Just spent some time next to the unit, yanking, twisting, knocking. I'm gonna leave things as they are until I put the system into service...

EJWash

Made a trolley for inserting and retrieving the torsion box/metal top into and out of the vacuum bag. I have some square steel tubing and some other metal odds and ends that have been laying-around the shop waiting to be useful. I used a set of wheel trucks from pair of roller skates that I found at Goodwill.

Speaking of vacuum bag, I hit a snag with the vinyl I ordered. The vinyl is 54" wide. I needed to trim 4" off one side to make tape (as it were) for sealing the edges of the bag. That brings the bag down to 50" wide. The torsion box is 76" long, 36" wide, and 4" thick. Add another 3-1/4" hight for the trolley. The guys in the movie Jaws needed a bigger boat, well, I need a bigger bag...

No worries mon! The waterbed industry to the rescue, don't-cha know! I found a new single-size 22-mil vinyl waterbed mattress online (free shipping) for $69.00. The mattress measures 84" X 48", and being a mattress, will have at least a 6-8" thickness to it. So far, so good. Of course the proof will be in the pudding when it arrives. Hopefully will get to bag this thing next weekend!

EJWash

After I made the bagging trolley, I got curious and played with the vacuum system. I am now a believer!

I placed an aluminum adult beverage can in a 1-gallon Ziploc bag. Used a hole pinch to make a hole in one side of the bag and simply held the vacuum line to the hole by hand.

EJWash

It didn't just immediately spring back into shape so the process must work.

You're going to have some fun continually coming up with new stuff to destroy.

Originally Posted by loNslo

You're going to have some fun continually coming up with new stuff to destroy.

I crushed a couple of beverage cans but nothing else. It does give me a sort of Gallagher/melon syndrome, but I haven't come up with anything else to cave.

EJWash

You've proven the concept for a full scale trash compactor.

Alright! The waterbed mattress was waiting for me when I got home yesterday.

I cut open one end of the mattress (head/foot) and bonded the vacuum connector stem. Then I made the first of what will be a few dry-runs of placing the torsion box into the mattress before I apply the epoxy to the torsion box and steel top for the final bonding. Needless to say, I am impressed and in awe of this entire subject and science.

I fired-up the vacuum pump and pulled the bag down to 21 in. hg., which took about 10-minutes. I noticed when the pump shut-off, the pressure gauge needle showed that I was losing pressure. Leak.

Of course, due to the construction of the mattress, there are overlapping seams. One of the seams runs the length of the mattress and is exposed at the opening. Although the mattress is made of 20-mil vinyl which is somewhat thin, and the bag is securely clamped closed, it does provide enough of a gap for a small leak. I smeared a small amount of silicone sealant over the seam. After I applied the silicone, the bag pressure was 20" in. hg.. After two and a half hours now, the pressure is holding there. While the silicone has stopped the leak, it does not adhere to the vinyl after it dries. When I seal the bag on the bonding run, I'll apply a bead of silicone the entire length of the bag opening. It will come off cleanly when I'm done.

I am not concerned with a small leak in the bag or the vacuum system. The rule-of-thumb for vacuum pressure is 70.56 pounds per square foot for each 1" of vacuum pressure. Which means that there is 1481.76 pounds per square foot (distributed equally) at 21" in. hg. on the box. My vacuum pump has a pressure switch that automatically cycles the pump on and off between 21"-19" in. hg.. This means that if there is a leak, the the bag pressure will cycle between 1481.76 and 1340.64 pounds per square foot (in theory). Only a drop of 141.12 pounds per square inch. Yep. That'll do nicely.

EJWash

You have been busy.

Looks like it will work. Not sure it will hurt you but FYI, silicone doesn't like to stick to itself (new atop old).

I'm going to leave the bag pressurized overnight (tonight) so I know where I stand leak-wise. The I'll remove the silicone from the bag. It rubs-off easily.

EJWash

Checked on the bag a few minutes ago. The vacuum pump cycled on and off three times during the ten hours I had the bag under pressure.

Now that I've seen this process in action, I'm considering is drilling holes in the top of the box. The vacuum pressure will draw the epoxy down into the holes, forming spikes when the epoxy cures. This will also give the excess epoxy somewhere to go thus avoiding the metal top sitting on too-thick a layer of epoxy on top of the box. I'm thinking 1/8" holes drilled 1" deep into the top of the box and down into the center of the matrix pieces. Comments?

EJWash

I haven't been keeping up but how many holes are you talking about? Those holes sound really big to me. I'm thinking tiny spikes like 1/16" diameter by 1/8" deep. Epoxy isn't that strong. A 1" x 1/8" epoxy rod will only be good for about 1/8" of the depth. Epoxy breaks pretty easily.

Rather than drilling holes I would just rough up the plywood and steel with coarse sandpaper. If you foam roller the epoxy the coating will be evenly distributed.

The torsion box is made of 1/2" MDF, not ply. Wondering about the integrity of it.

EJWash

Originally Posted by CafeenMan

I haven't been keeping up but how many holes are you talking about? Those holes sound really big to me. I'm thinking tiny spikes like 1/16" diameter by 1/8" deep. Epoxy isn't that strong. A 1" x 1/8" epoxy rod will only be good for about 1/8" of the depth. Epoxy breaks pretty easily.

Not all is going to be straight epoxy. First coat on both the steel top and box will be straight epoxy. Then one coat of epoxy with filler (West #407) mixed-in.

I'm probably getting a bit paranoid about the bond. Just thinking out loud. The top of the box has dozens of dimples from where the air nailer sank the brads in. More than likely the vacuum pressing will hydraulic epoxy into them.

LoNslo,

we are talking pretty thin coats of epoxy, right?

EJWash

Yes, thin coats. That's the beauty of the foam roller--just the right coating thickness.