Straightening a 1340 type fin can - Estes Shooting Star 1435 content
 

I'm not sure this is a question of building technique so much as restoration/rehabilitation of a part, but here goes.

I am a big fan of the Enerjet division 1340 derived models of Centuri and Estes. This fin can is part of a Shooting Star 1435 kit, I believe the only 1340 model that was sold inside a Range Box - and perhaps this is why. The fins don't fit in the closed box without taking on this squashed/curve arrangement. The not-in-catalog kit is I think from around 1986, along with the Discovery model, so chronologically in that gap between the Challenger II and Maniac.

I put the fin can into a 4-fin jig, clamped tightly at room temperature for a few months, and that seems to have accomplished nothing. My next thought is to (carefully) add heat to the process, and I am considering immersing fins and jig in just-boiled water. Or a heated bath a lower temperature. Another possibility might be some degree of hair drying warming - though that is harder to control of course.

At the moment, the fin can is the toughest/costliest of the 3 main components (vs. BT and NC) to get if you want to build a proper 1340/Phoenix Bird or whatever. Yellow is the easiest color to get, but still I'd like to be able to build a Shooting Star with the original parts.

Anyone out there have some experience in straightening some of these molded plastic parts, fins or otherwise?

Thanks in advance.

I don't think a hair dryer will get hot enough.
I would try a MonoKote-type (RC aircraft covering) heat gun

Heat it up really good in the fin jig.
Then shock-cool it in a freezer.

So much much hotter than 212F too? My fin jig is the plastic Estes one, which probably also would begin to deform if I reached the right temperature. Maybe I can come up with some metal method, blocks in a vice where I could at least heat/fix 2 opposite fins at a time.

My heat gun does a nice job of softening, deforming and melting PVC pipe, which is of course much thicker. It's just a challenge to stop short of real damage.

Does it need to stay original? If not then perhaps use contact cement to attached pieces of 1/32” plywood to each surface of each fin, use braces to flatten them down, and then shape the leading edges accordingly.

I have straightened Alpha III fins by dipping just one fin at a time in water that was just boiling for about 15 seconds, then carefully bending them the other way. It may take a few tries but should work.

Ah, thank you. This gives me some idea of how hot for how long may be needed, if the fin thickness and plastic are similar.

For the Alpha III plastic, it is barely hot enough but does work. Good luck!!

The 1340 fin can's fins are about the same constant thickness as the Alpha III's fins are at the root (they taper in thickness). So maybe hot water will work....

I need to remember this the next time I come across a warped Alpha III/IV/VI or relatives.

I was just looking at a 1340 clone discussion on YORF, and one poster contended that the fin can is polystyrene.
Searching polystyrene, I get:
Melting temp: 410-480F
Typical Injection Molding temp = 100-150F

So this makes me nervous about using anything near boiling 212F off the bat. I think I may start off with a water bath near the low end of the molding range, and go from there. I'd prefer to sneak up on the optimal temp for some gentle remolding, if possible. I have an ultrasonic cleaner that I believe can reliably maintain temps in that range. I think with water immersion I'm likely to get a more uniform effect, and avoid any surface cooking/blistering that can happen with heated air heat gun / hair drying.

Thanks all for advice / guidance on this.

It’s likely the injection temp given is under pressure so 150 degrees will likely do nothing at normal pressure, but I respect wanting to preserve this rare fin can.