The Ovation Fan Club
The Ovation Fan Club
Forum Search | Statistics | User Listing Forums | Calendars | Albums | Language
Your are viewing as a Guest. ( logon | register )

Random quote: "Ovation Guitars really don't get the respect they deserve!" - Alex Pepiak



Jump to page : 12
Now viewing page 1 [25 messages per page]
Warped & Cracked Tops...

View previous thread :: View next thread
   Member Communities -> Bottom Feeding Luthiery GuildMessage format
 
DanSavage
Posted 2017-02-03 6:22 PM (#532531)
Subject: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA

Reading Patch's thread about split top on his 'Book' Elite reminded me that I've been wanting to pass along this info about what I think is the root cause of the splits in the tops that happens all too often on our Os. Even my 'Book' Elite is starting to get finish cracks in the lower bout.

When Paul Moody had me re-top his 1113, it arrived with three splits that ran the length of the top from the upper bout to the lower bout, one each on either side of the bridge and a third that went right down the middle. Here's a pic of what the top looked like before I pulled it off the guitar.

In the process of pulling the top off the guitar, all fourn transvers braces pulled off the top. Since I wasn't going to be using the top, I just left them off. I went on with re-topping the guitar and didn't give it another thought, until recently.

Then, when pulling the tops off of the four guitars I'm working on now, I noticed something unusual. All the tops were cupped, to a lessor degree than Paul's 1113 top, but they all were cupped. Here's the 1113 top. This photo shows the cracks a little better. This top is the worst because it has no braces across the grain to hold the top flat.

And, the 1528 top.

The 1612 top.

Lastly, Paul's 1117 top.

So, I got to thinking about would cause all these tops to warp. All were different types of wood and different ages. Paul's 1117 was the newest, being rebuilt at the factory. The only common denominator was the finish -- poylester resin.

When molding fiberglass parts, one of the benefits of using epoxy over polyester is what's known as dimensional stability. In common terms, polyester resin shrinks. Not much, but it's enough that most quality parts are molded from epoxy. There are other reasons for using epoxy over polyester, but one of the big ones is shrinkage.

Stabilizers can be added to polyester resin to help minimize it, but it will still shrink. If polyester resin were used on one side of thin wood, like our guitar tops, and it were to shrink, it would warp the wood unevenly. Since the tops are firmly glued to the edges of the bowl, any shrinkage would eventually cause the finish, and even the wood, itself, to split.

So, the conclusion I've come to is that the finish cracks we so often see in our Os is caused by the shrinking polyester finish.

What can we do about it? Short of the factory using a different finishing system, Not much. I just thought I'd pass along this info to remove the mystery of why our guitars' finish cracks.



Edited by DanSavage 2017-02-03 6:32 PM
Top of the page Bottom of the page
leonardmccoy
Posted 2017-02-03 7:15 PM (#532532 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
December 2015
Posts: 215

Location: Katmandu
I always thought it's due to the A or fan bracing not providing the soundboard enough structural support right around where the bridge is located at when compared to the more structurally sound X bracing, or due our bridges being secured with screws through the top, thereby increasing the risk of it ripping the soundboard whenever it decides to lift off.

In any case, I'm glad my A-braced 1717 is more domed than anything.
Top of the page Bottom of the page
DanSavage
Posted 2017-02-03 7:58 PM (#532533 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
Yeah, with the tension of the strings, the tops will dome (belly) below the bridge. But, it you were to remove the top from the bowl, you'd probably see it warp as these tops have done.

All the other tops on my 'trophy wall' are similarly warped.

Edited by DanSavage 2017-02-03 8:00 PM
Top of the page Bottom of the page
Love O Fair
Posted 2017-02-03 9:55 PM (#532534 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
February 2016
Posts: 478

Location: Spin axis of a California map
Looking at those tops is like watching a crash reel. I don't doubt your conclusion on the polyester shrinkage, though I do wonder why so many cracks, especially ones that go all the way through the wood, result with the fissures opening outward on the finished side since the cupping force is upward and away from the bowl at the edges. I would think that the crack's major opening would be on the underside of the wood, and be more pinched closed on the finished side. Or are they? The photos don't really show the difference per side.
Top of the page Bottom of the page
Thunderbolt
Posted 2017-02-03 11:17 PM (#532535 - in reply to #532531)
Subject: RE: Warped & Cracked Tops...



Joined:
April 2014
Posts: 103

Location: Ontario Canada
very fascinating Dan, i really enjoy reading a lot of your posts! does the factory still use the exact same finish today? if so, is there a better alternative? "that stuff should be outlawed"
your pulling tops over there like your pulling teeth, curious how do you get them off?
Top of the page Bottom of the page
seesquare
Posted 2017-02-04 10:36 AM (#532542 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...


Joined:
November 2002
Posts: 3131

Location: Pacific Northwest Inland Empire
Makes sense. There are differential forces & material integrity, so when the polyester goes, it takes the wood fibers with it. Then, when the top is removed. the polyester attempts to "go home", and you get the cupping!
As to alternatives to finish materials, that's probably a production & cost issue. May be cheaper, or more efficient in sense of time, to use the polyester.
The Ovations I have reconstructed have used either varnish, speeded linseed oil, or lacquer, being pretty thin, too. Don't believe any have cracked, but some were about 15 years ago, now, & the new owners have not sent any complaints (yet).
Top of the page Bottom of the page
DanSavage
Posted 2017-02-04 11:08 AM (#532543 - in reply to #532534)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA

Love O Fair - 2017-02-03 7:55 PM

Looking at those tops is like watching a crash reel. I don't doubt your conclusion on the polyester shrinkage, though I do wonder why so many cracks, especially ones that go all the way through the wood, result with the fissures opening outward on the finished side since the cupping force is upward and away from the bowl at the edges. I would think that the crack's major opening would be on the underside of the wood, and be more pinched closed on the finished side. Or are they? The photos don't really show the difference per side.


Under normal circumstances, the wood swells and shrinks a little bit according to the ambient humidity. To prevent cracks in the wood on a flat-top guitar, the builder will dome the top a little bit as they're gluing on the braces. Martin guitar tops are built on a 28-foot radius dish. This doming allows the wood to shrink in lower humidity without splitting.

Here's what's probably happening. It'll be easier to understand if you have something to look at. I laid a piece of wood across the 1113 top, then weighted it to roughly simulate the top being attached to the bowl.



As you can see, the top has three main waves, each separated by the cracks. What it looks like to me is happening is that the polyester continues to shrink, but the wood doesn't. As it shrinks, the wood deflects inward. At some point, when the wood can deflect no more, either the finish will split or the wood will, usually in spots where there is no bracing on the underside to support it.

Top of the page Bottom of the page
DanSavage
Posted 2017-02-04 11:28 AM (#532545 - in reply to #532535)
Subject: RE: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA

Thunderbolt - 2017-02-03 9:17 PM

very fascinating Dan, i really enjoy reading a lot of your posts! does the factory still use the exact same finish today? if so, is there a better alternative? "that stuff should be outlawed"
your pulling tops over there like your pulling teeth, curious how do you get them off?


I couldn't say for sure, but I'd imagine they're still using the same finish.

Taylor is using a UV-cured polyurethane finish. Here's a couple of really interesting youTube video of their finishing system.

Taylor Factory Tour Part 3 of 4 - Finish Application

Taylor Innovation: Electrostatic Finish Spraying and UV-Curing

To get the tops off, first I pull the binding. Depending on the top, sometimes I also pull the purfling to expose the glue joint between the top and lining.

Next, I use an Xacto chisel to separate the top from the lining. This part takes a little while to do, maybe 20-30 minutes.

Top of the page Bottom of the page
DanSavage
Posted 2017-02-04 12:10 PM (#532546 - in reply to #532542)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
seesquare - 2017-02-04 8:36 AM

Makes sense. There are differential forces & material integrity, so when the polyester goes, it takes the wood fibers with it. Then, when the top is removed. the polyester attempts to "go home", and you get the cupping!
As to alternatives to finish materials, that's probably a production & cost issue. May be cheaper, or more efficient in sense of time, to use the polyester.
The Ovations I have reconstructed have used either varnish, speeded linseed oil, or lacquer, being pretty thin, too. Don't believe any have cracked, but some were about 15 years ago, now, & the new owners have not sent any complaints (yet).


Yeah, solvent-based polyester is probably the cheapest of the durable polymer finishes.

I used rattle-can Minwax polyurethane and it works pretty well and buffs out to a good shine. My only real complaint is that it's a little on the soft side, almost like lacquer.

I used this as a primer/sealer on Jay's Balladeer, then top-coated it with 2K Eastwood urethane. I liked how that worked out, so I'll probably be using this on all the guitars in the future. It's a little more expensive, but it works pretty good.

Top of the page Bottom of the page
seesquare
Posted 2017-02-04 1:58 PM (#532548 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...


Joined:
November 2002
Posts: 3131

Location: Pacific Northwest Inland Empire
How long do you let the polyurethane set up, before you buff it out? Fortunately, we have, almost year-round 40-to-50% humidity, albeit a bit drier in the cold months, with heating, so we don't have a lot variation of humidity. I'm usually giving the finish a full 14 days, before even breathing hard on it.












Top of the page Bottom of the page
tpa
Posted 2017-02-04 4:12 PM (#532550 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...


Joined:
December 2004
Posts: 406

Location: Denmark
Good observation and thinking. In theory a similar coat on the backside of the top might stabilize to some extent, but only to some extent. Partially due to even pull on front and back, and partially due to reduce the humidity variations in the wood. Do the plywood tops (Celebrities ...) show similar behaviour?
Top of the page Bottom of the page
2wheeldrummer
Posted 2017-02-04 6:02 PM (#532551 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
February 2014
Posts: 348

Location: moline,illinois
Very interesting observations as usual Dan,one does wonder how you can have a guitar like my 1972 Glen Campbell 1127 with a perfect top and another like patch's book elite that cracks right in the center of a section,do you think it has something to do with the stability of each piece of wood being different since they come from different trees so perhaps some have microscopic weaknesses not visible in the grain pattern that cause them to give under prolonged stress.

Your wall of replaced tops is like little a graveyard of ovations that have been resurrected by Dr Savage,maybe they're Frankenstienien guitars brought back by Dr Dan-enstien to haunt the night LOL.





(IMG_1157.JPG)



(IMG_1160.JPG)



Attachments
----------------
Attachments IMG_1157.JPG (58KB - 0 downloads)
Attachments IMG_1160.JPG (53KB - 0 downloads)
Top of the page Bottom of the page
leonardmccoy
Posted 2017-02-04 6:58 PM (#532552 - in reply to #532543)
Subject: Re: Warped & Cracked Tops...



Joined:
December 2015
Posts: 215

Location: Katmandu

DanSavage - 2017-02-04 11:08 AM

As you can see, the top has three main waves, each separated by the cracks. What it looks like to me is happening is that the polyester continues to shrink, but the wood doesn't. As it shrinks, the wood deflects inward. At some point, when the wood can deflect no more, either the finish will split or the wood will, usually in spots where there is no bracing on the underside to support it.

This makes a lot of sense. Those three main waves are evident on my 1717 as well. I can feel each wave when running my hand over the soundboard. *sadface*

Top of the page Bottom of the page
DanSavage
Posted 2017-02-05 9:38 AM (#532559 - in reply to #532548)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
seesquare - 2017-02-04 11:58 AM

How long do you let the polyurethane set up, before you buff it out? Fortunately, we have, almost year-round 40-to-50% humidity, albeit a bit drier in the cold months, with heating, so we don't have a lot variation of humidity. I'm usually giving the finish a full 14 days, before even breathing hard on it.


When spraying polyurethane, I've been waiting a couple of days, but I don't think that's enough. I usually test it by seeing if I can dent it with a fingernail. But, as I've been discovering, the Minwax polyurethane works good as a primer sealer, but it's a little soft for the final coats. That's why I'm going back to the 2K Eastwood urethane.
Top of the page Bottom of the page
DanSavage
Posted 2017-02-05 9:41 AM (#532560 - in reply to #532550)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
tpa - 2017-02-04 2:12 PM

Good observation and thinking. In theory a similar coat on the backside of the top might stabilize to some extent, but only to some extent. Partially due to even pull on front and back, and partially due to reduce the humidity variations in the wood. Do the plywood tops (Celebrities ...) show similar behaviour?


Spraying the backside might help keep it from cupping because of equal shrink rates, but that would introduce its own set of problems, such as decreased repairability.

Yes. The 1528 show above is a plywood top and it's cupped. The cross-grain would probably help keep it from splitting, though.
Top of the page Bottom of the page
DanSavage
Posted 2017-02-05 5:59 PM (#532566 - in reply to #532551)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA

2wheeldrummer - 2017-02-04 4:02 PM

Very interesting observations as usual Dan,one does wonder how you can have a guitar like my 1972 Glen Campbell 1127 with a perfect top and another like patch's book elite that cracks right in the center of a section,do you think it has something to do with the stability of each piece of wood being different since they come from different trees so perhaps some have microscopic weaknesses not visible in the grain pattern that cause them to give under prolonged stress.

Your wall of replaced tops is like little a graveyard of ovations that have been resurrected by Dr Savage,maybe they're Frankenstienien guitars brought back by Dr Dan-enstien to haunt the night LOL.



That's a good question. Why do some crack/split and others don't? I wish I had the answer.

Here's a pic of my 'trophy wall'. Actually, I keep these tops around as a reference library, mainly for the brace patterns. It will be expanding when I add the four tops to the guitars I'm working on now.



Edited by DanSavage 2017-02-05 6:01 PM
Top of the page Bottom of the page
moody, p.i.
Posted 2017-02-06 12:46 AM (#532567 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...


Joined:
March 2002
Posts: 15096

Location: SoCal
Interesting to look and see that two of those tops were mine......
Top of the page Bottom of the page
DetlefMichel
Posted 2017-02-06 10:13 AM (#532568 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
May 2011
Posts: 405

Location: Muenster/Germany
Many old A-braced Ovations have "waves" on the top where the braces are. Mine had a cupped top between the 2 outer braces in front of the bridge, at least 5-6mm deep.Looked awful and I was afraid that the top would break.
I picked up all my courage and built a simple construction that I could put in the guitar and thus make enough pressure on the top from inside so that it became nearly straight. Then I used an infrared lamp and carefully heated the top from outside, so that I could hardly touch ist ; I would estimate 50-60° C. I proceeded with this for about half an hour, let the whole thing rest over night and repeated the procedure. The waves on the side of the top (where the braces are) are still there but the rest is satisfactorily plain again. No cracks, no problems.
Sure the finish will shrink with the time, nearly all plastic materials do. I am an Optician. If you use older plastic eyglasses frames and you don´t make the lenses a little smaller time after time the frames will break, that´s no big surprise for me.
But maybe we could remove the tension of the finish with little heat? Did you try that one of the curved tops?
Top of the page Bottom of the page
jay
Posted 2017-02-06 11:19 AM (#532569 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
January 2009
Posts: 1119

Location: Texas
There is a 50 year old rosette in that picture.
Top of the page Bottom of the page
tpa
Posted 2017-02-06 2:07 PM (#532577 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...


Joined:
December 2004
Posts: 406

Location: Denmark
https://www.youtube.com/watch?v=CXX36b_mlMo
Top of the page Bottom of the page
Love O Fair
Posted 2017-02-06 7:43 PM (#532601 - in reply to #532531)
Subject: Re: Warped & Cracked Tops...



Joined:
February 2016
Posts: 478

Location: Spin axis of a California map
Detlef... that is a very interesting story and result. I don't think I'm ready to dare that for starters on anything nice, but my niece has a trasher that I think I'll try it on just to check it out. Thanks for the recipe.

Oh, and what was your construction made of? How much pressure did you adjust it to? I'm thinking some kind of MacGyver-type thing with threads that can be used as an expander, braced against the inside of the guitar's back with flat wood, and connected to another piece of flat wood cut to fit the specific shape of the cupped area and pressed against the inside of the top.

Edited by Love O Fair 2017-02-06 8:01 PM
Top of the page Bottom of the page
DanSavage
Posted 2017-02-06 9:06 PM (#532603 - in reply to #532567)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
moody, p.i. - 2017-02-05 10:46 PM

Interesting to look and see that two of those tops were mine......


Yes, but I don't think that has anything to do with how you treat your guitars. :D
Top of the page Bottom of the page
DanSavage
Posted 2017-02-06 9:24 PM (#532604 - in reply to #532568)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
DetlefMichel - 2017-02-06 8:13 AM

I picked up all my courage and built a simple construction that I could put in the guitar and thus make enough pressure on the top from inside so that it became nearly straight. Then I used an infrared lamp and carefully heated the top from outside, so that I could hardly touch it ; I would estimate 50-60° C. I proceeded with this for about half an hour, let the whole thing rest over night and repeated the procedure. The waves on the side of the top (where the braces are) are still there but the rest is satisfactorily plain again. No cracks, no problems.
Sure the finish will shrink with the time, nearly all plastic materials do. I am an Optician. If you use older plastic eyglasses frames and you don´t make the lenses a little smaller time after time the frames will break, that´s no big surprise for me.
But maybe we could remove the tension of the finish with little heat? Did you try that one of the curved tops?


Wow! You're a brave man to apply 150-degree (F) heat to an otherwise perfect guitar, all in the name of BFLG science. LOL!

Actually, 150 F degrees would be barely warm enough to get the resin to its Tg temperature. Usually, it's up around 200 F degrees, so you were pretty safe. (Whew!)

When I was flying model airplanes, I covered my models with Monokote (known in the hobby as 'Moneykote') which is a heat-shrinkable mylar film with an a heat-sensitive adhesive combined with pigment. Moneykote was shrinkable to a certain point, but it would only shrink so much.

I tried heating the lower bout of Paul's 1113 top with my handy-dandy heat gun, which can easily get materials up over 200 F degrees. It did soften the finish, which allowed it to deform a little bit. But, as you noted, without holding it into place, it returned to its original shape as it cooled.

The heat-deformation of the top would not unlike a bowl-bend. As you experienced, when I did this to Jay's Balladeer, I needed to clamp it into position, then heat it and let it cool while still clamped. Even so, it took several cycles to get the bowl to the point I wanted.

Still, this does make for an interesting discussion.
Top of the page Bottom of the page
DanSavage
Posted 2017-02-06 9:25 PM (#532605 - in reply to #532569)
Subject: Re: Warped & Cracked Tops...



Joined:
June 2012
Posts: 1611

Location: Lake Forest, CA
jay - 2017-02-06 9:19 AM

There is a 50 year old rosette in that picture.


Yep. Between the top from #485 and my 1617, there's almost 100 years of combined Ovation history on that wall. :D

Edited by DanSavage 2017-02-06 9:26 PM
Top of the page Bottom of the page
DetlefMichel
Posted 2017-02-07 9:34 AM (#532612 - in reply to #532601)
Subject: Re: Warped & Cracked Tops...



Joined:
May 2011
Posts: 405

Location: Muenster/Germany
Love O Fair - 2017-02-07 2:43 AM

Detlef... that is a very interesting story and result. I don't think I'm ready to dare that for starters on anything nice, but my niece has a trasher that I think I'll try it on just to check it out. Thanks for the recipe.

Oh, and what was your construction made of? How much pressure did you adjust it to? I'm thinking some kind of MacGyver-type thing with threads that can be used as an expander, braced against the inside of the guitar's back with flat wood, and connected to another piece of flat wood cut to fit the specific shape of the cupped area and pressed against the inside of the top.


Oh no, I´ve just used some pieces of styrofoam that I had left from a package for my printer...Idid not take measurements of pressure or temperature, I just followed my intuition. I could have failed badly with this, but all was better than the guitar top before.
The guitar is a 1979 1119 with an extremely fine grained spruce top. I never saw a sitka with such fine lines, the colour is normal but it looks like a red spruce. I guess that fot too many years there had been too hard strings on the guitar, and maybe it was not played for a longer time and stored in the case with full string tension.
I use now very light strings with less than 10 lbs tension per string and the guitar sounds and plays phantastic, it´s the best playing of all my Ovations, despite of several bad finish cracks, nicks, scratches and waves on the top. I can play it with a 2mm string action with no buzz and the neck, neck angle and frets are perfect.

I would advice all of you who use old A-braced Ovations, not to use the .12-.53 "tow ropes" on these guitars, better use lighter strings. I prefer the Thomastik "plectrum" .11-.50 by Thomastik-Infeld.

Recently I bought the 1619 "Dan Savage" with the bearclaw top and forward X braces and even this guitar sounds VERY impressive with the Thomastiks.

Top of the page Bottom of the page
Jump to page : 1 2
Now viewing page 1 [25 messages per page]
Jump to forum :
Search this forum
Printer friendly version
E-mail a link to this thread

This message board and website is not sponsored or affiliated with Ovation in any way.
Registered to: The Ovation Fanclub™ Copyright (c) 2001
free counters
(Delete all cookies set by this site)