How precisely does an archtop bridge need to fit?

[garybaldy]

According to the international standards of weights and measurements...

Less than a paper's thickness, enough to allow light through, and for that light to disappear when pressed. Just enough to assure that the strings will seal the interface rather than cause the ends to lift. Avoiding the base to be convex in any way is the name of the game.
Again, this is just what I strive for, and it seems to fit. For me.
In violin family lutherie, everything rests on two feet, that assures the greatest amount of movement along many axes. Some earlier luthiers used bridges with two feet, actually building an open space in the middle. Guitar lutherie is a relatively young art and it was Jimmy D'Aquisto who had an unquenchable thirst for innovation and understanding. He saw the bridge as an integral part of the top. On my own Jimmy D', the bridge is surprisingly thin, but the base is WIDE, and the transitions in depth are smooth. This was the way he saw ideal.
Either way, I believe that pressure at the outer edges of the bridge foot are more important than the centre pressure if the outer edges don't even have contact. But I am not but one person with my own notion about why and how things work.
I worked with a great luthier Al Carruth and he was CONSTANTLY evolving his designs. Low mass bridges, high mass bases that stored energy, archings, graduation depths changing with archings... it's all part of a system. One thing that was always a minus: Sloppy transitions and undefined edges. So when you see light at the edge of a bridge foot, some edge where the bridge goes from touching to space is not clearly defined. This means energy is sloppy at that transition point. Avoid that. It's just inefficient. There was a maxim: If it looks beautiful and has clean lines, it tends towards naturally clean sound. If you have a mug with wonky surfaces, it won't "ring" the way a beautifully crafted bone china cup will. Function follows design.
That slight smidge of light is to assure a better "seal" at the outer parts of the foot. Smooth and gradual transitions, defined edges.
In my narrow view of things anyway. I will never argue with someone else's success otherwise. I just try to understand how and why it is better.

Thanks!

[chris32895]

Thanks for all the inputs, all strung up it sounds pretty good and I see no gaps except maybe a smidge at the ends, which is fine with me.

One thing, though, is that I'm not 100% if the saddle's top is a good match for my guitar's fingerboard radius. My guitar has either a 12" or 14" radius on the neck while the top of the saddle has a too flat radius closer to 20" meaning when I get good action on the E A B e strings the D G strings sit too low resulting in buzzing on those strings alone. Raising the action will cure the low D G, but make the other strings excessively high. The original TOM saddle has a top radius closer to 12" and as such I did not have this issue with the stock bridge.

Solve one thing, another problem I guess, lol

[RJVB]

First, protect your guitar

Clever use of the case for that!

and with a flat cabinet scraper or wide chisel add a slight concavity to the centre part of the base. This is just the smidge needed so the string pressure pushes the bridge snug against the top

As I think I noted above, that's what my own stock bridge has, as evidenced from the build-up of fine dirt along the centre part of the base.

How long/large is your smidge? The only way I can picture though this concavity would allow string pressure to press the bridge more snugly against the top would be if it extends to some distance (probably well) beyond the location of the posts. And only then even if the base is thin enough that it will actually flex more easily than the top itself.
But that seems like a really large concavity to create "free hand" with a scraper of chisel?!

Solve one thing, another problem I guess, lol

Exactly what I ran into (and my fretboard is 16"). I think you're supposed to file down the saddle to create the radius you need. With the "terraced" aspect these micro-intonated saddles have it's actually not very difficult to lower individual "segments". Just put a file on slanted front side and take off material taking care you keep the file at the same angle. Once you're close to the desired height you do the same thing at the back (if slanted) and then recreate the top edge to preserve the original compensation. I've started doing that with my stock saddle and a file that's narrower than the segment width (the treble slots had become way too deep, plus I want the G string action to be as high as needed because of a high spot on the 1st or 2nd fret but the treble string action as low as possible). Looks a bit weird but also looks like it was hand-made

If you can, just order the AllParts equivalent with the bone insert. It probable has the radius you need, and the saddle should be exchangeable with your wooden saddle. Maybe you get the same surprise as I that you actually prefer the sound with that bone saddle!

[Jimmy blue note]

You have an all wooden bridge now right? That's easy to get string height and radius matching then. If you have nut files, or thin files or even exacto saw, you can cut grooves into the bridge saddle and cut down (as you would a nut height set) to adjust the radius.
While there is a debate as to whether the string should rest on top or into the saddle, I do cut into in order to get a good radius fit. I've seen this on a number of Benedettos and other high end guitar builds. It sounds fine.

[RJVB]

While there is a debate as to whether the string should rest on top or into the saddle, I do cut into in order to get a good radius fit. [...] It sounds fine.

You never get complaints about buzzing, even when digging in to get the maximum acoustic volume? Maybe because your slots are clearly V-shaped (but rounded at the bottom)?

It's probably purely my imagination but when I see slots like that for the trebles I can't help but fear those strings will cut deeped and deeper into the wood. Of course I grew up seeing the same kind of strings being used as a garrot to cut big cheese wheels in half and I wouldn't be surprised if heavy round-wound strings are much harder-wearing on the saddle wood!

[chris32895]

You have an all wooden bridge now right? That's easy to get string height and radius matching then. If you have nut files, or thin files or even exacto saw, you can cut grooves into the bridge saddle and cut down (as you would a nut height set) to adjust the radius.
While there is a debate as to whether the string should rest on top or into the saddle, I do cut into in order to get a good radius fit. I've seen this on a number of Benedettos and other high end guitar builds. It sounds fine.

You able to palm mute at all with a setup like that?

[Jimmy blue note]

You able to palm mute at all with a setup like that?

Those string guides are cut pretty deep on this Benedetto, no problem at all, but results may vary with the individual.
But they are also cut into the saddle even on the centre strings, which is by design on a number of Benedettos I've seen.
We're talking about compensating for radius curve here. If the string is resting on the top edge of the saddle (as convention dictates) the depth of the slot at the high and low string will only need to be twice the radial difference at the 12th fret, which is less than a mm. Take that and subtract the existing radius of the saddle and you're talking the tiniest depth to achieve a perfectly radiused arc on your saddle. You won't feel it in your right hand but your string height will.
Nah, it's not going to make a bit of difference to your picking hand. IMHO

[Jimmy blue note]

You never get complaints about buzzing, even when digging in to get the maximum acoustic volume? Maybe because your slots are clearly V-shaped (but rounded at the bottom)?

It's probably purely my imagination but when I see slots like that for the trebles I can't help but fear those strings will cut deeped and deeper into the wood. Of course I grew up seeing the same kind of strings being used as a garrot to cut big cheese wheels in half and I wouldn't be surprised if heavy round-wound strings are much harder-wearing on the saddle wood!

Ebony and Rosewood are hard woods. Harder than the plastic used for nuts. Probably on par with any nut material functionally. Violins traditionally use ebony as a nut material. When's the last time you had a string cut through your wooden bridge? And for the sake of argument, even if it did (which I've not seen), how much does that translate to as far as playing action?
I had a 1938 L-10 with a rosewood bridge. A lot of playing on that guitar. Never experienced a string cut through the bridge. And even if it did, wouldn't that be an issue with any bridge, slotted or unslotted? If it was indeed significantly lower than the other strings, couldn't the other slots be matched? Maybe I take this for granted because, as a luthier, setting string depth at the nut and the saddle is an operation done without the slightest amount of thought; it's just a part of a set up.
For that matter, set the strings for the proper radius, take the saddle off, sand the top edge off with a belt sander so it's resting on the new slot depth and now it's sitting on top, right?

On a bridge or a nut, the string starts vibrating on the point where the saddle/nut meets the string. Set your intonation from there and the string is true. Set your depth to where you want it and you have a radius match. That's the beauty of a wood bridge saddle

[RJVB]

Nah, it's not going to make a bit of difference to your picking hand. IMHO

I think the question was "can you mute the strings my laying your palm on top of the saddle without letting it hang over".

And I think the answer to that is "palm-muting that way will probably be a little less efficient but you can learn to get a similar enough result".

FWIW, the strings were about sunken as much in my reso saddle (until I had to raise them to compensate for belly and/or cone sag) and I didn't really notice any difference in palm muting efficiency. Different animal though, of course; it never ceases to surprise me that my palm can more or less rest on the bass side saddle post without causing any noticeable muting (on my archtop).

Edit: depends on why you mute too, no? If the goal is to stop notes (rather than getting the "pizzicato" sound from classical guitar technique, or the muffled delta blues bass sound) aren't you better off doing that just before the saddle anyway?

[RJVB]

Heh, I did say that I realise it was certainly just my imagination at work!

Violins traditionally use ebony as a nut material. When's the last time you had a string cut through your wooden bridge?

Actually, I think the traditional nut material for violins is ivory; no idea when they shifted to ebony. Possibly with the move to steel E strings, to mellow the sound of the open string a bit? You're right that I'm not aware of any problems with that nut slot but I didn't become interested in this sort of question until I started using gut strings and got a violin with an ivory nut. A wood violin nut is pretty wide though, compared to a saddle.
As you know the violin bridge is made of maple, so a much less hard wood, and it's narrow. On better modern bridges the E string nut slot has a small piece of harder material inserted under the steel E string (ebony or bone), and those strings are typically sold with a little felt patch to put between string and bridge.

For that matter, set the strings for the proper radius, take the saddle off, sand the top edge off with a belt sander so it's resting on the new slot depth and now it's sitting on top, right?

Yep. And that's only if you want it to look nice; you could also use a little file to take down material only around the slot.

That's the beauty of a wood bridge saddle

Why would that not be the same with a bone saddle? On an archtop, but heck you could do the same thing with a flattop saddle. On a steel-string even a bone saddle will get "slots" the moment you string it up, and I know classical luthiers who slot their saddles for a more precise attack and longer sustain (= prevent esp. the trebles from sliding over the saddle top).

Note that my original actual question to you was about buzzing. The usual question when someone complains about saddle or nut buzz is if the slot isn't too deep...

[2bornot2bop]

Owned a ridiculously number of arch tops. Not one had a “fitted” bridge. Nor did I worry over it. Play on.

[AllanAllen]

Owned a ridiculously number of arch tops. Not one had a “fitted” bridge. Nor did I worry over it. Play on.

Just because you didn't do it, doesn't mean the bridges weren't fitted.

[garybaldy]

This is my budget Chinese 125 'copy'. It came from the factory with the bridge base having a perfect fit with full contact. The saddle is pretty high with a fair bit of thread showing. That's partly because I shaped the top to match the fret board radius and lost depth at the ends. I'm thinking of gluing a shim to the underside of the saddle to beef it up. BTW the bridge is a dark stained 'white' wood!
FWIW the guitar sounds dead acoustically. I guess I can't blame the bridge for that. It's not too bad with the pickup.

[nevershouldhavesoldit]

When's the last time you had a string cut through your wooden bridge?

I've never seen it in 65 years of playing archtops. But I did break a nut by fitting a string too large for the nut because I was in a hurry. I fitted a 75 7th string to a guitar that had been set up for a 65, because I was ready to leave for a gig when I noticed that the core had broken and only the winding was holding the string in the peg. I had no more 65s and figured that a 75 would be fine for one gig, so I could widen the slot the next day. The end of the nut cracked off in the bag on the way to the gig, When I took out the guitar, I didn't notice it. I got about an hour into the gig before I felt a sharp edge against my hand while tuning up before a break.

The laws of physics are unbreakable. If strings are fitted properly and the bottom of the slot in nut or saddle is perfectly concentric with the arc of the string in contact with it, the pressure of the string is evenly distributed across the entire contact arc. The forces acting on the nut or bridge material from the string are spread out along the entire contact surface and are acting perpendicular to the contact patch at every point along it. This spreads out the pressure evenly so that it's minimal at any single point and least likely to cause damage to the nut or saddle.



But if the slot is not perfectly concentric with the string, string pressure is concentrated at the contact points and can damage the material under it. If the string is not on the bottom of the slot, it's pressing against the side walls and simple vector analysis shows you that the forces are pushing the sides of the slot outward. The worst case is a true V shaped slot, because all of the force is trying to push the walls apart.



If there's a tiny molecular flaw in the material (which is common in wood and most other materials used for nuts and saddles), it can propogate because of the pressure and become a crack or fracture. This is what's known as a stress riser. This possibility is one reason to maintain adequate material in a bridge saddle. The more solid the saddle is, the more resistant it is to propogation of a stress riser and the less likely a marginally cut slot is to result in splitting or spreading of the slot. So reducing the height of a saddle can make it subject to cracking if too little wood is left.

This is also a problem when the string is too large for the slot and is sitting on or just below the top edges. All that pressure concentrated on the angle between the slot and the top surface of the nut or saddle can break off the edge(es) of the slot if there's no penetration and crack the nut or saddle if the string is barely wedged into the slot (regardless of its shape).

[chris32895]

Owned a ridiculously number of arch tops. Not one had a “fitted” bridge. Nor did I worry over it. Play on.

If I have uneven action and buzzing strings then I think it's reasonable to look into it further

[RJVB]

I think this is exactly what tickles my anxious homunculus when I see a deep, V-shaped slot, whether or not the bottom is perfectly round and matching the string, partly because

If [...] the bottom of the slot in nut or saddle is perfectly concentric with the arc of the string in contact with it, [...] This spreads out the pressure evenly so that it's minimal at any single point and least likely to cause damage to the nut or saddle

and if the string is thin enough it will cut through softer material in time (see my remark about scoring bone saddles and cutting cheeses above).

I do notice (in wood and bone saddles) that heavy round-wound strings always leave an imprint on the bottom of a slot. Since they're not always perfectly stationary that must wear out the slot in time.

[nevershouldhavesoldit]

if the string is thin enough it will cut through softer material in time (see my remark about scoring bone saddles and cutting cheeses above).

Hard cheddar makes a decent nut, but you have to keep the guitar refrigerated.

[RJVB]

Hard cheddar makes a decent nut, but you have to keep the guitar refrigerated

And put up with cheesy remarks about your ditto playing?

I'd go for old parmeggiano though (seems more appropriate on here), or extra-old Leidse or possibly black brie. The latter two almost certainly won't even need to be refrigerated (and the brie will keep the cheese commenators away too).