induced arch

[Alec]

Has anyone tried inducing an arched top by clamping the soaked wood over a domed form and then later gluing on arched braces?

If so, do you join the two halves first or bend them separately. Also, how much of an arch can be made without risk?

I've been told that too much of an arch created by just gluing domed braces, can over-strain the wood.

But if the wood is soaked in water first and heat is then applied ( as in Graham McDonald’s instruments ) would the wood cope better?

It is my next project, so any thoughts would be very welcome.

Alec

[Luthier]

Alec!!!
If I may be so bold as to chime in here for you. It seems the Gibson lawsuit has overshadowed the threads and has loomed overhead. #I have never tried what you are suggesting. #I know that unless a waterproof glue were used, you would be asking for trouble. Also it would be tough to join the two halves after bending. #Many cheaper models use wood multiply laminates glued in a mold to achieve the shape they desire similar to the way a banjo resonator is made. #Hope that helps.

Don
Hiya cousin

[Alec]

Thanks ( as always ) Don.

As you know it is virtually impossible to get Titebond glue here in Italy. I believe Hide glue is not waterproof. So what kind of glue would you suggest?

The reason for inducing an arch rather than carving one, by the way, is mainly instinctive. The idea 'feels' right. ( scientific explanations have never been my forte ) I fancy doing a gentle curve all the way to the sides rather than leaving a traditional flat rim around the arch. Kerfling will be adapted accordingly for gluing space and strength.

The woods will be solid. Especially as we have that wonderful Italian Alpine spruce down here. Not that I'm an expert on wood. But Stradavari seemed to like it, so who am I to argue? If I'm lucky I might be able to find some pieces large enough a one piece top, which would solve the glue problem.

PS: Those OM kits of yours look great.

Alec.

[Bob DeVellis]

Vega seems to have used a single piece of wood for its cylinder-backs. I suspect there's a reason for that. I don't know what they did on their mandocellos or mando basses, but doubt they were a single piece. A top, of course, is harder still than a back because it can't be braced as agressively. I think a single piece of wood is really your best bet, Alec.

[Dave Cohen]

There was an article in American Lutherie several years ago now on building an Irish bouzouki with just such an induced arch. What the author did was press two bookmatched halves of the top plate onto forms and let them dry there. He then jointed the two arched halves and glued them together at the centerline with the aid of a jig. Rather than looking for speculation here, or trying to reinvent the wheel, you should go to the GAL website, look up that issue, send for it, and get the benefit of some past experience.

[Jim Garber]

I can't tell if this Howe-Orme guitar (http://www.vintageinstruments.com/museum/howormgtrfulpage.html) has a one piece top or not.

I have a similar Vega cylinder guitar that has a bent cylinder top (it dos look like thre is a seam, tho). I can try to check to see, but I would imagine that it would be one piece.

BTW I believe that Epiphone steam-bent their lower-end archtop guitars and that those tops were solid wood.

Jim

[Alec]

Thank you all for your thoughts.

Yesterday I managed to find some nice spruce big enough for single piece top mandolas. Also I decided to go for single piece mahogany backs for extra flexibility.

The article Dave suggested is very interesting, and in it the halves of the tops are heated in oven bags before bending. In my case it will be a single top, so I’ve come up with a rig idea. A domed sheet metal form is attached to a work table. The work table has a hole in it which takes a powerful light bulb. The wood ( soaked for a couple of days ) is then put on the hot form and pressed down by an other, identical metal form and clamped for a few days.

The local blacksmith is sorting out the metal forms for me next week. Please tell me if you think this won’t work for any reason.

Alec.

[camando]

Hi Alec

You might want to email or phone this Canadian luthier at neilscelticcross@shaw.ca #He has made hundreds of instruments with induced archs and feels very strong about the value of the technique. He can offer you some assitance I bet. He is listed in the builders section here at the Cafe under Celtic Cross. Good luck

Chris in Canada

[Dale Ludewig]

Alec- I tried doing this back in the late 70's. #I probably built about a dozen mandolins this way. #It was a simple arch, both top and back, no recurve. #I would guess the arch height was about equal to what you do when you carve one. #I never found that I had to soak or heat the wood. #It was about 1/8" thick. #I was trying to get an archtop sound without the effort of carving. #Perhaps it was my expectations or lack of skill at the time, but I was never able to get the sound I wanted from the method- not even close. #But please give it a try and let us know how it turns out. #Good luck!

Dale Ludewig

[thistle3585]

Just for your info, resorcinol glue is waterproof and is often used in the boatbuilding industry when bending parts that involve heat, moisture and pressure. The only downside, if doing a blond instrument, is that it has a dark glue line.

[nar]

Hi There,
I have had a number of emails this morning asking how I do my version of the induced arch for the 8 string family.
Instead of answering each one personaly I thought I might do it once on this forum.
First the way I do it works for me ,but maybe not for some one else. And I'm sure there are many other methods that work equally as well for other builders.
All my instruments have a 25ft. radius top and back. I cut the transverse braces for the top and back to this 25ft. rd. The top and back wood is resawed and book matched then glued up. After I run it through the thickness sander to get a parallel surface I lay it on a 1/4" thick steel mold that I rolled up to a 25ft radius. I then glue in the braces. The top wood is about 1/4" thick the backs about .100" thick. With the sides in a body mold and with the linings glued in I have a sanding bar with a 25ft rad. and sand paper glued to it.I lay this across the sides and sand the rim to a 25 ft. radius. I then lay the top or back on and after notching for the braces, glue it on starting at the neck block, then the brace tips and then slowly all a round the edge. And no it dosn't crack and yes it works [for me] I never use water or heat. After the the glue has had time to dry I drawn an elipse where the bridge will sit and slowly plane away wood radiating out from the bridge area, making it thinner near the edge until I get a "feel" to the top that I like. The back does not need this thinning.
When all is done the top will have a dome to it as will the back. I might add the sides are wider at the middle than at the neck or tail block[for the back only]. This also adds to the saucer shape to the back. I may have made a a couple of hundred instruments with this method and have never had a failure. I apply this technique to mandolins, mandolas, octave mandolins, mandocellos and bouzoukis.
Neil

[sunburst]

The wood ( soaked for a couple of days ) is then put on the hot form and pressed down by an other, identical metal form and clamped for a few days.
The potential problem I can think of is:
The wood will not be able to dry between two big pieces of metal. It would obviously have to be stainless steel, or possibly aluminum to avoid staining of the wood. Also I might anticipate problems with fungus.
It might bend fine without the water. I know a luthier who has experimented with inducing an arch in thicker spruce and then carving "as usual". I think he said he bent the wood with dry heat.

[Alec]

Useful information, gentlemen. Thanks.

The potential "soggy sandwich" effect which Sunburst pointed out, has made me modify plans. Instead of using a metal plate to push down on the wood, I am thinking now of a simple stiff rim around the edge with a leather strap over the middle. That should let the wood breath.