Anyone re-shape (with heat?) sunglass lenses?

[Rogviler]

I found some lenses I like for a helmet but they're not flat enough to fit flush without gaps. The sunglasses are only $1 so no big deal but I won't even try if others have and it just ruins the coating or whatever, so I thought I'd ask real quick.

Thanks.

 

[Collektor]

I'd advise against it. Most sunglasses lenses, especially the cheap ones, are made out of low quality plastic that can develop cracks in the lenses when they get hot. Also heating them up to the point where they might become malleable, if there's any coating on the lenses, that can flake off.