Dynamic stack repairs, covering

[czunit]

Ok, it's time to do the covering! The manual recommends that you mark the piece you're about to cover carefully.

For me, the key element is "where is the center? I want the ends to overlap by about 3/4 of an inch or so, on a flat section of the dynamics stack (so I'm not overlapping at a hole or a support).

Given that the squares (for me) are 3 inches in size we would want a 12 inch strip of pneumatics stuff plus a 1/2 inch foldover so I did 13 inches even.

Then measure the height of your stack with all spacers in it, and mark the vertical to about 1/2 inch taller than that with the stacks aligned so there is a 1/4 inch boundary. This way, if you slightly screw up the putting on of the cloth, that 1/4 will save you. If you're perfect, it will leave a nice little fold over or conversation piece in 50 years.

Anyway, mark the center of the 13 inches, then two points 1.5 inches from that centerline. These are the edges where you put your blocks. The key is to make sure the marks go up and down perpendicular to the bellows cloth end so it's a nice even line for all 5 of the blocks. They have to be square to each other, so also have a nice straight edge to check when you glue.



Then align the blocks and your spacers. You did print out spacers, right?



Note in this picture the left line is the one I used, the right line was measured from the right side which of course is a bit longer due to the overlap. Whatever.

Next up, time to GLUE!

[czunit]

Next up is gluing things. Prepare the hot glue, and get everything all lined up and ready to go. What I found that worked was this.

• Get the bottom square lined up on the cloth. Yeah, this is where all the lines make a big difference.

• Put your 5/8 spacer block in, and then the second square against it. Now you're ready to do two of them.

• Pick them up, hold the three items together, and move the spacer forward so it is NOT where the glue would be. Gluing the spacer to the cloth would seriously suck.

• Apply glue to the bottom sides of the two blocks.

• Place the assembly on the cloth, adjust to the lines (esp the left one) and press down for a minute. Use your ruler to make sure they are square and in line with each other. The instructions say to have some newspaper under it to provide a cushion, this is a good idea, I used about 5 layers of paper towels.

• Hold for a minute or two to let the glue set.

• Now get the next spacer and the next block. Make SURE you are installing it properly (having it 90 degrees off will suck). Put glue on the edge, make sure the spacer is not near the glue, and press it against the first two and the cloth. Align to the left line.

• Keep going till you have hit the top one. For that make sure you install it properly and not upside-down. Make sure you don't install ANY of them upside-down or out of rotation.

At the end you should have this.



Wait a few minuted, then rotate it 90 degrees, glue on the sides of the blocks (push the spacers away first so you don't glue them) then pull the cloth over them and smooth down. Not too much glue, you don't want glue on the inside to keep the cloth from coming down.

Press this new glued side against the paper, then repeat for side 3. Keep moving the spacers so you don't glue them.

Eventually you will have this:



Not bad for a start.....

[czunit]

Whelp, all done.

First part was getting the brass tubes back in. Turns out if you heat the tubes with your hot air tool (with a pliers holding them gently of course) you can press them in and they melt any remaining glue!

However there is not enough glue for a good seal, so it's time to MAKE MORE GLUE. And close the pneumatic up.

First, you heat up the tube again, then you brush on a bit of hot hide glue. Then press it into the hole to the right depth, then repeat.



Now, move the spacers out some and start dimpling all the holes for the screws. To be honest every screw hole now has a bit of hide glue covering it, but they are easy to see as little dimples in the fabric. I used a tiny drill bit to open them up, then put the screws in a bit for each of the adjusters and pads. Takes awhile, but once you have it closed you no longer have the structural strength in the stack AND you don't have the adjusters to limit travel. This is how you can rip things.



Anyway, with all of them done I covered the last side (glad it was flat and simple) making sure to glue the flap down so air can't get in between the pads of course. Another reason you want the last side on the simplest part of the pneumatic.

Then screw in the adjuster pads, being really glad you marked everything. Note: Use a brand new perfect condition flat head screwdriver that fits the screw heads perfectly. And put your fingers around the screws as you go down, if the blade slips and goes through the pneumatic cloth you get to start ALL OVER!



Then when it's all together and the glue has set scruntch it down and let the folds form.

And you're done! Look at how beautiful it is!!!!



Now you do the other one. A lessons learned post will follow this.

[czunit]

So.... Lessons learned:

1) This takes a long time and pre-work is critical. Make sure you mark everything, put everything in order, and of course don't mix up pads, or screws or anything. These thing were hand-made, so small differences will make a mess if you mix stuff up.

2) Marking the fabric is critical. Mark the bottom and top and sides and everything.

3) Sign your name in there; someone will know who to thank or blame in 50 years. Your name is important, put it on your work and make it quality.

4) Keep the fabric straight as you roll the sides and do them. A twist here will be a mess.

5) The 1/16 unit was... small. I think the tolerance is too close, as the adjusters are almost at the minimum. We'll see when I adjust it.

6) The glue is hell. You have to put enough for good adhesion, but too much runs the risk of the glue getting on the fabric and making a little glue mountain. If it's over 1/8 of an inch high it will interfere and possibly wear the cloth in short order. Which means you do it again!

7) Yeah, it's a job, but it is doable, and whatever I have here is light years better than some guy with pilobond.

8) Do it.

[czunit]

Post update: Mounted the unit in the Duo Art thingie and hooked the springs up with minimal tension. Interestingly enough the springs were pulled far tighter, I have no clue as to why but wonder if it's related to the pouches ripping apart. Probably not, but for starters small is best.



With the unit connected I put a line on the first bellows and sucked with my mouth. Sure enough IT COLLAPSED PERFECTLY! When I put my tongue on the hose it slowly opened back up, fair enough nothing is 100% air tight.

Video at: https://i.imgur.com/OHtfrVa.mp4

Thought: I should cap off the others and see if there is any pneumatic to pneumatic leaking.

Anyway, I went over to the 1/16 one and tried it. It "collapsed" and the linkages did move a little bit. I'll be darned.

The 1/8 worked fine as well. Moved a bit more.

However when I went to the 1/4 bellows it barely closed and I could hear air hissing. Blew into it gently and found the air was coming out around the brass fitting.

Guess which one did not get hide glue because it was "tight enough" and was not moving when heated. Major moral lesson: Always apply a coating of glue, do not count on what is in there already to seal. The difference is staggering.

Here's a nice little video of the fittings moving. https://i.imgur.com/hKlO6pk.mp4

[czunit]

Quick update. Warmed up the glue and re-glued the various fittings. All are now in snug, including the 1/4 inch bellows. Was a job getting it in, but it should be working now....

Will check in a few hours. I also cleaned up the accomp side stacks, will do some sanding tonight, I do need to make another little foot as well as another one is missing.

Thought: When I checked the bellows coming out I noticed that the top one (which is the 1/16th inch) was gapped to the same size as the 1/8 inch one below it. I wonder if Dad just used a pair of 1/4 inch spacers instead of a 1/4 and 3/16 spacer for the top (you have to add 1/8 to allow it a bit of clearance when "closed"). The result was that the top adjusters were pretty far out as opposed to being extremely "in" for my unit.

I'll continue to use the right spacers. Even if the top feels like there is no motion there *is* motion.

[czunit]

Leak update. With proper hose, bellows 1 and 4 hold vacuum fine.

Bellows 2 leaks a bit, but not if I plug the hose to bellows 3. This indicates a leak between 2 and 3. Same with 3, it leaks back through two. However with 3 covered the pair of them hold vacuum.

This.... might be an issue. I think I'll take it off and use the monocoat iron to re-flow the glue between bellows 2 and 3. It's not enough to collapse either but eh, why not do it perfectly.

Also when putting on hoses make sure to support the bellows so you don't rip anything. It's a complex system.

On to the other side.

[czunit]

Final thought: Tried ironing the junction between bellows 2 and 3. It doesn't collapse under normal vacuum and barely collapses when the other bellow is blocked off.

Given the leak is small, there is no clue where it is, and to be honest the dynamics work fine I'm going to declare this "good enough" and move on. I will be a bit more careful on the accompaniment side; that one is cleaned up and ready for covering.

Next weekend. Or the weekend after; stuff to do.