trimming bridges - various different theories, various constants.


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I'm would like to start a thread about bridge trimming - bridge fitting or cutting, here.

I was given this idea in the;

Strad's secret, our secret, secrets generally...

post, where the idea came up, almost immediately after, the subject of bridges was mentioned... of course, about that time came the idea regarding the various "secrets" different people may have, about this aspect of violin making.

Since this was soon also brought to our attention, as an aspect to take under consideration, my idea was another different thread, to take this up as a separate subject for attention, might help.

Well, those of you who know me, know my general feelings about such "secrets", which shall remain outside of the subject matter that I'm going to post about in this thread.

Other opinions are welcome.

Trimming bridges is an A to B job. Its one that is routinely called upon for luthiers to perform - and I believe some things that are mandatory to perform with regard to this task, in order to ask our violins, any violins of any quality or any age, to perform well, are also routine, and such fitting depends on certain mechanical aspects to be undertaken on any and every bridge blank, mostly uniformly.

 

Which brings up another interesting question. Bridge blanks. What differences do they make, and why do they make any difference at all in the performance of the fiddle?

 

That most of these things, these procedures, are strictly mechanical - functional - and universal and/or simply aesthetic considerations, is the theme of the post - and of my opinion.

 

That there are many different variations tackling the extant minutia having to do with such trimming, also having to do with various aspects of making.

Well, I will not take up such mysteries here - you'll have to get the various people who believe in such things to expound on their various (and usually opposing) personal belief systems.

 

That there are many very fine methodologies at work, I have no doubt.

But the various properties of the violin, that come before bridge "cutting, tuning and/or fitting" not only dictate most of those inherent tonal properties (things like; the general violin design or model, individual plate thicknessing, fingerboard height, curvature and scoop, soundpost placement , ff hole placement, and bridge positioning - according to the ff hole nicks - & etc.) that the variations having to do with final bridge tuning and fitting, are almost infinite, and not given to formulaic answers.

Again - oh well...

 

There are many formulaic procedures, though, that do have much to do with cutting brand new bridges, in order for them to fit individual violins, where they function well, and look professional, for various playing methods - that such a subject will, in my opinion, make for an interesting thread, well there's no doubt.

 

So as usual, any and all other opinions are welcome.

I'm going to take a blank bridge - and a violin of my own construction, and then make and show how I go about fitting it (the bridge) to the violin, and why I would do it in such a mannor.

I'll say, as I go, what I'm doing, and why I'm doing it, and I'll show what various things I do, simply for the attractiveness of the finished bridge.

More than these things I cannot show. In my opinion, there are no secrets - no mysteries to anything I do, and I am very mainstream in this regard. (bridge cutting, that is)

 

Details and photos to follow (as soon as I take some)

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I put a little clamshell on the back--barely noticeable.  I had some straight backs warp.

 

I’m interested in drop tones, but don’t have any ideas yet.

 

Waist width has a lot to do with determining the amount of rocking.  Making the kidneys more oval, less egg shaped helps bring out the middle strings, IMO.

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Craig,

 

I have no idea where you are going with this.  :lol:

 

So, let me put this spin on your thread: Anyone want to comment on Michael Darnton's  "clamshell" sides? That is, that the back facing the tailpiece is not flat but has a slight bow.

Rounding the backside slightly definitely stiffens the bridge and if you are given to making the backside very upright to the ribs (90o) it is an excellent idea. It will help prevent warping. I believe it also brightens the sound.

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Craig,

 

I have no idea where you are going with this.  :lol:

 

So, let me put this spin on your thread: Anyone want to comment on Michael Darnton's  "clamshell" sides? That is, that the back facing the tailpiece is not flat but has a slight bow.

I've seen bridges from Chicago done by Zenon Petesh from 40 years ago that had relief on the back, so it's not Micheal's idea.

 

Yes, more than one way to skin a cat...I do both flat and slight relief on the back, above the kidneys, depending on what I think that is needed.

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I want to make it clear that it was never MY idea. I was taught to make bridges that way 30 years ago at Bein & Fushi, and it was presented as a Sacconi/Wurlitzer concept. It's not an esoteric idea, and makes total sense, mechanically.

 

As long as I'm talking, I'll comment that the way I deal with all adjustments, including cutting bridges, is not to shape an instrument to try to make it something it's not, but to free it up and maximize it's output in a way that's clear and balanced, and increase substance and core in the sound. This usually doesn't involve micromanaging the bridge as much as making sure that I make one that doesn't get in the way. When the concept of tuning bridges first came out the people who were working with it examined a number of old bridges from good shops and discovered that they generally fell within the "good" parameters. There's a lot to be said for discovering something that works. And then just doing it.

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Craig,

 

I have no idea where you are going with this.  :lol:

 

So, let me put this spin on your thread: Anyone want to comment on Michael Darnton's  "clamshell" sides? That is, that the back facing the tailpiece is not flat but has a slight bow.

 

Thanks for asking that particular, Michael M.

 

Thanks for answering, Michael D.

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I've certainly found that bridges cut this way just "stay."  They don't develop double bends, they don't slo-slide across fresh varnish... they don't need constant thumb and forefinger adjustment...they just "stay."  They seem balanced and secure.

 

E

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 Making the kidneys more oval, less egg shaped helps bring out the middle strings, IMO.

 

Intriguing, but I am confused by the distinction you are drawing.  Here is what Wikipedia says as intro to their entry on ovals:

 

An oval (from Latin ovum, "egg") is a closed curve in a plane which "loosely" resembles the outline of an egg.

 

I think I may know what you mean but more clarification - or pics - would help.

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Ooh... exciting. Lots of things. I agree with M.D in that the bridge should be cut with the properties of the violin in mind. I also consider it crucial to have a method of cutting very precise bridges. eye-balling 4.2mm is virtually impossible. Very slight differences in bridge stiffness can have quite noticeable effects on the sound.

 

The curved back also helps avoid sympathetic string vibration.

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I've certainly found that bridges cut this way just "stay."  They don't develop double bends, they don't slo-slide across fresh varnish... they don't need constant thumb and forefinger adjustment...they just "stay."  They seem balanced and secure.

 

E

I'm sure that more of us here need more info about why these "clam shells" stay put. After constant tuning, these "clam shells" must still, also, tilt upstream. 

 

MORE PICTURES GUYS

 

Do I have to fix every bridge in the house, and apologize for every bridge I've ever done? :o I'm willing to experiment on my own instruments. Damn, I'm out of spare bridges, lead on.

 

Scott

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I put a little clamshell on the back--barely noticeable.  I had some straight backs warp.

 

I’m interested in drop tones, but don’t have any ideas yet.

 

Waist width has a lot to do with determining the amount of rocking.  Making the kidneys more oval, less egg shaped helps bring out the middle strings, IMO.

Ummm, do you mean more elliptic and less oval?

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I've certainly found that bridges cut this way just "stay."  They don't develop double bends, they don't slo-slide across fresh varnish... they don't need constant thumb and forefinger adjustment...they just "stay."  They seem balanced and secure.

 

E

As long as the strings continue to stretch, and the slack is primarily taken up at the peg end, the top of the bridge will follow the strings in the direction of the pegs. The shape of the front or back surface of the bridge won't really change this, except that it will give you some control over how the bridge warps as a consequence, and may also change your perception of how much the bridge has been pulled forward.

 

Feet oozing or sliding across the varnish:

Again, the shape of the front or back of the bridge won't really change the forces involved. Feet sliding fore and aft will be a function of a line drawn from the string groove through the center of the feet, and how it relates to the angle of the surface the feet are sitting on. Ninety degrees would produce no sliding forces on that axis.

 

On the transverse axis (feet moving sideways), the feet will almost always tend to slide toward the bass side, simply because the E string has higher tension with most string combinations. Again, the shape of the front or back surfaces of the bridge won't really effect this.

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I've certainly found that bridges cut this way just "stay."  They don't develop double bends, they don't slo-slide across fresh varnish... they don't need constant thumb and forefinger adjustment...they just "stay."  They seem balanced and secure.

 

E

 

I battle to understand why unless there is something more going on. I think David has got it 100% right.

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I was less than clear, sorry.  Yes, pegs pull the bridge top edge forward constantly, requiring regular re-adjustment.  I mean more that a bridge set up with the downward "vector" going from the top into the middle of the bridge foot seems more secure as I described than if the back is 90 degrees, where the "vector" is at the back edge of the bridge.  In the attached sketch, the top illustration is the more secure one?  (the dashed line is what I mean by "vector."  Sorry, no engineering lingo knowledge over here)  Relieving the back into a "clamshell" shape effectively produces the result in the top photo.

 

E

post-24591-0-13404200-1395225115_thumb.jpg

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I was less than clear, sorry.  Yes, pegs pull the top forward constantly, and the bridge needs to be re-adjusted.  I mean more that a bridge set up with the downward "vector" going from the top into the middle of the bridge foot seems more secure as I described than if the back is 90 degrees, where the "vector" is at the back edge of the bridge.  In the attached sketch, the top illustration is the more secure one?  (the dashed line is what I mean by "vector."  Sorry, no engineering lingo knowledge over here)

 

E

I'm afraid you have the geometry a little off. The angle of the string passing over the bridge in front of and behind is not the same. The angle behind the bridge is noticeably steeper. A straight line passing through the bridge should bisect the string angle. Doing this will usually result in a bridge in which the back edge is 90o to the rib structure.

The first drawing is the bisect ion of the string angle.

The second drawing is of a bridge with the back side set at an angle greater than 90o. This bridge will have the tendency to warp forward.

The third drawing is a bridge with the backside set less than 90o. This bridge will tend to warp backwards.

The third is set at 90o. This bridge in which the force passes through the bridge as straight as possible is the most stabile.

When fitting the bridge it is best to imagine this line of force passing through the center of the bridge rather than just automatically fitting the backside at 90o. On old instruments it can be difficult to find the flat surface of the ribs because of distortion and the neck set, saddle height and arching can be less than "standard".

That said, there us some wiggle room so 90o usually works well.

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post-53756-0-73816100-1395226791_thumb.jpg

post-53756-0-58675900-1395226854_thumb.jpg

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The "clamshell" of the back of the bridge should not be over done. A few 1/10th of a mm is sufficient . It is also important that the curvature of the front and back of the bridge are fairly similar. If one side is more curved than. The other the tendency will be for the flatter side to warp.

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The second drawing is of a bridge with the back side set at an angle greater than 90o. This bridge will have the tendency to warp forward.

The third drawing is a bridge with the backside set less than 90o. This bridge will tend to warp backwards.

 

Curious, I disagree. The tendency of the bridge to warp one way or the other is largely independent of the angle chosen to fit the bridge to top (all other things being equal). It has more to do with load distribution on the feet, front to back. This distribution can be equal, with the load path going through the center of the bridge, through the wide range of angles which will allow a bridge to stand, without sliding out from under the strings.

 

But hashing out these forces, here and now, isn't terribly important, since "standard" bridge angles work pretty well. We can discuss it  at greater length when we run into each other some time.

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Yes, there is a great deal of latitude in getting the forces to pass through the bridge properly and warping is usually because the feet don't fit well, especially in celli. My guess, David, would be that when we sit down to chat that we would be in perfect agreement about what makes up a good bridge and the forces acting on it and if not I would defer to you.

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Yes, there is a great deal of latitude in getting the forces to pass through the bridge properly and warping is usually because the feet don't fit well, especially in celli. My guess, David, would be that when we sit down to chat that we would be in perfect agreement about what makes up a good bridge and the forces acting on it and if not I would defer to you.

I think I might just have learned something. There is a "general" tendency to round the front edge of the bridge and there is a "general" tendency for bridges to warp backwards. General has included me, by the way. This all started years ago with my upright base.

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As long as the strings continue to stretch, and the slack is primarily taken up at the peg end, the top of the bridge will follow the strings in the direction of the pegs. The shape of the front or back surface of the bridge won't really change this, except that it will give you some control over how the bridge warps as a consequence, and may also change your perception of how much the bridge has been pulled forward.

 

Feet oozing or sliding across the varnish:

Again, the shape of the front or back of the bridge won't really change the forces involved. Feet sliding fore and aft will be a function of a line drawn from the string groove through the center of the feet, and how it relates to the angle of the surface the feet are sitting on. Ninety degrees would produce no sliding forces on that axis.

 

On the transverse axis (feet moving sideways), the feet will almost always tend to slide toward the bass side, simply because the E string has higher tension with most string combinations. Again, the shape of the front or back surfaces of the bridge won't really effect this.

Is bridge bending becoming less of a problem with modern synthetic fiber core strings and tail cords that don't stretch much?

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