CMR Humpty Dumpty
 

Pulled out a CMR Humpty Dumpty egg lofter that I started a few years ago (1983-ish). The reason it's been sitting in a shoe box since then is that while installing the top stage motor mount I applied the epoxy with a little too much enthusiasm and melted the styrene shroud (evidence below). I'd like to finish this to celebrate the 35th anniversary of starting the build: what can I use as a filler that will adhere to the styrene but not cause any more damage? Would Bondo work? Seems like Squadren Green/White would be too strong...
Suggestions?

CMR Humpty Dumpty
 

What great classic egglofter design! I printed the JPG attached to your post and the result came out right at 1:1. Was there any other printed materials that came with this? This design is not in the CMR section of Ye Olde Rocket Plans. Would be a nice addition.

Hey Buzz,


Huh - I thought I had sent plans over to Scott years ago - I've just sent them over. The only other sheet that came with the kit is for the generic pop lug (attached ). Any ideas on what to use to fill styrene?



S.

Bondo filler has even hotter solvents than squadron putty.
I would think you could use Squadron white or Testors Contour putty, but test them to see if they would melt it.
I think this would be a great application for Elmer's Fill-nFinish as it it water based and has zero possibility of melting the plastic. Yes, I have recommended a non-solvent product.

Good God, GH - pigs are flying and there's a Nor' Easter down belowl!!


I'd thought about F n'F, but not sure it would adhere to the plastic don't have any on hand right now, but I'll pick some up tomorrow after work and report back.


S.

Both Squadron and Tamiya Putty were meant for plastic models, so styrene is their intended material for use. Just don’t apply it too thick. I use Bondo on a variety of materials, but usually not on plastic. But it should be fine. I know Bondo Spot Putty will crack if applied too thick, and assume the others might. I’ve always applied Squadron or Tamiya sparingly. I just build up the application where I need a thicker fill.

Bondo putty has a much hotter "dope like" solvent package which would not be good for thin styrene.
Squadron, Testors, or Tamiya white putty should be fine, but I would test first as that capsule a s very thin.
Elmer's water based filler will stick, but I would "rough up" the surface to provide more "bite".

Yeah, I know pigs are flying (and it may be snowing in Hades) as I recommended a water based product.
I see the Elmer's product as having very few optimal applications, but this may be one.

Regardless of the filler/putty you choose, it's going to need at least four thin layers to fill that nasty scar. Don't try piling it on in one or two thick coats. It will not turn out nearly as well and will probably "chunk" off when you sand it due to not drying properly.

I've had good luck getting it to stick to styrene nosecones. I use some 220 grit to take all the shine off the plastic, then apply the FnF. I've never had any issues.

I've had to fix a few cones where the seam was huge, due to worn molds, I think, but was able to completely hide it.

Doug



.

I would agree with the above with the caveat that the rules change working with very thin styrene, vacuum molded parts, and such. I've messed up (melted) several CMR nose cones using Squadron putty, but I was using the green version. That might be 'hotter' than the white. At any rate, avoid using the green stuff.

Out of all the "organic solvent based" putties, Testors Contour Putty has the mildest solvent package. That is what I would try first. If still too "hot" then I would go with Elmer's. Guaranteed that won't attack the thin styrene, but has a long drying time.