Bridge and Saddle Measurement Differences

[Bill Cory]

Regarding measuring for bridge/saddle placement:

In kits, Martin recommends adding 1/10" to the scale length and placing the near (sound hole-side) High-E end, edge of the saddle slot at that measurement.

Stewmac, on the other hand, recommends adding 7/64" (about the same amount) to the scale length, but they say to place the middle of the saddle slot between the D-G strings at that measurement.

Clearly, they agree on the basic amount to add, but the difference in measurement point throws that agreement all out the window.

Martin's edge-of saddle procedure puts the bridge farther from the sound hole, increasing compensation, while Stewmac's center-of-saddle-slot procedure puts the bridge closer, decreasing compensation.

I'm curious -- why the difference? Is it, as Paul Hostetter said on his site (lutherie.net/saddle_angle.html)  a problem with Martin using an outdated system? Or is Stewmac way off?

I'm genuinely wanting to find out if either of these is closer to "correct," all other things being equal on the guitar.

Thanks in advance --Hoping for clarification

Bill

[Bill Cory]

Oops. I just realized the Healdsburg fest is next weekend. If you guys who could address this question are busy, that's okay! Have a great time in Healdsburg.

Bill

[Roger Häggström]

My experience tells me it's better to follow the Martin method. Both methods may work though. With a thick saddle bone I'd probably go with Stewmac.

[Richard Bales]

I rather think it depends on what strings will be used on the instrument.  Intonation is affected by string gauge, materials and manufacture and anything you do in the initial manufacture will need to be modified when the end user installs his favourite strings.  Perhaps there's a best-guess compromise, but I have yet to find it.

[Bill Cory]

I agree - lighter strings need more compensation. We're dealing with very small measurements, too, and not everyone can even hear such small differences in pitch. According to Mike Doolin, a 15/1000-inch change in string length results in a one cent (1% of a half-tone) change in pitch.

In working on this book revision, I'm tying to figure out just how deep I should go into this subject, since it's for novice builders who are building kit acoustic guitars. Since the two major kit providers offer different methods of measuring, I thought I'd ask for opinions.  Thanks  --

Bill

[David Collins]

If you measure a Martin guitar made today, I think you'll find Martin places their saddles much closer to the Stewmac rule, than they do to the method as you listed it from the Martin kit.

[Bill Cory]

That's interesting. I haven't measured a factory Martin recently. Ever, in fact. It would not be surprising to discover that the Martin "Handy Hints" booklet was completely incorrect about the correct measurement. I'm only talking about Martin's measurement (stated in their kit building booklet) to the "near" edge of the saddle slot, while Stewmac goes to the center of the saddle slot between D & G strings.  I tend to favor Stewmac's, myself, but I don't want to mislead anybody. It's not a whole lot of difference, but to someone with acute tonal hearing, it could make a world of difference. I don't have that hearing acuity anymore. Wish I did. Now, I think I'll find a Martin or two and measure them.  (Paul Hostetter, in an email, said to me that both of them have a much too shallow slot angle.) - Thanks -

Bill

[David Collins]

I agree with Paul, a steeper angle is certainly better.

I used to cut .110" back and the center (length and width), which by coincidence is right where StewMac's instructions put it. Today I don't measure the center, because it makes little sense to me to start there and then set the angle, as opposed to marking the high and low strings, letting that determine the angle itself.

On average a high E on an acoustic steel string will end up intimating well in the .040"-.060" range, so on a 3/32" width saddle I will mark the center (width) at the high E around .070"-.080". This leaves room to shape the intonation point somewhere near the front, leaving enough room to roll off some support in front of the break point, yet still room to shape the B back behind it without being too near the back edge.

Ideal intonation at the low E can cover a wider range depending on strings and setup (a bit too wide for a 3/32" saddle to always cover). I often find good results averaging around .180"-.200", but sometimes up in the .220" range, so I'll usually set the center of the low E around .170"-.180". This leaves me enough room for a support ramp rolling up from behind the break point (in most cases anyway), while not pulling the bass side too far back to still intonate the center strings behind the front edge.

If you do the math (no calculator in front of me so I can't tell you the angle), this puts the center just a hair behind the 7/64" that Stewmac lists, maybe a bit closer to 1/8". In intonation terms, the difference is less than a cent, so I'd say more or less the same.

[David Collins]

P.S. - Does anyone know how to teach my Autocorrect that when I say intonating, I actually mean that, not intimating?

[Bill Cory]

Thanks David -- that is helpful and good information. The angle-setting from high and low E strings is concise and clear. Could be helpful for kit builders, but only if they have the facilities to cut their own saddle slot. (Or the guts to simply angle the whole bridge. Ha-- That would make the guitar a great conversation piece!)

Bill

Ps. I share your ire about Otto (Otto Crect) -- he's an authoritarian dictator with little empathy for what we want to express. He can't be taught anything by us proles.

[David Farmer]

Bill, One thing I've run into and don't hear discussed much is string hieght and bridge rotation.

If you layout saddle location on an unstrung instrument with a top/bridge/saddle that rotates significantly under tension, the top of the saddle, sometimes moves toward the nut significantly but a low saddle on a shaved bridge almost none.

Once I did the trig and found something like .035" for a 2 degree rotation with 1/2" string height off the top.

It's something I started to take into account when routing slots on instruments with high string heights and/or weak tops.

I had a good quality factory instrument this morning with this problem. It has a 3/8"bridge that puts the strings 9/16" above the top. the neck is a bit overset. If I measure the slot location unstrung it should be ok but strung up, even with low action, the break points need to be moved back to the bone chipping  back edge to be tolerable. 

[David Farmer]

I just used an online calculator and it works out to .o15" for a 2 degree rotation. Throw in a little saddle lean and you can be out of range.

[Bill Cory]

Okay, that's new wrinkle. I wonder if the kit manufacturers, who are basically trying to repeat standard bridge/saddle/nut designs, take that into account in their calculations? I know I never thought of it.

That's a good thing to know, for sure. I'm going to hope that that's all considered and taken care of in the kit designs for the newbie builders I'm writing for. Thanks David --

Bill

Ps. That .015" is one more cent, plus or minus, thrown into the mix. I imagine, with a tall saddle, a tad high action and a saddle slot on too shallow an angle, it would be possible to remove most of the effect of compensation.