Model D12-20
(Originally a 12 string)
Converting to Short Scale Six String D12-20S

Circa 1965
Rosewood Back
Mahogany Sides
Spruce Top

Repair to play,
Replace broken 12 string neck with 24.9 scale  6 string neck, solid peghead
Thin neck to modern specs
Change 12 string bridge to 6 string, Repair top and side cracks
 Finish will be "Golden Era" sunburst
D12 was introduced in 1931

OK....almost a Martin!




Scraping finish away from multilaminated binding, preparing to remove top plate

Hang it out of the way and safe

Working a blade in to see how it feels.
That's all for now, going to Arlington to watch a Rangers game.

I decided that it was going to be a disaster going in thru the top of this instrument and I decided to stop, and reattach the binding.

This is a multilaminated binding that is old and brittle and you can see it coming apart as I reattach, so I am sealing that as well, as I go.

It will be getting a complete finish so I will not worry , it is over finished anyway.

All reattached and profiled, sanded high spots around cracks, and all finish removed.
Now for a new battle plan...

Backplate removal

Taking the T-shell off, the other will ride on the backplate

That's the original seam, not a break

Im using the 3 parts water, 1 part alcohol to loosen the glue as I go, very slowly it is releasing

Around the neck and end block, wetting and getting started before I get the knife into it

Both blocks are released, not too much residue to deal with

All and all, Id say that came off pretty clean and from the looks of it, Im not the first one in here
There is some old repairs and some glue that doesn't look factory

As well as some missing kerfing top, a few chunks here and there and I can see where someone knifed it apart before, there is some tell tale marks of it

And not from me...this is all the shavings I have and that is off the end blocks

No cracking n the backplate, that was my goal.

tacked down flat with some binding tape while it dries that little bit of moisture I used, you can see old repairs on the back as well

Glue was shot into the cracks on the top and sides, a few cleats here and there

Thin wall with cloth tape for reinforcement

Keeping it flat


Heating with the iron

A little at a time

One more pull

Not too much debris

The new bridge is smaller so Ill dress up that area

The new plate is about half as thick as original

Taking out the center crossbrace since it will now be a 6 string

A little heat and steam, I wont get things too wet, drying and heating as I go

Came off clean, now for bridge plate

Steam and heat, slow going, very strong bond

No damage, I can use it for a template

After filling the divots and leveling a bit
That one hole that is low needs a plug as can be seen below

After removing the old bridge indents and profile and looking at it here with the 6 string bridge, it will look clean in that area now

If I line it up with the upper set of holes that one hole is barely visible.
I will work hard to get the scale exact again since the old bridge had been on and off a few times so I will measure it all out before mounting anything

I sanded the bottom area fairly well here and shot a sealer on it to see what dark areas were left, I should be able to get it all pretty clean for the new finish

Back in the press


The neck I will use is a short scale 12 string neck that had a long peghead which I have already cut off to the 6 string length and have rough shaped it on the belt sander
The neck beside it is a new Stew Mac 6 string blank that Im using for a template.

Drilling tuner holes


Looking at the thickness of the template, I will get close to this then wait for the fingerboard installation to profile it to the board

I will take off the bulk of it quickly with the Sureform

The rest with my drum sander

I'm right on the template profile, should be good to go.
I learned how to hit a profile  when I was using Hughes Diamond drilling bits in my oil field days. :)

Ready for truss, fingerboard and final shaping afterwards

Bridge plate

i will use rosewood and Maple laminated, the rosewood against the body

Scoring the rosewood to get a good glue bite

Last dry fit

Hide Glued and go-bar clampage implemented

After curing
Flipping over the top which I waxed papered to save me some grief sticking things to the table

Ready to smooth up for the bridge, that will not be placed until the neck is on, for scale purposes


Making a solid truss, I have a 1/4 round hollow rod that fits perfect, tight in the sides and exact depth

adding a standard nut blank

That gives me proper placement to join at the body

Ill drill some index holes into some fret slots

using brass tube for index pins, this will impair drift under clamping

Dowel on each end of the rod

Hide glue encapsulation

Board on and binding tape compression
I will clamp it  on a flat bar as well, for 3 days

Frets back in and sides dressed, board oiled for the first time, more will follow

Sealer coat applied


I have the dovetail profiled for the new neck by using soap stone to mark and index and shaved wood until I contacted the body

Cleaning out the debris so that I can cut a section of spruce
That's not in short supply, My Log Home is made from Englemann Spruce and I have about 10 logs of it so I thought I would build a little log home in this Martin :)

Cut to fit the radius leaving room for the purfling it needs and ready to glue in
Not worried about the little gap where the original chipped a little, that's all under the fingerboard anyway.
After it cures I'll trim it over the dovetail

Hide glue applied

Cleating the top cracks with Spruce cleats

Cloth repair on the side cracks

Pressure applied to push crack together on the top lower bass bout, and some more cloth on the body.


Neck depth and width shaved to the specifications set out by Collings Guitars for the C10 model

A small vestige of that thumb stop is left for now.
Ready for final sanding and install

Final prepping for neck install. roughed up all surfaces that will receive glue

All outside sanding with the block is complete, all sealed  cracks are leveled

Now....wait.maybe this neck can be utilized, its just lying around here.....

But this one fits nicer

Heel tip cut off to length, good tight seal to the body

Inside repairs complete, inside shot with 10 parts lacquer thinner and one part lacquer, as an ultra light sealer
A little insurance in our Texas clime.

Mahogany veneer stripping, to use as build up where kerfing was broken out

After its to height, i can sand it all to profile in each area

I plan a temporary wood screw here to pull in the heel for retention during gluing
I have no fancy way and my customer knows me and I know him, so lets "Make hole"

All is now ready for glue-up, so Ill pull that out and heat some hide glue

Glue in the dove tail...
Radius block  used as a caul, for the extension to top pressure with cammed clamps.
Good squish from the glue upon clamping

Bearing on the crossbrace
Screw back in for a tight pull

A crossbar under the body to get a clamp on the heel, that's as full of a pressure as I can get,  time to cure 2 days under 100 watt lamp to pull moisture out.


From face of nut to forward wire at 12th fret is 12-5/16, making the total scale 24-5/8"

Making an index mark over the bridge plate

I am trying some tinting with an aniline dye, 3 color and taking a look with the parts setting on it and binding scraped clean.
There are some stains too deep to come out so we will see how it looks when the clear hits it, I'll protect the bridge area and then glue it down before spraying any more clear on the top, then I'll add on the back and move forward


After glue and clamp, adding on more clear to the top and then on to the back install
Sides have been shaded to subdue the reddish mahogany, and the back will receive the same treatment

I have the watchdogs looking after it

I'll get it cleaned up and ready

There are a few loose braces I'll need to tack back down

Curing for a day

Lost a set of pics so I'll pick back up with the back on and the outside binding, scraped to profile

This is a good time to notice how brown the neck Mahogany is compared to the body

Reshading around the bindings and on the back completed

A crack appeared the next day, and it is an old crack that has a long cleat already under it
I'll fill it with hide glue and try to get it to flow in and on top of the cleat, then add a little pressure

A little wax paper to keep the clamp from sticking

Crack stabilized and first neck tint added

one coat of clear to seal it, now I can look around to see if I need to shoot any glue into small cracks and crevices that may need it.
After that Ill add some more clear

Even with the neck taking the same tint colors as the body with an addition of reddish brown, it still wants to look a little more  brown than the body.
Refer back to pics of unfinished neck

3 more coats to go, then I will buff it and check the fret level, add the pickguard and see what see will do


All buffed and polished, pickguard installed, new end pin
I did not do the thick coating, I did like the old Martin with 4 coats production finish, and then I  0000 steel wooled, then machine buffed and polished.
I'm staying will all Martin stuff for the heck of it
Tuners installed, I used 2 bushings since it was missing 2 of the originals

Wetting the Martin decal for the peghead

unfortunately, it must have been very old, it just fell apart when I wet it down.
So Im looking for another if anyone out there has one let me know

After I got the 2 outside strings on I saw a problem...
The bridge was set to what I thought would be accurate side to side but I may have gotten a little drift during clamping, Im off 1/16" to the bass side so I have to come up with a battle plan

Plugging the old holes with hardwood dowel

Sanded to profile

Darkened with dye

Using StewMac gauge to determine where the new center to center should be.

You can see how far I have to go over

Index holes drilled

Back up to full profile, another coat of dye and some tung oil to seal it

Strings ride good on the neck now so I dodged that bullet...
Working with a temporary saddle and nut... I want to cut  new ones from bone for this setup.
I have it to tension and I have 90 percent good fretting with a few buzzes here an there but there has been no leveling on the freshly installed old fingerboard so I am glad its this close.
Mental note to to self: pull plastic shielding from pickguard, that's why it looks dull in this pic!

Neck is very stiff with the solid truss so a couple days under tension with a little heat applied will come before a fret leveling but Im hopeful now I can get it the rest of the way back into at least a nice player with a spiffy look.


The neck is not reacting properly under tension, it has a twist, not a bow or warp, and it is to the treble side making it low  and giving me fits so I went to checking all the old fretwork since I haven't done leveling as I say, just testing it as it was, and after being under tension I will have another battle

Using my 16" radius block sander standard for Martin  with 320 grit...,  I saw that the fingerboard was at another radius which measures 20"so I tried to cut it back to a 16" but on these used frets I didn't make it, this is where I stopped
You can see 1 fretwire caught up with it, that's the place where the dust is solid at 11.

So now I will pull them all, and then I will change the radius of the fingerboard to 16" from 20" and then refret with tall wire and try to catch up with that twist in the fretwork.

Long 16" block arrives, lets get some 320 on it and level the board

First passes show it at 20", edges coming off first, now we will move along in stages as I block sand

Here I am down to a couple of first position finger divots that will not affect the fretwork, and one light depression at 9 and off the tip
That's as far as I need to go with the block leveler, the rest will be handled in the frets

reslotting to proper depth

This tool has one use, to bend flat fretwire into a radius

Nice to have, when you need it which is a banjo shop
The wire Im using is tall and I will stop it at the body and go with medium wire to the end.
The tall wire is made especially to help on pesky necks.
The smaller wire will help me to get the final result in the final leveling to make this neck play out.....I hope.
Also, I am slotting at .025", and this means less pressure on the fret tang, Im not looking to get more tension, its already a tight neck.

Fret tool with radiused insert installed , sealing as I go

This is as far as the tool goes, I will work by hand here
I have nothing fancy so I will take my arbor from the tool and use it to drive the final wires in

I can tap on top of it  to seat the frets

All in for the big wire. tapering the sides down

Oiling up the freshened rosewood, its really nice looking again

Now this time, I got getting contact almost immediately on the leveling with only 320..., so all is much better than before, I'm optimistic

All ends dressed, everything is ready to test out

I ordered a radiused and compensated Martin saddle from Stew Mac, that is unbleached bone for the old look

Now to dress off the ends of the saddle to fit the bridge contour and I'll be there for Jerry to give her a test run.


Its fretting in all the places it wouldn't before and seems nice and clear
From what I see, its 95 percent better than before, I need to see how it acts settling back in, and maybe a tweak here or there but it just may end up a player yet.
Thanks for watching, Vinnie