Whilst awaiting my RepRap extruder to be delivered from Germany I've re-visited vac forming.
I made a new clamping frame from 1.2mm steel, and used M4 dolts + wingnuts to fasten it:
I also drilled some more holes in the bed of my vac former, and attached sealant gasket gasket to the bed to improve the seal:
I made some molds by casting plaster of paris into the acrylic domes I got from Milestag:
Here's the molds after they had set:
Unfortunately, this was no more successful with 2mm acrylic than it was with 4mm. The problem is that the acrylic is not sufficiently flexible to be sucked completely into shape by the vacuum. The plastic failed to form around the vertical edges of the mold.
So I decided to try another approach. I constructed this phallic object:
The idea being that I push the frame down around the mold, I should be able to exert more pressure than the vacuum.
Here's the result:
And after cutting:
Which is almost what I want. To improve I need to:
1. Change the mold so that the acrylic can't fold underneath the mold. I'm thinking of a wooden pole with a rounded end.
2. Make the frame smaller. I used an A4 frame this time, but to make just one dome it's a bit too big.
3. Cut the dome out with a power saw. I used a hacksaw and cracked it.