Changer Fingers

[Bent]

Hi Richard, Yeah nerd-speak for sure huh? In layman's terms it can be put that the smaller an area the string touches the better.
I was told that Emmons PP arrived at 11/16" diam fingers as the optimum sound producer( I can see where everybody with an Emmons are rushing to measure)
This leaves a mere 1/16" on either side of the 9/16" axle hole. This is also an optimum sound producer - the very small thickness to transfer the string's vibration from the aluminum and down thru the axle and further.

So how far can we go the "wrong" way before the larger diam finger is detrimental to the sound? Most steels have 3/4" diam fingers I believe. The changer I am working on now will have 1" diam fingers on a 1/2" axle. This larger diameter enables me to put the string thru a hole in the finger. I liked that idea and thought I would give it a try.

This brings us to one other problem inherent in the common changer finger.
I was told be a very reliable source that a string needs not one but two points of contact on the surfaces that it rests upon. Take the rollers in the other end with their V-groves and two contact points for the string..one on either side. Three contact points are a definite no-no one is not as good as 2. Therefor, the changer finger is not tuned for optimum sound until we make those same grooves there. They need to be gauged to the string, same as on the rollers.

My take on this, as I see it at the moment...

[Pat Comeau]

Therefor, the changer finger is not tuned for optimum sound until we make those same grooves there. They need to be gauged to the string, same as on the rollers.

Bent i might be just blowing smoke here but i see one big problem with this idea of putting grooves in the changer finger , contrary to the rollers...the changer fingers gets scratched or grooves starts to form from where the strings are rubbing against the changer fingers , this is the results of raising and lowering the strings after months or years of playing, i know for a fact that aluminum fingers doesn't take long before it shows some wear on the top of the fingers and even stainless will show some wear but not has fast as aluminum, so my point is...if you make grooves in the fingers and they start to wear it will be harder to fix them as oppose to the flat surface that you can just sand it and polish it and be just like new with not too much trouble or work that anyone can do it themself.

Pat C.

[Bent]

Great point there, Pat. You are so right - when it comes to aluminum. An example here: A buddy of mine bought himself a new, very well known make of steel from the US not even a year ago. It has been played very little due to rapidly developing arthritis in his fingers. Recently, he went to change strings for the first time, and was horrified to see that the strings had already worn marks in the fingers. He send me a pic to verify. Sure enough I see the groove in the fifth string finger. Now this guy, who is used to playing a GFI with stainless steel fingers, is not used to this type of stuff. I calmed him down a bit when I told him how he can sand and buff out those marks.
This same problem, then, would manifest itself in your gauged aluminum rollers, will it not? By the way those rollers are on their way to you today.

Anyway... you just reinforced my decision of making the fingers out of brass so I can get them chromed and thereby hardened, to withstand the groove gremlin.

Or, if you still want to make them out of aluminum, get it anodized after you have the grooves cut.

[Ross Shafer]

hi all,

I had the pleasure of visiting Jim Palenscar's shop back in Nov....what a great guy and what a candy store!!...45 pedal steels on the floor! I remember being surprised that more than half the rigs I measured had finger surface diameters over .75" (.375" radius).

Some older steels I measured there have finger radii larger than .375" (.75" dia.) and the finger radius isn't concentric with the axle the finger pivots on. This is the case on at least two modern steels I know of too. The non-concentric finger string surface means that the contact point's distance from the nut changes the scale length by teensy amounts, as a linear changer (Lamar) or something approaching linear (Anapeg, Excel)....and no, I don't think it has any significant effect on intonation, if that was really a problem that no one was willing to accept, then tapered string runs would be ditched too....sorry to get a bit off topic there.

Most of the worn aluminum fingers I've fixed or seen badly worn seemed to have wear that indicates sideways movement of the string on top of the finger. I think this is due to two things. The strings being physically pushed sideways by the nose of the bar as one moves the nose perpendicular to the fretboard and the fact that on tapered string arrangements the finger is not moving perpendicular to the string so is actually scraping against the string as it rotates and pulls or releases tension. This would get worse as the angle increases as it does from the middle to the outside strings. Yes both these movements are minuscule but they're there and pretty much have to contribute something to finger wear. Is this a an argument for straight string runs...not sayin' just wonderin'. Straight string runs though very unlikely to ever be accepted by most players, do make sense to me for a number of reasons.

Also keep in mind that with no grooves the string contact is a single point along the string's cylindrical surface, a groove in the finger would provide two points to share the same load. With tapered string runs, a groove in the finger would not allow as much sideways excursion of the string. All in all, I think you might have less wear with grooved fingers all else being equal.

Of course using 7075 or 2024 aluminum instead of 6061 will cut down on wear too. Don't forget that the temper of aluminum has a big effect on its hardness and therefore wear characteristics. Lastly, our good buddy 'loomnum can be plated. Decorative anodizing will offer a better wear characteristics than nothing, but will wear thru. Hard anodizing would be the best route for wear concerns. No clue what it might do tonewise.

That was a nice diversion with an extra cuppa, but I can't have a beer tonight unless I get my butt in gear and do my morning run (torture session!) around the block....4 miles, its a big block!

have a good day y'all,
ross

[richard37066]

Ross -

RIGHT ON, my friend!

It might be well worth mentioning - with a reference to my "nerd-speak" quote above, that, since the string in vibration also "chafes" the finger that it, too, contributes to the grooving of the finger over time. Depending upon how the string is struck with the pick, it may very well "precess" about its' primary axis - first vibrating vertically and then, even, longitudinally across the finger.

I'm a little at odds concerning the "two-point" contact on roller nuts. To my way of thinking, the two points only provide a loosely-defined vise into which the string sits and, thus, a fairly well defined "point of contact". To my way of thinking, the string should make contact at only one very well-defined point - be it at the changer or a roller. The photo of the proposed changer finger does this quite well as the contact area of the string is reduced to almost nothing before dropping off into space. This seems to say that, as much as is practicable, that any contact point be made with the shortest possible radius. A "knife-edge" anyone? I know, I'm on that kick since I'm attempting to bring the PS210 changer into the modern world in my own design and knife edges have application in a couple of areas. Given my concerns about the "single-point" versus "two-point" conundrum I conclude that I've got to rethink my views concerning "guaged" rollers. I believe that it was Burt who provided a simple formula for cutting the grooves in rollers so as to make the tops of the strings planar - at the same level. This, as we know, provides "two-point" contact to the sides of the strings. Would it not make sense to cut the grooves in hemispherical fashion? A rounded-out bottom of the groove which provides single-point contact over a relatively short radius? An alternative (simpler?) solution would be to just turn the outside diameters of the rollers to whatever dimension so as to realize a "guaged" configuration - with a single point of contact.

Whatever. I've been in the throes of some sort of creeping crud and need my Nyquil fix.

Richard

[Farmer]

Richard, Check out this patent by David Jackson # 7759568 , it shows a knife edge on both ends of the guitar. One on the changer and a movable piece on the nut end. The patent was filed in 2006 and issued in 2010. On the Jackson web site they talk about the "edge". It looks like they are using a nut without rollers. Seems to me it would break strings, but maybe not. I presume they test vigeriously... Check out the Commemorative Classic 1034, the 4th picture in the top row shows, what looks like a straight edge.. Just a thought..... http://www.jacksonsteelguitar.com/guitars.cfm
Mike

[richard37066]

Mike -

Yup. It's the spittin' image of what Eldon posted above except used at both ends. Couldn't tell from the patent drawings but it doesn't appear as though the nut end rotates. My GFI has a solid rod for the nut across which the strings lay. Seems as though the strings would rub across the rod - and they do. The saving grace is that there is but a short piece of string behind the nut. If the string is stretched by, say, a 32nd (.03125") then the travel across this solid nut is in the order of .000651" or a little more than half a thou. Not enough to be concerned about.

What does concern me - and I'm gonna split a hair or two here - is that, in the pictures of the changers, the "drop-off" points do not seem to be in precise alignment. This seems to say that the scale length varies somewhat across the changer. Could be that final adjustments were not done in favor of getting a photo or two. To be sure, you can tune the thing up until its' on the money but what happens when the bar is placed at, say, the 12th fret? Will the resultant pitch be off by a number of cents on a couple of strings? Don't know. It's obvious that the Jackson folks are not content with doing things as they've been done for the last 50 years and are attempting to innovate in a positive direction. More power to them. It gives folks like us a few more things to think about. Like, we don't have enough to think about already!

Oh - another point of interest. There are only two locating holes in the bellcranks. Are we missing something by putting in 6,8, or 10 or, even, an updated version of the Blanton? Gotta REALLY think on that one.

Thanks for the reference. Very interesting.

Richard

[Ross Shafer]

Richard, I agree 100% with your first paragraph in your post that follows my earlier one. In my mind this further supports the theoretical/potential benefit of a V groove.

In my dreamer/nerdy mind...the best practical (?) (* more on that later) string interface for the string would sit in a radius that perfectly matches the string's diameter. The groove would come a bit shy of half way up the string. Then you're getting good full, near hemispherical contact with the string and the tone should follow...."too bad it just can't happen in the real world" sez my machinist/fabricator, make-aholic brain...regardless of how tight your machining tolerances are (how big your machining budget is!) you'll be hard pressed to match the diameters of any given string based solely on the string manufacturing tolerances...but even if you could have a perfectly matching radius it wouldn't be as soon as you stretch the string at which point the string diameter goes down a teensy bit and you're back to a single line of contact that's only marginally (if at all) better than lying on a flat surface ( conversely when you lower the string and reduce its tension, it gors and we're back to two points of contact. With a V groove the contact is doubled...sh_t howdy that 100% more contact!

* its later now: how 'bout little precision collets that grab the string around its circumference, now we're talkin! Highly impractical in many ways and talkin' about a can-o-worms and lots of extra bits to make.


The "Edge" type stuff is interesting and is essentially what is found on almost all regular guitars and it works fine there....I'm gonna split hairs here and I hope it doesn't get anyone's panties in a bunch, its not meant to...I'm just thinking out loud and sticking to plain old mechanics.

Bear in mind that on these "edge" type designs...there's only one edge. If in the static (open string) position the string comes off the finger perfectly tangentially then when the string is raised the "edge" is forcing the string to bend over it (damn,here's that pesky moving scale length again... I'm satisfied that its not an issue playing wise) maybe not so bad, but good? It's a bending moment and certainly a stress riser on the string...remember I'm splitting hairs. Now let's lower the string....back to my first sentence in this paragraph, there's only one edge and now the string is leaving the finger before it even gets to the edge. Of course it can be adjusted so that in the open position the string is already bending over the edge and when lowered still exits the finger on the edge...again you're bending the string over a very short distance with every change whether its a raise or a lower.....The Jackson Blackjack changer (super cool) is way different than the "edge" changer they offer, but it too has edges machined into the top of the finger that the string exits off of.

Admittedly the potential benefit or perceived benefit of such a system could outweigh my quandaries about it. I actually agree that the string exiting off an edge with nothing to mechanically dampen vibration where the string exits the finger is highly desirable. That is how it works on Lamar's linear changer and since the pull is a straight line the string isn't being bent and stretched with each change, just stretched.

Ain't nothin' (other than getting hooked on steel guitars) easy? Man , I gotta get some work done...that's it for me today guys!

[burt]

The cause of strings cutting a groove in the changer finger is mostly due to the raising and lowering action of the finger.

Think about it, the string has to stretch when it is raised (and contract when it is lowered), and this causes a miniscule movement of the string as it rolls over the changer finger, which slowly but surely cuts a groove in the soft finger. If the finger has an 'edge' profile, and is made from aluminum, the edge would quickly wear.

[Farmer]

Richard, On the patent site on page 2 of 4 the left figure shows the piece for the nut end. On page 3 of 4 figure 4 and 5 it shows how it is supposed to work. On the Jackson site the picture I told you about, lowers from the keyhead end. You can see the capscrews on the key head to adjust the lower setting.
http://www.jacksonsteelguitar.com/edge.cfm

patent no 7759568