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U-12 question (Page 2)
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The Steel Guitar Forum
Pedal Steel Archive
U-12 question (Page 2)
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| This topic is 2 pages long: 1 2 This topic was originally posted in this forum: Pedal Steel |
| Author | Topic: U-12 question |
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Ken Lang Member Posts: 2467 |
posted 30 November 2000 07:27 PM
Perhaps that old thread about surface tension was in referance to material stress. To my knowledge surface tension is a term used only for liquids. Material stress is used in referance to the extreme outer fiber of a given shape. In a round shaft it's the distance from the center of the shaft to the outside. In a 3/8 dia shaft the distance to the extreme fiber is 3/16. Pushing on the shaft from one side creates two forces. The closest side to the force is the extreme fiber put in compression. The other side, the extreme fiber is put in tension. If you have ever bent anything, even a twig, you'll notice the side opposite the force is what breaks first. That's because that extreme fiber was put in tension beyond the stress point and it cracked. We've all seen that a 2 x 4 is stronger if it is laid side ways with the 4" side vertical and weaker with the 2" side vertical. Same deal. Which ever axis the force is on, it will be stronger when there is a greater distance from the center (or neutral axis) to the extreme fiber. Same deal for a hex shaft of 3/8". If the flats are where the force is, it will be no stronger than a round shaft. If the force is at one of the points of the hex however, it will be stronger, because the distance from the center of the hex to the point is greater than the distance to the flat. These are not engineering formulas made up that the material has to follow. Obviously, the formulas were derived from observing how materials behaved. For shaft bushings there are great new things being made. One is a composite, a steel ring on the outside to hold the round shape and a composite on the inside for wear. I just bought a pile of them for some projects. They have a 3/16 inside dia and around 7/16 dia outside. They were 67 cents apiece, and are used in machinery that sees far more abuse than a steel. |
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C Dixon Member Posts: 5912 |
posted 30 November 2000 08:50 PM
Bob, Very respectively, that would not solve my problem. The trouble I am having would remain unless I find a way to keep the LKR cross shaft from twisting when the E's are lowered to begin with. Jim, The 8th string comes back flat BUT not as flat as the 4th string. The reason for this is, the 4th string bellcrank is moving more than the 8th string bell-crank because it is naturally further away from the stop because it is twisting much more than it is bowing. Take care both of you and thanks for your input. carl |
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Bobby Bowman Member Posts: 1271 |
posted 01 December 2000 12:01 AM
If you guys insist on looking at this only from the crossbar viewpoint, then I suggest something more like what Zane had in his ZB'S and BMI's,,,,,a 3/8's by 1' flat bar. A friend of mine made a few guitars with these and put a hefty bell crank on top of the flatbar and man, it was a fine and super smooth playing guitar. We didn't check for what you're experiencing Carl, mainly because we didn't have those changes on it. I still contend it is more the string than anything else with some contribution from the return spring and/or friction and even less contribution from the cross shaft,,,,unless the cross shaft is very weak, feable, flimsy and not fairly stable at both ends. It seems, and I'm not 100% sure of this, that I remember that inertia and kinetics have an influence in something like this. I think you may have to design and incorporate some kind of a "counterforce" or "inhibitor" perhaps behind the bellcrank that's adjustable into the system,,,,maybe even somthing simple kinda' like a "helper" spring that could compensate for the difference. Otherwise you may be on a dead end street. BB
[This message was edited by Bobby Bowman on 01 December 2000 at 12:14 AM.] |
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Michael Johnstone Member Posts: 2535 |
posted 01 December 2000 04:16 AM
I tried helper springs and even reversing bellcranks that pushed on immovable stops,etc.to neutralize the bend in the shaft and all I got was stiff,weird feeling pedals,flexing in my SECONDARY linkage and the suspicion that I was pi$$ing against the tide or trying to invent a perpetual motion machine.I also fooled with and even replaced the return springs(heavier)trying to find the sweet spot-which helped maybe 10% but still basically no cigar.All my other changes on those strings(4&8)worked like butter.It was the INTERACTION of the changes-raising or lowering from an already lowered string and then releasing it back to the lowered note-that's the problem.Switching to a steel shaft was the only thing that substantially helped. -MJ- [This message was edited by Michael Johnstone on 01 December 2000 at 04:19 AM.] |
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Jim Smith Member Posts: 6399 |
posted 04 December 2000 10:35 PM
Carl, any luck with your fix? I just spent an hour woodshedding on the phone with Jerry Fessenden and we came up with an idea that sounds like it might be worth a try. Turn down a portion of the shaft to a cylinder as close to the problem puller as possible. Screw a cam made from a round hard nylon cylinder with an off-center hole on the changer side of the shaft. Properly adjusted this should overcome the shaft flex and can be "tuned" by rotating the cam. We "think" it should work but haven't tried it. It should have the same effect as a bushing, but is easier to manufacture. ------------------ |
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Michael Johnstone Member Posts: 2535 |
posted 05 December 2000 02:55 AM
Jim- I'm trying to picture the cam rig you described but what does it push against to counteract shaft bowing? -MJ- |
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Jim Smith Member Posts: 6399 |
posted 05 December 2000 06:50 AM
Sorry, I was pretty sleepy when I wrote that last night. The shaft bows toward the changer so the cam would push against (brace) the changer side of the cross shaft. It's the same idea some manufacturers already use instead of a center strip with bushings, and serves the same purpose. |
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Jim Smith Member Posts: 6399 |
posted 05 December 2000 09:06 AM
After stewing on this some more, I think what's happening is that on the first lower the puller rotates around the shaft (normal) and bows it a little, causing the shaft to also rotate around the puller a little bit (not normal). When the second lower kicks in, the pressure is relieved in the shaft so it "unbows" and lets the puller rotate a little more. ------------------ |
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Jim Smith Member Posts: 6399 |
posted 05 December 2000 10:38 AM
Jerry's going to build me a special stop to mount behind the 8th string E-D# puller. That should stop that booger from moving any further, or snot!    |
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C Dixon Member Posts: 5912 |
posted 05 December 2000 03:30 PM
I wish to thank everyone who has responded. Means a lot to me. The problem is NOT the shaft flexing. Looked at it too many times. The shaft is twisting!! So the cam-lock would not help it I am going to replace the entire undercarriage with ALL stainless steel #303 parts. Even the bell cranks. Then use stainless steel pull rods. That is the best I know to do. I am going to mill these myself on my lathe and milling machines. I have thought about this more than you can imagine. I am convinced this problem has been with us from day one, but because not all steels are set-up to do these changes in their set-ups, most were never aware of it. But as more and more single, double and triple raises and lowers come into into use (where one is held and the other is engaged and released), I think more and more are going to hear this "untrue" return. Oh what hath man wrought huh? Thanks again folks and God bless always, carl |
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Jim Smith Member Posts: 6399 |
posted 05 December 2000 06:47 PM
Carl, you said early on in this conversation that your cross shafts are aluminum. In that case I can believe you when you say that your shafts are twisting more than they're flexing. Before you replace the entire undercarriage, please make yourself just one stainless shaft for the knee lever in question. As Michael said early on, only double changes will have this tuning problem. Single changes are duplicable each time and thus tunable. I do believe you will end up with stainless shafts before you are done though. The twisting of the aluminum translates to longer throws because part of the travel is spent doing the twisting. I don't think stainless bell cranks and pull rods will buy you anything though, other than more weight. |
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