Doin the Sport Grill Warp

[dhvidston]

Greeting!

The original sport grill on my 71 Mach is in good shape except for a raised warp on the center lower section of grill.

Any thoughts on how to flatten out a plastic grill? I've thought about clamping it between two boards and using a hair dryer or heat gun to soften it as I slowly clamp down on warp. (?)

Thanks for your comments..

 

[c9zx]

An approach similar to that worked for me. If you use a heat gun be very careful not to melt the piece. Chuck

 

[1973grandeklar]

Also be very careful anytime you apply heat to a thermoplastic. Not only can you melt it, but all injection molded parts have an inherent molded in stress. This cannot be avoided as this is part of the molding process. What could happen is heating up the part will start to relieve this stress and the part will warp even worse. Your idea of fixtureing the part is the correct way to do this. This would prevent the good parts of your grill from moving. Also keep the heat low. Not sure what the material is for the front grills, but the heat deflection temperature is usually much lower than the melt transition temperature for polypro type materials, but if this is an amorphous material, these temperatures can be very close (think butter in the frig compared to on the kitchen table).

 

[dhvidston]

Also be very careful anytime you apply heat to a thermoplastic. Not only can you melt it, but all injection molded parts have an inherent molded in stress. This cannot be avoided as this is part of the molding process. What could happen is heating up the part will start to relieve this stress and the part will warp even worse. Your idea of fixtureing the part is the correct way to do this. This would prevent the good parts of your grill from moving. Also keep the heat low. Not sure what the material is for the front grills, but the heat deflection temperature is usually much lower than the melt transition temperature for polypro type materials, but if this is an amorphous material, these temperatures can be very close (think butter in the frig compared to on the kitchen table).

Thanks for your detailed response... especially the low heat tip..

will let you know how it turns out

 

[coilwire]

Instead of using a heat gun try a hair drier. You have a more controlled heat source with it. I have used it in the past with good results.

Jim

 

[luxstang]

Not to hijack the thread but does this also work wit a warped front spoiler? Mine bows on the diver side.

 

[1973grandeklar]

Not to hijack the thread but does this also work wit a warped front spoiler? Mine bows on the diver side.

This always depends on wether the plastic is a thermoplactic or a thermoset. Typically, car stuff is thermoplastic and can be re-melted/softened. Some of the underhood stuff is thermoset and cannot be re-melted/softened.

Fiberglass that uses a hardener is a thermoset type.. If your spoiler is a fiberglass unit it will not work. However, if it is the ABS type plastic this could work.

I should note at this time, that plastic is highly elastic. That means that it will stretch, especially when it is exposed to heat. Thus you have to deal with the warp and the stretching of the plastic. Since the original part has a fixed volume of plastic, stretching means the part is getting thinner and longer. This is almost impossible to fix.

The best way to do this is to build a fixture/jig to hold the part. By the time you spend the time and money doing this, it is cheaper to buy a replacement part.

 

[luxstang]

Ok, thanks.