Bridge angle question

[AndyPanda]

I was taught (40 years ago) to very slightly angle a bridge back towards tail.

Recently I picked up two used mandolins, same model and brand. One has a CA bridge professionally setup. The other has the stock bridge that I fit. I was just looking closely and noticed that the mandolin with the CA bridge and pro setup seems to be leaning forward.

I tried taking pictures and wasn't sure what I should line my camera up with. I noticed that the neck angle is very different between the two mandolins - so when I tried lining up using the fingerboard/strings plane as horizontal, then the CA bridge was only slightly leaning forward and the bridge I fit was drastically leaning backwards. When I tried to use the arch of the top to line up my camera shot, I noticed that on both mandolins the bridge is ahead of center of the arch (this is where it intonates properly on these mandolins). Which has the bridge feet on the down slope of the arch. (this all leads to questions for another post - I looked at Gilchrist mandolin pictures and the bridge is much closer to center of the arch)

So ... should I make the bridge perpendicular (or slightly back tilted) to the top at the point on the top where the bridge needs to be to intonate correctly?

I made a crude drawing to illustrate what I mean - I drew three planes: One is the horizontal plane of the entire top, second is the plane of the arch at the point where the bridge feet need to be, and third is the plane of the fingerboard.

[Stephen Perry]

This is an interesting question to do with philosophy of setup. The arches are so wonky on mandolins (and other curvy things) that a reasonable working method is about the best I've come up with. On violins, I put the bridge back perpendicular with the rib / top plane. I use a square to set this, on the end of the top. I just eyeball the mandolin bridges, but never a lean forward. Probably should develop a more coherent philosophy on that. Really, I suppose one should bisect the break angle to to get the vector right down the middle on average, but I suspect we'd have some scooting bridges. Or some such effect. Best I can offer is to have the bridge perpendicular to the rib top edge or slightly back. These things come in all over the place on angles and such, and just because a "pro" set something up doesn't mean it's optimal. There's no particular "book" that we all follow, to my knowledge!

Good question always fun.

[Phil Goodson]

Perhaps not directly applicable to mandolins, but IIRC, Santa Cruz Guitars sets their guitar saddles at a 10 degree angle towards the tail of the guitar with the top of the saddle at the point of "perfect intonation" or as close as possible. (The 10 degree angle would be measured from the perpendicular at the point of virtual intersection of saddle with guitar top.)
They say that if you thereafter lower the saddle, you will also be changing the compensation (because of the angle) and will thereby keep the intonation correct.
Seems that similar angles on a mandolin might tend to do the same.
And, of course, this angulation would also help to prevent the 'forward lean' that we always look for after changing strings and such.

[sblock]

The fact is that tiny amounts of tilt in the bridge saddle (a few degrees) do not affect the tone of the instrument. You can lean you bridge saddle back a small amount, or forward by a small amount, or arrange for it to be perfectly perpendicular to the strings, or perfectly perpendicular to the fingerboard, and IT WON'T MAKE ANY DIFFERENCE to the sound. What matters much more is the fit of the bridge base to the top! The bridge base should never be tilted (that is, lifted up out of contact) in any way, irrespective of what the saddle is doing, and its feet should be matched to the exact curvature of the top. But if the base leans a little forward or backward matters very little. Unless your bridge base is way off, don't worry about it. The things that matter most are the contact with the top (to conduct vibrations) and the position (to get the intonation right).

Most bridge saddles naturally tend to develop a small bit of lean over time, anyway, especially with constant changing and tightening of strings, and these parts can periodically be straightened with a bit of finger pressure ("burping the bridge"), made easier by a reduction in the string tension.

And NO, you certainly do not need to arrange to bisect ("split") the string break angle by leaning the bridge/saddle slightly backwards, to send the downbearing force vector directly onto the top (with no forward or rearward component). Mando bridges are pretty hefty and have large contact areas, and they are not like the much thinner banjo and violin bridges. As a result, they show almost no tendency to "walk" forward or rearward under the small amount of resultant force when the string break angle is not perfectly bisected.

Worry more about getting your intonation just right with bridge positioning and correct compensation, I say. These things count for much more!

[HoGo]

I usually try to bisect the angle of the strings, but if the top arch is weird (often) and the bridge is going to sit on the downslope towards neck I fit it closer to perpendicular to rib plane. Otherwise the ends of bridge feet may look funny when much more wood is removed from tailpiece-side.

[Phil Goodson]

Could the holes for the adjustable bridge posts be drilled at a slight angle to achieve these things? Or is there a downside to angled posts? I guess the underside of the saddle would have to be angled to accurately rest on the wheels. Maybe more trouble than worth.

[Stephen Perry]

Angled seating surface and non-vertically redrilled holes have been evident on mandolins I've worked on. I've done the angled seating surfaces where the holes are sloppy.