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Bridge Positioning
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23548		 Page 1 of 1
Author:  Mike OMelia [ Sun Aug 23, 2009 5:25 pm ]
Post subject:  Bridge Positioning
I am trying to locate the bridge on a 14 fret OM, 25.4 scale. Of course, the saddle is canted. Which point along the saddle slot should measure 25.4? The high e, low e, or just in the middle?

Mike
Author:  Jeff Highland [ Sun Aug 23, 2009 6:09 pm ]
Post subject:  Re: Bridge Positioning
None of the above!

You will need some compensation even on the high e string.
But first check your scale length (nut to centre of 12th fret X2)
Some nominal 25.5 fretboards are actually 25.34

Now use the Stewmac fret calculator to give your bridge position.
http://www.stewmac.com/cgi-bin/hazel.cgi
Plug in your true scale length as determined above, use the acoustic guitar option and it will give you distances for high and low E strings to the breakpoint on the saddle.
Author:  woody b [ Sun Aug 23, 2009 6:13 pm ]
Post subject:  Re: Bridge Positioning
Neither. First, some poeple, (including me) use a 25.34" scale, but it's usually called a 25.4" scale. Measure from the nut to the center of the 12th fret. If it's a true 25.4" scale it will measure 12.700. If it's a 25.34" scale it will measure 12.670". Take this distance, (we'll use 12.700" but be sure to measure) and place the center of the saddle slot at the high "e" the 12th fret measurement + .090" from the center of the 12th fret. The low "E" will be the 12th fret measurement +.215" from the 12th fret. This makes the high "e" measure 25.490" from the nut, and the low "E" measure 25.615" from the nut. This is just the way I do it. I do all of my measurements from the 12th fret. I hope I done a decent job explaining. I'm not much of a teacher.
Author:  SteveSmith [ Sun Aug 23, 2009 8:30 pm ]
Post subject:  Re: Bridge Positioning
I'm getting ready to set the bridge on mine as well. I shortened the fretboard about 0.030" at the nut end. So should I use the nut to 12th fret distance when setting the bridge or do I need to add 0.030"? I'm thinking I should add the 0.030" but figured it was a good idea to ask.
Author:  Mike OMelia [ Sun Aug 23, 2009 9:03 pm ]
Post subject:  Re: Bridge Positioning
OK, Thanks! That's why I asked. I will get that saddlematic.

BTW, the link for the fret calculator did not seem to work for me... unless I misunderstood.

Mike
Author:  SteveSmith [ Sun Aug 23, 2009 9:13 pm ]
Post subject:  Re: Bridge Positioning
Mike O'Melia wrote:
OK, Thanks! That's why I asked. I will get that saddlematic.

BTW, the link for the fret calculator did not seem to work for me... unless I misunderstood.

Mike


Mike, see if this works http://www.stewmac.com/FretCalculator/
Author:  SteveSmith [ Mon Aug 24, 2009 7:48 am ]
Post subject:  Re: Bridge Positioning
Thanks Todd, that's what I thought.
Author:  TonyKarol [ Mon Aug 24, 2009 8:55 am ]
Post subject:  Re: Bridge Positioning
Hmmm ... I seem to recall Mike Collins saying that if you comp at the nut, you move the saddle FORWARD the same ammount ... not back ...


I do it a bit simpler than some .... my slot has a 3mm back set from e to E ... I add 2.5mm to the 12th to saddle (half the scale), and measure that in the middle of the slot between D and G .... I use a 1/8 saddle on most guitars, 3/16 on multis and baritones.
Author:  SteveSmith [ Mon Aug 24, 2009 10:15 am ]
Post subject:  Re: Bridge Positioning
Now I'm getting confused. Here's how I'm thinking of this:

1) Compensating at the nut end makes the strings slightly shorter so tuning to pitch with open strings would require a bit less tension.

2) If I set the saddle at a normal distance (12th fret + 1/2 scale + standard compensation, i.e. what Todd said) then fretted notes should be a bit flatter than with only an uncompensated nut. This would give a similar result to what I already do - I tune a bit flat so fretted notes, especially on the first 3 frets, will not be too sharp.

3) If I move the saddle another 0.030" closer then the result would be an even shorter string with even less tension required when tuned to pitch. So the effect of making fretted notes more flat would be even more pronounced but then would tend to be offset somewhat by the shorter fret to saddle distance which would move the note sharper?

I suppose I could build a spreadsheet and do the calculations, including the effect of change in tension due to fretted notes, but I'm sure someone, somewhere has already done this.

As I said, I'm a bit confused.
Author:  SteveSmith [ Mon Aug 24, 2009 12:53 pm ]
Post subject:  Re: Bridge Positioning
Todd Stock wrote:
Time to drag out Excel and determine the impacts.


I was afraid of that. I'm off to do some research so I can understand this better.
Author:  Mike Collins [ Mon Aug 24, 2009 1:52 pm ]
Post subject:  Re: Bridge Positioning
[quote="TonyKarol"]Hmmm ... I seem to recall Mike Collins saying that if you comp at the nut, you move the saddle FORWARD the same ammount ... not back ...

Wow!
if i said that i'd better get to rehab! idunno
You still have to have saddle set back with a shorten f.b.
It depends on the string gauge,& string height most of all.

I made a simple neck jig.
Tuners on one end & adjustable saddles on the other.
I used a shortened by 1mm f.b. and a regular one.
I set action to the string gauge and type.
Then adjust into with a Strobe II tuner.
Then I make the guitar & set the bridge & saddle for those strings.

Mike
Author:  Darryl Young [ Mon Aug 24, 2009 3:29 pm ]
Post subject:  Re: Bridge Positioning
Here is the "bible" on scale length and string compensation (including nut compensation) written by David Collins in a post at the link below......very, very good information!!! The post is roughly half way down the first page. Most all questions in this topic are covered at the link below. Save it in your favorites.....are better yet, copy it to your PC at home.

viewtopic.php?f=10101&t=22597
Author:  SteveSmith [ Mon Aug 24, 2009 3:56 pm ]
Post subject:  Re: Bridge Positioning
I've been doing a little reading and I can immediately see that Mike's empirical approach is probably the way to go if you're going to get it right on the money.

Looks like there are three variables to consider simultaneously:
1. Lower pitch strings have more tendency to go sharp when fretted then do higher pitch strings.
2. The pitch of the string is proportional to the tension.
3. The tension is proportional to the mass of the string.

A mathematical solution could be generated if the data for the strings were available but it still may not give you a useful result.

This acoustic is for me and it is a prototype for several features and I already have a long list of changes I need to make. I am thinking I'll just set the saddle by measuring from the 12th fret 1/2 of the scale length + the compensation from a calculator like StewMacs and see how well it intonates.

I am curious though, if you compensate both nut and saddle does the saddle compensation increase or decrease when compared to the standard numbers produced by the StewMac calculator?
Author:  Jeff Highland [ Mon Aug 24, 2009 4:27 pm ]
Post subject:  Re: Bridge Positioning
The saddle compensation is all about getting the fretted octaves at the 12th fret in tune. (and other fretted notes in this region)
The nut compensation is about avoiding sharpening the first few frets.
Whatever nut compensation you use, just use the nut to 12th X2 as your scale length.
Author:  SteveSmith [ Mon Aug 24, 2009 4:41 pm ]
Post subject:  Re: Bridge Positioning
I will quit overthinking and press forward. Thanks all!
Author:  SteveSmith [ Mon Aug 24, 2009 9:18 pm ]
Post subject:  Re: Bridge Positioning
Todd Stock wrote:
I'm guessing most folks use actual nut to 12th, as fret templates cut a fret slot at the nut, versus actually cutting the board at the nut location.

Good point. Well, I'll for sure do it one way or the other ;) Either way I'll learn more about intonation so it's all good.
Author:  Tom West [ Tue Aug 25, 2009 12:49 pm ]
Post subject:  Re: Bridge Positioning
Mike: I use a "story stick" about 3/4" by 1/4" by 30" long with a hook on one end like a hook rule. The 12th fret position,the actual scale length position,the compensated high E position at the front edge of the saddle and the compensated low E position at the front edge of the saddle are maked in the stick with a sharp knife. With the hook on the nut end of the fingerboard it is very easy to see exactly where you are both at the 12th fret and at the saddle slot. You will need one for every scale you use.I use about 3/32" compensation at the centre of the saddle slot. Also use a wide saddle approximately.200".Take care.
Tom.
Author:  TonyKarol [ Tue Aug 25, 2009 3:10 pm ]
Post subject:  Re: Bridge Positioning
Sorry Mike .. wrong Collins !!!

And just to be clear, I thought it said subtract the nut comp from the added saddle comp .. so for instance, if you nut comp 30 thou, and you regularly saddle comp 150, then you would use 120 instead .... dont know htough, I have never tried that approach. I could be totally mistaken on what was said.

I cant say for sure, I have been using nut comp on every acoustic I have ever made, long before I ever heard of Buzz F ... I still use the same saddle comp numbers, adn then adjust the saddle peak as required. Tommy Emmanuel was playing one of my baritones this past week and he noted how well the upper register intonation was. Thats good enough for me ... bliss
Author:  SteveSmith [ Tue Aug 25, 2009 3:27 pm ]
Post subject:  Re: Bridge Positioning
TonyKarol wrote:
...
I cant say for sure, I have been using nut comp on every acoustic I have ever made, long before I ever heard of Buzz F ... I still use the same saddle comp numbers, adn then adjust the saddle peak as required. ... ... Thats good enough for me ... bliss


So now I KNOW which way I'm gonna do it [:Y:]
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