just curious, has anyone experimented with the use of plastic (acrylic / perspex???) side panels????

maybe even to make a slightly more rigid bonnet

the stuffs quite easy to work / fold (hot air gun should do it (with patience) )

it comes self coloured

and could be bonded with Sikaflex etc...

plus it cant oxidise / rust

seems to have many plusses

just wondering are there any reasons no one seems to be using plastics that i may have over looked.....

suggestions / ideas v. welcome

Bloody expensive?
Scratches easily?

I was talking before about using Acrylic sheet for windows and body panels, but nobody seemed to be interested.

I have used Acrylic in a number of non-automotive applications and have become quite versed with it if I may say so myself...

When sculpting compound curves, it can be quite tricky, and unless you come close to liquifying it or you have made a press you will never get it so do some curves. For a shape such as the bonnet / hood, you could probably get away with a wire or foam mold in the shape of the desired panel, lay the sheet of roughly cut plastic overtop and slowly work at warming it up until it starts to curve to the mold under its own weight. I find that using the hottest setting on your hot air gun and staying a good distance away allows for more material to be heated at once, allowing more even temperature changes throughout. You must be careful not to overheat parts, and it is better to go too slow than to rush it, because you can easily create bubbles or a milky discoloration in the panel. Also keep in mind that you should apply heat to the OUTSIDE face of the curve, or in other words, only to the convex side. You can form the sheet with your hands if you are wearing a pair of CLEAN and THICK gloves - new welders gloves are ideal, but a new pair of gardening gloves will also work. Once you have achieved the desired shape, allow the sheet to cool down a slight amount and observe the activity of the panel. The panel will most likely try to straighten out a little bit, and let it. It isn't a bad idea to expose the entire surface of the working piece to heat, it will harden as it cools and cause the surface to be slightly more scratch resistant than before. You can always go back and curve it more, but if you overheat it once there's no going back. If you are extruding any pieces, be extra careful to maintain sufficient thickness across the panel, as plastic sheet has a tendency to draw itself out more than you want it to. After everything is nice and cool (do not try to accelerate the cooling process by dousing with water or blowing cold air, as this can cause stress cracks or other deformities) you can cut it with just about any scroll or jig saw. Before you whip out the blades, however, run a line of 2" wide painter's mask[ing tape] along the edge of where the panel is to be cut. This will ensure a nice straight edge without scratching the surface. After cutting you can remove the tape and sand down any rouch edges using a medium grit sandpaper rather than a file, unless you want to take out big chunks. I've done bevels and tricky engraving with a woodburning pen in the past, but it demands patience.

Various thicknesses and compounds are available for different applications, but I prefer Acrylic or "Plexsctuct" sheet over Lexan or Perspex when it comes to introducing curves into a flat panel. I find the Acrylic to be more predictable and forgiving when cutting than lexan, which will sometimes shatter.

As far as durability goes, a heat-formed panel of acrylic will develop a harder surface than it has off the shelf, but it can still be susceptable to stone gauges or key scrapes. For a piece that is mostly parallel to the direction of travel, such as side panels, you should be able to get away with painting them in the inside if painting is desired. This is an R/C car modeling trick, which will ensure that the paint always has a lusterous shine and is protected from scratching. For other panels like wings, painting should be done on the outside, since ANY abrasion to the wheel side of the wing will strip paint better than your mother's liver and onions! If you use a good automotive paint, it should create a fairly hard and tough layer of pigment that will provide additional protection from scratches. Crylon Colors now makes a spray paint that chemically bonds to plastics, which can produce very pleasing results on acrylic.

Unless your engine bay is very well cooled, I would not suggest using acrylic sheet for the engine cover without some sort of insulation attached to the back (easily done with the right double-sided tape, pop rivets, or adhesives as long as any painting is to be done on the top side). Acrylic will usually start to yeild its form at around 200F or 90C, so if your engine bay temps come anywhere close to this, beware.

Lexan or Perspex will be more scratch resistant than "acrylic" sheet, and is much better for windscreens and side windows than softer acrylics. Even though it may not last as long as automotive glass, it is much cheaper and can easily be replaced, especially if the desired panel is a flat surface. Lexan is used in many of the FIA windscreens as well as the ALMS, JGTC, BTCC, and a number of other racing series' cars for its light weight, durability (a rock that would smash a glass panel will bounce off of a lexan or acrylic panel), and economy.

All of these materials can be found at most hardware suppliers. In the US, a 3'x5' acrylic sheet that is .1" thick will usually run $25 (or around 15 pounds) at Home Depot. The most important thing that you can do is to experiment - exploring the limits of different materials, how thickness effects integrity and molding, and various methods of shaping may take some time but you'll be glad that you have the experience...

I'd be more than happy to answer any questions you have about forming materials like this, and I'll be sure to keep the board updated on my progress (of course, I'll have to build my car first!)

Good Luck!
-MR

On some of the cars I've built, I've used 0.9mm and 1.2mm polypropylene sheet. It has a "leather" texture on one side, and is plain on the other. It's available in black, white and primary colours.
It's very tough, and flexible, yet will withstand direct hits from rocks and stones. The main problem is, it looks fine on cool days, but on hot sunny days, it expands slightly, and looks a bit baggy!
Acrylic doesn't like sharp blows, and will crack.
All plastics will show scratches, even polycarbonate.
I don't think there is a readily available plastic that will withstand the heat from the engine/exhaust without distorting/discolouring.

I totally agree with Rorty - Acrylic expands something like 5 times more than glass does, so you'd have to leave gaps or curve it in a way that allows the whole panel to inscrease and decrease size. Another thing is that painted acrylic will generally absorb a lot of heat. Even on a mild day, if the sun is bright you will wind up with some droopy pieces.

All in all, if plastic is used in small sections on the body work in places away from road debris where tolerences are forgiving (Trunk/boot lid, mirror covers) it will work pretty well. Any part that is going to be close to your engine or exhaust without extensive insulating will leave you with less than thrilling results.

Lexan or Perspex can still be used for windows, and should serve you well. Do save the form that you used, however, becasue there most likely will come a time where you will have to replace a panel or two.

Fiberglass may be your best bet for show-quality results, though. In the long run, it will probably save you a good bit of time, money, and fuss.

Definately do experiment though! If it were me being told to use fiberglass instead, I would feel like maybe I left something on the table... Learn the materials and adapt them in a way that will make you proud of your work.

-MR

I saw a Lotus 340R which had a one piece polycarbonate body. The guy got the idea from the radio controlled car his son had.

I don't remember the amount, but it saved an incredible amount of weight over the glass fibre body, even though it was something like 5mm thick. Looked great too as it was unpainted - you could see all the bits which were usually hidden (not much in a 340R!)

Andy, I've seen that car too, at a recent hillclimb. Most impressive......

fibreglass, tho lower weight per mm, will need to be thicker than alu to have strength.

Using alu is so much easier - read my site and the bit on fibreglass if you want to know the hassle involved.....


atb

steve

I dont want to put anyone off fibreglass - its very rewarding to take a finished part from a mold after a lot of work.

However, alu for the sides is straightforward - anything else is masochism!

atb

steve

thanks for the info, it never fails to amaze me, the amount of knowledge within this community.

taking expansion into consideration looks like i will still go down the alli path...

Like Rorty, I've used polypropylene sheet with a texture on one side, but for the interior panels. I know Ron says to use hardboard covered with vinyl, but it'll get wet and soggy in no time. HDPE is light, waterproof and looks fine. HOWEVER, I installed the driver's side on a cool day, and now we're having a heatwave it looks baggy. By contrast I installed the passenger side outdoors during the current warm spell, and once I'd moved the car back into the garage it became as tight as a drum. I'm going to re-do the driver's side as a result of this.

Couple of photos at the bottom of this web page.

Cheers,

Eddy