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Topic: Pivot Point For Scissor Fingers |
Les Ford
From:
British Columbia, Canada
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Posted 21 Nov 2023 10:13 pm |
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I'm making a double raise double lower changer and would like to shorten the finger scissors as much as possible in the interest of reducing the overall depth of the cabinet. To do this I want to raise the lowering finger pivot closer to the axle shaft.
I am concerned that this may have unhoped for consequences on the stiffness of the pedals or some other unintended result.
I want to go from this:
To this:
It seems to me that there would not be a significant change to the raise tension but the tension to lower would be reduced and the distance of the pull on the finger would be reduced but a higher spring tension would be required to return the lower finger to the zero point.
Am I reading this correctly, and is there anything that disqualifies this approach? |
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John Hyland
From:
South Australia
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Posted 22 Nov 2023 12:22 pm Re: Pivot Point For Scissor Fingers
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| Les Ford wrote: |
I'm making a double raise double lower changer and would like to shorten the finger scissors as much as possible in the interest of reducing the overall depth of the cabinet. To do this I want to raise the lowering finger pivot closer to the axle shaft.
I am concerned that this may have unhoped for consequences on the stiffness of the pedals or some other unintended result.
I want to go from this:
It seems to me that there would not be a significant change to the raise tension but the tension to lower would be reduced and the distance of the pull on the finger would be reduced but a higher spring tension would be required to return the lower finger to the zero point.
Am I reading this correctly, and is there anything that disqualifies this approach? |
I believe you are correct that the raise action is only affected a small amount and also the return action will require a stronger spring. And extra stiffness.
A few things though. The lower travel pull length will increase and might become excessive and be totally out of balance with the raise distances. Also as you have shown a longer spring. This goes counter to the physics of springs where a shorter string has more resistance than a longer one of the same wire and diameter.
I also see you have shown 2 raiser and 2 lowers. You might consider the 1970s sho bud style which is out of fashion but does give a reduced cabinet size. I don’t have a picture but they look like a long vertical bar with two horizontal bars pivoting off the vertical. Edit:  |
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Les Ford
From:
British Columbia, Canada
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Posted 23 Nov 2023 11:07 pm
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Thanks John,
I'll try to take your points into account. |
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Bruce Zumsteg
From:
Harrisonville, Missouri, USA
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Posted 24 Nov 2023 7:50 am
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| Les, you don't have to give up the triple raise and lower in order to shorten your changer. The Encore model that I designed has triple-triple, and only a 3" front apron and a 1 1/16" string height above the top of the deck, and it plays great. I have designed and experimented with dozens of variations of the scissor changer, with the goal of improving the pedal action, return issues, etc. It's a trial and error procedure. To start, make a version of your desired dimensions for one string ( it doesn't have to be fancy), and put it on a test board with one string at your desired scale length. I use an E note (.014) to test). From that, you can tell which way you need to move the rivet and the contact point of the lower finger with the string finger. You will probably have to go thru this procedure 3 or 4 times to get what you want. Good Luck! |
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Les Ford
From:
British Columbia, Canada
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Posted 26 Nov 2023 8:48 am
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Thanks Bruce,
I'm always looking for a magic bullet but I guess there's no substitute for figuring it out the hard way.
Sometimes I feel like I get mired in the "error" part of that trial and error equation.
I'm trying to shrink the changer down to where it can be shoe-horned into an eight or nine string lap steel that uses palm pedals and knee levers. This setup, if I can make it work, with the two raises and two lowers would fit into a Weissenborn body depth. |
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Bobby D. Jones
From:
West Virginia, USA
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Posted 14 Dec 2023 10:29 am
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I like Mr. Zumsteg's idea building 1 and work with it on a test bed, To prove design, Before making the rest to fill a changer.
Sometimes things look good in design, But will not work in reality.
Your design is shortening leverage, May lose some leverage in the changer. But look at the whole pull train. You have pedal to pedal rod, pull lever to cross rod, And bell crank to pull rod to regain any leverage lost at the changer.
Good Luck in project. |
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