab. Hot hide glue is a bit more forgiving in this regard because it's more slippery, and it doesn't grab instantly like titebond. However, time is of the essence with hide glue too, because it must be in clamps before the glue cools too much.

I've had two neck resets go array because they wouldn't clamp shut after applying glue (both with titebond). They just seized up. It cost me a lot of time to steam them out and clean it up and re-fit the dovetail (had to re-do the shims too). You don't want this to happen, and it will if your dovetail fits too tight. However, it should be fitted so that the last of the gap is closed by the clamp.

It's hard to know how much the final saddle height will change due to the top and neck bowing under string tension, but I would guess that you would need to reduce the saddle around 1/32" to achieve the same string height after applying string tension (but that's just a guess).

Is the fingerboard already glued on? If this were my project, I'd install the rod, glue the fingerboard on, and do the finish work before installing the neck. That way, you can clamp it in place and put some strings on it to verify that your angle is indeed correct. This eliminates (most of) the guesswork regarding your final saddle height. I've made clamping cauls in the past, which conform to the radius of the fingerboard, but also have slots for the strings to pass through. In lieu of this, you could use a narrower block as the top caul and install only four strings, and tune them a bit higher to compensate for the additional tension of the other two strings. Be sure the rod is adjusted so the neck is pretty straight under string tension. Not doing this could throw off your numbers considerably.

For a flattop guitar, the back caul should be padded and tapered somewhat so the clamp sits square.

I also like to use a bar clamp across the back of the guitar spanning from the tail block to the neck heel. A flat, padded caul works for the tail block. For this, you'll also need to make a fitted caul that conforms closely to the shape of the neck heel. To pad clamping cauls, I like to use 1/8" rubberized cork automotive gasket material, which I purchase at NAPA. Weldwood or similar contact cement is best for adhering the cork to the caul.

This may sound strange, but I also install strings during the gluing procedure. Not at full pitch, but maybe about half tension, just to be sure that the top part of the heel is pulled flush against the sides. This requires fingerboard cauls that are slotted for the strings to pass through like mentioned above. The bar clamp mentioned in the above paragraph will eliminate the possibility of the bottom of the dovetail pulling away and leaving a gap between the heel and the side. All of this is to help ensure that the end result will be the same as your dry run. Any minor difference between the dry run and your final gluing will cause a huge change in the end result.

The dovetail should fit tightest at the bottom of the dovetail. This should ensure that it never pulls loose. Only apply glue to the walls of the dovetail and the bottom of the fingerboard. It's unnecessary and undesirable to apply glue elsewhere. Always dry rehearse your gluing procedure, clamps and all, before actually applying glue and doing it for real.

I've got several neck resets in the works, so I might post some pics here as I go. Let me know if there's any aspect of this which could be better explained in a photo, and I'll do my best to accommodate.

[stoneaxe]

Thank you for the reality check!
I had light clamp pressure on the dovetail, and it was still proud - your advice is well taken and will probably save a lot of anguish. I will fit it perfect.
The comment on having the FB glued on and the neck complete to check it prior to glueup also makes sense.
As is obvious, I do not have the experience to make the judgement calls on this sort of thing, so the advice here is of tremendous value!

The truss rod is a double acting one, an inverted steel U shape like this-
http://www.lmii.com/products/mostly-...tyle-truss-rod

I have the groove cut and a piece of wood prepared to glue over the top of the rod. I was going to use epoxy to glue in the rod and wood filler, avoiding getting any glue in the rod interior of course.