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I’m curious how much compensation many of you build into your bridges.
Using various calculators around the google, and reading different texts, I find that the recommendations vary widely from 2.5 to 6mm on the bass side of a 25.4” steel string with light gauge strings.

Please share your data

Thanks,
Dave

2mm for high e
2.5 for b
1.5 for g
1 for d
3 for a
3.5 for e

String height also plays a factor.
Usually more comp. is needed for higher action.
This with a 3mm saddle width.


Mike

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Mike Collins

I slot the bridge at a specific angle and then place it .1in further then the scale length and it comes out perfect every time. Well, we all know it's never perfect but it's so close that even the professional musicians that have my guitars don't complain about it

I've used the SM calculator and have not had any problems, at least with light gauge strings and a reasonable action.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The StewMac fret calculator is always a good resource.

Anyone used this?


https://www.liutaiomottola.com/formulae ... sation.htm

I used it on the last few (3 ukes and 1 guitar) and they turned out well. I used the calculator to establish the angle on the 6 string and then fine tuned the saddle. On the ukes it was helpful because one was low g and one was high g and the calculator accounts for that.


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I just use a 1/8” drop back on the saddle from treble to bass. 1/8” saddle and mark compensation points with the bent unwound part of a low E string after the guitar is set up with appropriate action and strings.

For bridge location I put a StewMac straightedge against the nut, Mark the center of 12 with a pencil and a second mark downstream in the appropriate location. Typically around 0.12” or so measured in the midline.

Works for me.

To rout a slot on the guitar with a new bridge I have a crowned 1/8” metal bar 1/8” high to use for a surrogate saddle and when the two e’s are right I mark it and that’s where I cut the slot.

I am sure there a lot of more elegant methods out there.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

[quote="Terence Kennedy"......................
To rout a slot on the guitar with a new bridge I have a crowned 1/8” metal bar 1/8” high to use for a surrogate bridge and when the two e’s are right I mark it and that’s where I cut the slot......[/quote]
Much the same here except I use hard maple, touch of CA to hold it in place and then ihat routs off when cutting the slot.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I will make this short
EACH GUITAR IS DIFFERENT
there
actually the best thing I can tell you is to make a model of a neck
put a fret board on a 2 by 4 and make a saddle movable
you only need to do one string at a time,
The variable of this are
Gauge
Height
neck relief

it is about the string and the fret plane
the higher your action and more neck relief the more compensation you need.
I learn formulas don't work as they don't take into consideration these variables.

once you male this thing and play with if you will see the point on intonation.

the higher up the neck the more important this can be. I can't tell you what you need no one can with certainty you have to
figure this out for yourself.

I personally allow .1 in compensation length then work the saddle for each string once the guitar is set up.

I use 5 7 9 and 12 and adjust for the best at those points.

I also use some nut compensation as well.

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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

I made up a similar device, but a bit more complicated, to determine the correct compensation for the nut as well. Fretting the strings makes all the fretted notes go sharp. You can get the lower fretted notes to play in tune by moving the frets closer to the nut, but rather than figure out how far to move each fret it's easier just to shift the nut forward, toward the first fret. This reduces the need for saddle compensation, so you actually have to do both at the same time. Trevor Gore goes into this in detail (with equations!) in his book. You can get most guitars 'arbitrarily close' to perfect intonation on every note this way, but it's probably not possible to get to perfect. For one thing,the bridge is glued down to a top that's moving more at some pitches than others, and that messes up individual notes.

I forgot, I move the nut forward to the first fret too. How much do you guys who do that move it? I simply cut the zero fret nut face end of the FB with my fretting saw so it's about half a saw kerf forward which is about .012in.

EDIT: and when I started doing that I wondered how to measure compensation. Do you take half the scale length and add to that or do you measure from the nut face to the 12th fret which now is a hair shorter and add to that? I have done the former.

I move the nut forward the usual 1/2 the kerf of the fret saw or about 0.012 and measure to the center of 12 and add my compensation to that.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

my allowance is about a .030 slant to the bass side
that gives me a bit of room to intonate the nut in the 1st position
Alan I would love to hear what you are doing.

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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

Just reread this thread and it prompted me to tune up and check the intonation on my last OM as I do things a bit weird these days.
Intonation at nut, 1st and 12th fret are good, within ~1 cent everywhere, so it seems to be working.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

So just to be clear I will use easy fake numbers. Say your scale length is 100mm. You cut the end of the fretboard 1mm shorter to compensate the nut end. and on the saddle end you will compensate with 3mm

If you then measure from the nut face to the 12th fret you now have 49mm. So to compensate the saddle you would measure from the 12th fret to the saddle center 49mm + 3mm for compensation = 52mm

OR

You take your 100mm scale length in half 50mm. So to compensate the saddle you would measure from the 12th fret to the saddle center 50mm + 3mm for compensation = 53mm


?

Introducing nut compensation reduces the requirement for compensation at the saddle.
Nut compensation is introduced to correct intonation on the lower frets, but will lower the note at the 12th fret, so saddle compensation will need reducing.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The topic of compensation has been here many times. If you want a thorough treatment, then certainly Gore/Gilet discuss various approaches for both steel string and classical guitars. I recommend these books strongly.

For my classical guitars, I follow the Gore/Gilet methods for empirical intonation, including the optimization of intonation across all frets. I prepared a calculator that uses this approach with Excel. You need to load the Solver Add-in. I can email the example shown in Gore/Gilet Design page 100-103 to anyone who asks. Classical strings vary tremendously, so you need to do this with a target brand and gauge, but know that intonation will likely change with a different string type.

For steel string guitars, I find the StewMac calculator works pretty well for standard tuning and scale lengths. I prepared my own "neck specification" calculator that includes a compensation calculator that reproduces the SM factors for saddle compensation, but also gives me control over simple nut compensation and saddle thickness:
https://www.mullinguitars.com/calculating-guitar-fret-spacing-fingerboard-dimensions-and-string-setback.html

Things are more tricky when you try to work out compensation for other scales and tunings. As John stated, every guitar is different -- and every string! Brad gave a link to a very good online calculator by Liutaio Mottola. I tried to adapt the the Mottola calculator for a fanfret baritone and got frustrated with the fact the the internal operations aren't transparent. Instead, I adapted the work of Saajk Elmendorp (2010: American Lutherie 104: 56-60) and made my own spreadsheet. His calculations do work, but you will need to generate some specifications for strings that are not readily found on packages or online, including tension, core diameter and weight per unit length. I found I could start with data published by D'Addario for their strings, sacrifice a set to get the weight data, and apply these under the assumption that other manufacturers strings will be ... similar. That's worked well for my baritones. Even better of course would be to build a neck mock up where tension can be measured for your particular string and scale. If you want to go to the trouble, my calculator is linked:
https://www.mullinguitars.com/2015/10/compensation-calculator-for-steel-string-guitars.html

The amount of compensation you will need at either end depends on the strings, scale length, and action height, at least, so it's hard to give general rules. I generally cut the nut slot about 2 to 2.5 mm forward of it's 'theoretical' location, and use a somewhat wider nut to allow for adjusting the compensation later.

As Gore points out, anything you do along these lines is likely to be better than doing nothing. One 'quick and dirty' method that works well: If you've only been compensating the saddle, try splitting the difference. Move the nut up toward the first fret by about half the amount you've been shifting the saddle back, and then shift the saddle half as far as you've been used to.

One of my students came in with a modern reproduction of an Elizabethan 'bandora'; a sort of bass cittern with metal strings. It was very popular during the lifetime of it's inventor, and went out of use after that. Modern ones, based on wood cut illustrations and the like since there are no surviving originals, have terrible intonation issues, and this was no exception. The bridge had already been re-slotted once, and there was no room to move the saddle any further, so we thought we'd try the nut end. We played around a bit with toothpicks under the strings, and finally decided to re-cut the nut slot at slant of something like 5-6 mm from treble to bass. It worked very well. Several other of the local early music players have commented that it's the best bandora they've heard, mostly, I suspect, because it plays more or less in tune. Interestingly enough, when my student went looking for the old wood cuts, they all showed a clearly angled nut. I suspect that people making the modern copies thought: "That can't be right!", and cut the nut straight across. Maybe the old boy knew better.

I haven't REALLY done compensation, the arch top has the bridge you can easily file to correct; and I haven't noticed any problems with it since I made the new bridge that is set up for the nylon strings I have on it. I'm an easy customer. But I'm reading stuff to be prepared; some day I'll make a classical or a steel string with frets, and not moveable frets, and I'll need to know.

The other day when I read about bridge rotation; something I STILL don't understand how you can measure something so small; I found this AWESOME beast. What do you call it when the scale is RADICALLY different from first to last string? Luckily it has a compensating bridge/saddle. A little of that might be interesting, but full out crazy is pretty outlandish. It does look cool. I bet it's heavy!

Torzal natural twist. 15 degrees at the bridge, and 20 degrees at the neck, and the "fanned scale?"

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Why be normal?

Making the most of some twisty problem wood? Nah--actually that's pretty cool. Really nice laminations.
Dave

It's know as a Fan Fret, or multiscale.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Do you guys actually set up to a specific string set though? I've always figured an average is what we should be going for. If you set up someone perfectly for 11's what happens when they switch to 13's?

All things being equal, heavier core strings will require more compensation. This becomes really obvious when you intonate heavy strings on electric guitars with adjustable saddles and run out of adjustment.
Even same gauge strings from different manufacturers can have different core diameters, and hence different ideal compensation.
Lesson of the day: 3/32” saddles on acoustic guitars are a bad idea.


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Ken the way you measure bridge rotation is to fix a lightweight lever to the bridge, I use a length of 600 mm stuck with bluetack (poster putty, whatever), then keeping everything steady, drop the string tension and the ends of the lever move a few mms. Quite enough to measure. A bit of trigonometry gives the change in angle. You are looking for around 2 degrees on both SS and Classical.

I find it useful as a test - obviously after completion- as to whether I got the stiffness of the top right. Like any beginner I overbuilt my first few.

Cheers Dave

I just use the inclinometer app on my phone and bluetack. Free and to 0.1 degrees.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.