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Topic: Double-raise question |
Bruce Wandmayer
From:
Sedona, AZ
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Posted 16 Mar 2017 11:12 am |
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I'm setting up my U-12. The first string raises F# --> G on pedal 5, and F# --> G# on a knee.
Putting the rod farther out on the crank gives more throw; attaching it farther out (away from the axle) on the changer gives less throw, right?
Which will give more mechanical advantage for the G# raise: attaching the rod farther out on the crank and changer, or closer in to the point of rotation for both?
Seems to have to be one or the other, as I don't want to cross them.
Thanks for any help.
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Bruce Wandmayer
Sedona, AZ
Steel on the rocks: shakin', not stirred |
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Charlie McDonald
From:
out of the blue
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Posted 16 Mar 2017 11:46 am Re: Double-raise question
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| Bruce Wandmayer wrote: |
| Putting the rod farther out on the crank gives more throw; attaching it farther out (away from the axle) on the changer gives less throw, right? |
I sympathize with your confusion.
More mechanical advantage would mean a shorter throw, where the pull rod connects closer to the cross shaft.
For a longer throw, the rod connects farther from the cross shaft (axle). |
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Bruce Wandmayer
From:
Sedona, AZ
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Posted 16 Mar 2017 12:49 pm
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Yes, I understand that the farther out the rod attaches, the greater the arc it will describe, making a longer throw.
It seems that if I set the bell crank up for a longer throw, the changer (receiver) will have a longer throw as well, reducing the advantage gained by the bell crank.
What I'd like to know is which one sum-totals more throw: both longer or both shorter? The G# raise needs a lot more than the G raise.
This is a lot of words; an experienced tech hopefully knows what I'm talking about.
Or I could just experiment with both setups and see which works better. My guess is longer bell crank throw.
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Bruce Wandmayer
Sedona, AZ
Steel on the rocks: shakin', not stirred |
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Ian Worley
From:
Sacramento, CA
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Posted 16 Mar 2017 4:45 pm
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The answer to your question depends on the geometry of your changer fingers. You didn't say what make/model guitar.
If it is a pull-release changer with rigid fingers, then the relationship would be 1:1 when both ends of the rod are positioned equidistant from the center of the pivot.
If it's a modern all-pull changer, there is compound leverage at play in the scissor mechanism, which changes all of that. This also varies quite a bit from builder to builder and their various changer designs.
Length of bell cranks, number of pull points, etc. vary significantly too.
As you suggested, experimentation will be the fastest route to a solution that suits your needs. |
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Dave Meis
From:
Olympic Peninsula, Washington, USA
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Posted 16 Mar 2017 5:46 pm
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Further from the axle on bell crank, closer to the axle on the changer will give you the most travel .. if I understand the question.  |
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Jon Schimek
From:
Lyons, Co - USA
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Posted 16 Mar 2017 6:12 pm
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I just went through this exact thing.
My conclusion:start with this rodding chart:
https://www.steelguitar.com/rodding.html
And then experiment from here if you need
Jon
_________________
MSA Vintage-XL, Pre-RP Mullen
Nashville 400 w/blackbox, Space Echo. |
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Tony Glassman
From:
The Great Northwest
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Posted 16 Mar 2017 6:45 pm
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| When considering leverage at the bell-crank only, the crosshaft is the fulcrum. So the farther the pull rod is placed from the fulcrum (on the bell crank), the faster and stiffer will be the change - assuming all other leverage variables (@ changer and pedal) are the same. |
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Ian Worley
From:
Sacramento, CA
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Posted 16 Mar 2017 8:20 pm
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I think folks are missing the point of Bruce's question. He clearly already understands the basic leverage principles that everyone keeps explaining. The question was:
| Quote: |
...Which will give more mechanical advantage for the G# raise: attaching the rod farther out on the crank and changer, or closer in to the point of rotation for both?
Seems to have to be one or the other, as I don't want to cross them. |
He's simply asking which of those two combinations will provide the longer pull, all else being equal.
On newer Sho-Bud with a set amount of pedal travel, placing a rod in the outermost holes on both the bell crank and the finger in combination produces a much longer pull than if that rod is moved to the innermost holes on both. It just depends on the leverage created by the scissor geometry, which varies from brand to brand. I would speculate that in most cases on an all pull guitar, furthest from the pivots will produce the greater mechanical advantage. In any case, it's an easy five minute experiment to find out. |
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richard burton
From:
Britain
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Posted 16 Mar 2017 10:19 pm
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Scroll down this page and click on 'wraparound changer raising' and you can see the movement of the scissors during a raise (on a Carter type of changer finger), and you can then see the best position to locate the rods
http://www.steelguitar.com/maps/changer.html# |
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Charlie McDonald
From:
out of the blue
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Posted 17 Mar 2017 8:51 am
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I understand the question better thanks to Ian.
From the Carter rodding chart, the only string 1 reference I could find:
I think you'd have to put the PB-2 connection to R-2 for the half-step change, as shown on Jim's link to the rodding chart.
https://www.steelguitar.com/rodding.
If you wanted the pulls quicker, they could be moved toward R3 (I think). |
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