Further adventures in scale length..For the children...

[Jackknifegypsy]

..acquired a one-off, mini-guitar, in near perfect condition, lower bout less than 9", with a 25 CM scale length, but Saddle midpoint is 26.5 CM. I want to give this to a 12 yr old and want to make certain it's as good as I can make it.

Just trying to see if it would tune at all, put on the lower E string, and a minimum height saddle (Without changing the plastic bridge there is no way to get any decent action without the saddle just barely clearing the front edge of the bridge) and it comes up very sharp, at least 9 cents.

Moving the saddle point back ---as per previous information----with a bone chip to the furthest it can be placed against the back of the (top-loading) bridge, does not make the low E any flatter.

What am I doing wrong? Does the bridge need moved further forward to allow saddle to be at 25 cm? I am not against removing and replacing the bridge, but that seems counter to previous information.

Pic below.

http://s1244.beta.photobucket.com/us...couch%20guitar

[ZekeM]

Hey jack, what gauge strings are you using? With such a small guitar you may need lighter strings. If the ones you are using are too heavy it could be bowing the neck and shortening the distance from but to saddle. Take a look and see if this could be what's going on.

[Jackknifegypsy]

Triple checked, no change. This guitar is solid, with steel reinforcing, though smallish.

Something else is awry.

On another parlor guitar I just checked, I have a 29.2 CM scale, and a midpoint on the saddle at 29.2. With compensation I have the low E all the way back to 29.8 and it's still 8 cents sharp. I can't go any further back without going off the bridge. Which I'll do but I still can't figure out why the ironclad rule of 2x + Compensation isn't working.

I know that this has been done to death but these discrepancies must be pointing to something else going on that I haven't yet learned.

[charles Tauber]

Originally Posted by Jackknifegypsy

a 25 CM scale length, but Saddle midpoint is 26.5 CM.

It is really a 250 mm scale length, that is 125 mm measured from nut to 12th fret? It really has 16mm of compensation? I'd start by re-measuring those. Admittedly, I don't have much experience with 250 mm scale length guitars.

If you are serious about having a 12 year-old learn to play the guitar, unless the child is abnormally small, this isn't an appropriate instrument on which to seriously study. 9" wide, 250 mm scale length guitars aren't "parlour guitars".

The shorter the scale length, the more compensation that is required. For your 292 mm scale length, it is telling you that 8 mm of compensation isn't enough. (I can't imagine that 16 mm is still not enough on the 250, but that's what it appears to be telling you.)

One of the things repeatedly stated is that one can't define a single amount of compensation that is required. It depends upon a bunch of variables, one of which is scale length. The 3 to 5 mm that is sufficient for a 650 mm scale length guitar isn't enough for a scale length that is less than half that. I'd be surprised, however, if it needed as much as 16 mm or more.

[arie]

i have a similar guitar on my to do list -needs intonation work. one thing i can say is that you should have all of your strings fully stretched and up to tension when doing comp work. relax one string, insert "chip of bone", bring back to pitch, figure out comp, repeat for all of the strings. don't think that it's a martin d18 and it can handle med gauge wire. you need to be using something in the .010~.046 to .011~.048 range. i've had good luck using silk and steels on guitars like that one.

you need to have neck pull and bridge rise at "playing tension" to compensate accurately. simulate all aspects of the actual playing condition as best as you can first before tackling intonation.

i can say from experience that guitars of that quality and scale length are a real handful to intonate properly. ones i have seen new out of the box were nearly unplayable. your fret slots might not even be cut to the right spacing. you have your work cut out for you.

[Jackknifegypsy]

Once more into the breech: Errata: Scale length is 505 mm, not the 25 CM I OP'ed, as Charles subtly points out.

Note: this guitar has a "zero fret" so that is from where I am measuring to the 12th.

That distance is 250 mm.
The distance from the 12th fret to the existing saddle midpoint is 255 mm.

The additional compensation I placed is 15.8 mm. And it still plays sharp by nearly as much as it did without the 15.8 mm I added.

So, immediately----if this were a 650 mm length guitar---the existing saddle is 5 mm off.


What you are all saying is that a guitar like this does not conform to simple: 2x scale plus y Compensation.

As Charled notes: what is appropriate for 650 will not be for a guitar of this type, so to get this thing to play well may be impossible without doing what Arie says: Take each string and fiddle with it until each string is intonated as best as can be with the existing bridge and changing bridges to get a more uniform standard of compensation will not work?

[charles Tauber]

Originally Posted by Jackknifegypsy

Scale length is 505 mm

That is still a very short scale length by guitar standards. Even short for a lute.

Note: this guitar has a "zero fret" so that is from where I am measuring to the 12th. That distance is 250 mm.

Measure from the center of the zero-fret, as best as you can. If that distance is 250 mm, then the SCALE LENGTH is 500mm, not 505.

The distance from the 12th fret to the existing saddle midpoint is 255 mm.

So, on a 500 mm scale length, that is 5 mm of compensation. On such a short scale length, not enough.

The additional compensation I placed is 15.8 mm. And it still plays sharp by nearly as much as it did without the 15.8 mm I added.

So, if you measure from the center of the zero fret to the saddle position you've created, it measures 515.8 mm? That's a mighty accurate ruler you have, to measure to .8 of a mm.

I'd expect that 15 mm (or even 15.8 mm) would be too much.

So, immediately----if this were a 650 mm length guitar---the existing saddle is 5 mm off.

It isn't "off". It's a "correction" that accounts for the difference between theory and reality.

What you are all saying is that a guitar like this does not conform to simple: 2x scale plus y Compensation.

I don't think anyone is saying that. I'm certainly not. "Y" is dependent upon a variety of factors and is a different amount for different combinations of those factors.

so to get this thing to play well may be impossible without doing what Arie says: Take each string and fiddle with it until each string is intonated as best as can be with the existing bridge

That is always how it is done.

changing bridges to get a more uniform standard of compensation will not work?

If the saddle is in the wrong place, that will work. But, it assumes the frets are in the right place, as Arie mentioned.

Before you go crazy and start ripping the bridge off, make sure you know what you have and what needs to be altered to accomplish the desired result.

[arie]

you know, in this pic:



the string doesn't appear to be actually resting upon the zero fret (or just barely). if not, you'll need to make that happen.

also,
the way you've wound the sting upon the post is wrong. it needs to exit at the bottom of the wrap and angle upward toward the zero fret.

[Jackknifegypsy]

'If the saddle is in the wrong place, that will work".

505 is the distance that the existing midpoint of the saddle ----as it is now situated, is telling me what the Scale length is (looking at it bass ackwards). But 500 is where the midpoint of the saddle SHOULD BE.

So the saddle is long at the midpoint by 5mm and should be moved closer to the front of the bridge, which--- with modification ----is possible to correct. But, unless I use individuals saddles for each string, then the Low E will be even closer the front of the bridge making it even sharper than where I placed it, 15.8 mm back from the new 500, proper scale length. And moving Low E back is impossible without a new bridge allowing a further setback than 16mm (rounded, for the skeptics).

Just checked again, to give the strings a couple hours to stretch out and the low E and A are both flat by 10 cents, in need of being tuned up. They will likely be even more stretched by late afternoon.

Arie: Thx, didn't know about the post wrap or that the zero fret ---obviously----needs the strings to sit 'zero'.

[arie]

no need to let the strings sit and stretch, they can be fully worked in 10 minutes tops buy stretching them out by hand on the guitar.

read my previous post - there's important info in it that you are overlooking.


cool -cross post.

[arie]

it's been my experience with guitars like yours that the nuts are just way too big. in terms of height, width, everything. in a zero fret guitar the nut only serves as a guide to the string. it should corral side to side movement only, while providing a proper angular approach to the zero fret with minimal hindrance.

[Jackknifegypsy]

Not just the strings, the guitar was not acclimated yet to the work area, which used to be a side room off the kitchen, with a higher temp, no crossventilation, and about 30% less humid.
Since then, I have been banished to the basement by GF. Will check again in about 2 hours.

[arie]

one more thing:

would you post us a pic or two showing us how you are measuring? lay your ruler, tape measure, whatever on the guitar and show us how you are coming up with these figures. i think i can see a bit of a block here and once it's been cleared up you might progress a little more easily.

show us a solid measurement from the middle of the zero fret to the middle of the 12th. forget about saddle position for now.

are you really kermit the frog?

[charles Tauber]

Originally Posted by Jackknifegypsy

505 is the distance that the existing midpoint of the saddle ----as it is now situated, is telling me what the Scale length is (looking at it bass ackwards). But 500 is where the midpoint of the saddle SHOULD BE.

So the saddle is long at the midpoint by 5mm and should be moved closer to the front of the bridge, which--- with modification ----is possible to correct.

I've done my best to explain it to you on numerous occasions, but failed.

I wish you the best of luck with it. I hope you are able to figure it out.

[Jackknifegypsy]

http://s1244.photobucket.com/user/ea...c945b.jpg.html



I can't eliminate the distortion on the pic. But the 25 CM lines up directly on top of the 12th.