Official Luthiers Forum!

I've been thinking about steel-string bridge design lately and have a question or three. I see most drill their pin holes in a straight line, 90 degrees to the center-line. Yet the saddle itself is rotated to provide compensation. This arrangement has the string break angles increasing progressively toward the bass strings. This provides for increased torque on the bass side of the bridge but a minimal shift in the axis of the rocking couple.
I have seen some designs with the pin holes drilled in a radius across the bridge. Providing less torque on the center strings and a less precise rocking couple axis. Still some with the holes spaced equally off the saddle, which would have even torque but the biggest shift in axis. From what I have read it is the rocking motion of the bridge that drives the soundboard. My first question is, Am I understanding all of this correctly? If not please clarify for me. I am not an engineer.

If I am correct , than it stands to reason that each of these arrangements would have an effect on how the bridge drives the soundboard and thereby tone and amplitude. So my next question is how do you do yours? and what are the benefits as you see them?

Thanks, Brian

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I asked a similar question after watching a video where the guy states he doesn't slant the angle of the bridge pin holes because he believes this might inhibit the bridge rocking back and forth. Al pointed out to me that this motion isn't the main sound producer of the guitar. The bridge bouncing up and down in the monopole mode is probably the biggest sound producer. The bridge rocking fore and aft is the long dipole mode where the motion is higher frequency and low amplitude.

On this comment:

"I have seen some designs with the pin holes drilled in a radius across the bridge. Providing less torque on the center strings and a less precise rocking couple axis."

I would say that the height of the saddle above the soundboard sets the torque the strings apply to the bridge. The angle of the strings from the saddle down to the bridge sets the downward pressure of the string on the saddle.......and probably has no affect on the torque.

All in all I would say the angle of the string over the bridge is more important than the location of the pin holes (in-line, angled, or arced).

_________________
Formerly known as Adaboy.......

There's more to it than just the bridge pin holes. The size of the bridge, the braces behind the bridge, their angle, the coupling location of the X-brace to the bridge, the bridge plate size, all have to do with the rocking motion of bridge so it's all a system. To say that the relationship between the saddle and the bridge pins have a significant effect on the rocking motion of the bridge would be rather bold IMO. Everything works together. I would say the size of the bridge plate in relation to the bridge and the location of the x-brace in relation of the bridge have far more to do with the effect on long dipole (rocking of the bridge) than most other aspects of the top.

The scale length (string tension) and what pitch the strings are tuned too have the most to do with the torque applied to the saddle/bridge/top. This is the force acting on all the other components. Less tension=less force; more tension=more force.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

I drill them to follow the slant for equal break angle, but on a slight radius just because I think it looks cool. You can cut angled slots coming up from the pin holes to further increase the break angles, and vary the depth of them to even out the angles if using a radius or non-slanted pin holes.

If you use a flat bridge surface, rather than arching it to the radius of the saddle (which I do, so this doesn't apply to me), then the pin radius actually does make sense. Otherwise the middle strings would be at a sharper angle due to the varying saddle height.

As for rocking motion, my thinking is that equality of break angles is far more important than location of anchor points. How do you determine the optimal location for anchor points anyway? Even if it makes a difference, I don't see why it would be a clear positive or negative one. The slanted saddle already throws off symmetry of force application points compared to the bridge axis.

You can use a perfectly horizontal saddle though (but still with minor compensations carved into it), by putting the major slant at the nut instead, slanting all the frets along with it. Somebody posted a picture of an old guitar like that a few months ago, over on AGF I think. But I'd say fan fret bridges pretty much prove that symmetry isn't a necessity

I tink you are "over thinking" on this.
I think the strings are pulling from the top of the saddle.
I don't think the pin layout has anything to do with the torque of da bridge...
It may affect the downward pressure to the saddle,
but, I don't think even that makes much difference,
varying an 1/8" or so.

I agree with what you have said, it is a system and everything works together. But by changing any one part of a system haven't you altered the way it performs? Whether it is drastically or subtly, for good or bad, it has changed in function. A change in break angle also produces a change in both downward pressure on the saddle as well as forward pressure on the saddle. Both of theses forces combine to provide the torque that drives the soundboard. According to Roger H. Siminoff's " The Luthier's Handbook" ".....the taller the saddle above the soundboard, the greater the leverage and torquing motion at the bridge..." and "...increasing the action increases the leverage at the bridge..." But really the change is not about the saddle height or at least it's relationship to the soundboard or bridge plate that would cause this but rather the increase in break angle.....Yes? So is there benefit to be had by having the bass strings, or any strings for that matter, produce more torque?



That was my initial thought, but I can see advantages and drawbacks to any of these approaches.
Thanks, Brian

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I think Judy Threat among uses holes in a curved line. I heard it was just so the plate would be less prone to cracking along a straight line due to drilling them that way. A radius or slant spreads the holes around a bit so they don't weaken the wood as much along the grain. I always wondered about what ideal distances are for each hole from the bone edge though.

_________________
"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

Bryan Kimsey has some good information and pictures of Collings and Martin bridges on his website. www.bryankimsey.com

_________________
Good judgement comes from experience. Experience comes from poor judgement.

I feel that break angle and string diameter comes in to play when spaceing the end pins from the saddle. The larger strings are better suited to closer pin spaceing than the thinner strings for better break angle and compensation for intonation.