Martin Neck Resetting
1931 000-45 12-fret
About the instrument
This 1931 Martin 000-45 was obviously made as a special order. In fact, Richard Johnston looked up the original factory record when he was researching his book, "Martin Guitars - An Illustrated Celebration of America's Premier Guitarmaker." He's had full access to the company archives and has turned up the most amazing stuff.
The 12-fret 000 size guitar had been "upgraded" a couple of years earlier, so this one is a late example. In addition, it was originally ordered as a left handed seven-string guitar, for a Montana cowboy musician named Horace J. Ingram. Old Horace probably doubled-up the first string, as did many of the cowboy and western musicians of the time.
The patient:
The conversion from 7-string had been done very neatly and the owner of this guitar wants it to be playable, so he's leaving it as a 6-string. Apart from the 7-to-6 string conversion it's all original and in fine condition. The only real finish damage is on the face.
Here's a shot of the back of the peghead showing the plug that covers the old tuner hole and scar from the back side:
I took this picture to show the 3/4" plug most clearly. From other angles the wood grain is more favorable and it is a very neat repair, hardly noticeable. The repaired hole in the front is 3/8" in diameter and goes right through the torch inlay.
It seems that most factories didn't change peghead inlays if they were adding strings, they just punched right through them. The hole is consistent with a Grover 4:1 banjo peg, which would have been a logical choice for an additional tuner.
We had an original 9-string D-28 in the shop a few years ago. The additional three pegs were regular 90-degree guitar gears mounted crookedly on the end of the peghead with the tuner posts drilled through the Martin decal.
Inside the original seven holes are evident in the bridge plate, which was neatly inlaid and redrilled with six holes.
The neck has pulled forward with time and the action is really high. If I lay a straightedge on top of the frets, I'd like it to just touch the TOP of the ebony bridge (providing that the bridge is of normal 5/16-3/8" height. That way with a saddle projecting 3/16' above the bridge, I'll have 3/32" action at the twelfth fret. You can see this one is no where near the mark:
By this measurement, I can tell the neck has pulled forward almost 1/4" at the nut.
Unfortunately, someone had pulled out all the bar frets and shimmed them higher to compensate for lousy action and fret wear. I wish that person had been a little more careful:
Every fret has chips and file marks around it! After resetting the neck, I'll have the fretjob from Hell.
Lets get on with it. . .
The Operation
Wide, very low tack masking tap will protect the top from radiant heat and scratches as I loosen the end of the fingerboard:
My heat source is a block of aluminum heated in the oven at 400 degrees Fahrenheit. I frequently use the electric heat blankets, but for this job I wanted the most precise control. I know that whatever happens there'll be a limit to how hot the wood gets!
I'll feel underneath to monitor the heat penetration, and when it's quite warm to the touch, I'll start testing with my knife. My knife is a regular flexible putty knife I've carefully ground to an extremely fine tapered tip. I ground it by simply rubbing it on flat surface covered by 320 grit silicon carbide waterproof paper. It took about 2 hours to get the blade to just the right flexibility, so that when I press it down to a flat surface it makes a smooth contact all the way out to the very edge. I keep the blade sharp and polished by buffing it with emery compound on my buffer at least once a week.
With the block still in place, I'll start lifting the fingerboard. Once I'm confident that the glue joint is parting cleanly, I'll remove the block and loosen the fingerboard right up to the 13th fret.
Once the fingerboard is loose, I'll pull the 13th fret and drill a 1/16" hole through the fret slot and into the pocket at the end of the dovetail joint:
Now I have an access hole for my steam needle
My steam generator is a small pressure cooker to which I've added a hose fitting. That way I still have the pressure relief safety valve in place. When the pressure gets too high, the valve lets off some steam and my hose won't blow out. Although I'm steaming the joint from the top, I get good penetration of heat and moisture immediately through the joint, thanks to the 1/8" gap at the end of the fingerboard.
Look below the fingerboard, and you can see the cloud of condensed steam emerging from the edge of the fingerboard from frets 12 to 16. The steam is shooting out almost all the way across the top and condensing on the finish. The steam is HOT as it comes out, so I'm wiping furiously with clean cotton rags to keep the heat and moisture from damaging the finish.
For more modern instruments I have a fixture to press the neck out while I'm steaming. This guitar is a very valuable and delicate one, so I'm taking my time, steaming more slowly and removing it without using my clamping fixture, which gets in the way of the view and wiping effort.
By waiting for the steam to do its work, I'm able to remove the neck without any finish damage:
It's time to cut the heel of the neck to change the angle. I can make a pretty good estimate of the amount of material I must remove from the neck by a simple calculation. Remembering that the neck had pulled forward nearly 1/4" I can make a simple calculation:
Essentially, the neck had pivoted at the 12th fret where it joins the body. If I want to pivot the neck backward 1/4" all I have to do is divide the distance from the 12th fret to the nut by the distance from the bottom of the fingerboard to the heel cap. If I then divide 1/4" by that amount I get a result of a little less than 1/16" of material I must remove at the bottom of the heel to allow the neck to pivot backward the right amount.
I'll then scribe a little line on the heel cap to indicate the depth of cut and I'll place the neck in my special fixture. (I only use this fixture on rare occasions when I'm working on a neck that needs to have a substantial cut made, and which has a delicate finish.)
I can adjust the table of this fixture so that the neck protrudes exactly the amount I need, namely 1/16" at the heel and zero at the fingerboard. I have a flat chisel with an extremely fine acute cutting angle. I use this chisel in a diagonal slicing motion to slice off the end of the neck where it touches the body:
You can see the light area where my chisel sliced off the neck, and the dark where the original undercut surface still remains:
Now, I'll undercut the area from the finished edges to the dovetail, so I won't have to fit too broad a surface when I'm making my final adjustments:
I'll make my final neck angle adjustments by slipping fine sandpaper (180 grit) between the body and neck, holding the neck in place, and drawing out the sandpaper. That way I'll get the neck to fit exactly, even if the body edges are not perfectly straight (they never are.)
After each pull of the sandpaper, I'll check the neck angle and "string line" (side-to-side alignment) with a straightedge.
Now that I'm confident that I've set the correct neck alignment, it's time to refit the neck. I'll prepare a couple of mahogany shims and sand them to a taper by holding them on my coarse sanding plate and block sanding from above with finer sandpaper:
I'll slip the shims into the dovetail pocket and jam the neck in on top of them.
When I take the shims back out, there'll be shiny pressure marks where they fit against the sides of the joint.
I can also use carbon paper, chalk, or dentist's articulating paper to highlight these areas, but here the shiny spots are very clear. I'll scrape and block sand the shiny areas and try the joint again. By repeating the process I'll eventually get the shims to fit very tightly with the neck sitting correctly in the joint. At this point I'll recheck with my straightedges and if everything's all right, then I'll glue and clamp the neck with cauls to protect the fingerboard and body.
I used hide glue to reassemble this vintage Martin because that's the glue they used when it was built, and that's the glue a future repair tech would expect to encounter.
Here's the finished product.
The heel shows no signs of removal and fits just like it did from the factory.
I was very careful to preserve the alignment over the body because of the pearl trim around the end of the fingerboard:
After restringing with light gauge steel strings I can tell the original bridge and saddle combination is way too low! If I make a new saddle to rise 3/16" above the bridge, this guitar should have ideal action.
The neck reset is completed, the angle is set correctly and if the frets were in good shape, all I'd have left to do would be to level the frets a little and make a new saddle. This guitar would play like new.
And it will, after refretting. . .