09-02-2012, 08:29 PM
(09-02-2012, 03:23 PM)Rickabilly Wrote: Of course the other way to dome the plastic is to vacuum form it which is far easier than you might think on parts in this size range. You can do this for up to 10mm or 3/8" acrylic sheet just depending how thick it is you might need more heat soak time or pressure, I recommend just 1mm as once it is domed it gains a load of strength and it's easier to cut and trim.
1, Get three square pieces of any metal plate around 6mm or 1/4" thick and each big enough to leave 12mm or 1/2" all round the lens, so a three inch square plate for a 2 inch diameter lens
2, stack the three plates up and drill a 6mm or 1/4" hole in each of the corners,
3, set two of the plates up in a four jaw chuck and bore a hole through the face the same diameter as the inside diameter of the bezel ring,
4, take the third plate and drill a hole through it to hook it up to a vacuum/pressure source, in something this small your vacuum/pressure source could just be a large plastic syringe,
5, cut a disc out or perspex, acrylic, plexiglass or whatever else you call this kind of plastic sheet don't use lexan as it is fiddly on temeratures and water content when heat forming.
6, clamp all the pieces together, add a little sealant between the middle plate and the plate with the vacuum source hole, just enough to seal you don't want it or any fumes from it to get in contact with the acrylic sheet, let the sealant dry before starting the forming process, alternately cut a gasket out of cereal packet card or heavy paper.
7, pop the whole thing into a saucepan full of cold water and bring to the boil, hold it at boiling for a few minutes, then pull it out,
8, wearing gloves and making sure not to touch the plastic at any time push the syringe into the vacuum hole and suck some air out of the chamber behind the plastic, just enough to start doming the plastic, alternately you can add pressure with the syringe, it just means it'll bubble out not in,
9, when you have the dome where you want it hold the pressure constant and plunge it into cold water and hold it there for three to five minutes, less for thinner plastics, more for thicker plastics.
And there you have it new domed lens' for any guage costing pennies + a little work
Thanks Rick.Ed