patrickg
Veteran Member
JD, I'm not sure what low temp heat forming does to polycarbonate but if it doesn't reduce strength or do anything worse that put optically objectionable waves in it, you might be able to DIY (Do It Yourself) as you certainly could if you used Plexiglass. If it isn't in front where you look through it to drive at higher speed a few waves might be tolerable. I'm assuming that it is a simple curve, i.e. bent in only one direction, like if you picked up a 2x3 ft sheet of thin metal and flexed it a bit.
I also assume that you have a matching window that isn't broken. If that is the case you could use it to make a pattern. I would trace the top and bottom curves onto wood and carefully cut them out with a jig saw or similar and sand smooth. Next attach some thin sheet metal or realy thin plywood that will conform to the curved shape of the wood to make a form in the correct shape. Drape the plastic over it. Here is where it gets experimental...
Since I further assume that you don't have an oven or kiln big enough to hold this stuff and probably not a semi-pro paint curing heat setup, you would use flameless heat sources like heat lamps (careful if you use a hot air gun like the ones for striping paint) to uniformly warm the part where the bend is desired and the part next to the bend a bit less. Do not rush it,let it heat up gradually till it gets soft enough to relax and conform to the bend. Once bent, remove heat source and let it cool on its own (no chilled water "tempering" baths).
Oh yeah, if I were doing this, since I usually don't guestimate things like this real well, I would make the piece oversized a bit and cut it down to size after bending. Course sanding with mechanized tools and patience work for me. Go slow as the sanding will heat, and if rushed, melt the plastic making a mess out of the abrasive. Do not drill polycarb or plex with a wood or metal cutting bit. There are bits, expressly made for this. They are not expensive nor made of exotic alloys, they just have different angles so they don't bind or try to "thread" themselves inito the hole and ruin your efforts. I usually bend first and drill second, again because I don't have much experience in knowing where the hole will end up after the bend. Ever drill thick lead or copper? Takes special bits as regular bits try to thread into the material and jam. Plastic like polycarb or plex will do that and shatter the plastic or at least make a "star" crack pattern around the hole.
If you have access to a saw with a plastic cutting blade, practice on some scraps of the material you will be using and if successfull you could save time and effort cutting the thing to a fair fit before sanding. There are "special" plastic cuting blades for "saber" saws (scroll saw, jigsaw, whatever you blokes call 'em) as well as for table and other circular saws. Like the bits, not expensive and work way better than regular blades. I still remember tha time I got some 3/4 inch think plex (military surplus) and tried to make speaker enclosures out of it. Cut with a table saw, it melted as it went through the blade and welded itself back together behind the blade allbeit with a heck of a surgical scar. Tried hand held saber saw, same results. once cut, even though welded back together I could break it on the line but got a rough R O U G H edge. What looked to be simple became a night mare.
I suggest trial cuts and sanding on scraps before chancing your freshly bent window. Hope I didn't make this sound hard, it really isn't. Remember to check up on polycarb to see if it "likes" to be bent as easily as plex. Plex would work but does scratch and breaks more easily.
Good luck,
Patrick
I also assume that you have a matching window that isn't broken. If that is the case you could use it to make a pattern. I would trace the top and bottom curves onto wood and carefully cut them out with a jig saw or similar and sand smooth. Next attach some thin sheet metal or realy thin plywood that will conform to the curved shape of the wood to make a form in the correct shape. Drape the plastic over it. Here is where it gets experimental...
Since I further assume that you don't have an oven or kiln big enough to hold this stuff and probably not a semi-pro paint curing heat setup, you would use flameless heat sources like heat lamps (careful if you use a hot air gun like the ones for striping paint) to uniformly warm the part where the bend is desired and the part next to the bend a bit less. Do not rush it,let it heat up gradually till it gets soft enough to relax and conform to the bend. Once bent, remove heat source and let it cool on its own (no chilled water "tempering" baths).
Oh yeah, if I were doing this, since I usually don't guestimate things like this real well, I would make the piece oversized a bit and cut it down to size after bending. Course sanding with mechanized tools and patience work for me. Go slow as the sanding will heat, and if rushed, melt the plastic making a mess out of the abrasive. Do not drill polycarb or plex with a wood or metal cutting bit. There are bits, expressly made for this. They are not expensive nor made of exotic alloys, they just have different angles so they don't bind or try to "thread" themselves inito the hole and ruin your efforts. I usually bend first and drill second, again because I don't have much experience in knowing where the hole will end up after the bend. Ever drill thick lead or copper? Takes special bits as regular bits try to thread into the material and jam. Plastic like polycarb or plex will do that and shatter the plastic or at least make a "star" crack pattern around the hole.
If you have access to a saw with a plastic cutting blade, practice on some scraps of the material you will be using and if successfull you could save time and effort cutting the thing to a fair fit before sanding. There are "special" plastic cuting blades for "saber" saws (scroll saw, jigsaw, whatever you blokes call 'em) as well as for table and other circular saws. Like the bits, not expensive and work way better than regular blades. I still remember tha time I got some 3/4 inch think plex (military surplus) and tried to make speaker enclosures out of it. Cut with a table saw, it melted as it went through the blade and welded itself back together behind the blade allbeit with a heck of a surgical scar. Tried hand held saber saw, same results. once cut, even though welded back together I could break it on the line but got a rough R O U G H edge. What looked to be simple became a night mare.
I suggest trial cuts and sanding on scraps before chancing your freshly bent window. Hope I didn't make this sound hard, it really isn't. Remember to check up on polycarb to see if it "likes" to be bent as easily as plex. Plex would work but does scratch and breaks more easily.
Good luck,
Patrick
