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First 150mm/6" Ball shell


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#1 Aspirina

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Posted 26 November 2018 - 11:12 AM

I share with all of you the first and maybe the last ball style shell that I made.
Despite the good result and the good appearance of the shell, it took me much more work than usual. The task in general without hemispheres is very laborious.
 
The shell is made from a "rubber" ball. I used 15 wraps of kraft paper to make the hemispheres. Once assembled, I finished closing it with 20 rolls of paper tape changing the orientation of the poles in each pass. The last layers are kraft paper with white glue to gain rigidity.
The stars are comets of D1 Glitter of 20mm, I added some 50g 2x2mm Bismuth trioxide crackling stars primed with black powder.
For the burst I used coated rice hulls in a 4:1 ratio, the black powder used was 8h milled vine charcoal, boosted with 4g kclo4 flash. The lift charge was 130g of the same black powder of the break charge granulated in a 1x1cm squares screen.
 
Here some pics:
15cg2fb.jpg
 
24mu79w.jpg
 
 
The day of the fire was very bad weather, you can feel the bad audio, the video was recorded in a smarthphone, the format is in vertical, bad to be able in youtube,
 
Ther mortar is made in cardboard, still new like the first shoot. In my opinion the shell rise to much and the break was to soft.
 
Here the video with all the process pics, skip to 1:22 to see the shoot:
 
I hope you like it, greetings from Spain.
 

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#2 dlking59

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Posted 26 November 2018 - 08:30 PM

Looks good to me. Appears as if you put alot of work into this project and it was a success.



#3 OldMarine

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Posted 26 November 2018 - 09:41 PM

Don't give up! The gaps in the break were simply due to the gaps you left in the hemis. Other than that it was awesome! Very nice work and video.
Come on! Name one other hobby in which you cheer as your money and hard work go up in smoke!

#4 BengalFlair

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Posted 27 November 2018 - 10:20 AM

CONGRATS!!



#5 Aspirina

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Posted 28 November 2018 - 11:13 AM

Thanks for the answers guys!


«The first great virtue of man was doubt, and the first great defect was faith» Carl Sagan

 

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#6 memo

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Posted 28 November 2018 - 12:26 PM

great pasting and construction  , my shells look sloppy next to yours.

 

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#7 dynomike1

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Posted 01 December 2018 - 08:20 AM

Didnt see much wrong with it  but your right  probably 7:1  would have been better.

That sounded like a lot of work.


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#8 Mixer

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Posted 02 December 2018 - 09:54 AM

 

I share with all of you the first and maybe the last ball style shell that I made.
Despite the good result and the good appearance of the shell, it took me much more work than usual. The task in general without hemispheres is very laborious.
 
The shell is made from a "rubber" ball. I used 15 wraps of kraft paper to make the hemispheres. Once assembled, I finished closing it with 20 rolls of paper tape changing the orientation of the poles in each pass. The last layers are kraft paper with white glue to gain rigidity.
The stars are comets of D1 Glitter of 20mm, I added some 50g 2x2mm Bismuth trioxide crackling stars primed with black powder.
For the burst I used coated rice hulls in a 4:1 ratio, the black powder used was 8h milled vine charcoal, boosted with 4g kclo4 flash. The lift charge was 130g of the same black powder of the break charge granulated in a 1x1cm squares screen.
 
Here some pics:
15cg2fb.jpg
 
24mu79w.jpg
 
 
The day of the fire was very bad weather, you can feel the bad audio, the video was recorded in a smarthphone, the format is in vertical, bad to be able in youtube,
 
Ther mortar is made in cardboard, still new like the first shoot. In my opinion the shell rise to much and the break was to soft.
 
Here the video with all the process pics, skip to 1:22 to see the shoot:
 
I hope you like it, greetings from Spain.
 

Correct me if i`m wrong, but I think you say that the outer layers are not Kraft, but paper tape (indicated by the whiteness in the pic) this most probably means that the hemispheres made from the Kraft are a lot stronger than where the outer layers span the join (the weakest area ) - which doesn`t help when trying for a good symmetrical burst. Straw board or newspaper hemispheres are preferable.

 

A  6" shell would need approximately 16 outer layers of Kraft paper which has a mean tensile strength of around 7.5 kg/cm - Adding or subtracting layers if this tensile strength is different. This combined with adding 1gram of slow perc flash per 1" shell diameter should get the burst that you require.

 

 

 

 


Edited by Mixer, 02 December 2018 - 10:01 AM.

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#9 dlking59

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Posted 02 December 2018 - 09:08 PM

Looks good to me. I will be happy when I put one up like that.



#10 Aspirina

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Posted 04 December 2018 - 04:10 PM

 

Correct me if i`m wrong, but I think you say that the outer layers are not Kraft, but paper tape (indicated by the whiteness in the pic) this most probably means that the hemispheres made from the Kraft are a lot stronger than where the outer layers span the join (the weakest area ) - which doesn`t help when trying for a good symmetrical burst. Straw board or newspaper hemispheres are preferable.

 

A  6" shell would need approximately 16 outer layers of Kraft paper which has a mean tensile strength of around 7.5 kg/cm - Adding or subtracting layers if this tensile strength is different. This combined with adding 1gram of slow perc flash per 1" shell diameter should get the burst that you require.

You thinking right, next time I will change that method. Yes, the hemis are made with kraft, the shell was closed with paper tape and some layers of kraft, this wrong way of construction and only 4g of flash cause the soft opening of the shell.

 

 

Didnt see much wrong with it  but your right  probably 7:1  would have been better.

That sounded like a lot of work.

 

 

Looks good to me. I will be happy when I put one up like that.

Thanks guys!


«The first great virtue of man was doubt, and the first great defect was faith» Carl Sagan

 

My stuff:

https://www.youtube....w_as=subscriber

 





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