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Topic: Pull Release Bellcrank failure |
Tim Toberer
From:
Nebraska, USA
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Posted 14 Feb 2025 11:32 am |
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I have been trying to come up with a new design for bellcranks for my pull release. My goal has been to simplify the construction, but also to make it adjustable. I thought I had it figured out only to be foiled again!
To simplify things I went to a one sided bellcrank as opposed to the Marlen style butterfly design. Instead of using a slotted stop, I switched to a one sided lock barrel, which physically attaches the rod to the BC instead of just having the BC push against the slotted stop for lowers. This eliminates making a separate slotted stop, and I found a cheap throttle stop that fits the bill perfectly. (If it only worked!) I believe this is the problem. On lowers with 2 notes on the cross shaft, as I tune one open note (with nylon nut) the the opposite finger with the other note moves as well, making it impossible to tune. Hard to explain, but on a pull release the open note is balanced by the spring and the string tension, so when you change the tension on one note, the other note self adjusts back the the original pressure it seems, finding the equilibrium.
This is hard to explain, but from what I can tell lock barrels will not work on a pull release, where you want to both raise and lower a note. I am still trying to wrap my head around this, because
it just seems like it should work, but doesn't.
My new bellcrank design would work brilliantly on an all pull design, and will still work on raise only or possibly lower only notes on a pull release I believe (which are not tuned by a nylon nut, but at the keyhead and screw stops). It is a bit crude, but easy to make and completely adjustable. I will post some pictures when I get a chance. Going All Pull would solve alot of problems, but would greatly complicate the changer design and would be much harder to build acoustic. Back to the drawing board! |
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Fred
From:
Amesbury, MA
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Posted 14 Feb 2025 12:21 pm
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| If I understand what you're saying, the cross shaft has to be pulled tight by a spring against a hard stop. You should be able to tune the floating finger with the nylon nut and the cross shaft won't move. When you lower, the finger stops against the body or an adjustable screw. |
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Les Ford
From:
British Columbia, Canada
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Posted 14 Feb 2025 12:42 pm
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| Pictures would be helpful |
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Tim Toberer
From:
Nebraska, USA
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Posted 14 Feb 2025 1:31 pm
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| Les Ford wrote: |
| Pictures would be helpful |
The bellcrank is just a 1/4 thumbscrew with the sides filed flat and a hole drilled for the "lock barrel". The housing is just a 5/16 slot milled just shy of 5/16 so the nut will clamp it in place. I just spent another few hours fiddling with it and am just about to give up for the day.
The 4 double lowers are on the right with the lock barrel on the spring side. The 1st raise is on the right with the lock barrel on the other side. |
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Ian Worley
From:
Sacramento, CA
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Posted 14 Feb 2025 2:44 pm
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I'm not sure I completely understand the issue from your description, but it sounds like in general it is most likely what Fred described above. When properly set up, the only way a conventional pull release lower would exhibit the behavior you describe would be if the bell crank and cross shaft are moving/rotating as you turn the nylon to tune the open note, thus affecting other notes on the same shaft. If so you would probably just need to tighten the lower return spring(s) to hold the shaft more firmly against the neutral stop.
I'm not certain exactly how your guitar is set up, but from what I can see in the pics it looks similar to an old Marlen, with the lower return springs connected to the ends of the lowering pull rods. The first four pedals on the right are all lowers, the last two are raises, the screws on left side of the butterfly cranks along the rear apron are the neutral stops for the lowers, the right side screws are the pedal travel stops.
One other way this sort of issue could arise would be if you had more than one pedal or lever working the same pull rod, which I can't discern from the pics. In that situation the rods must be free floating with shaft collars or something similar behind the bell cranks. That sort of setup requires some additional means to tune the pulls. Since the rod is free floating you can't tighten the nylon without some addition means to hold the stop collar, like on an old Marlen or a barrel tuned Sho-Bud. The locking barrel clamps you described would not allow this.
_________________
All lies and jest, still a man hears what he wants to hear and disregards the rest - Paul Simon |
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Tim Toberer
From:
Nebraska, USA
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Posted 15 Feb 2025 6:56 am
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| Ian Worley wrote: |
I'm not sure I completely understand the issue from your description, but it sounds like in general it is most likely what Fred described above. When properly set up, the only way a conventional pull release lower would exhibit the behavior you describe would be if the bell crank and cross shaft are moving/rotating as you turn the nylon to tune the open note, thus affecting other notes on the same shaft. If so you would probably just need to tighten the lower return spring(s) to hold the shaft more firmly against the neutral stop.
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Thanks for the responses! I actually got it to work, sort of. So it isn't the bellcrank that was causing the issue. Which is great news! The bad news is I thought I knew how to setup my guitars, but there are some mysteries still. Acoustically it sounds like S$#!&!, but what do I expect, it is an olive can resonator  The acoustic aspect is a bit of a novelty, and I am using this guitar as guinea pig for my new bellcranks and experimental tuning.
I basically loosened everything up and went through my process again and it worked. This was the third try and took almost the whole day. I am not sure what I did differently. I think you guys are right about the return springs not being tight enough.
Another problem I found was getting the highest note to tune properly. I originally was trying to set it up with a whole step raise with a half step lower, but I found that the whole range of my changer finger wouldn't cover that. G-A raise and G-F# lower. So I had to change the whole tuning. I changed to a slightly higher gauge, but it wasn't quite enough. I guess I still have a lot to learn! |
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