Official Luthiers Forum!

I hate opening up topics that have been covered so many times, but as I start preparing to set my 12th bridge, I'm going back through some notes and searches, and I'm getting conflicting information. I've probably gotten lucky in the past, as my guitars have intonated pretty well, overall, with a couple of 'less than desirable' outcomes. So I want to really nail the intonation on the guitar that's on my bench right now.

Here's my issue: I have one of the Stew-Mac Saddlematics, and it's fine for getting the scale length (nut-to-12th fret X two). But then the little pointer arrows are giving me a position that conflicts with what other builders are doing (it tells me to position the bridge at least 1/32" too far forward).

For example, on a Martin 25.34 scale, using a 1/8" saddle width, and following the Saddlematic instructions, I'll get a compensation of 3/64" on the High E, and 9/64" on the Low E, to the 'front' of the saddle slot. That's considerably more (1/32" or so more) compensation than the figures that other builders are using, who suggest adding amounts such as .035 on High E, and .110" on Low E (John at Blues Creek?); add 1mm on High E and 3mm on Low E (I forget who); add .150 to 'middle' of slot, between D and G strings, and let the saddle angle take care of the rest (Cumpiano); add 2.26mm to 'middle' of High E, and 5.4mm to 'middle' of Low E; and comp 3mm to middle (roughly the same as Cumpiano's advice).

I like the suggestion of using the 'middle' of the slot, whatever your compensation is, b/c it allows you to move your bevels/angles out from the middle in both directions to intonate the strings (as Michael Payne, Cumpiano, and others have mentioned doing).

I'm thinking that the Saddlematic is giving me poor indications, and that I should use it simply to find my scale length, then go with some happy medium of compensation from there. Does this seem like the reasonable thing to do?

TIA,

_________________
Ken Mitchell
Durham, NC

Pretty good discussion from Chris Herrod here: http://www.lmii.com/CartTwo/Intonation.htm
From this, I have used my home-made Saddlematic to register 2/32 and 5/32 to the front of the saddle as a starting point for bridge placement, then file back more compensation for the B string during setup till my strobe tuner shows it is A-OK.

Ken, for what it's worth, I use .10 to the middle of the slot between the D and G strings and have never had a huge problem with intonation. I have recently become a fan of wider saddle slots since they can be tuned better.

I go to the middle of the slot and use a 3/32" saddle.

_________________
Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

Ahhh this can be a great topic. To start off this , remember that you may never get perfect intonation on a fretted instrument . The reason is you are trying to match a static dimension ( scale length ) to a dynamic dimension ( working string length ). I lie to set my saddle up using the actual line of the 1st and 6th strings . Along the line of the 1st string , if I am using a 3/32 slot I will hit the front of the slot. If I am using a 1/8 saddle I go to the middle.
I take the scale length and add .100 to it. Then allow an extra 1/8 to the 6th string for the compensation angle. On a high action you will be dead on , and if you want a lower action you can move things a bit closer .075 comp length for a lower action and light gauge. I would rather be 2 cents flat the 2 cents sharp. You have to plan the saddle to the action height and string gauge you are using .

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

The way you use the saddlematic is NOT to give you your final compensated string length.
It is purely to measure to the front of the saddle slot for positioning your bridge.
This is convenient because you can insert the saddle to have something positive to measure against.
This method still assumes that you will cut back the break point on the saddle to somewhere around the middle of the saddle width.

Sorry, I meant I use a 5/32" slot.

_________________
Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

So being less than proficient in the hearing department,due to a career in a shop with power tools, what are some recommendations for equipment and/or software to use to measure pitch when adjusting intonation?

Thanks,

Mark

_________________
A world without music would Bb.

A strobe tuner.

_________________
Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

So, if I'm reading people's posts correctly, I'm still seeing a range of between .031 and .100 for compensation on the High E, with the low E being 1/8" further back (The Stew-Mac unit and their website suggest 1/16", or .062, of compensation on the High E, with a 3/32" saddle; 1/64" less if the saddle is 1/8" thick. These measurements are to the front of the bridge slot).

I understand that the amount of compensation varies according to saddle width; I understand that the bevels you shape into the bridge are for fine tuning the intonation; and I understand that the amound of compensation has to be adjusted to some degree depending on string guage and height (moved backward for medium guage, and higher action, correct?).

So, if we're talking about a bridge that's 1/8" thick, 2/32 and 3/32" action at the 12th fret, roughly 1/2" string height at the bridge, and light guage strings, am I correct to assume that I should shoot for somewhere between .031 and .062" of compensation at the High E string? (That seems to be the case for my guitars that intonated the best).

I hope that I'm not belaboring this discussion, and that it will be useful for someone beyond me!

_________________
Ken Mitchell
Durham, NC

Ken,
I think you are still using the term "Compensation" for two different measurements.
The stewmac instructions assume you will use a saddle which is crowned so that the string breakpoint is in the middle of the slot.
This is the true compensated length

Measurements to the front of the slot are for convenience of measurement, nothing more, and do not reflect the final compensated string length.

Have a look at the stewmac fret calculator which also gives bridge position lengths (but to centre of slot) If you take away half the saddle thickness you will end up with pretty close to what the saddlematic uses for front of slot setout

Thanks for that, Jeff. I had just about figured that out already from looking at their fret calculator figures. They give .088 for the High E, which when adjusted forward to the front edge would be somewhere in the .031 to .064" range, depending on saddle width.

I appreciate the input!

_________________
Ken Mitchell
Durham, NC