Official Luthiers Forum!

Maybe that is why I ALWAYS have problems with under the saddle piezo's

But in all fairness I always have issues with them on anyone's guitar. I hate the darned things but usually manage to get them to balance out.

Yo, Hesh

Me too is sorry to read that you tops are doomed.

Please, if you wish, send me some pics of your dish and bracing/clamping method and any other pics associated with makeing the tops, me will print them out and show them to the Shipebo curanderos at this weeks ceremony and perhaps they can do something about removing this curse for you.


blessings

Padma

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Audiences and dispensations on Thursdays ~ by appointment only.


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Hesh, to make things clear I fit my bridges to the theoretical radius of my top! I do leave a very thin overlap of varnish under the bridge though. As Todd pointed out, if there is a small gap at the wings (for Martin style bridges anyway), the slightest pressure will align things.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I agree that a radius block does a much better job than just taping a piece of sandpaper to the top. The main reason I do it this way is so I can glue the sandpaper down to the block. With the paper glued down, there is less tendency to oversand the under side of the wings.
Makes it much easier (and faster) to get an accurate arch on the bridge.
My block is domed on both sides. 60 grit on one side & 220 on the other. Once the fit is perfect, a few quick passes with a scraper (immediately before gluing) takes off the sanding scratches & makes a fresh surface for the glue.
I HAVE had trouble with bridges coming off... This method seems to have cured that.
P.S. I always sand my bridge plates in the dish, just before gluing them down.

Any one piece that requires a bit of clamping pressure to fit tight isn't going to be a big deal. But the cumulative effect of a lot of little things being clamped to fit, throughout the guitar?

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I am hating to hear sanding on a piece of paper taped to the top called "flossing." The usage was tolerable (even though a bit idiosyncratic) for drawing sandpaper through a neck joint. What does sanding on a piece of sandpaper fixed to a form by moving the part to be sanded have to do with flossing? It might make sense if flossing one's teeth consisted of a stationary piece of floss and movable teeth that are rubbed against it. Is fitting anything by means of sanding material off it now to be called "flossing"? It sets my teeth on edge.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I'm reading here that some use to scrape the surfaces prior to gluing. I saw it here so I'm writing here, even if it doesn't apply only to bridges.
I've been taught that wooden surfaces to be glued are not to be smoothed out too much before gluing to achieve maximum gluing strength. Actually, it would be better to leave them quite rough: for instance a cabinetmaker that veneers the traditional way would prepare surfaces with a toothed scraper before gluing with HHG.
Perfectly flat surfaces ain't good for gluing especially with water based glues because it's the glue that penetrates into the wood that makes the bond strong. Scraping also pushes down superficial wood fibers, closing wood pores and making the glue penetrating worse. The water in the glue may rise the fibers, but I wouldn't bet that is what I'd want in this case...
Personally if I need a strong bond I wouldn't sand the surfaces with a finer grit than 120... It's not that a planed surface won't glue at all, only I think the resulting bond wouldn't be as strong...

In my experience, the bottom of the bridge will become curved on the back edge from string pressure over a few years, regardless of how it is shaped to start with. The issue is whether the extra stress during the clamping of a flat bridge has a lasting negatve effect, and I have just not seen it.
The main issue I have encountered that causes me to fit the bridge more carefully on old guitars has to do with the front-to-back radius that is often created in the top and bridgeplate when a bridge lifts. Clamping a flat bridge in those instances can create extra stress that tends to crack the bridge through the pin holes. Though the bridgeplate can be heated and the top clamped flat, I have found that those guitars work better if I match this front-to-back curvature when shaping the bottom of the bridge.

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John

John, can you explain your method for matching this type of curvature in a bridge glue joint? I have seen people lay sandpaper on the top and just rub the bridge along the area where the bridge will be glued, but this might be more difficult in an old guitar where you have more front to back curvature.

Jonas

Finally something worth discussing!

What I be hatin be when people be all flossin dey pimped out guitars all over de internet.

http://www.urbandictionary.com/define.php?term=floss

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http://www.chassonguitars.com

Marco, this is a myth from the time when the glue bond was thought to be a mechanical attachment in the form of "fingers" of glue reaching into the wood. It was thought that scratches gave the glue a place to grab on to. Some of that does occur, but on a much smaller size level than used to be imagined. Actually, most of the strength of glue joint is from chemical attraction at a molecular level. Glue does need to wet the surface of the wood, but this is wetting that occurs at a microscopic scale. The glue itself is a rather weak material (with the possible exception of epoxy) and its thickness should be minimized.

The reason for toothing surfaces to be veneered is to provide a place for excess glue to go, so it won't form a bubble. This is a problem only when gluing a thin material such as veneer over a large surface.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Duh Padmas
Diamond impregnated dental floss...
*works great on Scroll and coping saws,
*cleaning out nut,
* bridge slots
* fret slots
* hundreds of other uses.

Great for dentures too!

$20 for a 500ft role, in an envelop to the Padma C/o dis here web site. Sorry no plastic or COD orders.

Order now!


blessings
Padma


PS: Tanx for the idea Howard. Lance, Brock and me, well we gonna cut you in for 10%

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Audiences and dispensations on Thursdays ~ by appointment only.


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OK Howard you're right as usual and I'm doomed....

I'll revisit my toot at some point and nix calling it "flossing" in your honor and instead call it "sanding" which, unless you have any objection seems to more accurately describe the verb.

Not that I am arguing mind you but when I floss a neck joint early on I do the heavy lifting so-to-speak with a piece of stinkin sandpaper stuck to the guitar body and I move the neck around instead of pulling strips. Maybe this is where I got confused (about this task...) and started calling sanding anything on what it's going to be mated to flossing.

FYI my business cards list me as a "Loothier" since I learned that spelling from you too.

We're all doomed I tell ya, dooomed......

Padma my friend I'll take two and forward the appropriate funds to this here web site c/o You! I also may take you up on this source that you have for removing curses....

Doooomed I say!


Atom bomb cake...

Indeed, surely I wouldn't glue a surface treated with a toothed cabinet scraper with HHG or titebond when searching for the strongest possible bond (unless maybe with epoxy), but still I don't know if a smooth surface with fibers pushed down is what I'd search for when gluing (especially on a dense, oily and close-grained wood). A too rough sanding ain't good either, but 120 is fine enough and even 80 would do for some tasks.
All I know is that the both the cabinetmaker I worked with and the luthier I had lessons with had similar opinions about it. The latter made me sand the bottom of the bridge (that has been previously scraped) to have stronger bond.

Anyway I'll try to do some specific test anytime soon to check what works better... trying it yourself is the best way, I suppose...

That picture is priceless!

Hi Marco - I like that you want to do some of your own testing, that's what I do too when trying to sort though some of the information that is in conflict with each other. Good going!

I like "lapping" as Todd suggested. But I think technically, first you rough sand, then you lap.

You didn't learn that spelling from me!

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Oh yes I did learn that spelling from you....



It was in this thread: http://luthiersforum.com/forum/viewtopic.php?f=10101&t=21071&p=292399&hilit=Loothier#p292399

Like it or not Howard you have had a major influence on many of us - some of it was actually positive!!! Seriously you are one of the guys who I have always listened to and I'll never be sorry for that.

Filippo I agree that this is a good discussion, kind of like the old days too, eh? I also agree with your surprise that I share regarding #1 in your post and 80 grit.

Regarding over built steel strings as I think that I mentioned I had a Gallagher in here that had a number of issues and it was new too... The neck was over set making a high saddle necessary and that lifted the bridge. The thing weighed over 6 pounds and reminded me of Internet dating just moving it around my shop... Anyway that bridge was also smashed onto some thick finish that was under the perimeter of the bridge and needed to be cleaned up/fitted and reglued.

The top was spruce, probably sitka but around .140 at the sound hole edges. As such the non-fitted bridge and the thick top were not liking the idea of being smashed together with brute clamping force and the bridge lifted along the back and both wings were up too. It was nearly self removing.

The owner was obviously not pleased with the guitar needing to be fixed so soon and the action made it nearly unplayable too. We reglued the bridge, discussed that the neck angle was over set and needed to be reset if the guitar was to be kept (it's not being kept) truss was adjusted and saddle lowered after a mini fret dress. It played better and hopefully will no longer try to toss it's bridge away.

So yeah there may be something to the idea that an over built guitar and possibly an inflexible bridge design, mine is pretty inflexible, may not stay in place well unless fitted well.

One assumption there is that the goal is "the most superior" bond you can get. My goal for all my joints is simply that the glue joint is stronger than the wood by a reasonable margin. From everything I've seen, wood surfaced with 80 grit easily meets that criteria provided everything is well executed. If things aren't well executed, the best surface prep isn't going to help.

I've only repaired about a dozen lifting bridges (none on my guitars) but none of the failures had anything to do with surface prep. Glue was always still well stuck to both surfaces. It's the glue itself that comes apart either from heat or more often, from too thick of a glue line.

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http://www.chassonguitars.com

That is precisely the point. A roughened joint will have a thicker glue line than a smooth joint. Less contact area. Therefore weaker, more prone to failure.

L.

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Cut to size.....Beat to fit.....Paint to match.

Exactly so.
Some will think a problem or operation to death, argue whether terms are correct, haul up scientifical fact based on recent tests, etc. to promote the "best" solution.
Others will just "do" based on longtime experience.
Almost all that has been said is good, but just imagine a beginner reading this. OMG, what do I do!?! Do I radius, sand, floss, scrape, lap, or just give up?

At some point rougher sandpaper would mean enough more glue to be prone to shear, but have you reached the critical point with 80 grit? My sanding disks are 80 and seem to be fine. Maybe there is less pull on the whole top than the bridge.

80 grit is absolutely adequate. I've been using it for all the guitars I've built and have yet to see a bridge pull up. 1000's of guitars came out that way from a production shop, if it was a problem I know the method would have been changed long ago.
More important is the fact that for rosewoods and ebony the surface must be freshly sanded (or scraped, whatever floats your boat) before gluing. Oxydized oils on the surface will compromise any glue joint.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I'm curious if people are actually having glue failures that they can attribute to surface prep with 80 grit or if this is, as Haans says, just "theory" and over-thinking. I've got 15 years worth of guitars out there and almost every single brace is surfaced with 80 grit and I have not had a single failure. All my scarf joints are surfaced with 120 and no failures. I scrape most of my bridges (mostly at the last minute to get rid of oils and contamination) but I use 120 grit to smooth the top after routing the finish off. Again, 0% failure rate. I also have glued up dozens of test samples over the years and never seen a problem due to 80 grit surfacing.

I have no problem to be solved. I'm simply suggesting that if any of you do, you would probably benefit by looking in other places first. Poor fit, not enough clamping pressure, too much open time, bad glue, that kind of stuff.

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http://www.chassonguitars.com

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