Bent and Mac -
Since I'm thoroughly enthused by this whole "knife edge" concept, I've made a good attempt at following Georg's progression as he thinks his design through. Rather than make a couple of assumptions, I'll be content to wait until Georg supplies further drawings.
I've picked apart his explanations and have come to the conclusion that he's leaving nothing to chance. His drawings are rudimentary. This is understandable. He's throwing out a concept and hoping that we will at least come away from it all with the gist of his thinking. Like you, I await further drawings which will include the "keyhead slider" and tuner arrrangement. When supplied, I'm confident that a lot of questions will be answered as we'll be able to view the whole thing, in toto. I, too, have a couple of questions but will hold them in abeyance until he's had a chance to assemble all of the parts for our perusal.
Patience is a virtue. Are you patient?
I am.
Richard
Project: keyhead changer on knife-edges
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richard37066
- Posts: 517
- Joined: Sat Dec 11, 2010 11:44 am
- Location: Gallatin, Tennessee, USA
Re: Project: keyhead changer on knife-edges
I try to eat well and get enough sleep so I won't be a patient!
Re: Project: keyhead changer on knife-edges
Patience, sure got lots of it. Spent all day rodding my steel after installing the new changer...like 5 hours just rodding it and it's still only 3/4 done. So yes, I have patience.
Did not ask out of impatience, simply wanted to try and understand what I was looking at, since the thing was there for all to see.
Did not ask out of impatience, simply wanted to try and understand what I was looking at, since the thing was there for all to see.
http://benrom.com/
21 BenRom pedal steel guitars, a Nash 112 and a 1967 TOS Milling machine with many cutters making one hell of a mess on the floor.
21 BenRom pedal steel guitars, a Nash 112 and a 1967 TOS Milling machine with many cutters making one hell of a mess on the floor.
Re: Project: keyhead changer on knife-edges
Im like you Bent , Mac , aint got the foggiest lol 
Russ
Russ-
Georg
- Posts: 457
- Joined: Tue Nov 03, 2009 10:38 am
- Location: Mandal, VA, Norway & Weeki Wachee, FL, USA
- Contact:
Re: Project: keyhead changer on knife-edges
mac639 wrote:I try to eat well and get enough sleep so I won't be a patient!
... same here, but I smoke too much so who knows what I'll end up as...Richard, I had to check up on "blivet", and yes, I am familiar with such "problems". Have had to deal with lots of them in my days as troubleshooting engineer - they're fun once they resolve themselves into nothing
Now, for anyone interested ... I still haven't found a suitable CAD program for all the coupled parts and potential blivets, so I continue pre-designing in the form of notes and simple drawings while juggling everything in my head.
A few points...
1: the "lower-return push-rod" is indeed too close to the "hinge point" - the knife edge between raise and lower. OTOH: if I put a regular "lower-return spring" at the lower end of lower scissor the spring has to be relative short as on all All Pull out there. Tension increases rapidly when short springs get stretched, and placed in the normal position the spring will have a tendency to act as a turning point - cause "reversing" - once the tension gets too high relative to all other pull-forces.
Bent, you may remember that I put an extreme 2 1/2 note lower on the extended low E-string on my Dekley, and to prevent the lower scissor from "reversing" (starting to raise) as the regular "lower-return spring" got tensioned, I hooked up the pull-rod for that change in a hole drilled at the very bottom of the lower scissor - in line with the "lower-return spring" itself. Thus, no nylon adjust-nut on that pull-rod ... I adjust it directly on the pedal-stopper. OK for one change like that, but definitely not to my liking or suited for my new design.
Same potential "reversing" problem for my knife edge changer, and a knife edge "hinge" will in addition become loose if such "reversing" happens. So to eliminate this very real problem entirely I will place the "lower-return spring" as low as possible but above or in line with the highest pull-rod for lower, so no "reversing" can take place no matter the pull.
To allow for long springs with much more stable tension for a given amount of stretch, I will use a "lower-return push-rod" and put in 20 centimeter long springs via free-wheeling bell-cranks. No lower-pull lost since the "lower-return push-rod" can be provided with nylon nut for adjustment and be used as pull-rod.
2: The changer scissors act as regular scissors set "half-open" as neutral. Pull on the "raise" scissor and the scissors open further. Pull on the "lower" scissor and the scissors will go towards close. On top this "open/close" action is pretty linear, so by setting the scissors on a knife-edge towards a fixed point - the neck-extension - and hooking up a slider on knife edge on the other scissor-half, the slider will be pulled/released as the scissors open/close.
3: By mounting regular tuning keys on top of those sliders, the individual tuning gear move linearly along with the changer and simply change tension on the individual strings by making them longer/shorter.
I have to take into account that each tuning key must be given space to move approx +/- 4 millimeter from neutral without running into and interfere with tuning keys on neighboring sliders. Since all sliders can be raised/lowered the same amount at the same time but in opposite direction, free space between neighboring tuning keys - with changer in neutral - should (ideally) be 8 millimeter lengthwise.
No compromises and/or short keyhead allowed here, although I know that I can get away with half that much free space for all regular E9 change-combinations.
As strings must go perfectly parallel horizontally, with a distance of approx 6.3 millimeter from tuning peg to bridge, the width of keyhead sliders and entire keyhead mount is pretty much set in stone. Favors small tuning gears.
4: The "wrapped" changer scissors - raise inside lower - favor thin pull-rods. I figured that if the Excel PSG can have wrapped changer scissors and thin pull-rods, so can I.
Major difference is I will have all tuning/changing action going on at the keyhead end and use regular tuning gears. Lets me focus entirely on tone and stability at the bridge end and along the neck, as all inner mechanics (pedals/levers/etc.) will use the "divide" below the keyhead nut rollers as reference point.
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richard37066
- Posts: 517
- Joined: Sat Dec 11, 2010 11:44 am
- Location: Gallatin, Tennessee, USA
Re: Project: keyhead changer on knife-edges
Georg -
AHA! I see - said the blind man.
The term "reverse" has been explained - but I have a question concerning that and it relates to the distance that the slider must travel. In addition, and since you've not explained the ±4mm tuner/slider movement, I may just be stepping out of bounds here and for which I apologize if I err.
I had no idea that you had made a 2½ tone change at one point on your instrument. However, and relating to the post that I made above, I'm confused as to why the slider/tuner must travel such a large distance. I am ASSUMING that this distance is required in order to increase/decrease the tension of the string. As I stated, a whole tone raise or a whole tone and a half lower requires movement of MUCH LESS than 1/16" at the changer. (.042-.049?) Your movement of ±4mm translates to approximately 5/32" in each direction. This is approximately 3.2 to 3.7 times the required travel on my instrument. (I think much better in inches as opposed to metric) Admittedly, it is difficult to extrapolate the movement required for a whole tone change to that of 2½ but, on the surface, it seems to be a bit exhorbitant. In a quickie experiment that I just now performed on my instrument, I find that the additional movement required for a ±2½ whole tone change (a "4th" in musical terms) requires but a smidgen more than the numbers quoted above. Given the leverages attendant to the long fingers, this implies that the lower end of the fingers must travel a horrendous distance in order to achieve your ±4mm movement. No wonder you're concerned with the "reverse" problem! However, given the mechanical advantage found at the lower end of the finger it would appear that such travel distances would not be required IF the slider/tuner movement were severely limited from that which you've stated.
Without getting into precise leverage measurements, I can relate that the bottom of the raise finger on my 5th string (whole tone, B to C#, .018p dia.) moves but 3/32 - 1/8" (2.4 - 3.2mm). Accepting my figures of .042 - .049"(1.07-1.24mm) movement at the changer, this implies a mechanical advantage of somewhere around 2 to 2½. Just for the sake of illustrating a point, if I DARE (Don't hit me!) to use those numbers in reference to your changer then the lower part of your changer fingers must move anywhere from 8 - 10mm (.315-.394") in order to see a ±4mm movement of the tuner/slider. That's a BUNCH, my friend, and takes the return spring a fair ways away from the force required to initiate elongation. The "reverse" phenomenon looms ominously! It follows, then, that a tuner/slider movement of as little as ±1.5mm (.059") would be sufficient to effect any desired change.
Without dimensions, it is impossible to calculate the mechanical advantage and, thus, the moments involved in your changer. If you can justify the ±4mm travel then I must stand severely corrected. If you have overestimated the necessary tuner/slider travel then it is obvious that life can be made much easier by relaxing this requirement.
I REALLY hope that I haven't stepped on your toes, Georg, since you know how much I enjoy these exchanges. You've been a bright light in my life ever since those first to-do's on the SGF.
Respectfully,
Richard
AHA! I see - said the blind man.
The term "reverse" has been explained - but I have a question concerning that and it relates to the distance that the slider must travel. In addition, and since you've not explained the ±4mm tuner/slider movement, I may just be stepping out of bounds here and for which I apologize if I err.
I had no idea that you had made a 2½ tone change at one point on your instrument. However, and relating to the post that I made above, I'm confused as to why the slider/tuner must travel such a large distance. I am ASSUMING that this distance is required in order to increase/decrease the tension of the string. As I stated, a whole tone raise or a whole tone and a half lower requires movement of MUCH LESS than 1/16" at the changer. (.042-.049?) Your movement of ±4mm translates to approximately 5/32" in each direction. This is approximately 3.2 to 3.7 times the required travel on my instrument. (I think much better in inches as opposed to metric) Admittedly, it is difficult to extrapolate the movement required for a whole tone change to that of 2½ but, on the surface, it seems to be a bit exhorbitant. In a quickie experiment that I just now performed on my instrument, I find that the additional movement required for a ±2½ whole tone change (a "4th" in musical terms) requires but a smidgen more than the numbers quoted above. Given the leverages attendant to the long fingers, this implies that the lower end of the fingers must travel a horrendous distance in order to achieve your ±4mm movement. No wonder you're concerned with the "reverse" problem! However, given the mechanical advantage found at the lower end of the finger it would appear that such travel distances would not be required IF the slider/tuner movement were severely limited from that which you've stated.
Without getting into precise leverage measurements, I can relate that the bottom of the raise finger on my 5th string (whole tone, B to C#, .018p dia.) moves but 3/32 - 1/8" (2.4 - 3.2mm). Accepting my figures of .042 - .049"(1.07-1.24mm) movement at the changer, this implies a mechanical advantage of somewhere around 2 to 2½. Just for the sake of illustrating a point, if I DARE (Don't hit me!) to use those numbers in reference to your changer then the lower part of your changer fingers must move anywhere from 8 - 10mm (.315-.394") in order to see a ±4mm movement of the tuner/slider. That's a BUNCH, my friend, and takes the return spring a fair ways away from the force required to initiate elongation. The "reverse" phenomenon looms ominously! It follows, then, that a tuner/slider movement of as little as ±1.5mm (.059") would be sufficient to effect any desired change.
Without dimensions, it is impossible to calculate the mechanical advantage and, thus, the moments involved in your changer. If you can justify the ±4mm travel then I must stand severely corrected. If you have overestimated the necessary tuner/slider travel then it is obvious that life can be made much easier by relaxing this requirement.
I REALLY hope that I haven't stepped on your toes, Georg, since you know how much I enjoy these exchanges. You've been a bright light in my life ever since those first to-do's on the SGF.
Respectfully,
Richard
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Georg
- Posts: 457
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Re: Project: keyhead changer on knife-edges
Richard,
I very much want you, and others, to "step on my toes" and question everything I release here. Deviating views and straight talk makes it sooo much easier to debug my design-ideas. If my toes (or ego) can't take it I'd better put on my steel-toed boots and hardhat
The +/- 4 millimeter is indeed the maximum travel-distance of the tuning gears lengthwise, to increase/decrease tension on each string for desired pitch change. And yes, I want to design in about twice of what I will ever need, simply because I don't like to build in avoidable limitations on this one-off instrument.
To expand: on my Dekley S10 I have 3d string raise slightly more than a half-tone and lower slightly more than two half-tones. This nearly 4 half-tone pitch-change in total is a "string-breaker" change - string breaks on changer-roller, but I love the effect.
I also have the "sub-low" or "extended" E string (normally only found on S12 PSGs) with a two half-tone raise and a five half-tone lower, a total of seven half-tones pitch-change on that one string. Would like to raise that low E four half-tones, which will give a nine half-tone pitch-change on it - near max of what the .056NW string can handle and still sound right.
Those are the extremes but I have, and use, "more than normal" pitch-change on nearly all strings on my Dekley S10.
If I land on "normal" horizontal tuning-pegs - find the right tuning gears, each tuning gear will be fastened in the "normal" way in a hole in a piece of aluminum on top of its slider.
These pieces of aluminum will slide past each other, giving the appearance of a continuous, stepped, keyhead which is a bit longer than most one-piece keyheads. Sloping it about 7 degrees assures even string-angle over keyhead string-rollers.
Each slider, with tuning gear, will roll near friction-less on one line of "PacMan" rollers, near and similar to those I will use as keyhead string-rollers. The far end of the sliders will be hooked up via knife edges to the changer scissors, which hold the sliders in place and minimize friction at that end.
As the entire keyhead will have its own frame to hold changer scissors and tuning gear sliders in place, and all tuning and pitch-changing takes place here, I can afford to fine-tune all details until it "just works", more or less as follows...
- I want zero mechanical hysteresis beyond the settling-effect in the strings themselves.
- I want travel-stoppers for all pull-rods integrated in the keyhead changer, to the point that a failing stopper on a pedal/lever in a worst case scenario can only lead to an overstretched pull-rod or broken bellcrank - no undesirable pitch-change.
- I want two-pitch changes on individual raise/lowers, so I can follow JI tuning principles for beat-free chords for all changes. Proper JI tuning is only possible on PSGs with very simple/limited copedents today, as they only have one pitch/change and can only JI compensate non-pedaled strings.
- I want zero "body-drop" almost no matter the load. This is probably the easiest point to design up to since my PSG won't have a conventional body, only a frame to attach neck, bellcrank axles,pedals,levers and legs to. Zero "body-drop" only competes somewhat with the next point.
- I want improved sustain and clarity. I have already built one steel with unique sound and more than twice the sustain (measured in decay/time) of the best of my "normal" PSGs, but mechanically it was no good so it ended up as a flower-stand. I want as much as possible of that sound/sustain in a flawlessly working PSG.
I am very interested in extracting what works, how it works, and what doesn't work and why, when it comes to other people's PSG builds and projects. If I can contribute with anything you can be sure I will.
I do not want to step on anyone's toes here, but when it comes to designing and building my own "one-off PSG" I have pretty limited interest in what other builders think is "necessary" and in how "normal" PSGs are (or should be) built.
I admire all your work and builds - as presented on this forum and elsewhere, but I have 5 "normal" PSGs today and do not really need another one of those. May even get rid of a couple or scavenge them for parts, since they more or less only take up space now that I have extracted all about how they are built. I only play my Dekleys.
I want to solve a few problems all PSGs I have ever owned or taken for a test-drive have had, simply because I like to solve problems. And in the process I want to test out some less used solutions, which I certainly don't mind getting critical feedback on.
If any of you find something useful amongst my "twisted" ideas, good. If not, no big deal.
All who want to "shoot" or "step on toes" are most welcome. My creative mind works best when presented with some resistance.
my regards
Georg
I very much want you, and others, to "step on my toes" and question everything I release here. Deviating views and straight talk makes it sooo much easier to debug my design-ideas. If my toes (or ego) can't take it I'd better put on my steel-toed boots and hardhat
The +/- 4 millimeter is indeed the maximum travel-distance of the tuning gears lengthwise, to increase/decrease tension on each string for desired pitch change. And yes, I want to design in about twice of what I will ever need, simply because I don't like to build in avoidable limitations on this one-off instrument.
To expand: on my Dekley S10 I have 3d string raise slightly more than a half-tone and lower slightly more than two half-tones. This nearly 4 half-tone pitch-change in total is a "string-breaker" change - string breaks on changer-roller, but I love the effect.
I also have the "sub-low" or "extended" E string (normally only found on S12 PSGs) with a two half-tone raise and a five half-tone lower, a total of seven half-tones pitch-change on that one string. Would like to raise that low E four half-tones, which will give a nine half-tone pitch-change on it - near max of what the .056NW string can handle and still sound right.
Those are the extremes but I have, and use, "more than normal" pitch-change on nearly all strings on my Dekley S10.
If I land on "normal" horizontal tuning-pegs - find the right tuning gears, each tuning gear will be fastened in the "normal" way in a hole in a piece of aluminum on top of its slider.
These pieces of aluminum will slide past each other, giving the appearance of a continuous, stepped, keyhead which is a bit longer than most one-piece keyheads. Sloping it about 7 degrees assures even string-angle over keyhead string-rollers.
Each slider, with tuning gear, will roll near friction-less on one line of "PacMan" rollers, near and similar to those I will use as keyhead string-rollers. The far end of the sliders will be hooked up via knife edges to the changer scissors, which hold the sliders in place and minimize friction at that end.
As the entire keyhead will have its own frame to hold changer scissors and tuning gear sliders in place, and all tuning and pitch-changing takes place here, I can afford to fine-tune all details until it "just works", more or less as follows...
- I want zero mechanical hysteresis beyond the settling-effect in the strings themselves.
- I want travel-stoppers for all pull-rods integrated in the keyhead changer, to the point that a failing stopper on a pedal/lever in a worst case scenario can only lead to an overstretched pull-rod or broken bellcrank - no undesirable pitch-change.
- I want two-pitch changes on individual raise/lowers, so I can follow JI tuning principles for beat-free chords for all changes. Proper JI tuning is only possible on PSGs with very simple/limited copedents today, as they only have one pitch/change and can only JI compensate non-pedaled strings.
- I want zero "body-drop" almost no matter the load. This is probably the easiest point to design up to since my PSG won't have a conventional body, only a frame to attach neck, bellcrank axles,pedals,levers and legs to. Zero "body-drop" only competes somewhat with the next point.
- I want improved sustain and clarity. I have already built one steel with unique sound and more than twice the sustain (measured in decay/time) of the best of my "normal" PSGs, but mechanically it was no good so it ended up as a flower-stand. I want as much as possible of that sound/sustain in a flawlessly working PSG.
I am very interested in extracting what works, how it works, and what doesn't work and why, when it comes to other people's PSG builds and projects. If I can contribute with anything you can be sure I will.
I do not want to step on anyone's toes here, but when it comes to designing and building my own "one-off PSG" I have pretty limited interest in what other builders think is "necessary" and in how "normal" PSGs are (or should be) built.
I admire all your work and builds - as presented on this forum and elsewhere, but I have 5 "normal" PSGs today and do not really need another one of those. May even get rid of a couple or scavenge them for parts, since they more or less only take up space now that I have extracted all about how they are built. I only play my Dekleys.
I want to solve a few problems all PSGs I have ever owned or taken for a test-drive have had, simply because I like to solve problems. And in the process I want to test out some less used solutions, which I certainly don't mind getting critical feedback on.
If any of you find something useful amongst my "twisted" ideas, good. If not, no big deal.
All who want to "shoot" or "step on toes" are most welcome. My creative mind works best when presented with some resistance.
my regards
Georg
Re: Project: keyhead changer on knife-edges
Georg, Thanks for the long and detailed excursion into your knife edge changer and general steel plans. There isn't anything constructive that I can contribute of suggestions or even critique, for that I know too little from the sparse drawings. The explanations you supply, well they are over my head and will be so until I see the finished drawings. This is partly because of the fact that my head is wrapped around my own building ideas these days. A bit of a load for a 64 yr old brain..not only build steels but learning how to operate the mill; how to make jigs for turning out different parts; how to make my hands adapt to working on a 1/1000 inch instead of on a 1/32 like I am used to. It is quite a learning curve and I am plugging away at it somewhat successfully.
At the end of the day my brain has OD'ed on this and there is just not enough power left to wrap my head around a revolutionary new changer.
..as much as I would love to.
I will follow with great interest, your updates in words and pictures and leave it to you and Richard in particular to discuss your ideas.
When the time comes for you to put your plans to work, I would find it most exciting to be able to turn out some of the parts from the finished, clear drawings as we discussed earlier.
As this project progresses, I will mostly sit on the sidelines and observe and try to learn as you go along.
Interesting stuff for sure and good luck with your project!
At the end of the day my brain has OD'ed on this and there is just not enough power left to wrap my head around a revolutionary new changer.
..as much as I would love to.
I will follow with great interest, your updates in words and pictures and leave it to you and Richard in particular to discuss your ideas.
When the time comes for you to put your plans to work, I would find it most exciting to be able to turn out some of the parts from the finished, clear drawings as we discussed earlier.
As this project progresses, I will mostly sit on the sidelines and observe and try to learn as you go along.
Interesting stuff for sure and good luck with your project!
http://benrom.com/
21 BenRom pedal steel guitars, a Nash 112 and a 1967 TOS Milling machine with many cutters making one hell of a mess on the floor.
21 BenRom pedal steel guitars, a Nash 112 and a 1967 TOS Milling machine with many cutters making one hell of a mess on the floor.
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richard37066
- Posts: 517
- Joined: Sat Dec 11, 2010 11:44 am
- Location: Gallatin, Tennessee, USA
Re: Project: keyhead changer on knife-edges
Georg -
Whew! I'm somewhat blown away by your last post. The fog has now really lifted and I find that my ASSUMPTIONS were the root cause of my contentious post! I had no idea that you were going to make such drastic tuning changes! I use the word "drastic" since my thinking has been severely limited by heretofore widely used margins, i.e., full-tone raises and 2½ tone lowers.
Given that, I can only apologize for muddying up the works and offer to assist you in any way that I can in order to see your vision come to fruition.
For the members who may still be pondering Georg's concern with the "reverse" effect, I offer the following: - I went to one of my favorite sites and used the interactive calculator for string tension. For the puny 5th string on my E9 tuning (.018p dia, 246.942 hz frequency) the nominal string tension is 26.1 pounds for a 24" scale length. If Georg were to raise that pitch by 2½ tones ( a musical "4th") to a frequency of 329.628 hz, the tension in the string increases to a whopping 46.5 pounds! That's a change of 20.4 pounds or an increase of 78%! This is well within the calculated breaking strength of the string but is indicative of the kinds of concerns that he must deal with. As Georg has stated, he's got to juggle string diameter, tension etc., and still have it "sound" good.
And Georg - I'm certain that I've posted this link before but I'll place it here again. It's very user friendly with several interactive functions.
http://liutaiomottola.com/
I'll make every attempt to not make too many assumptions in the future. Got myself into trouble on this last one. Won't do it again.
Richard
Whew! I'm somewhat blown away by your last post. The fog has now really lifted and I find that my ASSUMPTIONS were the root cause of my contentious post! I had no idea that you were going to make such drastic tuning changes! I use the word "drastic" since my thinking has been severely limited by heretofore widely used margins, i.e., full-tone raises and 2½ tone lowers.
Given that, I can only apologize for muddying up the works and offer to assist you in any way that I can in order to see your vision come to fruition.
For the members who may still be pondering Georg's concern with the "reverse" effect, I offer the following: - I went to one of my favorite sites and used the interactive calculator for string tension. For the puny 5th string on my E9 tuning (.018p dia, 246.942 hz frequency) the nominal string tension is 26.1 pounds for a 24" scale length. If Georg were to raise that pitch by 2½ tones ( a musical "4th") to a frequency of 329.628 hz, the tension in the string increases to a whopping 46.5 pounds! That's a change of 20.4 pounds or an increase of 78%! This is well within the calculated breaking strength of the string but is indicative of the kinds of concerns that he must deal with. As Georg has stated, he's got to juggle string diameter, tension etc., and still have it "sound" good.
And Georg - I'm certain that I've posted this link before but I'll place it here again. It's very user friendly with several interactive functions.
http://liutaiomottola.com/
I'll make every attempt to not make too many assumptions in the future. Got myself into trouble on this last one. Won't do it again.
Richard
-
Georg
- Posts: 457
- Joined: Tue Nov 03, 2009 10:38 am
- Location: Mandal, VA, Norway & Weeki Wachee, FL, USA
- Contact:
Re: Project: keyhead changer on knife-edges
Bent, I appreciate your offer to make parts. The inner mechanics with bellcranks, axles and pull-rods will look familiar to you, only mounted "lefty" and with a couple of transfer parts for the pedals where bellcrank axles will interfere with the keyhead changer.
Richard, most of the problems I envisioned for knife edge changers, seem to disappear into thin air as I get all parts designed together the right way. Looks like "traditional All Pull THINKING" is the only thing that causes problems.
For instance: my changer scissors on knife edges can't "reverse" for "lower pulls" - only traditionally bolted changer scissors acting on a traditional changer finger can do that.
So what I am left with is the advantage a push-rod attached to long springs has in that it increases stability and reduces wear, which is why I'm keeping it. Not sure if it isn't best to put the push-rod lower amongst the lowering-points than on the following drawing though, as the way I have turned the scissors now it works better the lower that push-rod is.
Here I have turned the top - knife edges for raise and lower - around, so the changer scissors get pulled open and forced by the string tension to line up correctly.
To make sure the drawing makes sense: the "greenish" raise is housed inside the "blueish" lower, as both consist of "U" shaped steel plate with the actual knife edges/seats "epoxy'ed" inside. Pull-rods then goes inside both.
The only slight complication is that the raise has to be "threaded" up inside the lower, between the backside knife edge and frontside seat for the fixed knife edge. This is just a question of shaping and dimensioning the raised "arm" for the seat for the movable knife edge just right - think that piece is a bit too wide for treading in my drawing.
Details:
I have measured and compared string spacing on all my PSGs - and what I could find mentioned various places on the web, and have landed on a width of 8.5 millimeter for my scissors. This is 2 millimeter more than what I started out with, and just .23 millimeter shy of the 11/32 inches that I have decided will be the actual string spacing at both ends of the PSG. No tapering.
The .23 millimeter deviation between 8.5 millimeter and 11/32 inch, will become free space between neighboring changer scissors. Thus, calculations should be pretty easy for you who prefer to have it all in inches, as you can use 11/32 string spacing as width-reference.
More details:
The changer scissors will be mounted in two sets of 5 each (for a 10 stringer) to provide for a "ridge/spacing" along the center of the keyhead. This "ridge/spacing" is for lining up tuning pegs perfectly for parallel strings all the way - using regular mounting of tuning gears, and happens to go perfectly with my intension to use rigid "T" shaped beams to mount neck and keyhead on.
The vertical arm of the "T" shaped beam is on the underside - stiffening up the changer, so on top I only have to put in a "fake" slider of exactly the right width in between the two groups of real sliders. I will know the exact width of the "fake" slider once I have the tuning gears at hand and can measure and test them for near-perfect (+/- 0.25 millimeter) line-up with strings on.
Just to mention it:
The "PacMan" rollers on knife edges I will use as keyhead rollers - both for strings and under sliders, can be full width - 11/32 inch, as I only have to taper them approximately 0.1 millimeter narrower at the edge so they can only touch each other near the knife edges they will be riding on if/when they slide sideways. If I choose adjustable knife edges for each string roller - which I am likely to do for that "last touch", these knife edges only need to be made 8 - 8.5 millimeter wide to keep rollers in place on their own knife edge simply because they will be too tight a fit near the center to move much sideways.
The "PacMan" rollers on top will obviously fall off if PSG is turned upside down with no strings on. I welcome this "flaw", as it makes these rollers and what is under them are quick and easy to check for wear and/or replace when changing strings - just pick them up and put them back in again without the use of any tools.
There will be several such "loose parts" and "apparent flaws" design into my PSG, as I want everything to work optimally when I play and allow for quick and easy adjustment and maintenance if/when the need arises. And, I want to minimize, or rather eliminate, the need for lubrication.
Richard, most of the problems I envisioned for knife edge changers, seem to disappear into thin air as I get all parts designed together the right way. Looks like "traditional All Pull THINKING" is the only thing that causes problems.
For instance: my changer scissors on knife edges can't "reverse" for "lower pulls" - only traditionally bolted changer scissors acting on a traditional changer finger can do that.
So what I am left with is the advantage a push-rod attached to long springs has in that it increases stability and reduces wear, which is why I'm keeping it. Not sure if it isn't best to put the push-rod lower amongst the lowering-points than on the following drawing though, as the way I have turned the scissors now it works better the lower that push-rod is.
Here I have turned the top - knife edges for raise and lower - around, so the changer scissors get pulled open and forced by the string tension to line up correctly.
To make sure the drawing makes sense: the "greenish" raise is housed inside the "blueish" lower, as both consist of "U" shaped steel plate with the actual knife edges/seats "epoxy'ed" inside. Pull-rods then goes inside both.
The only slight complication is that the raise has to be "threaded" up inside the lower, between the backside knife edge and frontside seat for the fixed knife edge. This is just a question of shaping and dimensioning the raised "arm" for the seat for the movable knife edge just right - think that piece is a bit too wide for treading in my drawing.
Details:
I have measured and compared string spacing on all my PSGs - and what I could find mentioned various places on the web, and have landed on a width of 8.5 millimeter for my scissors. This is 2 millimeter more than what I started out with, and just .23 millimeter shy of the 11/32 inches that I have decided will be the actual string spacing at both ends of the PSG. No tapering.
The .23 millimeter deviation between 8.5 millimeter and 11/32 inch, will become free space between neighboring changer scissors. Thus, calculations should be pretty easy for you who prefer to have it all in inches, as you can use 11/32 string spacing as width-reference.
More details:
The changer scissors will be mounted in two sets of 5 each (for a 10 stringer) to provide for a "ridge/spacing" along the center of the keyhead. This "ridge/spacing" is for lining up tuning pegs perfectly for parallel strings all the way - using regular mounting of tuning gears, and happens to go perfectly with my intension to use rigid "T" shaped beams to mount neck and keyhead on.
The vertical arm of the "T" shaped beam is on the underside - stiffening up the changer, so on top I only have to put in a "fake" slider of exactly the right width in between the two groups of real sliders. I will know the exact width of the "fake" slider once I have the tuning gears at hand and can measure and test them for near-perfect (+/- 0.25 millimeter) line-up with strings on.
Just to mention it:
The "PacMan" rollers on knife edges I will use as keyhead rollers - both for strings and under sliders, can be full width - 11/32 inch, as I only have to taper them approximately 0.1 millimeter narrower at the edge so they can only touch each other near the knife edges they will be riding on if/when they slide sideways. If I choose adjustable knife edges for each string roller - which I am likely to do for that "last touch", these knife edges only need to be made 8 - 8.5 millimeter wide to keep rollers in place on their own knife edge simply because they will be too tight a fit near the center to move much sideways.
The "PacMan" rollers on top will obviously fall off if PSG is turned upside down with no strings on. I welcome this "flaw", as it makes these rollers and what is under them are quick and easy to check for wear and/or replace when changing strings - just pick them up and put them back in again without the use of any tools.
There will be several such "loose parts" and "apparent flaws" design into my PSG, as I want everything to work optimally when I play and allow for quick and easy adjustment and maintenance if/when the need arises. And, I want to minimize, or rather eliminate, the need for lubrication.