Tips for 3D printed Nosecones..

[K'Tesh]

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).





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. In the photo above, you can see where I've only just started the process of sanding. Now it has a gloss shine that rivals the original part.




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!!!

 

[etoyoc]

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...

 

[K'Tesh]

Doug told me that they are using 1/50" layering on the prints.

 

[etoyoc]

Doug told me that they are using 1/50" layering on the prints.

That is about a .5mm row height. I don't know what options you have to control your row height, but the smaller the row height, the more precise the print will follow the curve and the less sanding you should have to do. Of course at .5mm row height, you have 2.5X fewer ridges to sand than I do at .2mm, but the ridges will be bigger. Of course, if all things were equal between the printers, it will take 2.5X times as long to print.

 

[dcbertelsen]

I think most were printed in 0.2mm but there may have been some 0.1mm parts. The camera shroud was 0.1mm IIRC. I'm still dialing in the new printer I built; print quality isn't quite up to the one these were printed on.

Doug

 

[tab28682]

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).


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. In the photo above, you can see where I've only just started the process of sanding. Now it has a gloss shine that rivals the original part.

I finish tons of ABS printed parts at work, typically in white, grey or black.

If you want white parts to reveal like dark parts during sanding, the best way is to apply a light coat of dark primer or even paint. This will stay in the low areas until you sand through to the bottom of the low areas.

A faster way to get a flawless finish is typically not available to the average rocketeer. After a coat of solvent and a drying, we often bead blast the parts and then prime with a coat of catalyzed polyurethane primer with good built out, like Dupont K-36 or other more economical equivalents. No hand sanding before priming. This cures hard, sands great and fills the surface imperfections nicely and saves significant finishing time over other methods.

A thin coat of CA still offers some benefits to finishing low temp ABS parts when using lacquer type products. Even after sanding all ridges from a part, we have seen the layer marks return after the plastic is exposed to lacquer type solvents from primer and paint. Most of the economical 3D printers print in low temp ABS.

This thin coat of CA keeps the solvents from deeply penetrating the part during priming and painting and then getting trapped by the faster curing outer layers of paint.

Thin walled ABS parts with simple shapes that need to be strong greatly benefit from a layer of .75 oz/sq yd. fiberglass cloth applied with thin CA.