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  #21  
Old 03-17-2019, 04:01 AM
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Originally Posted by Ez2cDave
You are entirely welcome . . . I believe that data should be shared, not hoarded.

A little more "FUN", from the same source . . .

https://rocketry.wordpress.com/ulti...-partial-builds

Dave F.
*Nods* I let Peter Alway keep the scale data I sent him, because it would probably be dumped post mortem when the building management cleans out my apartment. Also:

Looking at the paper nose cones in the plans links that you posted, I think it would be easy to make curved-sided ones (tangent ogive, secant ogive, rounded-tip conical, etc.) and other such nose cones--as well as transitions and boat-tails (tail cones)--out of paper or card stock, by using papier-mâché construction methods (see: https://en.wikipedia.org/wiki/Papier-m%C3%A2ch%C3%A9 ). The mold could be 3D printed or made of polyurethane resin, with the white or yellow glue/paper mixture being pressed into place in the mold cavity. The nose cones or other parts could be either hollow-cast or solid-cast (in the latter case, a screw eye could be "investment cast" into the wet glue/paper mixture).
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  #22  
Old 03-17-2019, 07:33 AM
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Quote:
Originally Posted by blackshire
*Nods* I let Peter Alway keep the scale data I sent him, because it would probably be dumped post mortem when the building management cleans out my apartment. Also:

Looking at the paper nose cones in the plans links that you posted, I think it would be easy to make curved-sided ones (tangent ogive, secant ogive, rounded-tip conical, etc.) and other such nose cones--as well as transitions and boat-tails (tail cones)--out of paper or card stock, by using papier-mâché construction methods (see: https://en.wikipedia.org/wiki/Papier-m%C3%A2ch%C3%A9 ). The mold could be 3D printed or made of polyurethane resin, with the white or yellow glue/paper mixture being pressed into place in the mold cavity. The nose cones or other parts could be either hollow-cast or solid-cast (in the latter case, a screw eye could be "investment cast" into the wet glue/paper mixture).


That's a very interesting idea . . . The idea of molding nose cones caught my attention.

With a 3-D printed mold ( I don't have a 3-D printer, but I have a friend that does ), it might be possible to "injection mold" nose cones, using epoxy in a syringe.

The two halves of the mold would be clamped together and the syringe attached to a threaded nipple on the mold . . . Of course, there would have to be a small hole to allow air to escape and the resin to completely fill the mold . . . . Once cured, the mold is unclamped and the sides are separated . . . Presto !

Thoughts ?
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  #23  
Old 03-17-2019, 09:03 AM
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Quote:
Originally Posted by Ez2cDave
That's a very interesting idea . . . The idea of molding nose cones caught my attention.

With a 3-D printed mold ( I don't have a 3-D printer, but I have a friend that does ), it might be possible to "injection mold" nose cones, using epoxy in a syringe.

The two halves of the mold would be clamped together and the syringe attached to a threaded nipple on the mold . . . Of course, there would have to be a small hole to allow air to escape and the resin to completely fill the mold . . . . Once cured, the mold is unclamped and the sides are separated . . . Presto !

Thoughts ?
If you can mix in some fiberglass matting, that might enable making it lighter and also less brittle. I would mold it with the bottom open to facilitate inserting the matting. But some experimentation will be required to find a way to keep the wall reasonably thin.


Doug


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  #24  
Old 03-17-2019, 09:06 AM
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Quote:
Originally Posted by Ez2cDave
That's a very interesting idea . . . The idea of molding nose cones caught my attention.

With a 3-D printed mold ( I don't have a 3-D printer, but I have a friend that does ), it might be possible to "injection mold" nose cones, using epoxy in a syringe.

The two halves of the mold would be clamped together and the syringe attached to a threaded nipple on the mold . . . Of course, there would have to be a small hole to allow air to escape and the resin to completely fill the mold . . . . Once cured, the mold is unclamped and the sides are separated . . . Presto !

Thoughts ?
Yes, that works just fine. Spray-on (in aerosol cans), wax-based mold release prevents the polyurethane casting resin from bonding to the 3D printed plastic mold. (Some resin casters even use molds made out of the same resin--such as, say, Alumilite--that's used to cast the parts themselves! As long as the mold cavity [and any places where the mold halves fit together] is sprayed with wax-based mold release, the cast part [and any excess resin] doesn't glue itself to the mold.) In addition:

Epoxy casting resins are also available, but they're more expensive than polyurethane (they do produce slightly more dimensionally accurate cast parts than polyurethane casting resin, but the difference is very small, and the mold cavity size can--if desired--be very slightly "nudged" in order to compensate for that). But even at the very worst, a cast resin duplicate part is just a tiny bit looser in the body tube than an original injection-molded or blow-molded styrene or ABS plastic part (or a properly sanded, sealed, and painted balsa nose cone that's used as the mold master part). Also:

Another method, which I used, is to create an RTV--Room Temperature-Vulcanizing--rubber mold (the platinum-cure rubber molds last longer and produce more dimensionally accurate parts, but I've used the cheaper tin-cure rubber with entirely satisfactory results), and produce solid-cast nose cones in it, and:

The rubber molds can also be made in two halves, and single-piece molds--which I used--also work fine. The nose cones can be lightened if desired (although small, solid resin BT-5 and T15 nose cones aren't too massive) by mixing microballoons (micro-bulb filler) into the resin, to lower the density of the cast part. Such single-cavity RTV rubber molds can also produce hollow nose cones, transitions, and tailcones by rotating the mold, even by hand (although roto-casting tables can be bought or built for casting such parts in quantity. This (see: http://www.ninfinger.org/models/rms...resin_cast.html ) article that I wrote, "Resin Casting for Rocketeers," covers the various resin casting methods.
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  #25  
Old 03-17-2019, 09:35 AM
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Quote:
Originally Posted by Doug Sams
If you can mix in some fiberglass matting, that might enable making it lighter and also less brittle. I would mold it with the bottom open to facilitate inserting the matting. But some experimentation will be required to find a way to keep the wall reasonably thin.


Doug.
What is preferable to use depends on the part size, and the flight stresses it's expected to undergo. Kevlar veil (it's rather like panty hose--in fact, actual panty hose might be fine for some applications) or the equivalent glass or carbon fiber cloth, and a long-curing (an hour or more) epoxy, or polyurethane casting resin, should be fine for model rocket nose cones, transitions, and tailcones (and fins, which could use foam cores). One "wets" the mold cavity with the resin (after applying an appropriate mold release), then presses the cloth into it (a gel coat can also be applied if desired--as is often done with molded fiberglass boat hulls--to give the finished part a shiny surface). Toward the top of that size range (BT-70 or so and up), more layers of the Kevlar, glass, or carbon fiber could be built up in the mold, to provide additional strength. Also:

For LMR/mid-power rockets, using heavier glass, Kevlar, or carbon fiber cloth would ensure ample thickness and strength. Another option that could be implemented along with the heavier cloth--although it would be best done outdoors--would be to use polyester resin. It stinks abominably until it has cured, but it is very strong and also has a little flexibility, which is good for such large rocket parts (the pre-made fiberglass R/C model airplane and R/C model sailplane fuselages--and R/C powerboat and sailboat hulls and racing car bodies--are made of heavier glass cloth and polyester resin). If you have neighbors with whom you are feuding, making such rocket parts in the yard or on a balcony or deck (when the wind is blowing toward them) could serve two purposes at once... :-)
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http://www.lulu.com/product/cd/what...of-2%29/6122050
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  #26  
Old 03-17-2019, 12:35 PM
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I've been looking at molding techniques and I am intrigued by the use of a "Compression Mold" . . . The two parts could easily be 3-D printed . . . Still doing research . . . Basic concept below.
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  #27  
Old 03-17-2019, 02:37 PM
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Quote:
Originally Posted by blackshire
). Today, one of the 3D printing folks could make such 5:1 BT-5 ogives.


I could easily 3D print 5:1 ogive nosecones (including the integral A.S.P. antenna or at least one with a flat truncated or open tip) in any BT size up to BT-80. The estimated cost in material for ABS plastic (at $15/Kg) is the diameter times the height (both in inches) times $0.30 . Mass production of more than one nosecone at a time will save on time and hence production cost. I have been printing 9 to 25 BT-20 sized ABS nosecones in a single batch.
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  #28  
Old 03-17-2019, 06:22 PM
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Quote:
Originally Posted by teflonrocketry1
I could easily 3D print 5:1 ogive nosecones (including the integral A.S.P. antenna or at least one with a flat truncated or open tip) in any BT size up to BT-80. The estimated cost in material for ABS plastic (at $15/Kg) is the diameter times the height (both in inches) times $0.30 . Mass production of more than one nosecone at a time will save on time and hence production cost. I have been printing 9 to 25 BT-20 sized ABS nosecones in a single batch.


Can a large 3-D printed nose cone ( BT-70 and larger ) be thin-walled, hollow, durable, lightweight, and shock resistant ?

What would the cost be to do a 5:1 BT-80 Ogive with .060"- .125" wall thickness ?

How much would it weigh and how long would it take to print ?

Thanks,

Dave F.
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  #29  
Old 03-17-2019, 08:18 PM
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A large BT-80 nosecone can take up to 8 hours to print at 0.2mm resolution, (or as little as 4 hours if I change the diameter of the print nozzle), the print would use about 100 grams of material with a 3/32" wall thickness (for ABS, or about 110 grams for PLA) At $15/Kg the plastic material cost is about $1.50.

I have made nosecones like this visit: https://forums.rocketshoppe.com/sho...29&postcount=35 for my Estes Panavia to Cherokee D clone http://forums.rocketshoppe.com/showthread.php?t=17244 .

I am currently limited to printing nosecones that are 400mm long (not including the shoulder which can be printed separately). I would only be able to print 4 of these larger nosecones at one time. I actually modified one of my printers with a 900mm high Z axis; however, there are still a lot of issues to work out and I have not been able to print anything over 600mm long.

Attached are pictures of a BT-20 size scale ASP nosecone I just printed. It took me minutes to draw the cone in RockSim, another few minutes to slice the exported 3D model with CURA software, and the 3D print took 3 hours and 2 minutes at 0.12 mm resolution and used about 7 grams of ABS plastic filament. The antenna is a bit flimsy but I think it will be OK for flight. I guess I will have to build and fly the scale ASP model to prove this.
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  #30  
Old 03-17-2019, 08:35 PM
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Quote:
Originally Posted by teflonrocketry1
A large BT-80 nosecone can take up to 8 hours to print at 0.2mm resolution, (or as little as 4 hours if I change the diameter of the print nozzle), the print would use about 100 grams of material with a 3/32" wall thickness (for ABS, or about 110 grams for PLA) At $15/Kg the plastic material cost is about $1.50.

I have made nosecones like this visit: https://forums.rocketshoppe.com/sho...29&postcount=35 for my Estes Panavia to Cherokee D clone http://forums.rocketshoppe.com/showthread.php?t=17244 .

I am currently limited to printing nosecones that are 400mm long (not including the shoulder which can be printed separately). I would only be able to print 4 of these larger nosecones at one time. I actually modified one of my printers with a 900mm high Z axis; however, there are still a lot of issues to work out and I have not been able to print anything over 600mm long.

Attached are pictures of a BT-20 size scale ASP nosecone I just printed. It took me minutes to draw the cone in RockSim, another few minutes to slice the exported 3D model with CURA software, and the 3D print took 3 hours and 2 minutes at 0.12 mm resolution and used about 7 grams of material. The antenna is a bit flimsy but I think it will be OK for flight. I guess I will have to build and fly the scale ASP model to prove this.



Hmm . . . Very interesting, Bruce !

What are the structural properties of the nose cone ?

Is is brittle and easily damaged ?

Are there different plastics that can be used ?

Advantages and disadvantages of each type ?

Sorry for the barrage of questions . . .

Thanks ,

Dave F.
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