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Bowl bend, Kinda!

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Roundback Rob
Posted 2013-07-28 5:49 PM (#473655)
Subject: Bowl bend, Kinda!


Joined:
August 2012
Posts: 27

Had a weird idea to avoid neck reset on ovation bowl. What do you think? Make one or more slices through bowl, from top to bottom somewhere behind soundhole area, and then clamp bowl in such a way, as to close the gap, created by the slices, and then do a fiberglass repair to the back, or inside of bowl. Maybe this would drop excessive string height? Could be dangerous to sound board/ Maybe Ill try it on a trashed body as an experiment.
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DanSavage
Posted 2013-07-29 2:11 PM (#473666 - in reply to #473655)
Subject: RE: Bowl bend, Kinda!



Joined:
June 2012
Posts: 1949

Location: Lake Forest, CA
So, if I understand correctly, you're talking about taking wedge-shaped slices out of the bowl to reshape the soundboard?

In effect, pulling the bridge down so it's back in line with the fretboard?

As long as you keep the repairs thin, it should work. Basically, you'd be seaming the edges of the bowl back together. I've done this sort of work when repairing fiberglass model airplane fuselages and for seaming the inlet ducts for one of the kits I sell.

Something to keep in mind before you start is resin compatibility.

The SMC bowls were molded using polyester resin.

Generally speaking the best bonds are chemical, i.e.: when the polymer chains are not fully cured.

When the polymer chains are fully cured, you must rely on a mechanical bond. This is what you get when you rough up the surface with sandpaper. The resin grabs onto all the nooks and crannies created by the grit of the sandpaper.

Also, polyester resin has poor adhesion properties, so your best bet is to use epoxy resin. The slower the cure, the more rigid the final part. Faster curing epoxy is more rubbery. Thinner viscosiy resin penetrates better into the nooks and crannies and will form a better mechanical bond. Thinner viscosity also wets out the cloth easier.

If I were to be doing this job, I would use MGS epoxy, which is what I use to mold my parts. It's very slow cure, very thin and is very strong when cured. But, it's pretty expensive and can only be bought in gallon-size quantities. Also, you must buy a gallon of resin, then two quarts of hardener. So, the cost for even the minimum amount is almost $200.

West System epoxy works pretty well, too. But it's probably a little thicker than you need.

Personally, I would use Z-Poxy Finishing Resin. It can be found in most hobby stores. It's reasonably thin so it wets out the cloth well and cures overnight so the final product is pretty rigid. Cost is ~$16 for two 6-ounce bottles - Resin/Hardener.

The best thing to do is to use cyanoacrylate glue (CA) to tack the edges together, then seam them with strips of fiberglass cloth and resin.

Once the edges are tacked together, and the surface is roughed up, lay two layers of 5-ounce cloth cut into 2-inch wide strips. This would probably be strong enough to hold the sections together. You don't want the seams to be too thick otherwise you might deaden the back too much.

If you want a smooth final surface, you would lay on a third strip of 1.5-ounce cloth. Or, if you wanted to get really tricky, you could lay some Saran over the wet cloth/resin to give it a glossy-smooth surface and feather the edge of the resin to hide the seam. I don't have access to the pics right now, but if you're interested I can post a couple of pics showing what I'm talking about.
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MWoody
Posted 2013-07-29 6:25 PM (#473670 - in reply to #473655)
Subject: Re: Bowl bend, Kinda!



Joined:
December 2003
Posts: 13899

Location: Upper Left USA

Split and weld? Sounds good but may take some practice runs. Seesquare did some Bowl bending with a jig and some heat but I think the net movement was small. I did a large wedge Jumbo on a homespun Adamas just to see if it could be done.



Edited by MWoody 2013-07-29 6:38 PM
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Roundback Rob
Posted 2013-07-29 10:38 PM (#473673 - in reply to #473655)
Subject: Re: Bowl bend, Kinda!


Joined:
August 2012
Posts: 27

I have an old celebrity I may experiment with. I might install blocks of wood inside guitar, on either side of slice, and screwed through the back of bowl, into blocks, and then predrill one block, but not the other, and drive screws through predrilled, and into the other block. This way i can pull the two blocks together evenly, and a little at a time. Thanks for the encouragement. I have seen beautiful guitars in the trash because neck reset was too expensive. If this works, maybe I can salvage them. I will need luck LOL
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seesquare
Posted 2013-07-30 12:12 AM (#473680 - in reply to #473673)
Subject: Re: Bowl bend, Kinda!


Joined:
November 2002
Posts: 3158

Location: Pacific Northwest Inland Empire
I surmise the top will eventually pop loose, if you alter the geometry in the bowl.
Best of luck!
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