Slightly warped resin hood

[cobraman]

I bought a resin 1962 Ford and the kit is pretty nice, clean pieces. However the hood is a little flat and I need to add a slight curve. I tried the hot/warm water bend and put in cold water and it did seem to work but later when I checked it it seemed to have returned to the original flat condition. Any other method to try ? Thanks

[Slick Shifter]

I am no fan of rosin at all.

That said: Rosin typically cannot bend metal.

I reckon that you can figger out the rest.

 

 

[Ace-Garageguy]

Correcting or warping fully cured composite or polymer parts is a tricky business.

Plastics generally have a "glass transition temperature", or Tg, above which they can be forced to change shape.

Cured plastics also have a "memory", and want to return to the shape they were molded in.

It can get complicated pretty quickly, because if the part was removed from its mold early, before full cure (or in the case of "styrene" parts, pulled from the mold before being fully cool), the plastic in question will take a "set" on its own, not supported by a mold, and can be difficult to correct.

To get most plastic parts (and resin parts are a type of plastic) to change their shape permanently, both the limits of the Tg and the "memory" need to be exceeded...and it's a crapshoot as to how hot you need to get, and how far past the desired shape you need to go to achieve the desired "springback" as the part cools. Just fyi...the Tg for most "styrene" grades used for models is around 212F or 100C...too hot to handle, obviously, with bare hands.

There's no telling what the Tg of your resin part might be...and there's just no other way to get a resin part reshaped.

I'd suggest you build a little jig that holds your part very securely, bent slightly past the final shape you want it to have. Then pour boiling water over it, slowly enough to heat it all the way through. After it's cool, remove it from the jig and see where you are.

Sounds like a PITA, and it is...but it's your only real option.

 

Edited November 20, 2019 by Ace-Garageguy

[cobraman]

Thanks guys. It may be something I will have to live with. It's not all that bad but would have liked to fix it if I could have.

[64SS350]

I always use a hairdryer, you can regulate the heat with settings and the distance from the work piece and duration of heat applied. Can also go back to tweek if need more movement, a little at a time is best so as not to crack surrounding areas. Also heat surrounding areas slightly ( ie: a body) for the same reason and also to help these areas change their memory also.

I have noticed resin tends to need way less heat than styrene, again a little at a time.

Also, if warping isn't bad, when finished with each round of heat, hit with some cool air. If working with a heavily warped piece, you can let heat come down more slowly, then maybe some cool air. Just play with it to develop the technique.

Edited November 20, 2019 by 64SS350

[cobraman]

Thanks, I can try that !

[restoman]

I have had some luck with warped hoods by over-bending the parts and binding them in that shape for several days. 

Very much like over-pulling collision damage, and hoping that when it all settles out that the shape or position is ok.

It's pretty hit-and-miss, though, and I've had to do it more than once to stubborn parts... I have found that resin is easier to re-shape than styrene.

Edited November 20, 2019 by restoman