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Transcript lightly edited for readability — filler and crosstalk trimmed, tool and proper-name spellings corrected. Speaker attributions added where clear.
00:18 — Q1. Tools for shaving back braces inside the body
James: Hello everybody, welcome to Council of Elders — we’re going to jump right in. This one is posted by John Layman: tools for shaving back braces. “I’m re-topping the guitar, and while it’s open I want to reduce the mass of the back braces. Since the sides are in the way, I can’t figure out how to cleanly cut the excess brace wood away — everything I’ve tried involves the handle hitting the sides and preventing a controlled, clean cut. Is there a tool, say a pull-type finger plane, that I can work from the edge to the middle of each brace?”
Max Monterosso: I think what he’s looking for is the bent-handle chisel. Jonathan, you’ve got one of those?
Jonathan: I may have one of those around. This may be crazy — it’s a relic of my grandfather’s, and it’s for boats. It’s a pull plane on a hinge, and it’s slightly convex. Probably too big for this, but if you had some smaller iteration of something like it, I imagine you could use it. It just came to mind when he showed the picture.
Like one of those old straight razors — for a giant.
Fun fact about that tool: it’s actually the basis of Ken Parker’s “Noah’s Ark.” If anybody has watched Archtoppery, the plane he uses with both hands — the one with the 12-inch radius — is built from that plane. Ben has taken one of those, disassembled it, and made the tool Ken Parker had been making for himself; Ken had no interest in selling or producing them.
James: StewMac has a butt chisel — you can see the angle there.
Couldn’t you just get in there with some violin planes? — If he’s trying to taper it down into the kerfing, that’s where the bent chisel earns it, but violin planes will definitely take the lateral mass off the brace.
Dan: I use the little tiny spokeshaves when you’re getting near the edge and want a measurable shave. They come in three styles — one’s dished all the way around, one’s curved in just one direction, and one’s flat.
Are those Ibex? — The box says Alden. They’re old — you can’t find those anymore, though Lee Valley makes minis.
James: The Lee Valley miniature hand planes are awesome — super useful. The violin ones go down to about half an inch long. There’s a tiny shoulder plane and a little block plane — you can see my hand there for scale. They look like Matchbox toys, but they are really, really functional. That’s the Veritas line from Lee Valley. I’ve also got a whole set of chisel bodies — just a bolt and a little ball, I think from StewMac — and I’ve made different pull handles for them. Wood River may still make something like that: big chunky chisel bodies with a hole for a mount.
Would a router plane work, on a sled? — Not easily; they’re too big. Stanley made some small ones, but the footprint is still much bigger than a finger plane. Butt chisels are small and short too — or go to the hardware store, buy a cheap chisel, and just cut two inches off it.
06:09 — Dan: I’ve got a Harmony body here that looks a lot like the one in his picture. This Two Cherries bent chisel works okay for the last few inches toward the sides, but there’s no good way to get all the way in. When I shape braces, I often put the scoop down — bevel down, shoveling it out — and I can pretty much get center-out on every one of these. The little butt chisel definitely fits in there well. And on his comment that he can’t reach the center: pretty much any finger plane can knock out the few inches in the middle, so you can get the outside with regular chisels.
James: That’s a bunch of options for getting into the different areas — hopefully that covers it.
07:20 — Q2. Favilla classical bridge reglue — Part 1: saddle position & compensation
James: Moving on: a classical guitar bridge reglue, from David. “I have a Favilla classical guitar on the bench, in for a bridge reglue — a low-to-mid-range classical made circa 1960, and an heirloom guitar for the customer. He basically wants it back in playing shape. He went away on vacation, and when he returned the bridge had delaminated from the top, taking a fair amount of finish with it. It also appears someone globbed superglue on toward the back of the bridge at some point, which I’ve begun removing. A few questions. One: is there a universally accepted way of positioning a bridge saddle on a classical guitar? The middle of the saddle on this one appears to have been placed at exactly the scale length — 25.125″ — without compensation.”
James: “Two: I’ve planed the underside of the bridge flat rather easily, but the area of the body where the bridge sits has a distinctive bulge, which I’ve tried to illustrate — I’m wondering what the approach should be here. And three: once one and two are resolved, then comes touching up the finish. Assuming I have the order of operations correct — the original finish appears to be nitrocellulose lacquer, and I was considering tinting nitro and brushing it on. It may be unorthodox, since I never see anyone brushing lacquer, but I like the idea. Thoughts on this approach would be appreciated, as well as how you’d approach it personally. Thanks, David.”
Doug Proper: Most classical guitars don’t have a compensated saddle — it’s fairly straight. As for the scale being exactly 25.125″: I’d question whether that’s actually the scale length. He’d have to double-check where the median of the scale is — the center of the 12th fret. If he measures nut to the center of the 12th fret and doubles it, my suspicion is he comes up with 25″ even, and that eighth of an inch — about 125-thousandths — is a normal offset for a straight classical saddle. In other words, the compensation may already be built into the number he measured.
David: I did check the scale length — nut to the 12th fret is 12-9/16″; 12.5625 times two is 25.125. And my 25.125 is to the center of the saddle, going by the outline of where the bridge sat. I’m not a hundred percent sure where it was originally placed.
13:32 — Doug: Okay — so there’s no calculated offset in this guitar, which could very well be because it’s an inexpensive instrument and nobody cared; they were making guitar-shaped objects. But here’s the bigger point: the bridge location has already been decided for you. If you move the saddle to some “universally accepted” position, your bridge no longer matches its footprint on the guitar and you’re exposing bare wood. In a repair, where the bridge goes is where the bridge was — if you’re reusing the old bridge, the saddle location comes with it. Move it even a sixteenth and you’re exposing wood in front of or behind the bridge.
David: Sure — in this particular case I think I’m boxed in. I was mainly curious in general; I haven’t seen much literature on it.
15:26 — Doug: In general it’s the same Pythagorean math you’d use for any acoustic saddle offset — somewhere in the neighborhood of 100 to 115-thousandths. But a classical saddle is never slanted toward the bass side the way a steel-string’s is: nylon strings stay so close in diameter from treble to bass that there’s no need. You take your actual scale length, use the height differential as the right angle of the triangle, and work out the hypotenuse against the scale length — that differential is your compensation offset. That’s the calculation if you’re making a new saddle, filling and re-cutting the slot, or rebuilding the tie-block area with donor wood. I don’t know about “universally accepted,” but that’s the mathematical way of knowing where the saddle is supposed to be. In this circumstance, though, you’ve been tasked with getting the bridge back on — not improving the intonation.
Did that answer that part of the question? — It did. Satisfactory.
17:37 — Q2, Part 2: the bulge under the bridge footprint
James: Moving on, David, to the second part: you’ve got a flat bridge now, but there are humps in the top, which you’ve drawn out in an illustration — and you can actually see it visually here; it follows your map.
What does it look like on the inside — have you looked at the braces?
David: I have. Everything appears to be glued down as it should be — that was an initial concern when the guitar came in, but everything is in place. But where that hump is, when I press down on it I can physically move it. That’s the concern: what to do about it.
Ian: Well, David — what’s the budget on this guitar?
David: I spoke with the customer, and we’re probably looking at somewhere between three and six hundred for the whole repair.
Doug: From a diagnostic standpoint — did you take a piece of plexiglass, a 1×6 or thereabouts, and clamp it to the face to see whether that flattens out under clamping pressure?
David: I didn’t do that, but I did lay a straightedge on it. There’s a pronounced bulge right where the bridge should be, and a bit of a dip to the left, below the centerline. I exaggerated it in the drawing.
Is that from being swelled, or from lifting grain? — Honestly not sure. The top may just be warped.
21:08 — Ian: The thing this guitar has going for it is that it’s nylon-strung, so you’re not fighting the horrendous tension of a steel-string. I would fit the top to the bridge and the bridge to the top a little — split the difference — to get as much surface area making contact as possible. But do what Doug is saying first: a dry clamp-up, and see whether the slack picks up and it flattens out. The name of the game is maximum gluing surface without putting so much pressure in the clamps that you build tension that works on that glue joint down the road. If it’s missing wood where the bridge pulled up, you can put a little patch in, but I don’t personally like patching over the top — without long grain in there it tends not to do much good. Fit it, glue it, and ship it on down. And if you want a do-over available, get all the old adhesive off and glue it with hide glue — if it ever comes off again, you can take another swing without it being destructive.
David: A quick question on that — what about sanding or scraping the bulge out, and going that route?
Ian: That’s exactly what you want the dry clamping to tell you first: whether that bulge deforms into an actual gluing surface when you clamp it up. If you take the bulge out and then clamp up and wind up with a dip there, that’s a bad result. Chances are pretty good it just needs to be reduced and brought into line — but clamp it first. If the bulge is impacting its ability to come together, you’ll see it: a weird gap around it, or you’ll find yourself putting more pressure on the clamps than you’d like.
24:46 — Doug: Once you’ve got the whole area cleaned up, make a plexiglass caul — an eighth or a quarter inch thick, exactly the size of your bridge — and clamp it down as if you were gluing the bridge, without glue. You’ll see through it and watch exactly what’s happening underneath, instead of imagining what’s going on under a wooden bridge. If you can sneak feeler gauges in and you’ve got gaps all over, you’ve got fitting work to do — whether that’s shaving the hump out of the wood a little, keeping an eye on how thin you’re making the top, or taking a carving knife to the bottom of the bridge to fit it to the top, though then you’re making more work for yourself. And if that puckered area flattens out on its own under the plexi, you’ve just got a punky, not-so-healthy patch of wood — which is going to swell anyway when it soaks up water from a water-based glue.
It may not be coincidental — that hump really seems to be following the grain direction there. “That’s a good observation.”
26:52 — Q2, Part 3: touch-up — why not brushed-on tinted nitro
Ian: David, that project is pretty hard to touch up — to actually improve — without a lot of effort. Definitely clean up the superglue; nobody needs superglue all over their guitar. And see that chip out of the finish at the leading edge of the bridge? If you want to address it, level it off — tape to your bridge glue line and drop-fill with Fill n’ Finish. A hard, crisp chip edge like that has all kinds of surface-tension issues for any color you float over it: lacquer or shellac will grab those edges and it’ll look terrible. Honestly, right now that’s in a neutral state — it looks like an old guitar that had its bridge fly off. And believe it or not, it is possible to make it look worse than that.
28:45 — Doug: Let me chime in, because I want David to have a direct answer to the question as he posed it. The thought of tinting nitrocellulose lacquer and brushing it on sounds like a fantastic idea to most people doing touch-up — right up until the first time they’ve done it. It’s a recipe for disaster. The color is suspended in a solvent that evaporates, so it never looks like what you put on wet. Then the solvents in your second pass penetrate what’s beneath, everything blooms up, you’re re-dissolving color with more color, and it winds up looking like something you’d normally make in a slow cooker. My experience with brushed, tinted-lacquer touch-ups: that’s a rodeo I never want to sign up for.
30:26 — Ian: James, bring that picture up again. The color of this guitar is not in the lacquer — it’s in the pore filler, plus a clear coat that’s yellowed over time. Maybe there’s a toner coat; probably not. So even if you mixed up that exact color, got it into a jar with lacquer, and got it on in one shot at the right density, it would still look wrong — very good from exactly one angle and ridiculous from the rest — because that’s just not how the color was arrived at on this guitar. Unless the stakes are really high on a valuable instrument, you can’t get there from here without a lot of consternation. And practicing finish repair on customers’ guitars — Doug could write an entire book on why that’s a bad idea, but it is a bad idea. With lacquer especially, your solvents interact with the parent material, so every swing you take softens the surrounding finish and makes the area of effect bigger. Then you get angrier, and your pants get sweatier, and you get something that looks halfway decent and think, “I could do better” — and you can never get back to the one that was actually halfway decent.
And it’s very possible it looks good in the shop — and you walk out into the sunlight and it’s very different.
On repairs like this I have to ask myself: is it better to have a guitar that looks like it’s had the history it’s had, or one that looks like someone’s really been in there goofing with it?
33:23 — Doug: If you are going to have a go at touching it up, have the conversation with the customer beforehand: the plan is a minimal touch-up so it doesn’t draw the eye — all the colloquialisms we give our customers — and the expectations for “making things disappear” are extremely low. A job like that means employing the smallest of techniques, not the most heroic. A little shellac with a tiny bit of amber — or amber with a touch of red or brown — just to dot some color in after the bridge is glued on, so it isn’t stark yellow screaming from across the parking lot; or a touch-up pen. But by no measure are we trying to make it look like nothing happened to this guitar. The least heroic, least adventurous effort wins.
David: What about generally sealing the wood — is there any concern with bare wood and moisture in the meantime?
35:14 — Ian: Once the bridge is glued on, it’s such a small area that a little shellac on there is pretty low-risk. But once again — everything you do draws attention to that spot. Right now it looks like finish fell off this guitar; you didn’t make it fall off. The moment you touch it, it looks like David did something to this guitar. And if you’ve got a chip with a hard edge, whatever you put in there will penetrate a little, darken the spot, and lip up toward the crisp edge — and now what are we doing? Building it to the tippy-top, sanding it out, buffing, matching sheen? Or is it just a layer of lacquer sitting in the bottom of a trough? A little shellac to seal it, fine — but everything you do on that becomes yours to own, rather than a guitar that’s simply got a chip on it.
David: That’s definitely what I needed to hear — do-no-harm seems like the play. I’ll also talk with the customer and see what they have to say.
Keep in mind, you could be the guy that nails his first touch-up right away. — And that’s important to say: we’re not questioning anybody’s skills. We just know the pitfalls we run into on this type of work.
37:43 — Doug: That’s why I always recommend the least heroic option first. A small touch-up is an act of camouflage, not finish repair — you’re making your interaction with the guitar less noticeable, not refinishing. Compare the series Ian did on that koa guitar: a sizable area, deep in the weeds on color matching and spraying, multiple applications over weeks. Something like this should be inside an hour, just to make it look better. And experiment somewhere that isn’t the guitar — a donor piece of mahogany — or on the areas under the bridge footprint you’re about to glue to, where you can scrape the shellac off afterward. Touch-up pens, shellac with a little powdered pigment, the ColorTone stuff — all fine. But once you start thinking you’re going to mix color into lacquer and ooze it onto a guitar with a brush, you’re signing up for a pretty involved rodeo.
James: So step one: don’t. “Or at least think deeply.”
39:53 — Q3. Heat bubbles in an Eastman DM2’s “antique varnish”
James: Next one: tiny bubbles. Great song, by the way. “Here you’ll see pin-tip-size bubbles — nitro finish; it got hot in the case. They’ll need a light amalgamator mixture applied to melt them back into the surface. I’m looking for advice on the recipe for said amalgamator. Straight retarder? Do I need lacquer in the mix I apply?” — from Little Creek Instrument Repair. There’s bonus information: the guitar is an Eastman DM2, and he doesn’t know the original finish schedule — “it’s nitro, I know that much.” And Tony in the chat says: “Don Ho, man.” Excellent reference. Michael Bashkin — you ever seen anything like this before?
Michael Bashkin: I have seen that before. It could be that the pore filler underneath is no longer adhering — it’s separated from the lacquer, and that’s what gives you that little bit of opacity. As for the lacquer question: I don’t think you’d need to add lacquer to a retarder to attempt this — then you’re actually building something up on the surface, and if you’re doing a spot repair, at that point you’re probably better off overspraying the whole back. As with anything in finish work, test it somewhere else first: pull a tuner and try a little underneath it, and see how the retarder behaves on the existing finish.
42:34 — Doug: You said this is a DM2 — is this the gypsy-style guitar? Because if it’s the gypsy-style DM2 from Eastman, from what I remember that is not a lacquer finish. It’s what they affectionately refer to as an “antique varnish” — an oil varnish underneath a shellac — and if you spray lacquer retarder on that, you’re going to have a bad day.
Ian: A word of caution even if it were lacquer: the idea that retarder is going to melt that back down into the pore fill is a long shot. Like Michael said — if you want to give it a whirl, give it a whirl small, under a tuner. And don’t spray retarder on the way you’d spray lacquer: mist it, go slow, work in little bits. If you go heavy and actually penetrate that full film thickness, you could be waiting three Christmases before it’s ready to be brought back up to a shine.
44:48 — Doug: If you’re sure it’s lacquer, that’s one thing — but if you’re not, be very careful how you proceed. Eastman’s fascination with alternative finishes has not been without risk, and you see this on a lot of their archtops. [The spec sheet comes up on screen: “Finish — Antique varnish.”] There it is. That’s an oil-based, brushed-on varnish over a hand-rubbed shellac — and that would also explain the tiny bubbles: an incompatibility between the oil varnish and the alcohol base in the shellac gives you exactly those little delaminations. Manufacturers love terms like “spirit varnish” as if that’s a definition of a finish; it isn’t. If he wants it truly gone, he’s talking about sanding and then shellac repairs — French polishing over it — and that depends on how well-developed his French polishing skills are.
Sometimes the answer is: you can’t build a time machine. What’s done is done.
48:26 — Q4. “Help me pinpoint my mistakes, please”
James: Next: “Help me to pinpoint my mistakes, please.”
Doug: Ron and I spent a good amount of time on this one-on-one on Sunday — I don’t think there’s a lot to be gained trying to unpack it publicly.
49:04 — Q5. Replacing a Yamaha System 19 preamp in an LD-10E
James: “Hi folks, newbie here, so please bear with me. I have a lovely early-’90s Yamaha LD-10E acoustic in for repair — I think all solid wood, made in Indonesia, and a lovely-sounding instrument. However, the electrics are letting me down. The System 19 preamp has a PCB populated with SMD electrolytic caps; many of these have leaked and destroyed the pads underneath, and repairing the traces is nigh-on impossible. So it looks like I have to replace the preamp. Does anyone have a schematic for a preamp I can build? I need two piezos in, treble, bass and volume, as well as a blend function. I may be forced to fit a Fishman pre, but I’m loath to cut a large hole in such a nice guitar — I’d also need to patch the blend-pot hole near the neck, though I could make a patch from the cutout wood. It seems this is a common failure point for this preamp series — has anyone else had problems with a similar system?” No pictures with it. Anybody want to tackle that?
That’s not something I’ve done. — Looks like he got an answer from Tony in the chat.
Not to be too snide about it, but I’ll tell you what I told everybody toward the end of my career working in a shop: at this point, I only really put in K&K pickups.
James: Nobody else? We’ll go with Tony’s answer, then.
51:39 — Q6. Gibson B-25: the chewed-up bridge plate
James: David Helmer has a free-range question. David, what have you got?
David Helmer: I reglued the bridge on this old B-25 for the music store I work for, and this is the condition of the bridge plate right now — I took the photo an hour ago when I strung it up. The guitar’s already sold, and I know who’s buying it; at some point it’s going to end up back in my shop. I’m trying to figure out how to encourage them to take care of it as the years go by, because eventually this has to be addressed. The belly behind the bridge looks healthy, though.
Ian: It would have been a lot sweeter to pull that bridge plate while the bridge was off, and get all that apparatus out of there.
David Helmer: I totally agree with you, but I’m switching jobs and just wanted to move on — it’s holding. And all the bolts make it monkey business.
Ian: It’s a B-25 — what’s the rough value on these right now? Low twos? “Two to three — maybe three-five. It’s a ’61, apparently.” So it’s in the realm of needing to be taken seriously. And the move of grafting something onto the back of that plate — Mark Steppman will pull your card if he finds out you did that. You could try taking the nuts off and getting the bridge plate out. You could graft something over the top of it with hide glue that’s easy to remove later — though I don’t really see how that would work. Anybody got ideas? James, you got anything with your new laser that would help?
Are those bridge-pin holes not even lined up with the back of the plate? — They’re off, yeah. And the last machine screw sits about three-quarters off the bridge plate.
Nothing for nothing, but that’s a candidate for a new bridge plate. I can’t think of a better one — you’re asking for a point right in the center of the bridge, where the whole top is folding at the seam of that plate.
54:48 — Doug: One other thing to point out, David — see that red adhesive squirting out at the front of the X-braces? That’s what David Collins calls Resorcinol. And everybody here can tell you: you’ve got a 50/50 chance with that stuff. Fifty percent of the time it’s the most tenacious stuff you’ve ever met in your life; the other fifty it falls right off. If you’ve got the tenacious half, you’re screwed getting that bridge plate out. And if you’ve got the stuff that falls right off, that guitar’s got one foot in the grave and the other on a banana peel anyway — the braces would be barely hanging on.
David Helmer: There isn’t a loose brace on the top or the back at all.
Ian: So it’s not an easy job. In my experience that stuff doesn’t care about heat — at least not the heat you can apply the way you would to take off a bridge or a bridge plate — and it doesn’t care about moisture. The vectors for making it fail are really limited, and you might wind up taking that whole bridge plate out by hand with Ibex violin planes. That’s not fun.
David Helmer: Would Max’s sander be the move to get it out of there, with all the hardware out of the way?
Ian: You could definitely give that a whirl. It’ll get you so far — whatever its radius is will leave you that much remaining next to the X-braces, and it will take a long time. “You’d be sanding for six weeks.” “I was shooting for four.”
David Helmer: I glued the bridge with hide glue, so when it comes off down the road, it comes off. Sounds good — I’ll just tell him to keep an eye on it.
James: All right — thanks, everybody. That’s some good stuff.