Now has suitable forms for all three sizes.
Size A - vform_r1_1.stl
Size B - VisorFormMedium_r1_0.stl
Size C - VisorFormSmall_r1_0.stl
These are vac forms to produce a PETG visor ( from 60 thou sheet ) for the Halo 4 Helmet Size A, B, C - see sources.
You need 2 of these on the 11 by 17 vacuum bed, to ensure the webbing only occurs between the back faces as per the photos.
This method turned it from a struggle to manipulate the plastic with bad webbing occurring to a single operation of directly pulling the plastic down on the vacuum and allowing it to form as it sees fit.
There is now no webbing on the critical faces.
Note the of the two forms
1: Painted, 2 coats primer / filler, two coats metallic color ( because I could ) 2 coats clear enamel from duplicolor rattle cans.
2: Plain straight off the printer at standard 0.2 mm resolution, no finishing.
Both formed very well, but the layers were just visible on the unpainted instance, whereas the painted version was very clear with no artefacts, so recommend painting forms by default.
The first time I pulled on the painted instance some of the clear coat adhered to the visor, I now use pledge spray on the form and the bed seal to help release the mold.
Both forms extracted from the sheet with a little compressed air into the edge and no marring or loss of clear coat.
Built a hot box and vac bed suitable for the form size, approx 11 x 17 inches.
Note the 1.1 form is mostly hollow, has grab handles for extraction and screw points to insert screws that will sit in the vac form bed holes to keep everything stable when in use, on a 1 inch matrix.
rendered image shows areas to be preserved in red and gold, so you have the visor, a surround that mates to the inside of the helmet, and the magnet mount points.
Place magnets on rear of visor to attach to helmet against magnets embedded in helmet visor edge.
Form includes overlapping edges so visor sits well and sealed right around.