17 May 2009,
Now that the chamber has been filament wound it is time to make a lid. If you haven't seen the winding page have a look before reading further - see full chamber-winder3.
The lid project starts with a rim being moulded in the mouth of the chamber. This was hand laid fairly carefully because this will become the air tight seal.
|The neck of the chamber was cleaned up by grinding off the rough glass at the join. This was puttied with an epoxy glass filler and sanded smooth. A layer of epoxy was painted over it to seal it. The area was covered with a release agent and a laminate was hand laid starting with surfacing tissue and followed by two layer of chopped strand mat.
|The new glass work extends about 40mm along the inner wall. Most of the new glass on the collar will be trimmed off and discarded. The man purpose of this collar is the align the lid. I expect to keep about 20mm of it.
Attempt one at the lid rim was a failure. One patch didn't release from the chamber and I'll be going it all again using new release agent. We are in for a week of wet weather so I may have to wait a while.
Take two of the lid project went much better. It is basically the same as before except I sprayed on several coats of PVA release agent and left it over-night to dry. It was still very difficult to remove but did separate intact this time.
|Here is the rim after a little bit of trimming.
I used the same inflated ball that I used to form the chamber end to form the domed shell of the lid. I burst one ball because there was a sharp dag of epoxy inside the chamber. I was concerned the temperature might drop and cause the glass to wrinkle but it set just fine. The plan was to add some more air to the ball if the ball began to contract in the cold.
|Here the rim is back in position and masked with plastic tape to prevent resin gluing it to the mouth. The ball's plug was left un-glassed so it could be deflated afterward. About two layer of CSM were used.
Another couple of days.
I let the resin cure for a couple of days because real work got in the way. Apart from a few small holes were the dome meets the rim it came out quite well.
|The shell of the lid sitting on top of the chamber.
The hole in the centre was patched and the junction of dome and rim was puttied to seal all the holes. The shell is not very structural, it only has to be strong enough to hold its shape when the thicker layer of structural glass is curing.
|A trial fit of the lid.
Because it is still lacking a handle - the lid was hard to get into position. Once in place it is fairly air tight even without having a gasket fitted. I'd guess this thin glass would only hold a few hundred millibars before failing so I didn't apply much pressure. There was still enough pressure to make it apparent I have a small air leak about 200mm from the tip. This was no surprise and I think it will be trivial to patch.
More time passes.
The leak wasn't trivial. I have to wait for the lid to be ready before I can see if my second attempt at a patch worked.
Today I added the rest of the glass to the back (that is the side which is inside the chamber). Twelve layers of thick woven glass cloth were used. This laminate is a bit over 6mm thick. Every second layer was rotated 45 deg to others. The total thickness is around 9mm.
|The lid under vacuum ready to be resin infused.
The vacuum infusion
went almost totally to plan. The only annoyance was resin did find a path to the vacuum line (probably via a crease in the bag.
This was the first time I used spiral binding as the vacuum channel running all the way around the job.
1'st of June.
It works!. The chamber has some leaks so I've only managed a fraction of a BARG so far but the lid fits and seals.