Dynamic stack repairs, prep work

[czunit]

Ok, new thread time. We have the spacer blocks, we have the first dynamic stack, now it's time to take it apart and prepare everything for re-cover.

First thing is to mark *everything* and take pictures before disassembly. It's very easy to jumble the parts and due to alignment and whatnot one really needs to know what went where when you try to re-assemble everything. It doesn't seem complex, but it is.

Fortunately dad marked the parts 50 years ago, so we can go with those markings. Note that each part has a letter (A-E) on the main bellows squares, and each of the three adjuster blocks also has an A1,A2,A3 through E1-E2-E3. This is important because the holes were hand drilled 100+ years ago so each part is slightly different and mismatching things will be a mess.



Ok, so here they are laid out. Note the numbers and letters.

Edit: Also noticed the "T" by each letter. This is because there are two of these stacks; the theme stack and the accompaniment. . We're working on the Theme, but dad must have been working on both of them. If you do both at the same time the problems would be geometrically worse if you didn't carefully mark EVERYTHING.

We'll take them apart but first we need to fix a few missing adjusters and see if we can do a rough spacing adjustment....

[czunit]

First problem is missing adjusters. When I disassembled them I found that one of the side adjusters was missing, and more interesting two of them were sheet metal screws. Dad...........



The right way to fix them is with 6/32 screws and nuts. You cut the screw head off, cut the length to 7/16 of an inch, then screw on a nut and solder it at the tip. I put flux on the threads before screwing the nut on the shaft which does help the solder flow. Then with 400 or so grit sandpaper make it nice and smooth and clean it up.



Then screw them in. The threads will match what's on the block, and you now have a proper little spacer foot.



Now with this done, we can do something extra: Do a first pass rough adjustment of all of these feet.....

[czunit]

Ok, so we have all of the feet on but as I looked I noticed they were not.... aligned.... very well. Granted I could just assemble the things and cover, but what if I could set an initial value to how much the stack should be compressed if everything was closed?

According to the manuals, when collapsed all of the bellows should have a clearance of 1/8 of an inch. The 1/2, 1/4, 1/8, 1/16 sizes are when expanded and are made with spacers that have that dimension PLUS 1/8 of an inch (the closed amount). So why not simply 3d print a few 1/8 spacers, put them in between each of the bellows pairs, and adjust the feet as needed so there is 1/8 of clearance.

Well, we have the marvel of a 3d printer....


And we can do this. I printed three spacers, then put them next to each foot adjuster inside the pneumatic and adjusted the nuts so they would just slide out. Took a bit, but it's done.


I also did measurements with the calipers, and yes they are now 1/8 when closed and the open width plus 1/8 when I have the expanded spacers installed. More on that in the next post.

So we have them adjusted, now let's remove all the parts and clean up the blocks.

[czunit]

Now comes the messy part: Cleaning up these darn things. They have two things that have to come off: First there are the adjusters, then there are the little brass tubes that are glued into the wood. Glued. Great. That would normally be the end of things but Dad in his glorious wisdom USED HIDE GLUE!

So we can just heat the brass tubes with an air heater, then gently pull them out with a small needle nose pliers. Not much force is needed, heat the tube for 30 seconds or so with air heat and wiggle it out.

And you get this....



With that done it's on to cleaning off the old leather and crud from the sides of these blocks.

[czunit]

The last part is pretty messy: That old leather crud has to come off and the surface has to be smooth. This is a mess and takes an hour plus to do right.

I didn't take pictures, but I will describe the process: First I cleaned off as much of the old leather crap by rubbing it first with my fingers, then a damp paper towel.

Then I used the monocoat iron I had from my RC days on medium heat with a piece of paper towel dampened in water to smooth off the burned and cruddy glue. The goal is not to get all the glue off, but to get the leather crud off and the glue softened and flat so when I put new hot hide glue on it will bond and smoothly connect to the pneumatic cloth.

I did use a bit of wetted 400 grit sandpaper with gentle strokes along the grain to get off most of the leather, then the hot paper towels to smooth it down. Not quite perfect, but good enough that I can now let everything dry and start mixing up some hide glue this afternoon. But first it's time for a nap.