Well, C9, you’re right, of course. This is, after all, a forum, and two guys B.S.ing doesn’t exactly constitute a forum. I’ll put down some random thoughts pertaining to acrylics and to Remco’s project.

First, m falconstein is right on. Remco needs to call in the pros.

Remco asks if his present hood might be used as a mold. Well …… conceivably, I guess, but we’re not talking fiberglas here. A piece of Lexan or acrylic would have to be really big to make a hood for an Imperial. It would have to be heated to a temperature of 300 degrees (plus or minus) then carefully and expertly placed on, and held to, the hood/mold. Male molds are successfully used in some applications. Cessna Citation windshields are formed on male molds. A sheet of stretched acrylic is hung vertically in an oven and heated at 300 degrees until it reaches the proper state of softness, or flexibility, or “rubberyness”. Whatever. It is then rolled out of the oven and is grabbed by four big dudes wearing asbestos gauntlets who quickly move it to a big sort of mushroom shaped tool that has been covered with a very fine textured felt. They carefully place the sheet on the tool and pull down hard on the corners and hold tension on it for a few moments until the material begins to harden. When the part is cold, they bandsaw it to a rough shape. They then put it into a fixture and use a router to cut it to the exact shape. The system works for them, but to try it for something as large as an Imperial hood could be challenging!

Our friend m falconstein utilizes vacuum molding in his business. This is the best and most used system for items with compound curves. Simple curves, like maybe an airplane cabin window, can be formed on a drum the same size and contour of the window. Usually vacuum is applied to hold the plastic snugly to the drum or tool. A Learjet windshield is a curved flat piece of stretched acrylic, but I’m not sure they use this method.

Stretched acrylic? Well, acrylic sheet comes in two flavors. “As cast” and “stretched”. The stretching process is interesting (at least to me). The acrylic comes in a big slab about six feet square and six inches thick. It is placed horizontally in a machine and pneumatic finger-like clamps are attached every few inches around the perimeter. Then heat is applied and the clamps pull outward and literally stretch the acrylic block until it is the desired thickness.

Why stretch it? During the stretching process the molecules … no, that doesn’t sound right … the polymers, maybe? …. I don’t know, are caused to realign themselves and make the product much stronger than it would be were it not stretched. This way a part, say a window, can be much thinner and therefore much lighter, and at the same time will be stronger than as-cast. Lighter weight is big time important to an airplane company.

Back to Remco’s Chrysler. A piece if cast is much less expensive than a piece of stretched. A hood made of cast would be thicker and heavier, and that ain’t necessarily bad. A man driving an Imperial may not be too concerned about weight, for one thing, and a thin hood would be likely to flex and flap up and down when he drives, because I doubt that he will want to keep the ugly supporting stiffeners that are under his steel hood. The object is to show off his engine under a see-through hood, isn’t it? He might do well to cut the largest tastefully designed holes he can think of in his present hood (without making total scrap of the hood) then firmly installing some thick (half inch or so) Lexan or cast acrylic windows on the inner surface of the hood. That way he could retain some of structural integrity he would lose when he cuts out that reinforcing support metal.

Well, C9, I told Remco I could probably tell him more than he really wanted to hear on this subject, and I’m sure I have done so. I hope everybody doesn’t put me on the “ignore” list because of it.

Jim