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Topic: Making new pushrods for a BMI? |
Lyn Kotuby
From:
Rhode Island, USA
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Posted 7 Dec 2022 2:59 pm |
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I picked up a BMI push/pull S12 earlier this year with the hopes of doing a massive copedent change from the universal it came with to Johnny Cox's D13 or Zane Beck tuning. I enjoy doing my own work where I can and learning as I go along (half the fun of pedal steel for me), but I'm really stuck working on the pushrods right now.
A little info on the BMI pushrods: the nylon tuning nut is permanently attached to one length of 3/32" 5-40 threaded rod (not sure how), which goes through the changer finger; then you slide on the metal and plastic spacers against the other side of the finger, which is then held in place with a length of music wire that you wrap around and cut to size once it's through the finger (lazily applied in the picture). This threads into a nylon hex coupler that seems to be pushed onto a 1/8" length of rod, which attaches to the bellcrank with a small cotter pin. Here's a picture of one of those rods on a good day:
Unfortunately, if you overtighten the rod, the threaded rod will push the other rod out of the hex coupler permanently (partially or completely) and the rod is unusable. More importantly, I'd like to be able to make my own rods so that I can add more lowers, or add new ones on pedals/levers that don't currently have one.
I'm at a crossroads now having sunk some money into 1/8" steel rod, 5-40 taps and tuning nuts to match the existing rods, and general frustration. Any suggestions on how to approach making pushrods for this guitar?
I've thought of trying to copy the ZB design I've seen pictures of, which would replace the nylon coupler with a metal one plus a nut, but I can't find any 5-40 standoffs anywhere locally. Am I better off switching everything over to 4-40 thread? Can anyone think of a design that doesn't require me wrapping music wire around the rod while it's already installed in the changer? |
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Bill Moore
From:
Manchester, Michigan
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Posted 9 Dec 2022 5:34 pm
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I have made push rods for 2 BMI's that I owned. The rod in your picture doesn't look right to me. The lowering rods on my guitars were thicker than 1/8", with the end connecting to the bellcrank tapered down to 1/8" so it would fit the holes in the bellcrank.. I think they were 5/64". The end going to the fat nylon spacer had a short thread, screwed very tight into the spacer. So the spacer needs to have different size holes at either end to fit the different size rods. The shorter rod, with the tuning nut, was 1/8" diameter. The spacer was long enough so there was room to make adjustments to the tuning nut and not contact the larger rod at the other end of the spacer. I made the spacers from round nylon rod, 3/8" in diameter. The tuning nuts were screwed tight onto the 1/8" rod, so when the tuning nuts is turned, only the threads for the smaller rod, at the spacer, will move. To me, it looks like someone tried to make a new rod and just didn't make it correctly. It the picture below, you can see the original hex nylon parts and also the round ones that I made. In the second picture, you can see the tapered ends that connect to the bellcrank. It was time consuming to make the rods, but I think the thicker rod is needed in order to be stiff enough to push against the springs at the changer.
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Ian Worley
From:
Sacramento, CA
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Posted 9 Dec 2022 10:54 pm
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Bill, I used to own that guitar in your pics, serial #1200. It was 5+5 when I got it ~2013, I just sold it recently.
I spoke with Don Fritsche when I first received it and he told me that the way they fabricated the original push rods (the heavier fixed section that connects to the bell crank at one end) was to grind a square tapered key on the end (see pic below), then heat the rod with a torch and drive the nylon end on such that it begins to melt and bonds firmly to the rod. The pic below is one of their originals, dismantled, actually a leftover from the same guitar in Bill's pics above. The nylon ends are 1/4" round x 1-1/4" long, the rods are 0.156", 5/32"Ø (which I believe is what Bill meant to say above). They would pre-drill a through hole in the nylon piece first that would slide over the heated rod on one end, and also provide the hole for the tuning push rod to thread into on the other. The original threaded actuator rods, the ones that go through the push fingers, are 1/8"Ø w/ 5-40 thread.
Lyn, I believe you could re-attach the displaced nylon(s) using the same method Don described to me, just put the rod in a vise or something and heat the end to near red hot, then press the nylon back on, far enough to bond to the rod. Alternately, a little JB Weld or similar epoxy would do the trick too. You can attached the fixed 3/16" tuning nuts using similar methods. If you've got some that are displaced you should be able to see the square tapered end like in the pic, unless the bad ones were someone's DYI units added later (which might also explain why they failed).
The wire wrap that stops the push spacer can also be just a small cotter pin or something similar, but I believe the wire was used just keep the overall assembly as compact as possible so that they won't hang up on adjacent rods when rotated. Keep in mind that once you've assembled these you won't need to mess with that connection again until you decide to change your copedent. It's not something I'd worry about (I didn't). Perhaps it's not perfect, but it's a really good system as designed. One other thing to note if you're fabricating additional rods, ideally the connectors should to be of staggered lengths on adjacent strings to avoid potential conflicts where one rod would rub against an adjacent lower and unintentionally activate it, and to avoid collisions or interference with adjacent bell cranks on the first two or three cross bars.
Also, you will not want to replace the nylon ends with metal threaded couplers as you suggest in your last paragraph. The same person designed both, but this is a completely different system than a ZB. The nylon couplers are an important part of the design. They function the same as a standard nylon tuning nut at the end on a typical all pull guitar rod, or on the raise end of your guitar - the tight fit and relative softness of the nylon is what keeps the rods in a stable position tuning-wise. A threaded coupler with a lock nut would require you to reach under the guitar and loosen, then re-tighten, the nut for even the most tiny and incremental of tuning changes. The tight fit of the nylon connector makes it so you always can tune the lowers reliably from the end plate without ever having to reach under the guitar. One other thing I will say about guitar #1200 in Bill's post, it had virtually no cabinet drop, and the extended tuning stability for the pedals and levers was the best I've experienced on any guitar I've owned. Rarely needed a tweak.
Good luck!
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All lies and jest, still a man hears what he wants to hear and disregards the rest - Paul Simon |
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Lyn Kotuby
From:
Rhode Island, USA
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Posted 10 Dec 2022 5:17 am
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Bill, Ian, thanks so much for the detailed posts! This is a huge help. I was completely stuck when I posted, but I think I should be able to fix up what I have now and make some additional lowers with the info you gave. Also learned a lot of general info along the way which I always appreciate!
You're both right - I think I was off on my measurements, the bell crank side of the rod is much thicker than 1/8", good spot. I'll be sure to double-check it before ordering more rod stock when I make additional rods later on.
Mine is #1154, so not far off from yours. I loved the sound and feel of it when I had it together, but someone had loosened or overtightened a few of the changes when I got it, plus a problem rod or two, so I decided to just change the copedent while I was at it...now it's been in pieces for a few months.  |
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Bill Moore
From:
Manchester, Michigan
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Posted 10 Dec 2022 5:30 am
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| Ian, very interesting, I sold that guitar quite a long time ago. I probably should have kept it. I'm pretty sure That I threaded the larger rods into the nylon. And I did mean to say that the rods were 5/32". Those BMI push/pulls are nice instruments. |
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