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  #1  
Old 03-13-2018, 10:28 PM
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blackshire blackshire is offline
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Default "3D printed 'vacu-formed' parts?"

Hello All,

Looking at various simple, scale boost-glider (and micro R/C EDF [Electric Ducted Fan]) subjects that had/have cylindrical bodies, ogive or elliptical noses, and truncated cone, truncated ogive (or un-truncated ogive or elliptical, in some cases) rear fuselages (examples include the AQM-38 and AQM-37 target drones, the Harpoon and Tomahawk cruise missiles, the larger Matador, Mace, and Snark cruise missiles, and numerous other UAVs and aerial targets), a 3D printing question occurred to me:

Is it possible to 3D print plastic nose cones and tail cones that are lightweight, like vacu-formed ones (such as the ones originally made by Competition Model Rockets [Apogee Rockets carries some of them])? If so, boost-glider (and R/C EDF) scale models of such vehicles could be built, using regular kraft paper rocket body tubes for their fuselages (the "3D printed 'vacu-formed'" parts could be made slightly thicker than the original vacu-formed nose cones, for durability), and:

Such parts--since they would be printed under computer-control--could also be made in other-than-axisymmetric (nose cones, tail cones, etc.) shapes. This would make possible lightweight scale boost-glider (or EDF) models of lifting bodies such as the BOR-4, X-23A, X-24A, X-24B, M2-F3, HL-10, HL-20, etc. (There was even a turbojet-powered version of the X-24A, called the SV-5J [see: http://www.google.com/search?ei=W5O...1.0.pBy1uwc9Dng ], two of which were built, but were not flown; scale SV-5J models would be "naturals" for electric ducted fan power.) Also:

In the cases of such lifting body models, as well as models of cylindrical-bodied cruise missiles, target drones, and UAVs, their tail fins (and wings, where applicable) could even be 3D printed as thin-skinned plastic halves. These could be strengthened with internally-glued sheet balsa (and/or fiber [beveridge board]) spars with ribs, to form semi-monocoque (stressed-skin, reinforced with internal bracing) structures. The "3D printed fin [or wing] airfoil halves" could also--*unlike* vacu-formed ones--have integrally-molded (actually, integrally-printed) spars and ribs (at least in part), which would minimize the need for additional internal bracing structures.

Many thanks in advance to anyone who can help!
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Last edited by blackshire : 03-13-2018 at 10:47 PM.
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  #2  
Old 03-14-2018, 10:10 AM
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kevinj kevinj is offline
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Not as light as vacformed plastic, unless we are talking about some thick vacformed parts. For comparison, a vacformed 40mm cone 60mm long using .030" stryrene is about 1-1.5g. A similar sized part 3d printed with a thin wall and no infill weighs around 5g, if it sticks together.

For larger models it's not a problem to beef up the 3d printed parts as you have a less stringent mass budget.

I've also been playing around with printing a part as a buck, and then pulling vacformed parts from that. Lots of surface prep involved if you don't want to transfer all the layer ridges from the mold to the parts.

kj
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Old 03-14-2018, 10:27 AM
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LeeR LeeR is offline
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I figure by the time I’m about 90, the 3D printers will produce, thin, smooth, highly detailed parts inexpensively.

Am I bitter? No. I have enough old rocket kits in storage that I could build them until I’m 100 years old. Why get sidetracked on making my own parts?

Actually, I do turn nose cones and other parts on my wood lathe, so I can do some old-school custom stuff.
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  #4  
Old 03-14-2018, 10:49 AM
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Quote:
Originally Posted by kevinj
Not as light as vacformed plastic, unless we are talking about some thick vacformed parts. For comparison, a vacformed 40mm cone 60mm long using .030" stryrene is about 1-1.5g. A similar sized part 3d printed with a thin wall and no infill weighs around 5g, if it sticks together.

For larger models it's not a problem to beef up the 3d printed parts as you have a less stringent mass budget.

I've also been playing around with printing a part as a buck, and then pulling vacformed parts from that. Lots of surface prep involved if you don't want to transfer all the layer ridges from the mold to the parts.

kj
Thank you! What is a "buck" (in the sense in which you're using that term)? It sounds like you're referring to a "master part," or what--in resin casting, and maybe also in roto-casting--is called a "mold plug" (a part around which an RTV [Room Temperature-Vulcanizing] rubber mold is poured, from which cast resin parts are then made). Most vacu-formed nose cones seem to be made by pulling the heat-softened styrene sheet ^over^ a plug (a hollow-cavity mold with one or more small air vent holes connected to a pump, to suck the sheet down into the cavity, is possible too, but making such a mold would probably be more labor-intensive). Also:

The ~5 grams mass figure that you gave for a 40 mm diameter, 60 mm long 3D printed nose cone sounds reasonable for a boost-glider (or EDF-powered) model (a 1.0 g - 1.5 g vacu-formed nose cone of those dimensions might actually be a little *too* lightweight [as well as a bit flimsy] for such a wing-supported model). In addition:

I don't know how easy (or difficult) this might be, but maybe 3D printed nose cones and tail cones for such gliding models could be intentionally printed generally a little too thin-walled (for an otherwise internally un-braced part), *but* could have an internal, integrally-printed "grid frame." (This would be rather like the chemically-milled integral "waffle iron" stiffening grids on the inside of the Thor [and later, the various long-tank Thor-Delta first stage] propellant tanks, which were thin-walled but quite stiff and strong.) Such "printer-milled" nose cones and tail cones would also use less of the plastic (fusible acrylic powder?), which would be more economical use of the plastic, which would go farther.
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Old 03-14-2018, 12:44 PM
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In vacuum forming the piece you use to form the plastic on is called a buck.

The best materials for a form to make nose cones with is solid metal with a smal air hole to aid in removing the part from the buck. The CMR machine used mainly 2 part metal bucks, the nose cone shape and an angled collar that the cone sat on. This made it easier to remove the part from the waste plastic.

I have experimented with urethane casting resin, 3d printed plastic and hardwood for bucks, and the solid metal ones are most desirable from a standpoint of ease f separating the part and less surface prep involved in the form.

kj
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  #6  
Old 03-15-2018, 09:00 AM
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From my (admittedly limited) experience with 3D printing I can't imagine anything that would come close to being as light as vacuform while being in any way structurally sound. For typical printing processes there's a recommended wall thickness of a bit more than 1mm (if I recall correctly), which would be lots and lots heavier than vacuform.
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  #7  
Old 03-15-2018, 11:23 AM
jetlag jetlag is offline
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Quote:
Originally Posted by LeeR
I figure by the time I’m about 90, the 3D printers will produce, thin, smooth, highly detailed parts inexpensively.

Am I bitter? No. I have enough old rocket kits in storage that I could build them until I’m 100 years old. Why get sidetracked on making my own parts?

Actually, I do turn nose cones and other parts on my wood lathe, so I can do some old-school custom stuff.


Alex and Sheree of Boyce are producing beautiful 3D printed kits that are smooth. They have a much better machine now that prints w/o the ridges.
And, he is going to acquire an even better machine going forward.
Very nice kits.

Allen
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  #8  
Old 03-15-2018, 12:49 PM
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Quote:
Originally Posted by jetlag
Alex and Sheree of Boyce are producing beautiful 3D printed kits that are smooth. They have a much better machine now that prints w/o the ridges.
And, he is going to acquire an even better machine going forward.
Very nice kits.

Allen


There's lots of things that can account for that. Short of SLA or SLS, you still have to deal with layers in any form of FDM/FFF printing. Acetone vapor for ABS printed parts, alcohol dips for PVB printed parts- I don't know what they are doing since they don't talk about it on their website.

In reference to 3d printed vs. vacforming weight- the Boyce Aerospace website says this about their Maxi V-2 fins: "Each fin weighs about 52 grams vs. the 18 gram vacu-formed fins, so additional nose weight will be required." So there is one concrete example of a 3d part being 3x the weight of a vacformed part.

kj
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  #9  
Old 03-15-2018, 06:37 PM
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blackshire blackshire is offline
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Quote:
Originally Posted by kevinj
In vacuum forming the piece you use to form the plastic on is called a buck.

The best materials for a form to make nose cones with is solid metal with a smal air hole to aid in removing the part from the buck. The CMR machine used mainly 2 part metal bucks, the nose cone shape and an angled collar that the cone sat on. This made it easier to remove the part from the waste plastic.

I have experimented with urethane casting resin, 3d printed plastic and hardwood for bucks, and the solid metal ones are most desirable from a standpoint of ease f separating the part and less surface prep involved in the form.

kj
Thank you for this information, including about CMR's tooling. I've never done vacu-forming myself (I've only read a "How-To" article about it [and about resin casting, which I've done] by David Merriman, many years ago). Vacu-formed parts can be quite thin-walled and light (like the Estes U.S.S. Enterprise and Klingon Battle Cruiser kits' plastic parts), but without internal bracing, such parts are pretty flimsy.
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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
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  #10  
Old 03-16-2018, 01:39 PM
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We have 4 3D printers currently running 2 Sindohs 201s and 2 M3D Micros. The Sindoh print near perfect parts, no sanding needed.

We however make mostly model kit parts. But the few rockety related items have been fine.


We will be getting our giant Promega in about a month or so.
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