Before sending your helmet casting off for chrome, make sure to sand the exterior and fill in any deformations that may have occurred during the casting process. This will require primer, and possibly thin coatings of filler putty.
Also make sure to have all of the mounting points for your subvisor and electronic components sorted out before this final coating. You don't want to be trying to glue or dremel things on a chromed helmet and risk accidentally scratching the expensive surface. Things to consider: Visor cutout, nose holes, ear mounting points, subvisor mounting points, and any mounting pads on the inside of the helmet for Arduino boards, voltage regulators, or wiring connections.
Contact your chroming service and ask what their recommendations for preparation are before sending your helmet off. Chroming non-metal pieces is a specific and very finicky technique. I paint my helmets with Krylon primer and wetsand the finish to 2000 grit paper, but each shop will vary.
A couple of places which can do this service:
Creations n Chrome
Coat of Chrome
Both have chromed my Daft Punk helmets before, and with excellent results.
The process for prepping a helmet casting will be very similar to how you prepped the master sculpt for molding earlier. After a cast part has been pulled, spray it with primer to reveal any dents or imperfections in the cast plastic surface. Fill these with a skim coat of bondo or other polyester resin filler. (pic 2
At this point I decided to glue the base for my ear pucks into place. After talking with my chrome shop, they said that having the outer "dish" shape of the ears separate for the chroming process would allow for a better finish, so those were left unattached - talk to your shop first to see what will work best, they may want the helmet with no ears on at all, in which case you may need to figure out a way to have these removable and held on with screws instead.
If you're gluing the ears in place, tack the base of each ear cylinder in place with small spots of hotglue to hold them in place. This is just to get the position right while you secure them with a more permanent adhesive. Once the placement is satisfactory, secure them in place with 2 part epoxy glue, letting it cure overnight. You may need to go back and sand some of the glue joints smooth - some evidence of this can be seen in pic 3
It may take a couple passes to get everything smooth. Once you've got all the imperfections filled in, spray the helmet with 2 more coats of primer (pic 4
). Allow this to dry for 48 hours, then wetsand the primer to a smooth finish. As with the master sculpt from before, start with 400, then progress to 600, 1000 then 2000 grit paper. Allow everything to dry overnight, then box it up and ship it off to your chroming shop of choice! (pic 5
I also placed a brace in the visor area for shipping, to make sure nothing was damaged in transit. With this much work, better to be safe than sorry. Materials needed:
- Spray primer (I prefer Krylon "Ruddy Brown")
- Bondo or similar polyester filler
- 2-part Epoxy glue (I prefer Loctite brand)
- Hot glue
- 400, 600, 1000, 2000 grit sandpaper
- Hot glue gun