When I use tenax to join fuselage halves, sometimes I get a sort of phantom seam. The plastic oozes out just like it should, but when I sand it off with a flexifile and prime it, under certain lihgt conditions a very slight depression can be seen running down the length of the fuselage, almost like the tenax shrunk the seam. Any ideas on what causes this and how to fix/avoid this problem? [%-)]
Thanks
It looks like it shrank because it did.
Tenax and similar solvent cements work by dissolving the plastic polymer. When the polymer resolidifies, it’s structure is more porous and open, initially, then it collapses slowly over a short period of time. The collapse is a plastic deformation (which is why the stuff is called plastic).
The easiest fix is to let the seam stand overnight before you sand it. You can also wait to do the final sanding until the next day.
The easiest prevention is to not use quite as much solvent, or not press the seam too hard. Pressing the seam hard, or pressing it too late will cause a rebound effect, especially with larger, more flexible parts. The plastic adjacent to the seam flexes when you press, then deflexes when you remove the pressure—and pulls the softened material in the seam apart like taffy. It may still form a ridge, but when the plastic collapses, it will be thinner, and sag into the seam.
Believe it or not, I learned this when studying crustal deformation and mechanics as a geology student. Deep in the crust, rocks behave like plastic.
Interesting Tri.
I know I’m smarter now.
Dont tell my wife, she would laugh.
Mike
Triarius must have stayed at a Holiday Inn Express recently…[:D][8-][:-^] Sorry, I just couldn’t resist.
Ross, I learned something today…thank you. I am a Tenax user and currently putting together a large, soft fuselage…your points will come in handy.
You’re welcome…even Devil Dawg…[sigh]
[;)][(-D]
ah. Thank you Triarius. I greatly appreciate the help.
Triarius.
That was a great explanation for a phenomenon that I have also wondered about. Thanks for taking the time to explain it.
Darwin, O.F. [alien]