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Dark comp question


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#1 cogbarry

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Posted 25 June 2012 - 06:18 PM

Hi all,
I'm planning on making an 8" double pedal shell (my first) and I actually have two questions, one, as the subject line is on dark comps, the other, a construction question.

1) The dark comp I found in Blesser's "Round Stars and Shells" was mostly oxidizer as I recall and it called for a prime? It seems a dark comp is useless if it requires a prime, at least in my application where the intention is to hide the outer petal for a few milliseconds. Is there a dark comp that will light without a prime?

2) I remember seeing a couple different methods of construction but I was having a hard time finding info with my searches today so I thought I'd ask here. One method was to construct the outer pedal and inner pedal as two sets of hemis, both pedals closed with the single snap shut, the other (I think Jim Widman used this method) showed a method in which the inner pedal hemis were snapped shut, fused/passfired and then spiked. It seems to me, there may be a need to contain the inner pedal with the spiking in order to achieve a symmetrical burst for the inner pedal. This is assuming you don't want a soft burst for some reason. Any thoughts here?

As usual, any input is appreciated and I hope these are good questions.

#2 FlaMtnBkr

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Posted 25 June 2012 - 07:27 PM

Do you have the dark relay formula? I will dig up mine but I don't know it's origin. I do know mine is not supposed to need a prime and is supposed to light all but the hardest to light formulas.

#3 Bcorso85

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Posted 25 June 2012 - 08:06 PM

Potassium Nitrate 75
Potassium Perchlorate 7
Antimony Sulfide 3
Red Gum 2
Charcoal 8
Dextrin 5

The black powder prime is always called for. In glitter, Tiger Tails, and other B.P. based Compositions that easily ignite. Whether necessary or not it is an assurance. An assurance against after all your hard work your beautiful double petal will not have a few stars blow blind because your dark comp wouldn't ignite. I believe a thin layer of B.P. will burn off and ignite instantly after the burst charge. If I was worried about putting the prime on, I would thin the layer of prime but add silicon or some metal to increase the heat generated while not rolling on such a thick layer.

Personally I have not constructed a double petal but I do want to help. Looking at the choices of construction I would personally go with Jim's method. Taking two hemispheres and snapping them shut is one thing. Snapping them shut with such a delicate inner structure is another. Stars can easily shift or fall down the walls when flipped and sometimes turned and slip just a hair. The fact that one 8 inch hemi has a bump from a smaller shell would provide a "male" end to slide into a "female' hemi. There is an indentation that should fit like a glove. Hopefully with this method you wouldn't have to play with the shell to get your perfect fit.

I am thinking on using this dark composition so please let me know how it works out for you.

Best of luck,
Benjamin
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#4 FlaMtnBkr

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Posted 25 June 2012 - 10:12 PM

wrong formula



Edited by FlaMtnBkr, 25 June 2012 - 10:12 PM.


#5 cogbarry

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Posted 26 June 2012 - 04:53 AM

Potassium Nitrate 75
Potassium Perchlorate 7
Antimony Sulfide 3
Red Gum 2
Charcoal 8
Dextrin 5

The black powder prime is always called for. In glitter, Tiger Tails, and other B.P. based Compositions that easily ignite. Whether necessary or not it is an assurance. An assurance against after all your hard work your beautiful double petal will not have a few stars blow blind because your dark comp wouldn't ignite. I believe a thin layer of B.P. will burn off and ignite instantly after the burst charge. If I was worried about putting the prime on, I would thin the layer of prime but add silicon or some metal to increase the heat generated while not rolling on such a thick layer.

Personally I have not constructed a double petal but I do want to help. Looking at the choices of construction I would personally go with Jim's method. Taking two hemispheres and snapping them shut is one thing. Snapping them shut with such a delicate inner structure is another. Stars can easily shift or fall down the walls when flipped and sometimes turned and slip just a hair. The fact that one 8 inch hemi has a bump from a smaller shell would provide a "male" end to slide into a "female' hemi. There is an indentation that should fit like a glove. Hopefully with this method you wouldn't have to play with the shell to get your perfect fit.

That is the formula, yes.

You're right, I really don't want any blind stars with this much work involved and I'm also worried about a weak inner break. I may not use the dark comp at all but if I do, I'll prime it.

The inner shell should be pretty stationary as this shell will be pasted in a WASP and will have a passfire tube holding the inner shell and male hemi together. I'll just need to make sure the indentation in the female hemi is centered.

Thanks for your input, I intend to video tape this shell. I will post a link. I'm hoping to fire it on the 20th or 21st of July. I plan to use some commercial stars I have acquired. One is a red mag star, the other white spider. These are 3/8 stars although the size varies a lot between 5/16 and 15/32 which I have separated with sizing screens. Obviously, the outer stars will actually be used as cores and I will roll a layer of something over them. Any suggestions?

I am thinking on using this dark composition so please let me know how it works out for you.

Best of luck,
Benjamin



#6 Bcorso85

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Posted 26 June 2012 - 02:19 PM

I was thnking to taday and another thought on the prime is the fact that compositions need a fuel to burn. Anything needs a fuel to burn; and this compositon lacks it. It was designed to burn, and burn very dark. The lack of fuel may suggest that it WILL burn, but it just needs a start or strong ignition and the red gum and charcoal will perform the rest of the way into your color star.

I have been having problems with my wasp lately. I can't get the rollers lined up correctly on a three inch shell. I had to mess with it!Posted Image
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#7 Bcorso85

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Posted 26 June 2012 - 03:00 PM

Another thing to consider. In the book titled the Fire Maker by Larry Homan, he published a letter on page 37 from Jim. This was in regaurds to a large double petal shell he constructed and shot at a club shoot. It was a flower pot that blew up the gun. Jim had considered the pressures pushing against the shell during lift off, but failed to consider the pressured pushing out ward. I believe his final conclusion was a hot outer prime containing magnalium. The stars rubbed together and made a spark, which in turn obviously ignited the shell instantly (lift set back). This was at the Western Winter Blast VII. This was a shell three times larger (24 inch). But things can happen on large and small scales. Physics is Physics. I hope you can consider this and I hope to see a sucessfull shell.
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#8 cogbarry

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Posted 27 June 2012 - 08:29 AM

I was thnking to taday and another thought on the prime is the fact that compositions need a fuel to burn. Anything needs a fuel to burn; and this compositon lacks it. It was designed to burn, and burn very dark. The lack of fuel may suggest that it WILL burn, but it just needs a start or strong ignition and the red gum and charcoal will perform the rest of the way into your color star.

I have been having problems with my wasp lately. I can't get the rollers lined up correctly on a three inch shell. I had to mess with it!Posted Image


Thanks for the advice on the dark comp. I think I'll skip this step for this first shell and simply size my stars well in order to achieve the uniform timing effect.

Which rollers were you having issues with? Do you mean the spherical bearings/guides? There are two sets, one is mounted to the flexible piece of aluminium on the right (machine is set up with applicator arm to your left), one on the rail to the left. Personally, I don't use the set on the right much as you need to keep adjusting it up as the shell grows to keep the shell from binding. The machine keeps the shell tight against the left set by itself which IMO makes the right set unnecessary. I do bring it down for the burnishing pass but that's the only time I really use it.

I simply adjust the left set to contact the shell just above the equator and hold the shell slightly to the right of center of the wheels on the servo motors as Ned's manual suggests. Others may give different advice but this seems to work well for me.

#9 Bcorso85

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Posted 27 June 2012 - 03:32 PM

Thanks. And yes the rollers on the right and left are out of alignment.
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#10 cogbarry

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Posted 28 June 2012 - 06:59 AM

Thanks. And yes the rollers on the right and left are out of alignment.


Hmn,
The right side rollers have more adjustments as I recall (don't have my WASP in front of me) including the slotted adjustment and a tilt. However, the left side rollers are fixed to the rail and only move up and down the rail, and they can extend in or out towards/away from the shell. I don't know how they could be out relative to the center of the shell (on the axis of the rail) unless you had your servo motors adjusted unevenly. ...or is there something I'm missing here?

#11 Bcorso85

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Posted 28 June 2012 - 09:38 AM

No I think I was just referring to the poition of the side rollers to the shell. I had the setting for a three inch right on, but now when i paste a shell the tape crimples up and starts rolling over one strip (not rotating the shell) and i get a large ring of paper (like saturns ring around the planet). I think I have to sit down and play with it. I just dont want to waste countless gummed paper when i have to paste 30 shells as it is. After Saturday when I start to play with the machine can I PM you for some simple advice?



Also I i do need some advice on the spoollete. Do you make a whole with a dummy spoolette to paste, and use the magnet to find the passfire, cut it out, and glue in a perminit passfire? I really need some better train of thought on inserting the passfire after pasting.
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#12 cogbarry

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Posted 28 June 2012 - 10:20 AM

No I think I was just referring to the poition of the side rollers to the shell. I had the setting for a three inch right on, but now when i paste a shell the tape crimples up and starts rolling over one strip (not rotating the shell) and i get a large ring of paper (like saturns ring around the planet). I think I have to sit down and play with it. I just dont want to waste countless gummed paper when i have to paste 30 shells as it is. After Saturday when I start to play with the machine can I PM you for some simple advice?



Also I i do need some advice on the spoollete. Do you make a whole with a dummy spoolette to paste, and use the magnet to find the passfire, cut it out, and glue in a perminit passfire? I really need some better train of thought on inserting the passfire after pasting.


You can PM me, sure. What your describing has happened to me though. The first time it was because the shell was binding against the right rollers because it had grown and the shell couldn't turn to change it's poles. If you stopped the WASP when it does this, I'll bet you'll find the built up ring of tape is locked between the rollers. This is why I keep this set of rollers back. I think this can also happen if the shell is slipping on the rubber wheels for any reason. I am far from an expert though, I've had my WASP since December. Jim (and others like Ned) offers great support, are you in the WASP users group?

I use an empty passfire tube which has tissue paper glued over the inside end to keep shell contents from spilling out, then I use a strip of masking tape, stick the magnet to it, and tape the magnet over/in the passfire tube on the outside of the shell. In the past, I used a wooden dowel to keep the magnet from falling down into the passfire tube but that was more trouble than it was worth. The magnet sticks pretty well to the masking tape and even if it fell in, those magnets are very strong, you'll get it out as long as it hasn't broken through the tissue paper and fallen into the shell. As a matter of fact, watch out when you extract the magnet as it may come out fast and smash into your other magnet. I don't think it's likely but I suppose this could cause a spark. Once the magnet is removed I simply fuse the shell with a time fuse. The time fuse is cross matched on both ends. Personally, I use the quick firecracker fuse for cross match. I peel off the outer layer of paper to expose the black match. I leave one side of the inner cross match unpeeled and long. With this rigid piece I push it through the passfire until I feel it penetrate through the tissue and crunch with my burst charge. This method seems to work well with me as I am comfortable that I won't have a dud, and the unpeeled section of paper fuse actually acts as quick match, so I don't have to worry about a significant extra delay in timing. I then fill the gap around the time fuse with string or just tissue paper to keep the hot glue out. I seal the time fuse with hot glue, then ad a fuse washer on the outside and fill that with hot glue as well. I hate flower pots so I try to make sure I protect the inside of the shell from lift gasses as much as possible.

Hope this helps.

Edited by cogbarry, 28 June 2012 - 10:22 AM.





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