Scale length confusion + newbie disappointments!

(long post alert)
Just completed another Dreadnaught concert, and Im really pleased with the final instrument... but!

The intonation is out, noticeably at the 12 fret (sharp)

I have previously struggled with a definitive position for saddle positions, I can’t find consistent advice. So I did some measuring!

The ‘book’ says 15 inches 381mm (nut to saddle)
However, My Koaloha is 385mm (nut-12 =190.5mm / 12-saddle 194.5mm)

I have CLEARLY got ‘my’ measurements wrong:
Dread.. 379.5mm (nut-12 =191.5mm / 12-saddle 188mm)
The fretboard was supplied cut by a VERY reliable source.

So, I guess I need to move the bridge back? Im just not sure where too/how far.

I know I’m learning, but it is a bit disappointing getting things wrong!
Can anybody advice please? I also need to know about tenor and soprano cause I got those wrong too!
(also how do I remove a bridge glued with titebond?)

hello
been there, made that mistake. this is all to do with compensation. depending upon the height of the string above the 12th fret, as you press it down to the fretboard, you stretch the string changing the pitch. so the note is higher than the 12th harmonic. to combat this, the bridge position needs to compensate for it by being a little bit farther away than you would imagine. i use the stewmac fret position calculator web page which gives you the compensated bridge position.
so you will probably either need to move the bridge or redo the fretboard, whichever is least horrible.
stick with it
Max

Stewart MacDonald is your friend,

https://www.stewmac.com/FretCalculator

Theoretical scale length is, nut to centre 12th fret x 2. Actual scale length is nut to centre 12th fret x 2 + compensation. Compensation is mostly required because strings don't vibrate as perfectly as theory requires. The thicker a string gets the less perfectly it vibrates. String height adds to the issue although the fundamental string thickness issue remains. Generally the shorter the string length the more compensation is required.

Yes, any time the centre 12th fret to saddle distance is LESS than the nut (inside) to centre 12th fret is then the intonation will be horribly sharp.

Something to check too. Make absolutely sure that you know if the fret board is made in inches OR mm. OK, for a concert, 15" is 381mm but for a tenor 17" is 431.8mm. Sometimes a metric tenor will have a scale length of 432mm or I've seen 440mm to. That 0.2mm difference between 17" and the metric 432mm makes a difference.

There should never be a need for negative string compensation so place the saddles leading edge for the compensation required for the skinny strings and this should leave the saddle thick enough to file the contact point rearwards for the thicker strings.

Anthony

I should add that the above information is based on very accurately placing the nut in relation to the centre of the 12th fret. The nuts position can be compensated too.

One of my ukuleles which has very good intonation has the nut moved away slightly from the centre 12th fret but it also has plenty of saddle compensation. The 2 cancel each other out. I'm not sure that I would recommend this but it works on one of my ukuleles.

Now of course the whole issue of what the instruments theoretical scale length is, can be confusing when builders do this. I find out by using the stewmac fret position calculator and measuring fret to fret in various positions.

Anthony

Hi Kevs,

Regardless of who cut your board you should personally verify the slot spacing. To do that I recommend you use a printed fret spacing guide; it's very easy to introduce errors while measuring to the precision required. All of the fret placement calculators that spit out a string of numbers don't factor in how easy it is to mis-measure or the cumulative error introduced in the measuring / cutting process.

If you're running a PC I'll suggest downloading Wfret and printing your own fret placement guides. You can find the download link on my website on the "general banjo construction tips" page (as well as a couple of other ways to calculate fret position), or you can print a very accurate concert uke fret guide from my Uke page here:

http://www.bluestemstrings.com/pageUke1.html

In any case, being relatively new to this, I would suggest you do a bit of reading to clarify how to place a bridge and to understand and calculate compensation correctly.

Scale length is ALWAYS going to be the distance from the face of the nut to the center of the 12th fret multiplied by 2 on a properly made instrument. Additional length beyond that is what is added for compensation. Compensation is added purely to handle the natural tendency for a string to raise in pitch as it is stretched from being pushed down during fretting.

In general it's best to add the compensation length as recommended by any of the standard sources. That part isn't difficult.

As far as your wonky bridge goes, sometimes you have to bite the bullet for this kind of error. If it were me I'd set up a pattern routing guide over the bridge and remove it by flush routing to the top. You can make a new bridge just slightly larger than your existing footprint if needed.

With a bridge glued down with Titebond you'll likely do a lot more damage to the soundboard by attempting to save it when removing it.

Depending on how far off you are and how your bridge is made you may also be able to fill and re-locate your saddle slot.

Thanks for taking the time to advise here.
I took the plunge and removed the bridge. I felt that “as I’m learning, I should learn to get it right”!
An instrument that isn’t ‘good enough’ isn’t good enough! I can’t play (or sell/give away) until its right.

So what next? I double the distance from nut to centre of 12th fret + add a bit of compensation (magic and prayer) ?
I

AHHH Rudy,

You replied while I was writing my post.... Thank you, I take on board your guidance, and thank you for the links.
I’ll check them out. You state to add compensation as recommended by standard sources? I am struggling to find these.

Thanks again

To add to the previously suggested website resources I figured I'd post a site I stumbled across a while ago when trying to get my head around compensation:
http://liutaiomottola.com/formulae/compensation.htm

Kevs-the-name said:

AHHH Rudy,

You replied while I was writing my post.... Thank you, I take on board your guidance, and thank you for the links.
I’ll check them out. You state to add compensation as recommended by standard sources? I am struggling to find these.

Thanks again

Click to expand...

Shouldn't be a struggle to find recommended compensation numbers on any construction print you might be using. The struggle might be to find a common number from any builder!

Again, I'd recommend doing a bit of reading to understand compensation and in particular, why it's somewhat of a moving target. The actual amount of compensation needed is based on a number of variables such as scale length, preferred action, your playing technique, string guages, string type, and even the age of the string. For ukes you'll usually find 3/32" to 1/8" recommended compensation, but that varies a bit from builders who prefer not to add ANY to builders insisting that each string needs a separate amount, with the resulting need for a compensated saddle.

Do notice this is such a debated point that at least one prominent maker provides a bridge with adjustable saddle points.

I'd personally opt for 1/8" for a concert and call it good.

If you really want to see this in action and have a "once bitten twice shy" feeling about your bridge placement I'd recommend you rig up a simple jig to hold your strings a bit beyond where your bridge will be located and simply try out your bridge with a bit of double stick tape to test positioning before actually committing to a location. This is a great way to see how compensation and saddle placement will work for YOU before gluing anything down.

Kev, maybe it's best to rethink your understanding of "scale length".

Firstly, when referring to scale length, (lets say 16" for example) the reality is that the actual scale length is from the edge of the nut to the center of 12th fret x 2 = scale length. Period, fini, end, thats it, not fooling. Thats the scale length! (and it's also referred to as the octave).

If it comes out to slightly under or slightly over 16",most people still refer to it as 16" scale length. So in that regard measuring from the nut to the saddle is really not what to focus on. Especially when calculating bridge placement.!

There's no reason your fretboard wouldn't be correctly cut if you bought from a reputable source, but remember that anything close to 16" is called 16" scale length. The fact is many fret slotting templates you can purchase are usually off in one direction or another from what they say they are, and that's no big deal.! Why? because you don't place the bridge and saddle based on the listed 16" scale length. You as a builder will simply measure nut to 12th and double that, then add compensation.

Ah yes compensation. Wanna know how to what that's supposed to be? The answer is "it depends". Thank you very much.

So here's the thing, don't let that be a problem for you. There are a few factors to consider anyway, like, shorter scale lengths often require more compensation than longer, softer strings require less compensation than harder strings, certain brands and formulas respond differently, so one brand may intonate perfectly and another not so well.

As Rudy suggested you can poke around and find some average amounts for a given size uke. Like 3/32" is common for a tenor. And that's a fine place to start. But know that there is no magic number to use. As a builder you'll have to get some experience under your belt to get a feel for why one instrument you're making would need a little more or a little less. As will any player who changes out strings and finds the intonation is not as good as the last set. And regardless if you like the tone of certain strings, they may just not work with the current setup.

So reglue your bridge at 2x the nut-12th measurement, add 3/32", and never measure from the nut to the saddle. There's no reason to. If you're a little sharp or flat you can file the saddle ramps in one direction or the other to get closer. But remember, that will be for the strings you're using, and the action you've set.

There, now you're a luthier with luthier problems and will have to find your optimum setup, and strings for the instrument you just built.

RPA_Ukuleles said:

So reglue your bridge at 2x the nut-12th measurement, add 3/32", and never measure from the nut to the saddle. There's no reason to. If you're a little sharp or flat you can file the saddle ramps in one direction or the other to get closer. But remember, that will be for the strings you're using, and the action you've set.

There, now you're a luthier with luthier problems and will have to find your optimum setup, and strings for the instrument you just built.

Click to expand...

THIS is some very useful advice thank you very much. (in fact everything that has been written is really helpful)
I will do exactly this!
...and learn! and once I get around this, i’m sure there will be the ‘next’ thing that causes confusion.

Making ukes is quite easy! making good ukes is bloody hard!

The simple explanation is; the intonation is controlled by the space from the nut to the 12th fret that has to be exactly the same as the space from the 12th fret to the saddle where the strings hit.

Some really useful and informative reading is on Dr. David Hurd's website http://ukuleles.com/
There is just all kinds of info and a section on compensation. Good reading!

kohanmike said:

The simple explanation is; the intonation is controlled by the space from the nut to the 12th fret that has to be exactly the same as the space from the 12th fret to the saddle where the strings hit.

Click to expand...

And there we have it....
Conflicting information.
What about the unknown compensation adjustment?

kohanmike said:

The simple explanation is; the intonation is controlled by the space from the nut to the 12th fret that has to be exactly the same as the space from the 12th fret to the saddle where the strings hit.

Click to expand...

plus a little bit more

Kev, this post above from wildestcat is the best so far to build on. Importantly please not that this is a METRIC Concert with a 382mm nominal scale length. You have stated that yours is a 381mm or 15" nominal scale length. That 1mm is important to take into account.

As stated, if you use a saddle material that is thick enough then you can get away with placing the saddles leading edge precisely at the nominal scale length mark with the thickness of the saddle being beyond this mark. Later on when it comes to fine tuning the intonation you file the saddle contact point to suit each individual string.

You move the contact point long if the intonation is going sharp and shorter if the intonation is going flat. And this brings up an important point. Even with classic/nylon/nylgut/flurocarbon strings each individual string needs a slightly different compensation. Perfect intonation will not come from a perfectly perpendicular saddle contact point.

So quoted saddle compensation is to the string contact point which is somewhere within the thickness of the saddle material. Like everyone else I'm reluctant to say exactly where that point is because of all the reasons already mentioned.

Based on Wildestcats post and my experience I suggest placing the leading edge of the saddle at the nominal scale length +1mm if the saddle is thick enough. If your using a thin saddle (2mm, 3/32" is only 2.4mm which is still thin, try 3mm) then you may need more. In your case of a 381mm scale length (double check) this should be at 382mm. After the instrument is built you will need to individually compensate each string.

If by chance you go a little too far with the compensation at the saddle, and the intonation goes flat then it is possible to CAREFULLY compensate the nut by moving it away slightly from the 12th fret.

EDIT again: I hate to say it but some are still giving wrong information as to the need for compensation. Its when a string is too thick or stiff to vibrate as theory requires that compensation is required. String height only adds to the problem. The underlying issue of string STIFFNESS doesn't go away.

Steel string instruments can have VERY low actions but still need LOTS of string compensation because steel strings are stiff.

Anthony

Sorry chaps - I ended up deleting my post as I was struggling with constant interruptions and an overdose of red wine at the time. The numbers didn't seem to match the photos. I'll have another go tomorrow!

Wildestcat said:

Sorry chaps - I ended up deleting my post as I was struggling with constant interruptions and an overdose of red wine at the time. The numbers didn't seem to match the photos. I'll have another go tomorrow!

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Such photos are incredibly difficult to take accurately because of parallax error. I was once a professional photographer and I struggle with such photos. What's important is are the numbers quoted accurate?

For what its worth I thought they looked OK.

Anthony

This really shouldn't be that difficult to get it close.

If you don't know the exact scale length the fret board was made to then you must measure from the end of the fret board at the nut to the middle of the 12th fret and then multiply X 2. I would do this in metric because it makes so much more sense to use numbers like 203mm X 2. But that's just me perhaps.

Then once you have that number for the scale length of the fret boards you bought, just go over to StewMac's website and use their free fret calculator to work out how much compensation is recommended. Just be sure to pick some nominal number of frets and "ukulele" and if you are going metric or imperial.

Down at the bottom of the fret position printout there will be the scale length with compensation number. In the metric case it will say + or - 0.5mm. As compensation is so dependent on a lot of things, you just don't know until you've really dialled in your building. BUT then there is the width of your saddle that gives you some room for adjustments if required.

anthonyg said:

Such photos are incredibly difficult to take accurately because of parallax error.

Anthony

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Can I say something here about obsessiveness? Sure scale length and compensation for string stretching are important, but more important things might be perhaps like how you thin your tops and brace things up for overall sound. Any string player worth his salt can compensate for off intonation by stretching the string while playing. It is really not that big a deal. As long as things are reasonably close, good enough. Play on!... Oh and also, few uke players play above the 5th fret anyway so who cares? It is not like most players are doing single string runs up at the 17th fret. I mean really. Who cares if you are 2 cents off at the 12th? We are talking about UKULELES here.