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Guitar Building = Continuous Improvement Process

I HHG a flat bridge sanded to 80 grit on the bottom to a cylindrical radius top, no problems. Strings pull the bridge into a radius anyway. If they don't, the instrument is perhaps overbuilt.

Right but what's the point in accurately radiusing to any number when what's desirable IMHO is that everything works as a system AND stays in place for a very long time. Meaning that the dome that results with a bridge on it that stays in place and works well with a neck angle in the ball park that is then precisely fitted as required to be properly set. Everything has to be final fit/flossed/set to fit and not to a spec anyway regardless of how accurate we produce any component. This notion of what dome radius number we individually may choose has a lot to do with the neck angle that we shoot for too. It's all a system and nothing in isolation will by itself a great guitar make.

I still think that suggesting that builders use clamps to make things fit instead of carefully fitting the parts together and obtaining a 100% wood-to-wood fit prior to properly (per the glue used) gluing in place is a recipe for failure at some point. That's why I look forward to John's posts in that I am probably missing something here regarding his methods and why this works for him.

Also, since we are talking about forcing bridges into place with clamps it should be considered that if one does this they had probably also consider not pre-routing the saddle slot because if the slot exists prior to distorting the bridge with brute clamping the slot bottom will no longer be flat. Wonder if John routes saddle slots after bridge gluing? This is another example of how easy it is to take an idea out of context and not consider all of the ramifications.

Didn't see your post Haans - so you too eh... Got me wondering if I have over thunk... this...

A good friend of mine glues his bridges flat, has been doing it forever, and makes some of the best guitars I've heard in the pre-war paradigm. Very light pressure clamps things together gapless in any case, and string tension will give the bridge/top/bridgeplate a nice arch anyway.
I've always been surprised by the technique of sanding the bridge bottom on the top. I would expect the top to move under the slightest pressure (unless overbuilt), so how accurate can it be?
I use a 5' cylindrical top, my bridges are sanded to 80 grit on a matching caul. Fits perfectly and light clamp pressure pulls things into place anyway. I don't rout a rabbet and expect the thin finish to be easily crushed by clamp pressure, I leave about 1/32"+ overlapping under the bridge. It's a small footprint and I've never had one pull up, which doesn't mean I won't at some point.

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

Well Hesh, "Some folk do like this, some folk do like that..."
I tend not to think too much about individual parts, but consider the whole. I have a rather large cyl. radius, but there just isn't that much gap on either side before gluing. There's so much stress on the top from the strings anyway, and unless you have your build room to a constant 1-2% humidity change, you will likely get some top movement anyway. I just had a top go concave, but ended up flat longitudinally because it was bent over the dish in the ribs. Ahh, Larsons...

The 40 grit comment was just for gross wood removal on the belt sander in the initial radiusing of the bridge blank before cutting it out. A second pass is done with 120 grit to remove gross scratches. It is later sanded on the top with 150 grit, then scraped before gluing. No scratches are left by this time. The bottom is as slick as a piece of glass. It is then glued with HHG.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Thanks Waddy I like your belt sander idea too and may... borrow it.... I have a problem hanging onto things on a horizontal belt sander and I can't begin to tell you how many time my nuts... and saddles have been smashed against the wall as a result....

Thanks for that Haans and not only were/are Larsons very cool so too are your very fine guitars!

Laurent thanks too - a lot of the bridge reglues that I see in my shop are factory guitars that under cut the finish and did not make a ledge on the bridge. I don't think that these bridges are fitted either in that they flatten out when off the guitar and I have to scrape in the fit before regluing. Not questioning your results either I just continue to find it curious that so many of you are doing fine with unfitted bridges and when a bridge is very suspect to coming off in time anyway.

Hesh,

On my guitars anyway the distance the saddle slot takes up across the top is so negligible I don't think it won't make a difference. On paper yes it may be distorted but in the real world not enough to cause a problem. When I fit a flat bridge to an arched top I can literally press on the wings and see no light through it at all. I don't have to use a lot of force to clamp it in place either so I'd be hesitant to even refer to it as a brute force method.

What is interesting to think about though is what affect on tone the flat bridge has as it creates a different stress field radiating off the wings. Good or bad? Who knows?

These forums present a perfect vehicle for overthinking... I like to keep it on the side.

Haans I resemble that remark...

JF in your described situation where there is very little gap in the bridge wings prior to clamping it may not make any difference. If I put an unradiused bridge on one of my tops there is enough gap that when clamping the bridge into place the saddle slot bottom distorts.

Why this matters is that if a client wants an UST pick-up and the saddle slot does not have a flat bottom it will need to be flattened. No biggy but being the sort who really does not want any other Luthier ever hacking up my guitars, I prefer to hack them up myself... I try to make it easy for things that are commonly installed later. In other words serviceability where things that are expected to be flat and true such as nut slots, saddle slots, etc. are important to make flat and true IMHO.

USTs are well known for being uber sensitive to saddle pressure along their entire length.

If you wanna get into the influence, if any, on tone let me know in advance so I can put on my athletic cup....

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...