Blue Ninja plastic fins fell off!

[Marc_G]

Hi folks,

This was my first experience with a D engine rocket. My son and I made a Blue Ninja which uses plastic cement to hold black plastic fins onto a motor mount area made out of the same black plastic.

I used Duco plastic cement (in a green tube) and thought I had everything glued on nicely, though there was some whitening of the glue at joints.

Rocket launched nicely but did what looked like some weathercocking on the way up. No major trajectory changes. Good parachute deployment and soft landing on the 18" chute. Picked up the rocket and found only two fins on it (both in the same plane, 180 degrees from each other, not neighboring fins). Looked on the ground; found no fins there. Looked around the launch area, no fins to be seen (though, finding them on the grass would probably be hard if I had to search a big area).

My guess is they came off under thrust or at ejection and are even now resting somewhere downrange.

This happened a week or so ago; tonight the boy and I finally got around to fixing the rocket. I had another BN kit because it was cheap on clearance and I wanted to steal the body tube and nosecone for another project. So we were about to put the two new fins on after removing old glue (which mostly flaked off), and I tested the remaining two fins. They pulled off quite easily.

I removed as much glue as I could chip away (most of it), and switched to "Household Goop" which is a nice thick strong glue. This stuff exactly:

http://www.eclecticproducts.com/household.htm

Put on heavy coat into the slots where the fins go, embedded the fins thoroughly, which squeezed out a bunch, then used that excess to make nice fillets.

I hope this holds! Has anyone had similar experience with plastic cement not bonding the fins to the body on one of these rockets? I used the same Duco glue on another plastic-fin rocket and the fins are on very tight.

Marc

[Jclark]

I have had a similar problem with an Estes Astrobeam, even after carefully scraping the chrome plating off, it still managed to lose its fins. I used Zap CA glue, the second time, and they seemed to be strong. I can't say for sure if that will work, because on the next flight the motor catoed, and blew apart the fin can. You may find some useful information here also: http://www.rocketreviews.com/reviews/all/est_blue_ninja.shtml

Jeremy

[Pippen]

Hi Marc, I had the same problem with the first small plastic Estes rockets we took out. They seemed fine until we launched them and then they fell to pieces.

I just checked the specs sheet on that Duco cement and it looks like it's good for wood, china, leather, glass, metal, ceramic and paper. Not the right stuff for plastic.
http://www.devcon.com/prodfiles/pdfs/fam_tds_207.pdf

This Testor's Cement for Plastic Models or something along these lines would do the job for you. Make sure to get the red packaging. I bought the blue thinking the non-toxic stuff would be better and it didn't meld the pieces together like it should have.
http://www.amazon.com/TESTORS-CEMENT-PLASTIC-MODELS-Toy/dp/B000T3RM9K/ref=sr_1_5?ie=UTF8&s=toys-and-games&qid=1278382414&sr=8-5

[SCE to AUX]

I've had a lot of problems getting those plastic Estes fincan assemblies to hold together using normal consumer types of plastic cement. Perhaps they aren't using the usual styrene plastic here? The good old orange tube Testors glue doesn't seem to soften the plastic sufficiently to get a good solvent weld.

The only stuff I have found that works reliably is an "industrial use only" product called "IPS/Weld-on #4052 plastic cement". Available from McMaster-Carr under p/n 7352A11

[GregGleason]

If you can find it (for bonding plastic) ...

Tenax-7R (http://www.hobbylinc.com/htm/tnx/tnx100.htm)

Greg

[gpoehlein]

Hi Marc, I had the same problem with the first small plastic Estes rockets we took out. They seemed fine until we launched them and then they fell to pieces.

I just checked the specs sheet on that Duco cement and it looks like it's good for wood, china, leather, glass, metal, ceramic and paper. Not the right stuff for plastic.
http://www.devcon.com/prodfiles/pdfs/fam_tds_207.pdf

This Testor's Cement for Plastic Models or something along these lines would do the job for you. Make sure to get the red packaging. I bought the blue thinking the non-toxic stuff would be better and it didn't meld the pieces together like it should have.
http://www.amazon.com/TESTORS-CEMENT-PLASTIC-MODELS-Toy/dp/B000T3RM9K/ref=sr_1_5?ie=UTF8&s=toys-and-games&qid=1278382414&sr=8-5

I don't use tube cement any more - liquid cement is much better (I actually melts the plastic and forms a weld between the parts. This stuff:

http://www.amazon.com/Quick-Dry-Cement-Applicator-1oz/dp/B00005CA7S/ref=pd_sim_misc_6

is much better than the tube stuff. Definitely stay away from the orange smelling goo - it is worse than useless. Tenax (if you can find it) is the best. Just paint it on the joint with a paint brush. My best plastic joints have been made by coating both parts with liquid cement, then coating again. It will mostly have dried by the time you get it on the second part - the second application stays soft a bit longer. Press the two parts together - you should see a bit of semi-liquid plastic goosh out of the joint. If you do, you can be sure you've got a great bond.

[SCE to AUX]

Tenax-7R seems to be getting harder and harder to find, probably due to concerns about the chemical content. It is essentially pure methylene chloride, which is a suspected carcinogen. The Tenax brand was always the most expensive way to buy the stuff, at $5 or more for a tiny bottle.

Most plastics suppliers sell an equivalent product at a much cheaper price. If you can find a chemical supplier who will sell to you, simply purchasing it as methylene chloride (or Dichloromethane) is an option.

This stuff evaporates VERY quickly, and should be used in a well ventilated area. It is also as fluid as water, and has absolutely no gap-filling properties whatsoever. The surfaces to be joined must fit together very tightly. It doesn't produce a real "glue" joint, but a solvent weld.

[Pippen]

This has me wondering what the least toxic option that really holds would be.

[SCE to AUX]

About the only method that would work without any kind of chemical solvent would be thermal welding with a plastic filler rod. Then you get to breathe fumes from the heated plastic...:D

[Marc_G]

FWIW, the Household Goop has cured for 24 hours (48 recommended for thick applications) and already seems to pass the wiggle test. My intuition suggested the prior bonds to be iffy, but I've got a good feeling about this one...

Next launch date will see this bird in the air; I'll report back results.

Marc

[Micromeister]

Bob mentioned one of the Weld-on products that is a good choice but this material 4052 doesn't fully cure for 7 days.

My favorite choice when not using MC or needing a heavier syrup thick solvent welding adhesive would be Weld-on 16. Unfortunately McMaster doesn't seem to carry this very useful tube type adhesive. It is available through most sign supply and other industrial supply houses. It was designed for acrylics but has proven to be great on Polycarbonates and used sparingly works well with styrenes also. it's is quite helpful with small gap filling as well. in a pinch we can solvent weld with MEK and Acetone as well, while not quite as agressive as MC they do the job.