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Repairing a old Gibson archtop

If you have a string instrument of any kind that needs fixing, a mistake you made in building a new instrument that you need to "disappear," or a question about the ethics of altering an older instrument, ask here. Please note that it will be much easier for us to help you decide on the best repair method if you post some pictures of the problem.

Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Thu Dec 29, 2016 9:25 pm

I can easily imagine that it will be even harder with a laminated top than with a carved top. That's why i ask.

Barry Daniels wrote:... A "cheap" archtop may not be worth this amount of work.


I am fully aware of that. The restoration of the guitar in this thread is completely uneconomic. But the guitar has an ideal value to me. Even given that, the repair of the thinline - i call it "Sorgenkind" ("problem-child") - is crazy, i know. Well, it sometimes is nice being crazy...

BTW: i am making good progress. I "only" need to cut a new mortise for the neck, free handed, of course, fill a few wounds in the bottom in order to get plane surfaces at the end blocks and glue in and trim the already fitted braces. (And probably make a new bridge or adapt the old one). If i am really lucky, the guitar will play again in February. But that's a good training for the next archtop build...

And the other one shown above? Question b) more or less points to stabilize it with the least amount of effort, which is just to make new braces and leave the top as it is now. But anyway it would be nice to learn if there is a possibility to do it better. (learning is alway nice...)
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Re: Repairing a old Gibson archtop

Postby Barry Daniels » Fri Dec 30, 2016 10:31 am

Oh, it's laminated? Then any repair of the type I mentioned would be less reliable. It would likely delaminate during the process which would make it worse off.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Fri Dec 30, 2016 4:24 pm

Which effectively means: forget about it, and concentrate on stabilizing the top as is. Maybe put some tension into the new braces. Won't it?

Anyway: thanks for the input.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Sat Dec 31, 2016 10:51 pm

Have a happy new year!

I have been brave. Really brave. After seeing Stephen Marchiones video on tuning a parallel braced archtop plate and demonstrating the permitted stability (and a few glasses of champagne) of the top i decided to dare a heavily scalloped bracing. I am still at 15 mm beneath the bridge, and even more in the formerly unstable area. Now the top seems to be stable where it needs to be - toward the neck and beneath the bridge and relatively mobile elsewhere. The tap tone height is a bit uneven, however. But it is still a clear tone everywhwere. Could i expect more from a top with this degree of inhomogeneity?

I am going to leave it as is if no one warns me to stiffen the top (by maybe a few additional braces) .

Image
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Re: Repairing a old Gibson archtop

Postby Barry Daniels » Sun Jan 01, 2017 3:08 am

The middle section is scooped out extremely low. The overly long f-holes also weaken that area of the top. I would add a bit of support back in. You could glue a strip or two of 1/8" thick spruce into the middle scoop of the braces and then smooth and blend them out. Laminated braces are not forbidden.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Sun Jan 01, 2017 8:13 am

Thanks. I will do something about it; i wasn't quite sure anyway.

Despite of that the top will be loaded less than usual: the guitar will remain a 5 string due to the extremely narrow neck, and these strings will be tension wise at most .011 flatwounds (i was actually using .010s and will probably continue doing so). There is another weak part: the neck. It does neither have a steel truss rod nor is it very thick. I do not want to straighten it a 2nd time.
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Dovetail joint question (was Re: Repairing a old Gibson archtop)

Postby Beate Ritzert » Mon Jan 16, 2017 9:10 pm

Meanwhile i managed to set the neck. Although i found it difficult because i a) used a dovetail with parallel flanks, not a v shaped one, and b) the heel of the body is round and oblique in any dimension, and apparently it has alway been, the neck has the intended angle and it is on the symmetry axis of the body (mhmm, mostly, but a lot better than 30 years ago).

Image

The shim was needed to get the neck angle well defined. Although it might look differently, the flanks of the dovetail fit well over 3/4 of the area - again better than before. The two breakouts at the outer edge of the end block will will filled in order to maintain the largest possible glueing surface.

My impression is that the connection between neck block and the rims to the body will be crucial to the stability of the guitar.

Now my question:

I could fill the dovetail with a shim and glue this both to the neck and the body - expecting that that will further stabilize the heel. The remaining part of the neck block will have good contact to the bottom; i thoroughly matched the whole surface of the neck block to the bottom. However the weakest part still seems to be the cutaway. I expect the torsion caused by the string tension trying to deform the ribs - it does when i try to move the neck.

Now i am really uncertain wether to insert the shim or leave it as is - the bottom and the neck heel will fully cover the gap, so it would be invisible.

Quite obviously i will have to glue the neck before closing the box if i am using the shim and hence even have to repair the finish around the neck extension before doing that. If the shim can be omitted, i'll be able to close the box and repair the
finish before glueing the neck.

Mhmm.
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Re: Repairing a old Gibson archtop

Postby Steven Smith » Wed Jan 18, 2017 2:10 pm

Can't make any suggestions but I am enjoying watching the process as you bring this one back to life.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Wed Jan 18, 2017 3:02 pm

Thanks. I am always a bit unsure if i am not boring all the professionals to death with my very amateurish stuff. (And if i do, please feel free to tell me...)

Back to my question: i have decided to shim the gap. The glue is already drying.
Stability seems more important than ease of neck reset, especially in this case. Furthermore - as the neck fits pretty tight in its pocket it should be possible to match the surfaces without the necessity to use glue.

So i can have both: finish the the body without the neck, repair the finish and attach the neck when everything else is done.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Thu Feb 02, 2017 3:36 pm

A small update. It turnded out thet the linings were too thin to hold the bottom reliably. I a few places its thickness was just a few tenths of a mm. So i decided to strengthen it. Well, i think it should work, but even i could have done that job better. A thick todo for the next guitar.

Image

And here a test of the fit of the body and a few final adjustments before glueing.

Image

Those tiny blocks in the channel if the binding did their intended job surprisingly well. Now the box is closed and upon first impression everything is fine. The body appears to be pretty stiff, and it gives surprisingly resonant tap tones. I am pretty curious how it will sound.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Mon Feb 06, 2017 11:43 am

Box closed, bridge adapted in height to line up with the frets, strung up. Still without the binding - i would like to be able to open it again easily if stability turns out to be lacking. But first signs are good: reasonable action, and it stays in tune almost immediately.

Image

And that baby is loud! Louder than my two large archtops. I never thought that a 15" thinline with a laminated top could reach such a volume.

No i hope that it'll stay stable... there'll be a lot to do: glue in the old binding (i'm going to use NC glue), clean up the finish and do some work on the bridge - the harmonics on the E string are a bit weak.

Thanks for those who did not turn away. Especially for the tips some of You gave me.
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Re: Repairing a old Gibson archtop

Postby Steven Smith » Mon Feb 06, 2017 2:20 pm

Very nicely done - it looks so much better. I like the way that you filled the holes!
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Archtop settling time (Was: Repairing a old Gibson archtop)

Postby Beate Ritzert » Tue Feb 28, 2017 8:23 pm

Please let me come back to this baby. It is still in the unfinished state shown in the last photo: in order to be able to open it in case of "emergency" the binding of the bottom is still missing.

Due to the very light bracing i am a bit unsure if it will be stable over long times, although it might be ok. But i really do not know. Within the first week, i had to reduce the height of the bridge by 0.5 mm, but since then it is mostly stable. Mostly means that weather changes have quite a noticeable impact (but far less that what i was used to with this guitar). That guitar has not truss rod at all.

If i check the arching with my fingers, i notice some kind of recurve near the heel, where there is no bracing and never has been. There also seems to be a tiny bit of deflection close to the filled bridge pickup hole which seems to increase when the action is increasing. Bass side only where the bracing came out a tad lighter than on the treble side. Not surprising - the force pulling the bending the neck forward increases with the action of the strings.

My criterion to judge the stability of the guitar is the string buzz above fret 12 on the D string. Above fret 12, the fingerboard radius and hence the action of the central string decreases. This is so pronounced that the string is unusable. This will change rapidly if the action goes up, so this is a nice criterion, and i decided not to fix the fingerboard unless i know the guitar is stable.

No my question: it now looks as if might be stable, and it would be more stable if i could lower the action of the strings. How long would You observe the guitar in its present state? Would another month be sufficient? More? Less?


BTW: i am happy with the sound, and i am already considering to replace the wound strings (Pyramid pure nickel) by bronce wound strings. Mainly because of the sound but also because bronce has a larger specific weight than nickel (does it?) and therefore the load of the top would be slightly reduced.
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Wed Mar 15, 2017 9:39 pm

May i refer to this side discussion in this thread, the 2nd problem child:
viewtopic.php?p=47173#p47173

Today i opened the box and found that:

Image

The lamination broke under the bass bar, so the latter is loose. And You might notice the hole of the large screw in the heel.

I am a bit unsure if i should spent much work in the neck - it withstood the load of .013 flatwound strings, and i tend to simple try to glue the broken heel and reinsert the screw.

But the top. The guitar must have stood in water for quite a while. Luckily the lamination appears to have survived the water. But even if i tried simply to reglue the bar, i would probably need to bring the top back into shape.

Even if i tried to reglue the bar i need to put the top into shape again.
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Re: Repairing a old Gibson archtop

Postby Paul Breen » Thu Mar 16, 2017 12:48 pm

Fixing the top on this one will be a bit of a crap shoot. The water/ moisture issues it suffered have affected/ weakened the glue between the top plies. Simply gluing the sprung brace with the glued on strip of plywood it ripped up may hold there but will the still attached portions endure? There is no sure fire way that I know of to cure a pressed top where the plies are de-laminating. You could try tapping the inside of the top with something hard and listen for changes in the sound to find them but this may only work if there are actually voids between the plies. If you find some, you could drill small holes partially through the top and hammer them with CA. You could also try this in areas adjacent to the braces even if you're not finding dead/ loose spots from tapping for extra insurance and hope for the best.

I worked on a cheap stand up bass last year that had advanced de-lamaniating problems with the plywood. The bass bar had ripped up the inside ply, it looked just like the loose brace in your picture. I told the owner it would not be worth the effort and only a re-top could make a reliable repair. He was hoping to sell it for a few hundred dollars if it could be made to play and I could do something on the cheap. I ended up drilling clearance holes through the top and putting in Black countersink wood screws. It set up just fine and he went away happy.

I fixed a cheap mandolin more recently for a guy on a fixed income where both braces ripped up the inner ply layer, I first just tried gluing them back down. One held on string up and the other did not. The loose ends where near the neck block of the mando and they terminated close to ribs. I ended up installing small dowels, like sound posts, from the tapered brace ends to the back. I was able to install them through a pick up hole in the the top, this was an "F" hole mandolin. The large pick up hole, in the case, actually contributed to the weakness in the top. That worked and it actually sounded probably as good as a mandolin of that quality could. The owner ended up with a playable instrument.

Good luck with this. You may need to come up with some unorthodox method, as I did, if you decide to pursue the repair. Or, maybe try your hand at a re-top?
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Thu Mar 16, 2017 4:02 pm

First of all: this repair is more a project of fun, to learn or test unconventional ideas, and it may take long. No economic condition except that i would like to use cheap woods or rests. I am in the lucky situation that the stability of the guitar was still large enough for .011 strings in its present stage. As long as i am careful, the guitar can only improve...

Paul Breen wrote:Good luck with this. You may need to come up with some unorthodox method, as I did, if you decide to pursue the repair. Or, maybe try your hand at a re-top?


There many more small issues with that guitar, so re-topping it will probably be overkill. Mostly because of the damaged lacquer on the sides an especially the bottom. It appears to be more problematic - here after cleanig it under the shower and immediately drying it with a very weak hair dryer. The tap tones are dull, compared to the top as well as those i remember from the thinline. My ideas on this are: glue back the broken pieces of laminate, open the split laminates from the edges and reglue those. Use either fish glue or HHG.

I still expect that the tap tone will remain a bit dull. Somewhere i read the remark that an archtop bottom worked out too thin could be improved by giving it a light bracing. Maybe that's that also a possibility here?

Image

Image


Back to the top: making a mold might be difficult as we do not know the original shape. But we do have at least a partial reference: the tone bars. At present my idea is to make a stamp which attaches to the top from under the bridge position. Of course with a bar keeping the positions of the end blocks fixed. This stamp shall push the top outside, and it should push it back into its original shape, if i apply moderate heat and moderate humidity maybe a few times. The gap between the top and the loose bar should close. When this is done, reglue the bar. Not earlier.

I am also considering staggered tone bars - please take this as rough ideas during the brainstorming phase i am now in: my impression was that the top lacks stability near the neck block. So i might give it a stiff bar sharply scalopped where it is overlapping with the existing bars. And also apply strong scalopping to the old bars, maybe not quite as radical as i did with the thinline. In addition two light bars at the lower block forming a V and also overlapping with the two existing bars.
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Surprise (Re: Repairing a old Gibson archtop)

Postby Beate Ritzert » Sat Mar 18, 2017 7:16 pm

@Paul: You are definitely right, the bass bar had indeed ripped the inside ply. That was clearly visible; You could also see the glue on the inner surface.

And that is the cause of a surprise: clamping the bar back to the top, roughly into its old position, brought out the old shape. Not fully, it is still a bit flat on the bass side, and it seems to be a bit flat overall. Now it looks like this:

Image

There was enough glue in the gap of the inner ply so that re-gluing under heat, moisture and pressue occured. The tap tones do not show any sign of rattling or defective parts. The joint appears to be "pretty stable" - but i must admit i do not trust it.

In stage 2 my heating arrangement was as follows:

Image


And now?
Remove the rests of the old PVA glue from the bar and bring in some epoxy?
Glue some wooden blocks to the sides of the bar and to the top?

Apply massive scallopping to the bars (leave them high under the bridge) and add one or more bars?

BTW: my impression is the top would profit from some reinforcement near the cutaway.
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Re: Repairing a old Gibson archtop

Postby David King » Sat Mar 18, 2017 9:42 pm

There must be a way of squirting glue into the laminations that have come apart from the inside with a blunt needle. Not sure how you would clamp unless you set up a giant plaster of Paris caul and an inflatable bladder to press the top against the caul.
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Re: Repairing a old Gibson archtop

Postby Paul Breen » Tue Mar 21, 2017 2:07 pm

Beate, the plywood top would have be laid up as single ply sheets, alternating 90 degrees with each layer. It would have been pressed and clamped up in a mold, with the tops final shape. The braces add some needed support under the bridge but the pressed, shaped plywood has quite a bit of strength all on it's own. It's really not surprising that simply re-gluing the loose brace brought back the original shape, or nearly so.

It's too bad the top was laid up with the inner ply nearly parallel to the braces. It likely would not have torn out the way it did, if the inner ply was at a right angle to the braces. The section that you have glued back in place is now anchored to a ply that is at a right angle and it will likely hold there because of that.

Things that might work with this water damaged top?

Maybe after the fact since you have already glued the brace down. I would have been tempted to continue pulling the loose brace completely off along with the plywood it's peeling up and then glue it back in. This way you would be gluing to the next ply down, which is at a right angle and less likely to give out.

Re-make the braces long enough to reach from rib to rib. Cut out sections of the lining just wide enough for each brace end, glue the braces in and add some small blocks glued to the ribs, right down on the brace ends. Configure the braces like they are currently shaped, keeping them tall where they are now. Start the tapper in the same places and curve them down similarly, leaving a bit more thickness along the way but ending up with them almost flat the last 1" or 1 1/2". A pressed top has no re-curve like a carved top. The thinned re-curve helps the entire top vibrate much like a speaker cone does, stiff in the middle but allowing the entire shape to vibrate up and down. I believe that the builders of your guitar stopped the braces where they did to help simulate the properties of a re-curved top. Make this too stiff and it might choke up the tone a bit... might, no way to be sure without having it strung up to hear what you end up with.

Pull the braces and drill some shallow holes into the underlying plays along and under the path of where the brace will be re-installed. Either wick CA into them liberally, sand the inner ply surface to bare wood and re-glue the braces in normally or use a good epoxy, like West System, pack the holes and then epoxy the braces down.

Like I already said, any therapy will be a bit of a crap shoot with no guarantees on the outcome. You could always turn it in to an electric, if you end up up unsatisfied with results to keep it an acoustic instrument. You seem very determined though, so keep at it and good luck getting it back into shape!
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Re: Repairing a old Gibson archtop

Postby Beate Ritzert » Tue Mar 21, 2017 4:40 pm

Paul, first of all: i did not intend to reglue that brace.
My intention was to try to bend it back and make use of the fact that the brace is the only thing that really reflects the original shape. I simply was not careful enough and the brace reglued by the heat.

Then: the bottom plate seems to have suffered a lot more from the water than the top plate; its tap tones do not sound well at all. If i want to restore the acoustic tone or maybe even improve it i need to take special care of the bottom.

Because of massive trouble in my original business, i did almost nothing on the guitar these days. The only thing i did is a tap test which gave a fairly uniform and resonant sound of the top. And i tried to measure the remaining deformation: the bass side is 2 mm flatter than the treble side, but the treble side appears a bit flat a well if You follow the curvature with the fingers. I would guess at max 1 mm around the bridge position.

Before i do any decision on the braces i would like to try to bring out the old shape a bit better, especially on the bass side. Actually the old braces are the only parts where the information on the old shape is preserved, and i would like to utilize as much of that information as possible.

My idea is therefore first to apply the inverse of the force that brought the top down in order to bring it up again. That would mean two stamps in bridge position immediately inside the braces (which have both never been loose there). Or maybe set the stamp on the braces and heat it up again. To my understanding i would not lose any of the options You suggested, so i am indeed a bit determined to try that first.

And i am willing to experiment.

BTW: X bracing might be a possibility as well?

A final note to the braces themselves: the size and shape You see be should typical for German archtops from the 50s and 60s. AFAIK it has been also used in fully carved tops with a recurve, and it is documented in the luthery book "Die Gitarre und ihr Bau" by Jahnel which is a lot older than Benedetto's book. To me it does not appear to be a special design for laminated tops, and it should be the reason why so many German archtops sound really bright (like the one i built myself using that information).
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