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Tips for 3D printed Nosecones..
#1
Lightbulb 
As everybody probably already knows, I'm trying to write myself into the Cineroc's history by creating the CinerocDV.  Part of this process is checking the 3D printed nosecones against the originals.  

Now, I won't be adding finished images until after my poll expires next week, so you'll have to wait until then for those.  However, I wanted to share what I've learned from sanding 5 of these nosecones now and one of the transitions (seen below).

[Image: 19558256486_a70a874131.jpg]

First, the black ABS is a lot easier to deal with than the white when it comes to sanding.  The white is good for concept checking as it shows up well against the black, however, when it comes to smoothing it down, it's harder to see.  Sanding the black is easy...  if it's sanded properly it's matt black (or grey), unsanded areas show up as glossy specks.  You see something shine?  Sand it some more.



Thin wall printed ABS plastic is fragile...  The layers of the ABS may not be fully fused to each other.  Want to check it?  pour some water in there and then try to blow on the piece.  It's a very good strainer, but not a very good "cup", as it will leak from every possible crack in the material.  The solution?  Acetone.  Before sanding it, "paint" it with Acetone, inside and out (while you're sitting outside).  Don't go too heavy on it (to the point you melt it to goo).  Just enough to melt the ridges some, and allow the layers to chemically bond to each other.  Acetone will trump super thin CA for this purpose.  Untreated thin walled ABS can crack when flexed, so be careful with it.  I don't know how well untreated would hold up under tension, so it may not be a good idea to rig your parachute in a way that will pull on it very hard.

I've sanded the parts with 320 grit to eliminate the ridges.  I tried using 600, 1200, and 1500 grit sandpaper, but remarkably, you can get a good gloss with 400 grit.  Good enough to make it very hard to tell a 40 year old piece of plastic from one made last month.  If you don't know what to look for, and the maker does a careful job, you might not be able to tell the difference.

I'm really pleased with this technology, and I'm sure that we'll all be printing our nosecones in the very near future (unless manufacturers do more to keep us happy (e.g. upscaling popular nosecone designs)). 

Pointy Side Up!
Jim

I want to say thanks to D. Bertelsen, and his team of students for all their help.  LW Bercini for his assistance, and J. for his invaluable support on this project.  Thanks Guys!!!
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NAR #100544

"The Guide says there is an art to flying", said Ford, "or rather a knack." 
"The knack lies in learning how to throw yourself at the ground and miss."

Launching is Optional... Landing? That Depends on Trees.

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#2
Thanks for the information Jim,
Very interesting about the differences between the black and white plastics.
I didn't know there was gaps and about the use of Acetone to seal it up.
Hans "Chris" Michielssen
Old/New NAR # 19086 SR
www.modelrocketbuilding.blogspot.com

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#3
What layer height are you using?

I have been having better success with nose cones with PLA than ABS, but I got some good ABS cone prints as well. I have been using .2mm row height, but I am thinking of moving to .1 with the idea that the layers would be smoother and there would be even less to sand.

I completely agree about sanding white, there isn't much to see.

Have you tried using Acetone to smooth the print? I haven't tried it yet, but I know others use vaporized acetone to smooth out the surface. Something to look into...
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#4
ABS is a notoriously difficult material with which to get good layer adhesion in an FDM print. I am having very good luck with PETG these days. a part printed with PETG is typically stronger than either PLA or ABS and is also a great deal more impact resistant and flexible.
NAR #96751, Level 2
Mayhem Rocketry, LLC
That's a nice rocket you have there...if you're looking for me, I'll be under my car.
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#5
I have been looking at getting some PETG. I have heard/read that it is better about warping than ABS. Is that true? How does PETG deal with heat?
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#6
I haven't run the hot-car test on a PETG part yet. In theory, it has a higher Tg than PLA. It's warping is sort of similar to PLA. It has no nasty odor when printing. The only downsides I have found to the stuff are that (a) it seems a bit stringy (needs more retraction on moves) and (b) is difficult to obtain in the colors I want.
NAR #96751, Level 2
Mayhem Rocketry, LLC
That's a nice rocket you have there...if you're looking for me, I'll be under my car.
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