Does anyone have any hints for heat-forming acrylic for taillight lenses? The problem I'm having is getting a consistent, smooth curve that matches the contour of the bumper guard so that I can mount them flush. Hopefully you can see what I'm talking about from the pictures. I tried casting these first, but kept getting all sorts of bubbles in the casting. Then I found some deep red acrylic (I have it in 1/16" and 1/8" thicknesses) that looks killer when it's lit using the little diffusers I bent for a backing. But getting these formed properly is driving me to drink. Right now I'm just using a heat gun, bringing the heat up slowly to about 120 degrees or so, then slowly bending them around a form and holding them in place. Any hints would be appreciated. Curt
What's the issue your having with using the form and the heat gun? If your a little more specific we might be able to trouble shoot it better
The problem is getting a consistent curve in the lens so that it matches the contour of the bumper guard. If you look in that last picture, I'm having trouble getting a smooth bend from top to bottom on the lens. On the 1/16" material (shown) there are ripples in the face. With the 1/8" material, the face of the lens is pretty consistent but the top and bottom edges curl out from the heat.
I don't have any real advice for you, Curt, other than keep at it and don't get frustrated. The reason I even posted at all is that it made me think of the future possibilities of 3-D printing and how this might be accomplished with that technology. Good luck, hope someone with better advice than mine posts it here for you.........Don.
You might have some luck by taking the ones you have bent already, and laying them over the form in an oven and turning the heat up a bit. Once the acrylic softens and takes shape, pop the oven door open so it cools quickly, before the acrylic has a chance to sag or flow. Getting some heat into the form will help. The form is acting like a heat sink, which is probably drawing the heat from the acrylic and causing the irregular bends.
Curt - you have a lot of shaping trying to occur there, with a flat sheet. Realistically, it needs to shrink along the vertical sides to not kink. I think pouring is still the best bet though. Is there anyway you can pull a vacuum on the mix prior to pouring? That would eliminate a lot of the captured air.
I think you need a male and female form, with allowance made for the thickness of the material between them. Heat the plastic in an oven until pliable, and press between the two forms. Keep pressure on and let cool completely before removing from forms.
The heat gun and inconsistent temp is the problem. A few degrees difference make the hotter part softer and bend before the adjacent parts then you see a kink instead of a smooth bend Put the plastic in an oven and heat evenly. A male and female form surely would give you the best results but I'd think you can get it by hand with even heat.
When you were trying to cast them did you pour the resin through a paint strainer as you filled the mould? That will help eliminate the vast majority of the bubbles.
Agree on male female form. Before you go there, let's see the male form, does it match your contour exactly? I'd try more heat and an accurate male form. Make your material a little large and trim to final shape, might get enough heat in it that the edges distort to get the shape/droop over the form. Never done this operation, just spent some time in plastic shops, throwing out ideas from what I've observed.
Most of the custom guys I know when making a tail light lens heat the material in the oven then lay it over the form that gives them a good consistent heat overall.
Curt, I have used a home-made thermo forming rig (oven/aluminum frames/ABS sheet plastic, vacuum, etc) to make small air box covers, seat pans, and other parts for motorcycles. Here are some notes I picked up. Make a wooden buck out of balsa wood that fits inside the bumper guard. (basically make a male form). Use an oven as others say, to get consistent heating. Sneak up on the heat you need. Putting too much heat in the part will ruin the clarity of the lens. Cotton gloves with leather gloves over them work ok, but if you get the temp too high you risk marring the surface of the lens. With a small lens, you can heat it with an infrared heater if it is size properly and hung horizontally over the top of the material to be heated, as long as it doesnt have a tip over switch. Cool with air from a fan or some other source.
I had a project that required a toilet tank with a clear window. I draped formed the acrylic in my kitchen, the tank had a slight compound curve to it. This was 1/4" acrylic worked fine....made a frozen pizza the next day. Take your time heating it start with very low heat 120-150 degrees and watch the acrylic for movement, same when cooling as they may spring.
here is a link to a post by slddnmatt on putting lights in bumper guards. It was a tech week post from several years ago. http://www.jalopyjournal.com/forum/threads/tech-week-bumper-gaurd-tail-lights.566437/
Once you get it figured out, make some extra while you are at it, in case you ever need to replace one.
All good info - thanks. I'm going to start by trying to heat it in the oven to even out the temp and see how it goes. If I keep striking out I may try casting again. I did use a strainer when pouring but no vacuum. I'll post again with progress pics. Or pics of me smashing my jacked up lenses with a hammer. Whichever comes first.
I've done vacuum forming with PETG (the plastic that soda bottles are made from). I don't know if you can get that in red though. If so, make the form, then use a shop vac to suck the plastic down over it, so you get consistent results. Use an oven for heat, as others said. A simple vacuum forming rig is pretty easy to build with some supplies from Lowes. For casting, the bubbles can be removed by pulling a vacuum on the resin before pouring, or by crushing them by curing the part under pressure. I cast a lot of parts here. Mix the resin with your colour dye. Pour the mold. Put the mold in a pressure pot hooked to your air compressor and run it up to about 70 PSI. Let it set according to your resin's directions.
Did you ever get this figured out? In the pic i saw... I think your form wasn't shaped the best. I'm experimenting with this as well.
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