Official Luthiers Forum!

How are people but those tiny little ledges used on the underside of bridges to sit flush atop the finish whilst also touching wood for gluing?

A router seems pretty dangerous for such a thing? Dremel? Scraping?

Thanks in advance.

G.

_________________
www.leddingtonguitars.com

I use a Dremel, but I'm sure scraping would work for a very small ledge. The Dremel with something like a stewmac router base is very easy to adjust at the depth you want.

_________________
Pat

Search the OLF for "rabbiting bridges" and you will see multiple implementations of the jigs that we use and others here have made and use.

This technique benefits from precision a great deal making a jig essential IME.

Found a thread for you: http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=46531&hilit=rabbiting

Like this?
Proxxon router, depth adjusted by fine screw bearing on metal plate epoxied under router, laminate trimmer bearing.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I like this idea of rabbetting the bridge, which is relatively simple, but to acheive the mating relief in the top is another issue. Particularly with the vast assortment of bridge shapes.
Seems to me the opposite surface is equally important. Dealing with radius of the top, depth of finish etc. makes this a bit more complex.
I would prefer to finish the entire top, not have to mask the bridge area and deal with ridges from tape and finish, and then route prior to attaching the bridge, but a satisfactory solution has yet to come my way.
Currently, I sand the bottom of the bridge to the arc of the top, register the saddle to the desired position, mask and finish. While this works OK, I think there is room for improvement.

B

_________________
My memory is so good, sometimes I remember things that never happened.

Nice going Colin!

We only inset the ledge perhaps less than .010" trying to maximize wood-to-wood contact and we relieve the finish to match on the bridge patch which is usually a HUGE expansion over that the f*ctories and even Luthier guitars that we have to reglue bridges on had. In the repair world there may be a less than stellar bridge patch as a lifted bridge can take fibers with it and usually does so any expansion of surface area is first catch-up and then hopefully an improvement. After all when we see it someone already messed it up during manufacture or in the care of the instrument or both.

Bri you're right the bridge patch and preparation is also important, very important. We like to fit our bridges to the top shape/dome and this can be a bit of an art. From using and knowing our platen on our belt sander to refining and final fitting with a single edge razor blade on the bridge bottom I don't want the final fit to require anything more than light pressure from the clamps. Of course we snug down the clamps firmly but I want to see only finger tip pressure necessary to seat the bridge AND wings during the dry run.

Lastly do a final scrape of your fitted bridge bottom and bridge patch, just a couple light scrapes on both surfaces to improve "joint energy" (not a stoner term... ) removing sanding contamination at the molecular level for a superior bond.

I love that sales pitch flourish at the end

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Brilliant... thanks guys!!

_________________
www.leddingtonguitars.com

You probably don't want to be flush with the finish, shoot for a few thousandths clearance

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

This is one of the most common repairs that we do, and as such, we’re not at liberty to go rabbetting other folks’ bridges, so everything gets the finish scraped to the perimeter of the bridge footprint. And guess what — at least 85% of our bridge reglues are originally ”let-in”. And often, especially on production guitars, but also on many big-name builders, the finish ledge is up to 1/8” or more. That translates to a good 15-30% less gluing surface. We also often see evidence that anomalies around that rabbetted edge keep the bottom from coming into good clean contact with the bare wood top.

Scraping all the way to the perimeter requires nerves of steel and a steady hand, but as with anything, practice makes perfect, and in the world of boutique instrument repair, nothing less is acceptable. And for the same reasons, this is how I do all my own bridges. I will scrape a tiny chamfer around the edge of my bridges, and when scribing around the bridge footprint, I’ll hold my scalpel at a slight angle that’s complimentary to the scraped edge of the bridge.


Sent from my iPhone using Tapatalk Pro

_________________
Mountain Song Guitars www.mountainsongguitars.com

Ken if you mean by "let-in" that the maker did not clear finish to the bridge perimeter yes of course that's how it goes. In fact I don't believe I've ever seen a bridge installed with finish cleared to the perimeter unless it's been reglued prior and a repair Luthier did it.

We don't like what you do and others too, no offense intended but clearing to the perimeter when done well with that uber steady hand loses serviceability for the next time the bridge lifts.... Or, in other words a bridge patch cleared to the perimeter originally is highly likely to suffer visible finish damage from the bridge removal process when and if the bridge has to be removed again because it lifts.

It's often the case the instruments that suffer a lifted bridge have good reasons. Poor bridge plate condition, high saddles, over rotation, loose braces, an a-hole for a current steward who lets it dry out over and over, and so and and so forth.

And you know what happens after you and I repair and reglue the bridge and return the thing to the owner? It often goes right back to being abused or if the underlying causes were not addressed including poor design when nothing in particular may be wrong the bridge may lift again.

The practice of clearing to the perimeter is widely done but again the hit that future serviceability takes makes it not a way to go for us. Bridge regluing should be absolutely invisible with no trace that it's ever been off and back on.

Regarding rabbiting you are right many makers leave lots of surface on the table with finish on it. Our inward rabbit may be .010" or less meaning that we very nearly clear to the perimeter for the same reasons that you do, more gluing area. Additionally the depth of our ledge is precisely done so that the bridge bottom is firmly in contact with wood.

These days only a few manufacturers are doing the rabbiting thing. Taylor, Collings are two that I am aware of but I am aware of a host of small Luthiers who rabbit as well. I rabbeted the last couple dozen that I built.

Anyway different strokes for different folks. We do agree on maximizing wood-to-wood contact area. I'll add that clearing finish to .010" of the perimeter also requires nerves of steel..... and a high pucker factor.

." Or, in other words a bridge patch cleared to the perimeter originally is highly likely to suffer visible finish damage from the bridge removal process when and if the bridge has to be removed again because it lifts."

That is why some luthier suppliers offer oversized bridges.

It's also why informed players often don't want a larger, heavier.... bridge. No one has to go there, clearing to the perimeter is not necessary and not doing so preserves the ability to keep the instrument original by using the original bridge.

There are tens of thousands of beloved guitars out here with BRW bridges. If we have to go oversized technically we cannot legally replace a BRW bridge with BRW..... To many this would be an unacceptable downgrade.

Wow. I think this is important.
I have always been a die hard advocate of scribing the entire perimeter. I even composed another of my usual rants on the subject and saved it as a draft because I'm sick of hearing myself take more lonely swings at a dead horse. Having Ken jump in and echo my thoughts was uplifting. Thanks Ken!

Hesh, I have so much respect for the experience you and Dave have, I almost always experiment with how you guys do things or, at very least, understand where you are coming from, even if I choose another way. I also try be open to advancing my definition of best practices.

To that end, what do you (or anyone else) think:

Every other joint except the neck joint is expected to be glued together and stay that way. If a bridge comes off, it's because of poor design, execution, or care. I believe they can be designed, made, and installed, to not come off. Certainly not with anywhere near the regularity that they do. I've always assumed the goal was to fix the underlying design and execution problem rather than concede that, because they sometimes come off, we should make them more serviceable, especially when making them more serviceable may add to the rate of failure.

Super thick finishes can be seen as part of the removal Problem. If a removal tool hits a deep rabbet ledge .010"inboard, it's still going to be dicy getting a hide glued bridge off anyway.
A bridge can be routed off as well if necessary. I think an argument can be made that routing should be a more common method.

I certainly don't want to make life more difficult for myself or the next luthier down the line. I have not yet seen a bridge that's cleared to the perimeter, glued with hide, with a thick ledge of finish that needed to come off but I can envision the problem. I'm interested in hearing about scenarios you have dealt with. If it's lifting, wouldn't it be showing above the finish anyway and give a starting point for removal? I've had good luck with inset bridges, Including rabbeted ones, by putting a back up layer of thin material in between a spatula and the top to reduce or eliminate any bruising of the finish.
Frankly, removing any bridge glued with non heat resistant AR glue is like taking candy from a baby and heat resistant glues require considering other methods of removal. (Tomahawk perhaps? )

As an aside, I have never, not on an instrument, or even a photo on the OLF, seen a rabbet that looked to be .010" or less.

It seems like a lot of this dilemma could be largely avoided if there was a little more margin for error in footprint size and bridge design. Then a small ledge would not be such precious real estate on a reglue and we could have our rabbet and eat it too.

Here's what's on my bench right now. An old Harmony sovereign. Glued with hide. showing the problem is not new. If it was cleared to the perimeter would it have come up? If I do it, will it make future removal more difficult? Should I just say, that's the future, my job is to glue it on the strongest way possible now? It lasted 50+ years. If I glue it better than the factory did, with a larger footprint how long will it stay on? Hmmmmm..............

From a builder and players perspective I see the flip side of this. If a larger bridge is worse than would a smaller lighter one be better? The un-glued trim ring around a rabbeted bridge adds almost nothing but weight. If that exact weight is necessary, why not get the added stiffness and durability of gluing it all down?

Again, I am only interested in doing the best work I can for the customer and instrument, not a gratuitous ego battle. I'm thinking hard on changing how I do things.

Hey David all good points and hopefully here are a few more.

"I've always assumed the goal was to fix the underlying design and execution problem rather than concede that, because they sometimes come off, we should make them more serviceable, especially when making them more serviceable may add to the rate of failure."

It's not about making something "more" serviceable but all about not taking serviceability choices away down the road. If how we fix something today precludes the same possibilities of similar, high quality work in the future we are reducing future serviceability. Clearing finish to the perimeter is often disclaimed to our clients when we see it up front as some finish damage may occur. You know why? Because it may and setting expectations honestly is important. There is also no evidence that our very minimal rabbit may add to any rate of failure, that's a leap.

Ken mentioned taking liberties of rabbiting someone's bridge bottom. How is reducing future serviceability by clearing finish to the perimeter not taking a liberty? Of course I see our roll as the "trusted advisor" who is authorized to do what it takes in terms of a best practice to safeguard and protect our client's valuable personal property. That's why they brought it to us, it's a trust thing.

I'll have to try to get a picture of the rabbits that we make. You barely can see them and they are .010" or usually less than that when Dave is doing it and maybe only .003ish upward depending on film thickness. The amount of added wood-to-wood that perimeter clearing folks get over us is mouse nuts.

We've had to remove bridges with our very own rabbit before. As mentioned we had a string of Fish Glue bridge failures ten years ago and many of those came back. We likely average several reglued bridges a week making any issue with our methods something that will come back to us in spades..... During these removals the rabbit never inhibited our ability get clean removals.

Importantly though because of the rabbit had we cleared to the perimeter the likelihood of visible finish damage would have been far greater.

Regarding the cool ole Sovereign clearing the finish to the perimeter won't make any future removal more difficult but it will make future removals more likely to have scope creep when one has to do finish repairs. Since some folks do lousy work it also increases the possibilities that someone is going to get their guitar visibly hacked-up around the bridge. That opens a Pandora's box for higher costs or something to go south.

You know I don't see my job as attempting to right the ills of the original maker. That's not something that I would do with a client's $75,000 D'Aquisto nor would I do it with a Mexican Martin. I do see my job as being free to improve upon the processes of the original maker's intent but not reengineer the thing. This means I expand bridge patches greatly too for the same reasons and don't consider that any more "liberty..." than my choice of glue.

Lastly is a bridge joint regardless of intent by the original maker reasonable to assume that it can be a "forever" thing? I think that you may think that it is and I know that I think that it's not. Musical instruments, really good musical instruments..... seemingly the best instruments in my experience are built on the edge.

If we prevent the bridge from ever lifting and bolt that SOB down with 1/2" nuts from Ace Hardware surely it will never lift. But how hard do I have to hit the stinking guitar to get an audible response when I play it with a hardware store of mass on the sweet spot of the top?

Looking at some of the best sounding and most coveted guitars in the acoustic realm they are often under built, had much service in the past and bridges tend to be on the small and less massive side of things. One pre-war Martin that we assisted in brokering the sale of some years ago comes to mind. It had been played by many famous players since it belonged to the venue. It's bridge had been on and off at least three times that we could tell and based on what we were told by it's owner. Fortunately it had never been cleared to the perimeter making regluing it again, invisibly completely possible.

Is it then my job to replace a vintage, little BRW bridge with an over sized honking bridge from Stew Mac or do I jump through hoops to preserve the original and when I can't I duplicate it but I don't change it, I don't make it bigger.... or at least I don't want to. It's a preservation thing to me more so than shooting to make any improvements on one level regardless of the possibility of degrading it on another level.

There is a LOT of prior work out here as you know that these days we look at the folks who did it with a critical eye as they shaved bridges and cut off fret board extensions. Really good work should never in any way preclude the ability to have really good work again some day if it's ever needed. That's my take on it. This is also why we would never do anything that makes servicing in the future more difficult or have a lower possibility of being straight forward.

Dave lots of folks clear to the perimeter. We can agree to disagree. I will suggest respectfully though that the next time you have to remove a lifted perimeter cleared, prior serviced bridge on a 63 Gibson in otherwise EC that try as hard as you can to not crap your pants when you see that piece of sunburst finish fly off the guitar because the finish was cleared to the perimeter.... . Yeah, yeah that may be overly dramatic but that's exactly what can result.

Lastly if anyone asked me to guarantee that a bridge that I reglued would never come off again I won't. I guarantee my work and if that happens and it comes back to me and it's not abuse or structural issues and I'm not dead yet I'll fix it free. But I honestly believe that bridge joints are not designed to be a forever thing and realistically and practically nor should be even though we can. What would result might be something like an Ov*tion....

Colin forgive me please for borrowing your pic to make a point AND I am not being critical of you. I applaud you for rabbiting your bridges!

Our rabbit is much smaller than this one. I can't know but if the inset is .100" in the pic you could fit at least ten of ours in this single rabbit. Our depth depending on film thickness may only be several thou.

As such with our rabbits the pallet knives being much thicker themselves don't get snagged on our rabbits making removal no more difficult and in terms of finish damage possibility less risky than clearing to the perimeter.

"I'll have to try to get a picture of the rabbits that we make"

Hey Hesh,
You need rabbits to make rabbits, mouse nuts won't work!

Yeah but rabbits lead in short order to many more rabbits......

Hesh, and other posters, the bridge in the pic is not a bridge "to be used".
It was a SCRAP bridge used as a quick test piece when I first made the jig.
Sorry for any misunderstanding, this was made clear in the original post
Not only is the rabbet far too wide, the depth is about 25/30+ thou! (Similar to finish thickness on Ova**ons)
On a bridge I would be using, it would be almost invisible, unless the light was just right.
My last one was about 15 thou wide x 5 thou deep (~4 thou finish)

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Here's one more thread from a couple of years ago also citing the serviceability concern of removing finish to the presenter of the bridge:

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=46893&p=620916&hilit=bridge+rabbit#p620916

Looking at your link, I see we had this exact conversation two years ago. mostly the same participants. I have no memory of it. It makes me feel like the time to take that long walk out on the ice is drawing near.



Very effective imagery!


I hear you Hesh.
Thanks for indulging me. (again)
I didn't intend to imply that you don't make rabbets as small as you state, just that everyone else's I've seen is at least several orders of magnitude larger, making them a pretty big exaggeration of what you're describing.

I have used a rabbet when I saw no other way, but until your mention of it, I've never felt the lack of a rabbet was the deciding factor in getting a bridge off cleanly. I've pulled a fair amount of bridges but I'm sure the number is nowhere near Dave's alone so I take your collective experience at face value.

I always warn customers of the impossibility of guaranteeing perfection. It's obviously far better to deliver perfection and surprised them than the other way around.


It's a fickle line. Frequently we are faced with builder intentions that are completely at odds with their engineering. We are tasked with making it work. There are countless examples. Gibson plastic bridges are one extreme . No one tries to preserve those. A more relevant one for builders would be guitars with those cute little traditional 1" wide bridges. The intention of the builder is clear but if it has a 1/16" rabbet subtracted all the way around from the footprint, and tall string height, I think it's poor engineering. If the bridge is lifting, I feel entitled to take the entire 1/16" that was thrown into the trash in the name of perfect looks and put it into service for my customer, Hopefully keeping the bridge on for at least the rest of their lifetime.
But as you say, the game changes again with vintage stuff. They get a pass on bad ideas.

I'm going to reverse my program though.

I'll use the micro rabbet as standard and only cut back the entire finish when I think its the only way. Certainly the Sovereign is easy. There is .250" of terrain to reclaim behind the bridge. I'm perfectly comfortable only taking 90% of it back. If you and Dave say it makes clean removal easier down the road, that's good enough for me. I only need to hear it a half a dozen times.


When that terrifying Gibby burst chip takes to the air, I doubt it will stop and salute at our silly little rabbet border. It will most likely sail on by and let out a mocking laugh as it parachutes into the eboney chips on the floor and quickly hits it's cloaking device.

And Clay, with new gene technology, making rabbits with mouse nuts is right around the corner.

OK at the shop now and found an old bridge that we use to set-up the rabbiting jig. The rabbit pictured is three times what we do, it's ,030" inset and around .010" deep. Dave is fond of using around 1/3 or so the inset of this one and only the finish thickness plus a thou or two for the depth.

One of the very cool things about this technique at least to me is that the bridge patch on the instrument is also cleared of finish to match resulting in a "pocket" of sorts. You can feel when the bridge drops into it's pocket for positioning even though we also make a masking tape well of sorts too. I'm always reassured when I know that I felt the "snap" of the bridge failing into it's pocket knowing that I likely didn't glue it on to the back of the instrument....

Dave my friend we are not getting any younger.... I often feel like I have not said anything new OR read anything new here or on any forum in years. It's likely that I'm here anyway because I need a life and maybe I like helping people too although in the last couple of days that's been under further review...

I never took any offense from anything that you wrote and even though some folks are uncomfortable, some males... with my directness at times Dave you are one of the ones here who I pay attention to. You're in my view both brilliant AND highly skilled with lots of experience and that makes you someone to listen to, always! Remember I'm just an old corporate puke/executive trying to do something that I actually like before I take that walk on the ice.... I'll add that it has worked out very well for me, I've never been happier!

We don't always rabbit either. At times our overhead for some POS repair is too high, how we do things and how long it takes so if it's appropriate for the instrument we might nix the rabbit. We only not rabbit with very thin finishes too so that the finish ledge does not preclude decent contact for very far.

For F's sake I just miced my favorite pallet knife to further illustrate how the rabbit, the ones that we do don't bother the pallet knives at all during a future removal if need be. It's .012" when out rabbit is 1/4 of that or so.

Anyway this method is not for everyone and if you can't do it quickly you will likely lose money on it too.

Lastly regarding removal with a rabbit you already have a finish ledge. Do you prefer to crush the visible finish ledge with no rabbit or crush the finish ledge just out of sight inside the rabbit....... I know what I prefer, when the client pays the bill...