Question about bridge/saddle compensation

[Mystic]

Hello
I am building first uke (concert) with a 15 inch scale length.
The on-line plans I found call for positioning the saddle about 1 mm less than 15 inches for "compensation", but most forums I read suggest moving the saddle back to compensate for string tension or measuring exactly to 15 inches
Anyone familiar with the rationale for shortenning the scale length?

Regards

Mystic

 

[Oldscruggsfan]

As I’m guessing you already know, the general rule on any fretted instrument is that the 12th fret is the halfway point between the nut and the bridge/
saddle. I don’t claim to understand compensation and for that reason will leave the explanation to folk with far greater experience.

When positioning the replacement bridge on my Famous FU120-P, I made a mark (on blue painter’s tape) on the bass side and on the treble side, precisely the same distance from the center of the 12th fret to the front plane of the saddle as from the nut to the center of the 12th fret, then glued- up the bridge to align with those marks.

Watch how Ken Timms does it. No, brother Ken doesn’t explain compensation but his videos are so pleasant and well done:

ukulele.bridge ken tomms - Google Search

 

[John Colter]

Theoretically, the bridge/saddle would be positioned so that the twelfth fret is at the mid point of the scale length. Playing involves selectively pressing down the strings over the fretboard to alter the pitch: this finger pressure stretches the string, causing it to sound slightly sharp.

To compensate for this, the point at which the strings meet the saddle should be positioned about 1/8" (or 3mm) further away from the twelfth fret.

 

[Dohle]

Hi Mystic. Welcome to the forum.

I don't mind you posting to Uke Talk at all and seems like you've already gotten some answers but a more suitable section of the forum for these kinds of questions is the Luthier's Lounge: https://forum.ukuleleunderground.com/forums/ukulele-building-luthiers-lounge.30/
Many experienced uke builders can be found there and are often happy to help. Just a suggestion.

 

[anthonyg]

Hello
I am building first uke (concert) with a 15 inch scale length.
The on-line plans I found call for positioning the saddle about 1 mm less than 15 inches for "compensation", but most forums I read suggest moving the saddle back to compensate for string tension or measuring exactly to 15 inches
Anyone familiar with the rationale for shortenning the scale length?

Regards

Mystic

This subject is a can of worms, and the answer could take page after page to fully explain.
As Dohle suggested, you're better off asking this question in the Luthier's Lounge.
A quick guess on my part is, if the frets have been cut to the rule of 18 rather than the more modern 17.817, then short compensation is good.
Do you know which rules your frets are cut too?
Use the search engine first. We have discussed these issues before on a number of occasions.

 

[John Colter]

I would not advise new builders to attempt to gain a full understanding of all aspects of compensation. At this stage, all you need is an appreciation of why a little compensation is desirable and how much to aim for - in this case plus 1/8".

It is highly unlikely that the frets have been calculated using the Rule of Eighteen.

A concert uke with modern fret placement and no compensation will sound OK when using only the lower frets (those closest to the nut) but is likely to sound progressively sharper the further up (towards the bridge) you play

There is no rationale for shortening the distance from the twelfth fret to the saddle. If this has been suggested, then ignore the suggestion - it is just plain wrong.

 

[John Colter]

"A quick guess on my part is, if the frets have been cut to the rule of 18 rather than the more modern 17.817, then short compensation is good"

This is a misunderstanding. Using the modern divisor will require compensation: using the rule of eighteen will not.

 

[anthonyg]

"A quick guess on my part is, if the frets have been cut to the rule of 18 rather than the more modern 17.817, then short compensation is good"
This is a misunderstanding. Using the modern divisor will require compensation: using the rule of eighteen will not.

Sure. I'm not an expert. I clearly stated that I was taking a guess, I asked if he knew what rules he fretted to and I suggested doing a search.
We have a friend on this forum who is expert so I will post a link to his article.
https://www.liutaiomottola.com/PrevPubs/RuleOf18/RuleOf18.htm

 

[70sSanO]

I’m not well versed in compensation theory.

Would a “relatively” safe approach be the measurement from the nut to the 12th fret, double, and add compensation of 2mm/3mm?

John

 

[John Colter]

I’m not well versed in compensation theory.

Would a “relatively” safe approach be the measurement from the nut to the 12th fret, double, and add compensation of 2mm/3mm?

John

Yep, that's it.

 

[anthonyg]

I’m not well versed in compensation theory.

Would a “relatively” safe approach be the measurement from the nut to the 12th fret, double, and add compensation of 2mm/3mm?

John

Meh.
Is this for rule of 18 frets, or the modern "rule" of 17.817 frets?
A year ago I would have given the same answer, yet this year, after I learnt of the implications of rule of 18 fretting, I ask a few questions first.
The Original Poster asked if there was a reason for his ukulele plans recommending for short saddle placement when every bit of advice he had read said go a little long on the saddle placement.
Well there might be a reason for this, and that reason is called rule of 18 fret placements.
So I asked if he knew which rules he used for fretting.
Its a can of worms.

 

[John Colter]

Hi there, Mystic,

Will you please tell us which plans you are working from and include a link to the online source, so that we know exactly what you are dealing with. I'm sure that would put Anthonyg's mind at rest.

 

[Mystic]

Hi there, Mystic,

Will you please tell us which plans you are working from and include a link to the online source, so that we know exactly what you are dealing with. I'm sure that would put Anthonyg's mind at rest.

Hi All
I am using the free online plans from Oak

Hi there, Mystic,

Will you please tell us which plans you are working from and include a link to the online source, so that we know exactly what you are dealing with. I'm sure that would put Anthonyg's mind at rest.

Hi All

I am using the free online plans from Oaktown Strings - https://www.oaktownstrings.com/free-instrument-plans
The frets have been placed using Stewmac fret calculator and the frets are LMI mandolin/dulcimer frets (.028 inch crown)
I will have to do more research on the rule of 18....I have not heard of this before today.
I am finishing the nut today and so would like to finalize bridge placement so I can glue the bridge tomorrow and begin adjusting saddle and nut height.
All advice welcome and yes...in future I will post questions like this to the Luthier's Lounge.

Regards

Mystic

Regards

Gary

 

[70sSanO]

Hi All
I am using the free online plans from Oak

Hi All

I am using the free online plans from Oaktown Strings - https://www.oaktownstrings.com/free-instrument-plans
The frets have been placed using Stewmac fret calculator and the frets are LMI mandolin/dulcimer frets (.028 inch crown)
I will have to do more research on the rule of 18....I have not heard of this before today.
I am finishing the nut today and so would like to finalize bridge placement so I can glue the bridge tomorrow and begin adjusting saddle and nut height.
All advice welcome and yes...in future I will post questions like this to the Luthier's Lounge.

Regards

Mystic

Regards

Gary

Personally, I think the future is now.

Lay out what you are using for the build; Oaktiwn/Stew Mac.

I find it hard to believe that you won’t get the best answer if you post your question in the luthiers subforum for this build.

John

 

[John Colter]

Hi Mystic, the answers I have given already will apply to these plans. Forget about the rule of eighteen, it does not apply here. I am looking forward to reading about your experiences in uke building. About twenty years ago, I was going through what you are doing right now. It is an interesting and absorbing process.

 

[anthonyg]

Hi All
I am using the free online plans from Oak

Hi All

I am using the free online plans from Oaktown Strings - https://www.oaktownstrings.com/free-instrument-plans
The frets have been placed using Stewmac fret calculator and the frets are LMI mandolin/dulcimer frets (.028 inch crown)
I will have to do more research on the rule of 18....I have not heard of this before today.
I am finishing the nut today and so would like to finalize bridge placement so I can glue the bridge tomorrow and begin adjusting saddle and nut height.
All advice welcome and yes...in future I will post questions like this to the Luthier's Lounge.

Regards

Mystic

Regards

Gary

OK, if you're using Stewmac as the fretting guide, then I agree with John, the rule of 18 doesn't apply.
Who knows why the plan suggested placing the saddle 1mm short, yet in this case, its incorrect and go with the standard advice instead.