interlocking, 3d printable, 3 inch shell hemispheres

[Simoski]

21st century take on the ancient fireworks shell, perhaps a better name would be:

 

scalable, interlocking, 3d printable, shell hemispheres

 

this is because you can easily scale them up or down to make 1 inch, 2 inch, 4 inch, 8 inch, 16 inch etc etc shells

 

here below the virtual representation of the top and bottom halves:

please shout out if you would like stl or gcode or if you have suggestions for improvement

 

 

top ( allows fuse entry and time delay, it also has space for your stars : )

 

bottom ( contains the combustion chamber to house BP H3 etc, it also has space for your stars : )

Edited March 20, 2018 by Simoski

[MrB]

Yeah.... No. Don't like it. 3D printing cores on which to paste paper to make the shell halfs, sure. But putting a bunch of plastic in a shell for no real reason, just rubs me the wrong way.

[Sparx88]

I don't see this creating symmetrical breaks especially due to the equator. May be more of a bow tie. And the snout or tube you have in there for time fuse will also work against symmetry and weight.

[Simoski]

Do I have the concepts correct? Should the timefuse be within the shell?

[Baldor]

From my point of view, the concept is wrong from the start. Filament is expensive compared to paper, plastic is not eco friendly, and the time of the 3D printer will be better used in other endeavours.

 

I think you can use the printer to make moulds for the hemispheres, and then use your mechanical skills to make a pasting machine, maybe 3D printed also.

[Arthur]

1/ I dislike plastic hemis because they have to be cleared up, there is no chance of them degrading like paper shreds.

2/ get the weight down

3/ Usually it takes a lot of effort to pull the loaded hemis close enough together to let the shell be solid in flight

4/ Yes I like the burst to start at the centre by either placing the time fuse there or using a paper tube and some QM.

5/ A design like that will be seriously heavy at 12 and 16" and hard to manhandle together. For big shells I like the hemi, collar and lid method where you can place the hemi on a ring stand then fill the collar, then fill the lid space and push it down. You do end up with two seams but it's so much easier than wielding a loaded 16" hemi in each hand trying to mate them up.

[MrB]

Do I have the concepts correct?

Pretty much, yes. I still think it's an extremely bad idea, but we all had those at one point or another.

[GalFisk]

PLA plastic (popular 3D printing material) is compostable, though it decomposes relatively slowly.

PLA is relatively brittle.

Some sort of snapping interlock would take up less space and not make the shell a lot thicker in the center.

All 3D printing plastics have low heat tolerance. A naked shell would probably not withstand the lifting charge.

3D printed objects are not airtight. A naked shell might flowerpot because hot gas can get inside.

Plastic shards raining from the sky may be unpleasant.

 

I still think it's worth doing some real world tests, just to see whether, and to what extent, these and other potential issues apply.

[TheWorkingsOfFire]

I print my own shells with PLA. It does decompose. Quiet rapidly in warm moist climates from my experience. I come out a lot cheaper by printing. I pay around $20 USD for one roll of PLA and with that one roll I print between 800 and 1000 shells from 1.75" up to 4". I only print them about 0.5mm to 1.0mm thick. And then I paste them like I would with any other shell and the pasting sticks and hold up very very well. I have perfect symmetrical breaks everytime. I just shot an experimental 1/8" thick walled 4" Ball with TT to FF and the burst charge was way way louder than the lift charge and after the Police left I laughed my A** off. My hands are still kinda shaky from the adrenaline rush from the whole ordeal. So to sum up all the confusion.. It totally works and is way cheaper than buying paper hemispheres. I only have the Longer3D printer for kids off Amazon for $169 USD and I'm pumping out (2) 4" Half hemispheres every hour and a half. I highly recommend you try it if you have the funds because it pays for itself very quickly. Just don't spread the word too quickly or they will find a way to charge us a huge ridiculous price for that also. Like with everything in The Workings Of Fire. That is an awesome 3D Render Simoski. It must have taken you awhile to design it, but the ball in the center to hold the burst charge would only weaken the burst and get in the way of igniting the stars that are lined against the inner wall of the shell. Very nice concept though. Have fun burning the world down fellow pyros!

[Bamboozler]

Hey TheWorkingOfFire,

 

Is this your entry level printer? LINK.

 

Also, any source for your hemi 3D models, or are they guarded?

Thanks!
Bam

[a_bab]

PLA does NOT decompose in any useful time. It does NOT biodegrade but rather, degrade.
Your buried body will be long decomposed and used up by plants before the PLA shards on the terrain you littered with will start to break down; it takes hundreds of years, possibly over 1000 - the truth is we don't know.

So filling the environment with junk plastic for a few dollars of saving doesn't justify it IMO.

I stay with carboard/paper.

[BiSkittlis]

I print my own shells with PLA. It does decompose. Quiet rapidly in warm moist climates from my experience. I come out a lot cheaper by printing. I pay around $20 USD for one roll of PLA and with that one roll I print between 800 and 1000 shells from 1.75" up to 4". I only print them about 0.5mm to 1.0mm thick. And then I paste them like I would with any other shell and the pasting sticks and hold up very very well. I have perfect symmetrical breaks everytime. I just shot an experimental 1/8" thick walled 4" Ball with TT to FF and the burst charge was way way louder than the lift charge and after the Police left I laughed my A** off. My hands are still kinda shaky from the adrenaline rush from the whole ordeal. So to sum up all the confusion.. It totally works and is way cheaper than buying paper hemispheres. I only have the Longer3D printer for kids off Amazon for $169 USD and I'm pumping out (2) 4" Half hemispheres every hour and a half. I highly recommend you try it if you have the funds because it pays for itself very quickly. Just don't spread the word too quickly or they will find a way to charge us a huge ridiculous price for that also. Like with everything in The Workings Of Fire. That is an awesome 3D Render Simoski. It must have taken you awhile to design it, but the ball in the center to hold the burst charge would only weaken the burst and get in the way of igniting the stars that are lined against the inner wall of the shell. Very nice concept though. Have fun burning the world down fellow pyros!

They really only weigh half a gram per hemisphere?? I tried printing hemis before but it didn't work very well. Could you send the stl files please?

[Bamboozler]

This thread gave me an opportunity to scratch the 3D printer itch. I've always wanted to get one, but never really found a need for one. Printing out a widget or three would get old and the printer would just sit. But hey, thinking there's some neat pryo stuff that can be made, as this thread notes.

 

TheWorkingsOfFire was kind to help with some related questions/models. That got me having some fun with a few related models designs. I have not yet gotten time to make BP fuel to try these out, so feel free to grab the STL file at the links below and give a try (can pass whatever file format Solid Works can generate if wanting to edit).

 

 

 

1lb salute heading - Understood that you can easily make a salute heading from a cardboard tube, kinda not the point for this project, its what can we make with the printer and use with pyro (if you feel guilty about fertilizing with a bit of plastic this isn't for you).

 

 

Below is a salute heading that can be slipped onto and glued to a 1lb tube. Around 35g of comp fills the payload cavity around 60-70% for binary mixing.

http://www.pcbwerks.com/pics/RS11.jpg

 

There is a fuse disc required and is a separate model (blue in the cross section pic above). The disc acts at the payload's cap.

 

Assembly order of operation:

• Pass fuse through disc center hole and glue into place, long enough fuse lengths on both ends.
• Glue fuse disc onto top of motor tube (fuse fills cavity above clay bulkhead to pass fire to payload).
• Set payload heading on table and fill with comp.
• Apply hot/wood glue ring to the payload heading or fuse disc and slide the tube into the payload heading to secure. (there are two vent grooves on the ID of the tube neck to allow the air to escape that is being displaced by the tube)

I made the two versions to test the report, one around 1.4mm thick payload wall and the second around 2mm+ payload wall. The slicing program (Cura) broke the thicker wall model into two solid walls separated by infill, the report was, as could be guessed, better with the greater confinement/thicker wall.

http://www.pcbwerks.com/pics/RS2.jpg

 

I print these with ABS filament and use ABS adhesive to fuse and layer separations, just mop it on where needed. I have an open printer frame (Ender 3 Pro) and may look into a cover to keep the environment at a higher/uniform temp to prevent layer separation. Separation was noticeably less when printing in the warmer kitchen vs. moving the printer to the cooler dinning room near a window (0 degrees F last night).

 

 

STL of payload heading

STL of fuse disc

Edited January 28, 2021 by Bamboozler

[Bamboozler]

4" Ball Shell 1lb Rocket Heading (1.4mm wall).

 

http://www.pcbwerks.com/pics/4inRB1.jpg

Illustration of a bit older revision, tweaked some features to improve printing.

 

Consists of 4 printed parts (STL download links)

• 4" Top Hemi
• 4" Bottom Hemi
• Leader Hook Cap
• Spolette

I print with ABS and use ABS adhesive like THIS and used it to glue the spolette or fuse pipe into bottom hemi (using an alignment rod while gluing). Cap might not be needed, allows air to escape when fusing the two hemis, carry over from the ball shell model.

 

Have no clue how the break would be with the 1.4mm wall ball, thickness may need to be increased to build more pressure. What I would like to achieve is to tune the wall thickness to create a good symmetrical break without taping (if even possible?). Just fill the shell hemis and use ABS adhesive to fuse the two together with ABS adhesive. There is a belt feature or overlap band in the center to help constrict and build pressure in the joint. Just need to start building some rockets and get to testing - work in progress.

 

http://www.pcbwerks.com/pics/RH13.jpg

Edited January 28, 2021 by Bamboozler

[DecimusMaximus]

On 1/28/2021 at 1:07 PM, Bamboozler said:

4" Ball Shell 1lb Rocket Heading (1.4mm wall).

 

http://www.pcbwerks.com/pics/4inRB1.jpg

Illustration of a bit older revision, tweaked some features to improve printing.

 

Consists of 4 printed parts (STL download links)

• 4" Top Hemi
• 4" Bottom Hemi
• Leader Hook Cap
• Spolette

I print with ABS and use ABS adhesive like THIS and used it to glue the spolette or fuse pipe into bottom hemi (using an alignment rod while gluing). Cap might not be needed, allows air to escape when fusing the two hemis, carry over from the ball shell model.

 

Have no clue how the break would be with the 1.4mm wall ball, thickness may need to be increased to build more pressure. What I would like to achieve is to tune the wall thickness to create a good symmetrical break without taping (if even possible?). Just fill the shell hemis and use ABS adhesive to fuse the two together with ABS adhesive. There is a belt feature or overlap band in the center to help constrict and build pressure in the joint. Just need to start building some rockets and get to testing - work in progress.

 

http://www.pcbwerks.com/pics/RH13.jpg

dude these are bad ass!! thanks for sharing. Did you ever test these out any further?

[Bamboozler]

To tell you the truth, as is they do not contain well enough for me.  I tried to reinforce with fiberglass packing tape and it improved but still not symmetrical, more of a horsetail break.  I've abandoned ship and use standard chipboard hemis.  However, with the model, I'm sure some creative technics could help to improve.

[DecimusMaximus]

14 hours ago, Bamboozler said:

To tell you the truth, as is they do not contain well enough for me.  I tried to reinforce with fiberglass packing tape and it improved but still not symmetrical, more of a horsetail break.  I've abandoned ship and use standard chipboard hemis.  However, with the model, I'm sure some creative technics could help to improve.

What if you gummed taped your 3d printed hemis? Shouldnt that provide the needed containment? I will test your stuff out soon but that will take time as I still need to print them and get comfortable with my press for the fuel.

[Arthur]

I'm much more interested in using 3d printing to make patterns round which paper hemis can be made, reusing the PLA many times.

[Bamboozler]

DM - Could very well do that to add the need containment, but my original goal with the 3D model was to bypass the taping process.  If taped on the model could be thinned out a bit for quicker prints.

A - That would work like a charm.