ok my plastic shell is sealed

[ST1DinOH]

so my breaks are weak.

 

i had a RW&B 3 i made from harvested (black mamba) 1.4 shells and the end result was almost a "rain" or "falling leaves" effect. real weak break.

 

as a self-professed noob to shell building i feel comfortable telling you i was under the impression that once i've xylened a shell i was ready to fire. now i understand that these shells are going to need a lot more than just a thin band of solvent to give me the break i'm after.

 

as of now the only thing i've tried has been duct tape, and some fiber tape, the fiber tape obviously had much better results.

 

can i expect much better breaks with an outer aplication of craft paper and wheat paste? much better than the fiber tape?

 

or would some combination of these two methods give me the best result?

 

my logic tells me that giving it a good wrapping with fiber tape, then applying an outer layer of pasted craft paper would be the way to go. but if all craft paper is the same as, or equivilant to, using fiber tape inconjunction with the craft-n-paste...then i'd just assume use all paper as it is far cheaper. that damn tape is kinda pricy and it goes fast.

 

thanks in advance.

[fredjr]

If you must use plastic then the fiber tape is the quick and easy method. Stores like Big Lots http://www.biglots.com/store_locator.aspx have the fiber tape cheap. Less than a dollar. If you want nice symetrical breaks ditch the plastic, get some paper hemis and paste them. The stars from a 1.4 shell are too small for a 3 inch shell.

[ST1DinOH]

If you must use plastic then the fiber tape is the quick and easy method. Stores like Big Lots http://www.biglots.com/store_locator.aspx have the fiber tape cheap. Less than a dollar. If you want nice symetrical breaks ditch the plastic, get some paper hemis and paste them. The stars from a 1.4 shell are too small for a 3 inch shell.

so would i be better off going all tape, all paper, or tape then paper over my plastic hemi's.

 

i don't mind doing both if it means better breaks, but if it's not going to make much difference at all then i'll just paste them.

[Mumbles]

It's kind of a hard answer. It depends on a few factors, namely, what you're bursting the shells with. I would assume black powder on hulls, but you may be using the harvested burst as well, which is more similar to KP on hulls.

 

I would start with the fiber tape. In my experience paste and paper doesn't stick particularly well to plastic, but others disagree with me. I have however gotten fairly good adhesion out of white glue. In my experience, the weak point is always the seam. It theoretically shouldn't, but I often find the two hemis just blown apart at the seam. Some fiber tape should fix this. From a purely stategy point of view, the best solution is fiber tape to "even out" the seam with the strength of the rest of the shell, and then paper to reinforce over the whole surface, say 3 layers.

 

It really comes down to experimentation. It's hard to give defefinite answers unless you do everything exactly identical to another.

 

Another thing, the seam has to dry before it can be fired. With Xylene, I'd give it around 24 hours. You don't mention any dry time, but just thought I'd make sure.

 

I do agree with Fredjr though. I always get better breaks out of paper than plastic. With small shells like these, there is actually very little extra work. A 3" ball shell only would need around 5 layers of pasted paper (double layers that is), so we're talking maybe an extra 15 minutes of work if that.

[ST1DinOH]

It's kind of a hard answer. It depends on a few factors, namely, what you're bursting the shells with. I would assume black powder on hulls, but you may be using the harvested burst as well, which is more similar to KP on hulls.

 

I would start with the fiber tape. In my experience paste and paper doesn't stick particularly well to plastic, but others disagree with me. I have however gotten fairly good adhesion out of white glue. In my experience, the weak point is always the seam. It theoretically shouldn't, but I often find the two hemis just blown apart at the seam. Some fiber tape should fix this. From a purely stategy point of view, the best solution is fiber tape to "even out" the seam with the strength of the rest of the shell, and then paper to reinforce over the whole surface, say 3 layers.

 

It really comes down to experimentation. It's hard to give defefinite answers unless you do everything exactly identical to another.

 

Another thing, the seam has to dry before it can be fired. With Xylene, I'd give it around 24 hours. You don't mention any dry time, but just thought I'd make sure.

 

I do agree with Fredjr though. I always get better breaks out of paper than plastic. With small shells like these, there is actually very little extra work. A 3" ball shell only would need around 5 layers of pasted paper (double layers that is), so we're talking maybe an extra 15 minutes of work if that.

man i love this place...

 

whoever coined the old adage "you learn something new everyday" has never been here. it's only 4:30 and i'm up to 6 or 7.

 

i was under the false assumption that xylene type solvents bond and dry instantly...like a pvc glue. i had been building and launching these 3's within about 20 minutes.

 

that definatley explains the rain type breaks i'm getting. in fact i'm suprised the shells even contained the heat long enough to get thoes stars burning...

 

lol

 

this explains a lot.

 

well it sounds like 1/2 my problem has been my impatience, the other 1/2 obviously is the lack of any kind of tape/paper spiking.

 

once again...thanks all for the help.

[ULTRABUF]

I've lit off a total of five 3" shells, 4 of which were successful. I recovered the unsuccesful one, the visco time fuse didnt light so I need to put a new lift cup on it. I got pretty good breaks out of them. I used plastic hemi's, and I wrap a length of fiberglass tape around the seam, and two wraps diagonally to make an X shape. I then paste two layers of kraft on using the 3 strip method. I have a 4" TT shell I'm working on that I spiked and pasted in the same way, hopefully I will have a video of it up sometime.

[ST1DinOH]

I've lit off a total of five 3" shells, 4 of which were successful. I recovered the unsuccesful one, the visco time fuse didnt light so I need to put a new lift cup on it. I got pretty good breaks out of them. I used plastic hemi's, and I wrap a length of fiberglass tape around the seam, and two wraps diagonally to make an X shape. I then paste two layers of kraft on using the 3 strip method. I have a 4" TT shell I'm working on that I spiked and pasted in the same way, hopefully I will have a video of it up sometime.

well you're doing much better than me

 

i've sent up 5 3's in total, 3 of them never lit and i lost them, 1 of them blew underwater, and the only good one had a break no louder than a paper bag filled with air as the stars glided back to earth.

 

a fellow pyro buddy of mine, who's about the same spot i am with this whole thing, had a few more and he had one go off on the ground, and a nice 50/50 bh alum + perc go off just fine...then again thats not gonna need much confinement at all to give us the boom we were after.

 

had we allowed the xylene to dry and added some fiber tape the salute would have been a lot lounder i'm sure.

 

well thats that...time to spend more money

 

i'm getting the impression that i'll be living check to check for the next year or so...i'm a friggin addict.

[qwezxc12]

Something else to consider...if you're making the shells properly, you'll be sweating to get them closed...tapping around the top and bottom with a dowel or somesuch while pushing down in order to get the two hemispheres to mate. If they fit together easily and you can here stuff rattling around after they're put together, you underfilled them. If you've filled them properly, you won't be able to apply the xylene, then just push them together without consolidating the contents first.

 

I seat them tight, then pry the seam apart ~1/16" to wick the xylene into the seam. The shell goes into a press for 10 minutes or so (or however long it takes me to assemble another shell). I knocked together a light frame just for compressing shells while the solvent sets:

http://www.apcforum.net/files/IMG_0011nSmalln.jpg

 

Optimally, the assembled shells cure" overnight before taping.

I tried KP on rice crispies for burst in 3in and 4in shells, and while that worked, 5:1 BP on crispies + a slow flash booster seems to work just as well in plastic shells with minimal taping and is cheaper (less KClO4).

 

Another burst that worked for me was a type of Benzolift rolled 4:1 onto crispies: The ratio was 60:40 Copper OxiChloride catalysed whistle / BP...I milled everything but the Perc together, then mixed in previously milled Perc. In fact all of the 3 and 4in shells in the August show I did were broken with this.

 

Good luck! Better breaking plastic shells is a topic many are chasing...

[ST1DinOH]

Something else to consider...if you're making the shells properly, you'll be sweating to get them closed...tapping around the top and bottom with a dowel or somesuch while pushing down in order to get the two hemispheres to mate. If they fit together easily and you can here stuff rattling around after they're put together, you underfilled them. If you've filled them properly, you won't be able to apply the xylene, then just push them together without consolidating the contents first.

 

I seat them tight, then pry the seam apart ~1/16" to wick the xylene into the seam. The shell goes into a press for 10 minutes or so (or however long it takes me to assemble another shell). I knocked together a light frame just for compressing shells while the solvent sets:

http://www.apcforum.net/files/IMG_0011nSmalln.jpg

 

Optimally, the assembled shells cure" overnight before taping.

I tried KP on rice crispies for burst in 3in and 4in shells, and while that worked, 5:1 BP on crispies + a slow flash booster seems to work just as well in plastic shells with minimal taping and is cheaper (less KClO4).

 

Another burst that worked for me was a type of Benzolift rolled 4:1 onto crispies: The ratio was 60:40 Copper OxiChloride catalysed whistle / BP...I milled everything but the Perc together, then mixed in previously milled Perc. In fact all of the 3 and 4in shells in the August show I did were broken with this.

 

Good luck! Better breaking plastic shells is a topic many are chasing...

wow...impressive press (pun intended).

 

ok so, let me run this back to make sure i'm at least accumulating some knowledge.

 

1.snap em together (should be hard to do to ensure it's full) then run a fingernail around the seam to open it up a bit.

 

2. apply some xylene to the seam, allow the capilariy action to get the solvent in there

 

3. put it in a press and let it cure for a at least 10 minutes

 

4. tape it (wrap the whole thing up)

 

5. paste it (multiple footabll shaped segments of craft paper and wheat paste)

 

6. dry it (at least a couple days)

 

7. light it

 

lol

 

holy crap man, my shell assembly time just went from about 20 minutes to 3 days.

 

http://us.movies1.yimg.com/movies.yahoo.com/images/hv/photo/movie_pix/miramax_films/kill_bill__vol__2/gordon_liu/bill.jpg

patience young grasshopper.

[qwezxc12]

I let the shell dry overnight *before* pasting or taping...that way the solvent has somewhere to evaporate to. Good pyro takes patience, I guess. You can go for bringing serious pyro fu or...

http://www.rice.edu/projects/thresher/issues/84/970124/AE/Ninja.final.gif

[ST1DinOH]

I let the shell dry overnight *before* pasting or taping...that way the solvent has somewhere to evaporate to. Good pyro takes patience, I guess. You can go for bringing serious pyro fu or...

http://www.rice.edu/projects/thresher/issues/84/970124/AE/Ninja.final.gif

ah yes...i see...

 

so should i leave them in that press the whole time (day) or just for 10 minutes to allow it to set.

 

i mean if i'm gonna start making as many shells as i'm hoping to make i don't want to have to build a crap load of these presses.

 

and what kind of psi are we talking here?

 

i don't want to blow the thing apart pressing it. is it just enough to keep em together or are we talking more than that?

 

the only reason i ask is because i see a hyrolic floor jack in the picture above and i know you can generate lots of pressure with one of thoes bad boys.

 

i've got access to a ton of trigger clamps and a vise...i'm sure i could rig something up on that order...unless of course i need more psi.

 

oh and LOL @ farley...to bad he had to do heroin and hookers...he was a funny guy, such a shame. but for the record that was his worst movie.

[ULTRABUF]

Hmmm I guess I should have waited a bit longer before I taped the shell. Oh well, plenty more opportunities for refining my process.

On a side note, you may have seen in the arial shells thread that I had a 4" plastic hemi crack after I applied solvent and snapped it together with the other half. Well, I waited till the next day to try another hemi because it was cold out, and when I did it I had 4 hemis crack, and on a couple the crack was kind of wide and I could just tear off the rim of the hemi. I was using acetone at first for a solvent and this worked fine for 3" shells, but I thought this might be the problem. I tried methylated spirits instead and another hemi cracked. I thought maybe I was using too much solvent so I tried meth spirits but I used less. It seemed to work better but I still noticed a very small crack at the equator. I was sick of refilling the top hemi by this time though so I just said screw it and taped the shell up. Any insight on what the problem is?

[Mumbles]

First of all, ethanol is not a solvent for polystyrene. Xylene, Acetone, DCM, toluene all work but not alcohol.

 

To tell you the truth, it sounds like you have some shitty hemis. You haven't been storing them in direct sunlight, have you? Other than that they may be cold and brittle. Perhaps try storing a few hemis indoors over night and see if it works better. Other than this, I don't know what the problem is. You don't mention anything out of the ordinary. On the contrary actually, I am fairly rough on my hemispheres and have never had one crack ever.

[Phildo]

I've applied some serious pressure to my 3" hemis from Cannonfuse and never had one crack so I have to agree you have some defective ones. Where did you buy them?

 

I also twist the 2 halves after gluing to spread the solvent. I figured since that's what you do when gluing PVC plumbing pipe, it can't hurt.

[qwezxc12]

Lah yes...i see...

 

so should i leave them in that press the whole time (day) or just for 10 minutes to allow it to set.

 

i mean if i'm gonna start making as many shells as i'm hoping to make i don't want to have to build a crap load of these presses.

 

and what kind of psi are we talking here?

 

i don't want to blow the thing apart pressing it. is it just enough to keep em together or are we talking more than that?

 

the only reason i ask is because i see a hyrolic floor jack in the picture above and i know you can generate lots of pressure with one of thoes bad boys.

 

i've got access to a ton of trigger clamps and a vise...i'm sure i could rig something up on that order...unless of course i need more psi.

ST1DinOH,

 

I leave the shells in the press for ~10 minutes...just 'till the solvent sets in the seam. This ensures that a tightly filled shell won't push the male/female mating edges of the shell apart while the solvent is still wet. It also means I don't have to hold the shell together after glueing...I can be making another one.

 

After ~10 minutes or so, the shell comes out and air dries overnight to fully cure before taping / pasting up.

 

Use common sense if you clamp a shell with a press...how hard do you push one together by hand? 40lbs? 50lbs? That's all you want to emulate...The press is just for holding the shell until the solvent sets. I apply pressure just until the dissolved polystyrene forms a bead around the seam, no more.

 

Bar clamps, pipe clamps or a vise would do the same...I use the press because 1) I already have one and 2) none of my wood clamps could fit a 6in shell.

 

snip...I also twist the 2 halves after gluing to spread the solvent. I figured since that's what you do when gluing PVC plumbing pipe, it can't hurt.

 

Phildo,

 

I couldn't twist my assembled shells if I tried...it takes a few minutes of tapping and pushing with a big wooden dowel / hammer handle just to get them to seat fully. When I shake one, the only thing I want to hear is a few grains of BP rattling around inside.

[ST1DinOH]

ST1DinOH,

 

I leave the shells in the press for ~10 minutes...just 'till the solvent sets in the seam. This ensures that a tightly filled shell won't push the male/female mating edges of the shell apart while the solvent is still wet. It also means I don't have to hold the shell together after glueing...I can be making another one.

 

After ~10 minutes or so, the shell comes out and air dries overnight to fully cure before taping / pasting up.

 

Use common sense if you clamp a shell with a press...how hard do you push one together by hand? 40lbs? 50lbs? That's all you want to emulate...The press is just for holding the shell until the solvent sets. I apply pressure just until the dissolved polystyrene forms a bead around the seam, no more.

 

Bar clamps, pipe clamps or a vise would do the same...I use the press because 1) I already have one and 2) none of my wood clamps could fit a 6in shell.

alright thanks. i kinda figured you weren't pumping too much psi in that jack but hey...when i saw that hydrolic jack i had to ask.

 

glad it's only 10 minutes, i was holding them tight for a ten count but if i fill them as full as you guys are recomending then that ten count wouldn't be enough to contain the inside forces trying to re-open the shell.

 

now onto my shortcomings in geometry class...

 

is there a formula for the football shaped templates i see people using for cutting thier craft paper?

 

or better yet...

 

a printable template for different sized shells?

 

and does the weight of the craft paper matter much?

[ULTRABUF]

Shit I totally didnt think of alcohol not being a solvent for plastics! Thanks for the heads up, completely slipped my mind. I think storing them in the cold is the problem, they've been in a box out in the shed since I bought them earlier in the year, and its been decently cold lately. Hopefully the spiking and pasting will help give this shell a decent break since its not glued.

[FrKoNaLeaSh1010]

I have never had good luck pasting plastic hemis. I was always a fan of the fiber tape. I would run one strip horizontally along the seam and then run strips vertically around the shell. Number of strips depends on the size of shell. And with the right break I have never had a problem with weak bursts or shell failure due to the hemi not being strong enough...you dont need to paste you can just use the threaded tape however it will take some practice and the right break.

[ST1DinOH]

I have never had good luck pasting plastic hemis. I was always a fan of the fiber tape. I would run one strip horizontally along the seam and then run strips vertically around the shell. Number of strips depends on the size of shell. And with the right break I have never had a problem with weak bursts or shell failure due to the hemi not being strong enough...you dont need to paste you can just use the threaded tape however it will take some practice and the right break.

i'm assuming there won't be much difference with salutes.

 

currently, aside from star shells, we've been toying around with a 50/50 perc/alum mix that works quite well.

 

would it make much difference in the report if the shells are contained (fiber tape wrapped and/or pasted) or does it not matter much at all when dealing with flash?

 

i'm talking strickly 1.75's and 3's here...nothing larger.

[FrKoNaLeaSh1010]

Well I dont have much experience with the 50/50 but I know normal 70/30 perc/al needs relatively no confinement. I have shot ping pong balls full of flash fused and having one layer of duct tape and they worked perfectly as aerial salutes. My normal aerial salutes are 9/16" ID tubes by 1 1/2" shot out of a small 3/4" by 3 1/2" mortar which work perfect with the tubes however even the thin ping pong balls work good enough with high grade flash powder. I am pretty sure with the amount of flash you need for a 1.75 or 3" aerial salute it is going to self confine itself anyway. The ping pong balls I shot out of 1.75" commercial 1.4g tubes. I only taped the ping pong balls to make them a little more snug in the tubes but I am sure no extra reinforcement is required with that amount of flash powder.