1919 Gibson A-4 Mandolin: New Bridge & Crack Repair, Pt. 2

Continuing to repair cracks on the Gibby mandolin.

You may recall that four years ago I fixed the center seam crack. Guess what? It opened up again. Gently pressing down on the top revealed the crack had come unglued. I think the length of the crack meant it was under stress and glue just won't hold it shut.

So this time, instead of just gluing it, I figured I'd cut some cleats with my new cleat cutter and put them in there for a very solid repair.

First step was to make a bunch of cleats production line style.

I won't need all of these, but it's so much fun I couldn't stop making them!

Don't look at this picture if you're squeamish.

I settled on four cleats, and then drilled the access holes as I did on the last repair.

I wanted the cleats and the cauls to conform to the arch of the top as closely as I could make them.

So I taped some 100 grit paper over the crack. I used double-sided tape for the paper, and knocked down the tack a bit by putting it on my shirt and removing it a few times.

Then I sanded a few small blocks of pine for the cleats.

Here's one of the three cauls, showing its arch.

Maybe this is overkill, but I wanted to put as much leverage onto the top when gluing the crack and cleats as possible.

Note that I labelled each caul as to its location - top, middle, bottom. Each curve is a slightly different.

Then I put sandpaper on each caul and shaped the "top" surface of each cleat using the radius on the caul. The top being the side that will be glued under the crack.

Each cleat is numbered so it would match the correct location under the crack.

I wanted to ensure as close a fit of the cleats as possible under the crack - since the top is arched, I figured I'd arch the cleats too.

As with the previous crack, put the wire though the body, then slip a cleat on, then the brass tie block, and tie the block onto the wire.

I taped the cleats down so they wouldn't get tangled up. The wires are fairly long and I envisioned a mess inside the mandolin other wise.

Then apply glue to the crack and the cleats as usual.

Thread the wires through the cauls, then pull the cleats though, wind the wires around the tension tuners, wind them tight, and let the glue dry. Again I have waxed paper over the crack so the glue won't adhere to the cauls.

This made for a very solid repair.

You can see that you need a bunch of tuners for a long crack. I have an ancient Lyon & Healy parlor guitar in the repair queue with long side and top cracks, so I'll need to cook up a few more of these for that job.

I'll do the finish touchup on the mandolin in the next post.

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1919 Gibson A-4 Mandolin: New Bridge & Crack Repair, Pt. 1

You may recall my Gibson A-4 mandolin from work I did on it a few years back.

The action on it is a bit high. I've lived with it for a while, but I decided to bite the bullet (or the ebony...) and make a new bridge.

A-style Gibsons of this era have a fixed, non-adjustable bridge, unlike F-style instruments, which have an adjustable bridge. On a more modern instrument, I would simply shave some height off the bridge to lower the action, but I don't have the heart to take a file to the original bridge. So I'll carve a new one instead.

I also have some new cracks to fix. I just procured a really cool, clever crack-fix tool kit, so this is a great opportunity to try it out.

I see a lot of these mandolins with cracks up near the fingerboard. Mine had one on the other side which I repaired, and now I need to fix this one.

The Stew-Mac crack tool kit consists of a plug cutter to make cleats and an air gun to help inject glue into cracks, as well as some wire and tie blocks (more on that later).

Here I am making some cleats for the crack. I've done this by hand in the past - but the plug cutter lets us make nice looking cleats quickly and easily.

Here's the cutter with a few cleats. Since the top of the mandolin is spruce, I used spruce. They look great.

We need to make a caul to help put leverage on the crack to level it and make it tight.

I grabbed a piece of scrap pine for the caul.

I also laid out the cleats in the approximate location I want them under the crack, and marked the caul with the location of the holes in the cleats to line them up.

I sanded the bottom of the cleat to the same curve that the mandolin has on its body where the crack is. Wanted to make it fit as closely as possible so as to maximize the tension I'll put on the cleats.

Drill holes in the crack that will line up where we want the cleats - and where we made holes in the cleat.

Cut a length of spring steel wire for each of the cleats - about 12 inches (3 cm) long.

Thread the wire through the holes into the body and pull it out through the soundhole.

On the other end of the wires, thread a cleat on, then tie a brass tie block on.

Here's the air gun. There's a suction cup on the end. Connect it to a compressor running about 10 psi.


Spread some glue over the crack, and use the gun's air pressure to help force the glue into the crack. I've just spread the glue by hand in the past, but having it under some pressure really helps get it into the crack.

The glue has a working time of about 5 minutes, so I had everything ready to go. Five minutes seems like a long time, but it goes by quickly when you have a lot of steps in the process.

I'd prefer to use hide glue, but I used Titebond because of the longer working time. No way I could do all this in the 60 seconds hide glue would start to set in.

Here's he crack with the glue injected into it. Looks good.

Spread some glue onto the top of the cleats where they will contact the underside of the mandolin's top where the crack is. Be careful not to get glue onto the top of the mandolin.

I also put some waxed paper inside the body near the crack to keep glue from winding up where I didn't want it.

Put some waxed paper over the crack so glue won't adhere to the caul.

Then I slipped the wires through the holes drilled in the caul, and pulled the wires through, until the cleats seated up under the crack on the inside of the mandolin.

Now for the clever part.

Pull up the end of the wire outside the instrument, clip off any excess, and then wind it onto the tuner/tension tool from the kit.

Then wind the tuner to pull the wire upward, and thus, the cleat up tightly into contact with the underside of the body.

Did I say clever?

So we have one tuner for each cleat.

Couple of things: the tuners are slotted, so the wire, which is a bit stiff, is tricky to get into position on the tuners. I put my finger over the slot to hold the wire down as I wound up some tension.

You don't need a lot of tension. You'll feel when the cleat is pulled up tight.

Stew-Mac sells extra tuners - I bought a couple. I would be easy to make these in your shop - using the tuners of your choice (i.e. not slotted) mounted onto a block. I plan to do this.

But overall, it's a great kit and, again the concept is very clever. You need cleats to help hold some cracks together, and this helps to clamp them into place.

Here's a mirror shot of the cleats from underneath.

You think it's hard to get a mirror into a guitar body and take a picture, try a mandolin!

The cleats look great - totally professional. And the repair is very solid.

Next time - more fun with cleats! And some finish touchup.

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ca. 1936 Regal-made ex-Banjo Bill Carson Dobro Tenor Guitar Restoration, Pt. 5: Fingerboard, Tuners, Nut, Saddles and it's done!

Home stretch on the ex-Banjo Bill Carson Regal-made Dobro tenor guitar.

I'm going to re-dye the fingerboard. I'm not sure of the species of wood used, but I've read a lot of references indicating Regal, Kay, Harmony and other Chicago makers often used pearwood for fingerboards, then dyed them to make the look like ebony. In fact, quite a few Regal ads refer to an "ebonized fingerboard."

At any rate, I used some naptha to wipe down the board and remove any sawdust residue and dirt.

This is what I've been using to stain fingerboards. Fiebling's leather dye.  It's what Stew-Mac used to sell for this use. Now I see they've changed to a brand of India ink.

I will probably switch to the ink going forward. I've used the leather dye for some time, but I have found it lacking. For one thing, it's really messy. And for another thing, as I found out on this guitar, it stains bindings. For some reason, I though it didn't, but it does.

You can see I did mask the neck binding, but some dye still got on the binding. I scraped it off, no big deal, but it's just a pain. I think any kind of dye is best for a new unfretted board. A lot harder to apply to to an existing instrument. I've done it in small areas, but not a whole board until now.

Maybe the India ink will be better. This is not something I do a lot, so it will probably be some time before I find out.

It's easy to apply. I used a small brush to paint it onto the board. And over my nice shiny new frets. The dye won't adhere to the frets, but you will need to wipe excess off. In hindsight, I should have dyed (died? lol) before I fretted the board.

The whole board after a coat of dye. The wood really drank up the dye - I did a couple applications to make the finish even.

Then I installed the tuners.

First I trimmed the dowels I used to fill the old tuner holes using a flush cut saw.

One of my pet peeves is people installing new tuners that require new holes. Eventually someone may have to replace the tuners and deal with the holes.

Sure, you can leave the holes, but that's sloppy work and leaves the holes open for moisture to get in and rot the wood. It's not difficult to find tuners that will mount the same way as the originals. The owner and I believe the originals were banjo style tuners - how hard could it have been to find some?

After the dowels are cut flush, I used red mahogany stain to finish them. Not a perfect match, but the dowels' end grain will be protected and from a few feet away, the holes won't be obvious.

These nice Five Star tuners will go into the guitar. They have planetary gears, are good quality and have the proper 'period' look.

Note the arrow showing the little locator pin on the base. This penetrates the headstock and keeps the whole tuner assembly from rotating under string tension.

Slip the tuners through and tighten them down.

From the back. They look nice I think.

Now to make a new bone nut. The original nut was cracked on the high A string, so I need to make a replacement. I use bone. It's the best for tone hands down.

I use a string spacing rule to mark the inside strings. Mark the outside strings - maybe 1/8 of an inch from the edges of the fingerboard or whatever is appropriate.

Then find a set of marks on the rule that line up with those two marks and use the inner set of marks for the inside strings. The rule was made for guitars but works fine for 4-string instruments; just need to find the appropriate marks.

I use an X-acto saw to mark the initial nut slots - just enough to hold the strings in place.

Then I use a half-pencil laid on the first fret to mark the nut. This mark is approximately the maximum depth to file the slots down to. In other words, we will wind up filing a bit shy of the mark.

The mark is not super accurate, it's an estimation of the slot depth. In practice, I put the string on, file each slot a bit, check the string's height at the first fret, etc. I like to get my fret slots so the string can be at its lowest height - thousandths of an inch - over the fret.

Here's the half-pencil. Sand a pencil to half its diameter - flat - on one side. You can't resharpen them easily, but pencils are cheap, right? A belt sander is ideal but be careful you don't sand your fingertips in half too!

I do have one of the Stew-Mac nut slotting gauges and have used it some. But it seems so clunky to me to take on and off - using different gauges for each slot - that I usually go with the old method and get the slot depths by eye.

Part of the way there. The low string is out of its slot - I was probably filing it.

Once the slots get a bit lower than the top of the nut, file or sand the top of the nut down. The final depths should put the wound strings about halfway down in their slots (half of the string exposed) and the unwound strings should sit just below the top of the nut. Hard to explain but if you look at a nut and ponder you should get it.

Note how close I am to the depth mark. On this nut, I actually wound up making the slots a bit deeper than the mark - again - the mark is a guide - it's not the final measurement.

Filing the nut slots. I have a set of gauged files. They're nice because they are not just gauged for width - they also are rounded so the slots will have rounded edges so the slot bottoms will be rounded and strings will not hang up on.

In this shot, the slots are done. I just need to file the top of the slot more round and sand the ends of the nut level with the fingerboard.

Hey, that stain came out good, huh? Looks like ebony.

The finished nut along with the plastic original.

I polish the bone up to 6000 grit and use fine polishing compound to make it look like a piece of jewelry. I also like to file any sharp corners off so the player's hand won't get hung up on them.

And the nut fitted on the guitar.

The end pin was very loose fitting in the body. So much that it kept slipping out.

So I took some toothpicks, fit them around the pin and glued them in. The pin itself isn't glued, it can still slide out, but it's a much tighter fit now.

Before you say, "man, what a redneck repair," I'll tell you that I learned this technique to fill a hole from Dan Erlewine's repair book!

After the glue dries, clip the ends of the toothpicks. They only protrude into the hole enough to grip the end pin.

I'm not sure you could do this from outside the guitar - since I had access with the resonator off, it was easy.

One other 'feature' on this guitar - the end block is not centered on the end. Note how the hole is off-center on the block - it's in the middle of the end but the block is not.

Since the string height is now changed due to the neck reset, I need to make new saddles for the bridge.

The original saddles were made from a soft-ish wood, so I decided to use maple instead. Should get better tone and volume.

I cut the saddles on my fabulous Hegner scroll saw. Thank you, TMD!

File the saddles to thickness to fit into the aluminum spider.

Overview of the fitting. I got so focused on the job that I didn't take more pictures, sorry!

You can see the saddles are a press fit into the slots on the spider.

The saddles wound up with small slots on top to hold the strings in place - those pencil marks are about where I made the slots - and the saddles are filed round on the top like a standard acoustic guitar saddle would be.

Then polished up the resonator and put it back together.

The lucky owner is really happy with it. He's a fabulous banjo player, so this is right up his alley.

The tone is very nice. I expected it to be harsh and metallic, but it's not at all. It's fairly bright, but it's very clear and almost delicate in tone, with great note separation. I believe most of the tone comes from the resonator alone - the body is so thick that it doesn't vibrate and contribute to the tone at all.

I feel privileged to have worked on such a fine - and historic - instrument.

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