Greeting and Salutations,
I recently bought a 1924 TB1. The springs that serve as the hinge are broken. It sort of functions to a degree by the remnants of the springs sticking into mating halves of the door, but I want to fix it. I have an MB for reference. The FONs of the two instruments differ by only 28, so they were quite possibly in the Kalamazoo factory at the same time.
Getting the remnants out may be quite a task. I have tried heating with a soldering iron and pulling with vice grips. I expect that the springs fit into a hole under the brace and the remedy will involve removing the braces. That is doable, but, rather like removing the bridge from a flat top guitar, not something that I look forward to with glee. The brace has "PAT.APPLIED FOR" stamped into it. I wonder if there are any patent drawings for the trapdoor design available on the net?
There are lots of tiny torsion springs available, but finding one the right one could be modified to work may be quite the task. Any ideas?
Thanks much,
ajc
I have the same problem with a trapdoor PB3. I thought about replacing the springs, but I couldn't find any springs that would work, altough I did discover that some old wire coat hangers are the same diameter wire and probably could be bent into springs with a lot of work and some decent equipment.
To remove the old ones, heat is not the answer; things usually expand with heat, so the old springs would actually get tighter. There is also the possibility of holes that they mount in, so, in my opinion, the safest method would be to remove the braces.
I never followed through with mine because not only did the sprigs/hinges break, but the clasp mechanism was missing. I have been searching off and on now for 50 years for an original replacement door.
I have seen pictures of a number of these banjos where the broken springs were replaced with simple cabinet door hinges. They look like garbage, the doors don't appear to close properly, and one pretty much loses the original purpose of the moveable door.
I never found much difference between open and closed on these trapdoor banjos. I tried twist ties to hold it closed, but now just play it as an open back. I would still prefer the original set-up, though.
Thanks for the reply!
The idea behind the heat was not an expansion/contraction thing, but to soften old hide glue that may have been holding the pin. It the way you take a bridge or neck off of a guitar or to pull a piece of pearl out of a fingerboard. I suspect that the spring remnant is not just straight, however. I have seen a patent drawing online for the old Charlie Christian/ Guy Hart pickups and wonder if something similar might be out there for the trapdoor. It does have "PAT APPLIED FOR" stamped into the trapdoor brace. That, of course, would not mean that Gibson would have done it that way throughout the trapdoor period, but it might provide a clue as to what is under the brace.
I have also seen the hinges. I would rather not use that remedy.
A luthier once told me that he had used springs from wooden clothes pins. He did not elaborate.
Because there is no way to "see" how the springs are mounted, I am afraid the braces will need to be removed. I will never use conventional hinges, either.
The "PAT APPLIED FOR" was probably for the entire trap door idea, and not for some other product mounting, such as that pick up.
Good luck on this, and please post results.
As kids we saw match shooters with a little piece of sandpaper to ignite the wooden matches with this same spring.
I reverse the blades to make mutes and banjo shop clamps.
But the idea that these springs could be used by a luthier is intriguing. Totally possible. Trap doors snap open and closed.
People can wind new springs.
I use rare earth magnets in the resonators themselves to ease this situation. I have other vintage customers who don't want additional holes in the rim and resonator
For these people, this is an acceptable if not truly vintage or restored usage. We want what works and the originals.
Otherwise freezing with a little dry ice should get parts to contract. We joked here several years ago about freezing capo spikes. Never meant to be.
Edited by - Helix on 01/30/2023 05:17:00
