New CA bridge installation: bridge angle?

[Billkwando]

I'm in the process of fitting a new CA bridge to a The Loar LM-310, and I wanted to confirm that I have the bridge angle correct.

Currently, the flat part on the top of the saddle is at the same horizontal angle as the fingerboard. I've seen other pics of mandolins where the bridge seemed to lean back slightly, toward the tailpiece. I didn't know if that was by design, like maybe to create more of a break angle for the strings, or if having it perfectly level with the fingerboard was right, or if either one was fine?

In the process of fitting my CA bridge, I noticed that it was leaning back slightly toward the tailpiece, so I flipped the bridge base around and started fitting it the other way, which landed it perfectly, which is how my Loar looked with the stock bridge. The only issue with that is that I had fit that stock bridge to the mando top as well (previously), so I can't be 100% sure it had been level before.....but I'm pretty sure it was, because refitting a bridge that was basically already fit by the factory shouldn't really change the angle, unless I was sanding drunk. (I wasn't)

Did I do the right thing by turning it around, or would it not have mattered either way?

Thanks!!! :D
Bill

[sblock]

People make a bit too much about bridge angle, in my opinion. Sanding a bridge base so that the vertical saddle lies few degrees off the precise perpendicular to the fretboard, one way or the, won't make a difference to the sound. But most folks aim for a perfectly perpendicular saddle, which is fine. But if you want to introduce a bit of lean toward the tailpiece, that is OK, too.

This should NOT be confused with a different situation, namely, that of a bridge that was originally sanded to be perpendicular, but has now developed some lean (usually due to string pull). In this situation, the base of the bridge no longer fits tightly over its full surface to the top of the mandolin, because of the tilt. This will diminish the sound. Usually, this misalignment involves an angle that develops between the base and the saddle.

The point is that the bridge base must contact the mandolin top over its full surface. The saddle can lean a little, so long as the contact is maintained.

[Billkwando]

Perfect! That's exactly what I was kinda thinking, but I just wanted to confirm. Thanks!

[Ivan Kelsall]

Go for a perfectly upright bridge. If you hold it upright while you get the first tension on the strings,it'll stay upright.
To prevent more being sanded from the front / back of the bridge,sand it from side to side not back & forth. Here's well known mandolin builder,Wayne Henderson doing just that - 5 mins into the clip.
Ivan
Several other builders do the same - it works fine, & remove the bridge saddle to keep things 'low down'.

[Billkwando]

Go for a perfectly upright bridge. If you hold it upright while you get the first tension on the strings,it'll stay upright.
To prevent more being sanded from the front / back of the bridge,sand it from side to side not back & forth. Here's well known mandolin builder,Wayne Henderson doing just that - 5 mins into the clip.
Ivan
Several other builders do the same - it works fine, & remove the bridge saddle to keep things 'low down'.

I'm not talking about the saddle, FYI, if that's what you mean. I'm talking about the physical angle at which the bridge feet are sanded.

Thanks for the sanding tip, but I already picked that up from the frets.com article, and later made a video of my own about it, when I was fitting the stock bridge to The Loar (which was definitely level with the fretboard, which is what inspired me to ask about it):





Because The Loar is a cheapo model, I just wanted to get confirmation that its angle was correct before I potentially went down the wrong path with sanding my CA bridge. Since I was only sanding the old bridge at the existing angle, I hadn't needed to give it any thought, until I got a virgin bridge (I should add an annotation to the video for that, in case someone has a new bridge, but it does clearly show the bridge as level, at least).

[amowry]

I like to angle bridges back so they bisect the string angle. That way the force from the strings is going right down through the centerline of the bridge, and there's much less tendency for the bridge to pull forward with repeated tunings. Many bridges have posts that fit loosely in the holes in the saddle, so it's easy for the saddle to get pulled forward.

[amowry]

I happen to be fitting bridges today, so here's a quick photo of the jig I use--there are a couple different-sized wheels for different bridge angles and arch heights. I prefer to move the bridge forward and backward, not side to side, because the arch is less pronounced from front to back. However, you do need a jig to hold it at the right angle.

[Billkwando]

I happen to be fitting bridges today, so here's a quick photo of the jig I use--there are a couple different-sized wheels for different bridge angles and arch heights. I prefer to move the bridge forward and backward, not side to side, because the arch is less pronounced from front to back. However, you do need a jig to hold it at the right angle.

Yeah I kinda wondered, for mandos that arch lower, in a more pronounced way, at the tips of the bridge, if there was no choice but to go front to back, at least for the final fitting.

Edit: I'm pretty sure I could make a jig like that, looking at your design. I could cut a hole in a piece of wood with a hole saw, and use the round leftover wooden cylinder from inside the saw for the wheel.

Saw different sized holes for different sized wheels.

[Loubrava]

Hey Billk, I'm the other guy who may be fitting a CA bridge to a Loar 310 & as I've never worked on an instrument I'm learning a ton from you and the guys responding to your questions, good timing for me �� Looking forward to hear your final results. I'm thinking I'm going to have to do my first set up on the 310 and if you end up with good results I'll attempt the CA bridge install it would probably be fun doing just for the experience.
Lou

[Ivan Kelsall]

I installed a CA bridge on my first good mandolin,years before i ever heard of the Cafe. Common sense told me that if i sanded it back & forth - the usual way,it might rock on the base & become rounded,so,i sanded it from side to side & it came out perfect. If there was any advantage in having the bridge at an angle,the i'd expect more builders to fit them that way. IMO,if a bridge is sitting at an angle to the top, & not perfectly perpendicular to it,then the string pressure will tend to try to push it one way or another. You need the pressure to be acting 'vertically downwards' to prevent that,
Ivan

[Billkwando]

Hey Billk, I'm the other guy who may be fitting a CA bridge to a Loar 310 & as I've never worked on an instrument I'm learning a ton from you and the guys responding to your questions, good timing for me �� Looking forward to hear your final results. I'm thinking I'm going to have to do my first set up on the 310 and if you end up with good results I'll attempt the CA bridge install it would probably be fun doing just for the experience.
Lou

Hey! I'm glad it's helping. I try to cover all the bases with my questions, so that other folks who come along after can benefit from it, as well as making videos whenever I feel like I can help present a useful piece of information with visual examples or a demonstration. I'm not sure if you've seen any of them, but I also did a couple about installing a pickup in the 310. You might find that useful.

[Br1ck]

When I got my Silverangel, I noticed the saddle was slightly angled toward the tailpiece like it had been bent. E mailed Ken Ratcliff who said he makes them that way. Makes sense to me to counteract string pull. The bridge base is straight up. Anyway, it works well.

[amowry]

I installed a CA bridge on my first good mandolin,years before i ever heard of the Cafe. Common sense told me that if i sanded it back & forth - the usual way,it might rock on the base & become rounded,so,i sanded it from side to side & it came out perfect.
Ivan

Yes, definitely, if you sand front-to-back you need a jig to hold it steady.

[Ivan Kelsall]

Hi Andrew - Apparently Gail Hester says that she fits her bridges by sanding side to side. It simply seemed like common sense to do that,maybe based on the fact that i've made dozens of Banjo bridges & had to sand them like that. The feet on a banjo bridge are way too narrow to risk rounding them off,
Ivan

[amowry]

Makes sense to me!

[Kalasinar]

My Eastman's stock bridge had bent posts creating a lean towards the fretboard. I'm grateful for the info I found on the Cafe, otherwise I never would have found out about Cumberland Acoustic bridges. When I bought one I bought their fitting jig too...and I must say, I'm not sure I would have done very well without it. I do recommend it. I had to make a slight adjustment to mine (increased the gap for the wheel adjustment screw) to get the angle I wanted, but it did the job fine. Took a lot of work but it was really rewarding. Steve Smith provided great instruction and support throughout the process too.

[Willie Poole]

I always sanded mine going front to back and then looking at them and if the bottom seemed rounded I would take a knife blade and scrape off the rounded wood to make it flat. always worked for me but the gig seems like the way to go, I`ll try making one for myself...A good post with lots of good info...

Willie

[Billkwando]

Hey Billk, I'm the other guy who may be fitting a CA bridge to a Loar 310 & as I've never worked on an instrument I'm learning a ton from you and the guys responding to your questions, good timing for me �� Looking forward to hear your final results. I'm thinking I'm going to have to do my first set up on the 310 and if you end up with good results I'll attempt the CA bridge install it would probably be fun doing just for the experience.
Lou

Hey Lou! My results are up!

https://www.mandolincafe.com/forum/s...26#post1590926

[sblock]

I installed a CA bridge on my first good mandolin,years before i ever heard of the Cafe. Common sense told me that if i sanded it back & forth - the usual way,it might rock on the base & become rounded,so,i sanded it from side to side & it came out perfect. If there was any advantage in having the bridge at an angle,the i'd expect more builders to fit them that way. IMO,if a bridge is sitting at an angle to the top, & not perfectly perpendicular to it,then the string pressure will tend to try to push it one way or another. You need the pressure to be acting 'vertically downwards' to prevent that,
Ivan

Ivan, sorry, but you have the vector physics just a bit wrong. You wrote "IMO,if a bridge is sitting at an angle to the top, & not perfectly perpendicular to it,then the string pressure will tend to try to push it one way or another." This is not true, in fact, because the strings break at an angle over the bridge (this angle is typically about 15 degrees or so), running from the tailpiece up to the saddle, and then turning through about 15 degrees to run directly parallel to the fretboard. The direction of the force that the strings exert on the saddle is along a vector that BISECTS the opening angle. This opening angle is the supplement of the break angle, i.e., it's 180-15 degrees, or about 165 degrees. Half of that is 82.5 degrees. IT IS NOT 90 degrees. The string force therefore "aims" mostly downward (perpendicular to the top), but it's also about 7.5 degrees towards the front of the mandolin. If you want your bridge to sustain ONLY a "downward" force, that is, a force straight through the saddle, then you need to lean it about 7 degrees backwards at the top, in a direction towards the tail -- not perpendicular to the top. This is exactly what Andrew Mowry does, apparently. Please read his post, above. And just because more builders don't do this should not be taken to mean it's wrong, or that there is "no "advantage" to it, as you wrote. The advantage is that nothing slips with constant re-tunings or string changes!

[sblock]

I thought it might be useful to illustrate this point with some diagrams, since it's hard to visualize the vectors otherwise. The top diagram shows the "traditional" bridge setup, which is typically oriented perpendicular to the fretboard, and (very nearly) perpendicular to the mandolin top, at the top point of its arch (on an F5, anyway). In this situation, the base of the bridge experiences a small component of force towards the headstock (horizontal force; shown by the red dashed arrow), which, after multiple string changes and lots of string loosening-tightening, can often result in undesirable shifts of the bridge base, or in forward saddle lean. You hear complaints about this all the time on the Mandolin Cafe! The lower diagram, however, shows what happens when the bridge base is sanded in just such a way that the string break angle is bisected, so that the bridge saddle now leans about eight degrees toward the tail. In this case, the string downbearing force is perfectly aligned to act straight through the bridge, and there is no longer any horizontal component of the force at the point of contact between the bridge base and the mandolin top. This type of "rear-leaning bridge" will show a greatly reduced tendency to shift or lean over time. It's all simple vectors. Several luthiers now do this routinely, in fact (see the replies in the thread above). It's a superior way to fit the bridge to the top, in my opinion. Here is the diagram -- please click on the picture to expand it on your screen:

[Beanzy]

Shouldn't your drawing take into account that many fretboards nowadays don't arrive at a paralell angle to the top?

[sblock]

Shouldn't your drawing take into account that many fretboards nowadays don't arrive at a paralell angle to the top?

Not sure what you mean by that comment. The top of a carved-top mandolin (an F5 model, for example), is continuously curved, and it is simply not meaningful to state that a straight line (the line of the fretboard) is "parallel" to a curve! No line can ever be considered "parallel" to a curve; the word "parallel" only carries meaning when referring to two lines. That said, the point where the bridge is usually positioned on an F5 is very near the apex of curvature of the top (that is, the crown of the top). At this position, the LINE TANGENT to the top is very nearly (that is, almost exactly) parallel to the fretboard. On the F4 model, by contrast, the bridge is positioned a bit rearward of this apex, due to the shorter neck at the point where it meets the body. Anyway, if you look at my diagram, you will see that the curvature of the top at the bridge position is completely immaterial! What matters is that you bisect the string opening angle with the tilted bridge. This break angle is a just a bit smaller on an F4 compared with an F5, due to the lower fretboard height and some other features. And the break angle is yet again different on a flat-top mandolin, or on a bowlback. None of that matters! What matters is that there is zero horizontal component acting on the bridge base due to the string downbearing force when the bridge leans rearward in such as way as to bisect the string opening angle (which is the supplement of the string break angle). Study the diagram, and you will see why that is so, and why the curvature of the top at the bridge position does not matter. Only the string break angle matters.

[Beanzy]

I mean most people are building the necks at a 5 to 6 degree angle the other side of the bridge so the strings are approaching the top angled from the neck side too.

[sblock]

I mean most people are building the necks at a 5 to 6 degree angle the other side of the bridge so the strings are approaching the top angled from the neck side too.

Beanzy, NO, that does not matter, as I've already written. Yes, most necks are angled back (on A- and F-style mandos, anyway). And yes, most tops are curved (ditto). But fretboards have to be straight (!), and they run very nearly parallel to the strings. And those strings need to break over the bridge saddle at some angle: it's the amount of this "break angle" -- ONLY! -- that matters for this discussion. Not the neck angle (whatever it might be), and not the top curvature (or lack thereof). The key point to understand is that the bridge angle should bisect the supplement of the string break angle (this supplement is the string "opening angle" at the break -- see my diagram, where it is labeled clearly). When that happens, the component of force at the base of the bridge, arising from the string downbearing pressure, vanishes in the horizontal direction (and by "horizontal," I mean parallel to the strings/fretboard). This type of rear-leaning bridge will exhibit no tendency to slip, because there are no slipping forces acting on it. Not so for a "vertical" bridge. If you study the diagram, you will see why.

And, if you read this thread, you'll see that Andrew Mowry (Mowry mandolins) and Ken Ratliff (Silverangel) have already implemented this principle in fitting their bridges. It works, and it's based on some basic physics. Vertically-set bridges have to rely on a certain amount of friction between the top and the bridge base to hold them firmly in place. The rear-leaning bridges we have been discussing do not: they are in equilibrium with the static forces on them, irrespective of friction! This small rearward lean may seem counter-intuitive to you and some others, but your "common sense" can be fooled. Physics does not lie.

[Beanzy]

Why doesn't the angle on one side of the bridge matter if it matters on the other?
I would have thought that would have to be factored in when calculating where the force was going to act in relation to the foot of the bridge making contact with the top. I understand the break angle is what it is in relation to the strings, (and just needs to be measured there) but feel the drawing does not represent the effect of neck angle on the point of interest ie. the contact of bridge foot with the top.