Crossette problem

[lloyd]

"You are saying to put an excess amount of comp in the pump and press to where the pin is above the entrance to the slot then eject to the entrance of the slot and trim off and eject?"

-------------------

That's generally the way they're made, yes. You put just a LITTLE more comp in than necessary to keep the pin off the top of the sleeve. Then you press it OUT until the pin contacts the sleeve. You trim. Then you rotate to the slot to eject.

 

I try to keep the excess down under 1/8", so that it trims easily, and can also be easily re-screened back into the batch for more. It's also beneficial NOT to try to just 'slice it off', but to scrape it off in thin layers until the knife is flush with the end of the sleeve. That helps prevent 'chipping-out' around the periphery, and also to prevent chips from making pockets in the surface. You want the trimmed face to be SMOOTH, without defects.

 

I think it goes without saying that a straight knife is necessary, not a curved one! (but I'll say it anyway <grin>)

 

Lloyd

Edited May 20, 2017 by lloyd

[Merlin]

Got it figured out. Pressed 0.35" thick disk of electric green dried and crossettes of D1 glitter. Glued together with NC-BP around fuse hole and Carpenters glue around the outer circumference. My test worked fine as far as pieces staying mated. Went up green but didn't get crossette break effect on this one. May have over done the break charge. I will add 5FA NC slurry to interior to help with ignition and Top off with 70-30.

Thanks for the drying and joining advice Lloyd.

[lloyd]

Merlin,

What did happen on the intended break? Some minor diagnosis might tell what to do.

 

It sounds like you have a handle on it, already. But shout if you need to collaborate. I've made so many crossettes (commercially) I can hardly count them. And the color versions were always tricky. BP crossettes? "Piece of cake"! <grin>

 

Small crossettes (say, smaller than 30mm o.d.) may require more-energetic burst than simple 7:3. It gets 'problematic' at that point, because most amateurs don't want to handle sensitive magnesium-fueled flash mixtures (or maybe I should say shouldn't handle them! <grin>).

 

Lloyd

Edited June 21, 2017 by lloyd

[Merlin]

Upon reviewing slow motion video it appears that it stayed green to the apex then a very bright flash of light and then nothing. It's like stars blowing blind in a shell. They are 1.75 inch crossettes with the star cavity filled with 70-30. Perhaps too much break? Maybe the interior should be primed?

[Mumbles]

Did the crossette or audio give any sound when the break charge went off? If it really was blown blind you'd probably still hear the pop or crack. Likewise if the D1 portion was destroyed, you'd probably still hear it and probably see a cloud of sparks.

 

The other common mode of failure is jetting. You often see a brighter flash with this, but little to no sound. Sometime the top portion of the crossette will shoot off randomly in some direction, but sometimes it doesn't. With a crossette made of two compositions, I could see this happening and kind of extinguishing the flame before it can transfer to the D1. This mode of failure generally means you need more confinement of the break charge either in terms of a longer nipple so more comp is available to confine the cavity, better fire transfer from the nipple, or using a shot.

[Merlin]

It wasn't a pop or Crack sound it was an extremely loud high velocity blast with several echoes. I am thinking the 70-30 is too powerful. Maybe it needs to be slow flash. There was a fuse in contact with the green comp through the D1 comp so perhaps the break occurred before the D1 could light. Maybe I should not have the fuse ignite a the instant the green burns through? Perhaps set the fuse depth 5 mm above the D1 comp and reduce the green to 0.30"?

[DavidF]

I've only done a few crossette shells but I have had good luck right out of the gate. I make 1" diameter shotless crossettes. To burst them I use a small dose of salicylate whistle, then a pistol primer, then top off with whistle. The timing is quite good this way. This is a radical way I came up with and it worked so well I just didn't want to change anything, for fear I would take a step back.

 

The whistle is soft-granulated, and pressed lightly into the bottom of the shot hole. This allows very rapid fire transfer, and I think it's better than futzing with fancy fuses. The pistol primers might not even be necessary. But, I think they make the comets crack more uniformly. I'm not suggesting others do what I do, at all. It's just what works for this guy that always has to be different

 

I made crossettes that burst erratically or only jetted, shortly after my run of good ones and I traced it back to increasing the pressing force by 50% - not the smartest move. They were too hard to work right.

 

This is my first crossette shell. Sorry for the poor video. The whistle was 70-30-1-3 benzoate whistle, so I really think the primers made quite a difference.

 

https://www.youtube.com/watch?v=2i_kmSBXOxk

 

The whole reason for choosing this method was to eliminate distracting flashes of light from a relatively dim effect, and I was glad it worked

[DavidF]

Lloyd, now you tell me! I have tried so hard to leave 1/8" and trim it cleanly in one go, and it never works. It always leaves the pockets you mention. It's obvious that they can't help the timing. Now I just weigh them and trim the stickout. Lots of work for sure.

 

My knife blade is curved a bit too- up and down though, not side to side

[Merlin]

This is my first crossette shell. Sorry for the poor video. The whistle was 70-30-1-3 benzoate whistle, so I really think the primers made quite a difference.

 

That was a great shell! A crossette shell with perfect timing! I am just trying to get a single crossette right! I have never made whistle. The idea of pressing into a rocket sounds a bit dangerous so I just never made the comp.

I think I have my particular problem figured out. I think I should time it so the glitter comp lights from the bottom and burns a bit before the burst.

The way I had it set the burst occurred the instant the color comp burned out so the glitter was burst before it could ignite. I suppose without really thinking about it I intended the flash to ignite the glitter.

I do have a question. Do you really need to entirely fill the cavity of the crossette with 70-30?

I am using a Wolter 1.75 pump and the cavity will hold a significant amount of flash.

Edited June 21, 2017 by Merlin

[lloyd]

No! You may find that you are best off by actually filling the cavity (in terms of reliabilty and burst pattern), but you might want to 'cut' your flash about 50:50 with Cab-O-Sil, and see if that's enough power for you. When we did large crossettes, we usually 'cut' the flash.

 

Lloyd

[rsambo]

Lloyd, would you mind stating what burst you would typically use for a smaller 3/4 inch crossette ?

 

thanks,

Sam.

[lloyd]

Sam,

For 3/4" crossettes, I use a form of "hyperburst" made with 2u magnesium, K-dichromate, and finely-milled perchlorate. Even then, I have to 'dilute' it 50/50 by volume with Cab-O-Sil.

 

But, it's not stuff to be fooled with. It's impact AND friction sensitive, and will explode with a loud report in an open pile of less than 0.3g!!!

 

I would throw everyone out of the mixing facility when it was time to make it. Then, I said my prayers before mixing. It's terrible stuff, but very effective!

 

Lloyd

Edited June 21, 2017 by lloyd

[Merlin]

OK I am going to try one tonight half filled with 70-30 and finished filling with 5FA. Already made it before reading post. If it doesn't work I will try cutting with Cabosil. Thanks Edited June 21, 2017 by Merlin

[lloyd]

Oh... I forgot... I didn't mean "by weight" in Cab-O-Sil, but by volume! That would make a HUGE difference! <grin>

 

If you BP-finish, be sure to "shake 'em up" after filling, or they'll not burst uniformly, bottom-to-top.

 

Lloyd

[Sparx88]

Oh... I forgot... I didn't mean "by weight" in Cab-O-Sil, but by volume! That would make a HUGE difference! <grin>

 

If you BP-finish, be sure to "shake 'em up" after filling, or they'll not burst uniformly, bottom-to-top.

 

Lloyd

 

I have a question about cutting the flash for this. I have the problem of the crossettes either jetting or being blown up. When they jet it happens when I fill them up, and blown up when under filled like m80's. Could this be fixed by granulating the flash with just alcohol? Or leaving it alone and mixing in rice granules or screened fine vermiculite to pass fire more quickly allowing me to use even less flash?

[lloyd]

'Diluting' the flash with a substance like Cab-O-Sil (or rice hulls, or grits-o-cob) will tend to improve that situation.

 

A crossette is best-made "fully-filled", but often the burst can be too-powerful, tending to fragment the piece, instead of breaking it into large segments.. Diluting it with inerts improves that situation.

 

I find Cab-O-Sil to be the most-effective of all diluting materials, although I have used them all, with various degrees of success.

 

Lloyd

Edited June 21, 2017 by lloyd

[Mumbles]

Some dilutants, like granular BP, have the added advantage of helping to obscure the bright flash resulting from using 70/30. This is most advantageous in dimmer and more delicate effects like charcoal and lampblack streamers. With colored crossettes and even glitters the bright flash is less distracting.

[rsambo]

Sam,

For 3/4" crossettes, I use a form of "hyperburst" made with 2u magnesium, K-dichromate, and finely-milled perchlorate. Even then, I have to 'dilute' it 50/50 by volume with Cab-O-Sil.

 

But, it's not stuff to be fooled with. It's impact AND friction sensitive, and will explode with a loud report in an open pile of less than 0.3g!!!

 

I would throw everyone out of the mixing facility when it was time to make it. Then, I said my prayers before mixing. It's terrible stuff, but very effective!

 

Lloyd

 

Thanks,

 

doesn't sound like that would be much fun to mix. Is there a reasonable alternative to the hyerflash and the fine magnesium. You can probably tell I'm struggling with my 3/4 inch crossettes. 1 inch and above no problem but in the smaller sizes it's a challenge.

[lloyd]

Sambo,

 

The only solution I know of for crossettes that small (besides 'hyperburst') is "tied shots" with a chlorate/antimony sulfide 'dark flash'. They're a pain to make, but Mike Swisher has done an elegant job of teaching pyros how to make them. I don't have a vid... he taught us in-person at an FPAG meeting.

 

Lloyd

[Merlin]

There are a number of formulas at procreations under compositions. It does appear they are all extremely dangerous.

[Mumbles]

John Reilly gave an alternative method for making shots that doesn't involve tying. If anyone is interested I'd be happy to post my notes. Encasing 70/30 in a shot can help a bit over loose in some cases. This is more for jetting vs. not jetting, but may help a little bit for a more concentrated explosion.

 

Edit, I decided to go ahead and post it.

 

Originally posted on 6/6/06 by John Reilly

 

http://groups.google.com/group/rec.pyrotechnics/browse_thread/thread/ad1938a90753687a/70aab6618a1aa20b?hl=en&ie=UTF-8&q=John+Reilly+rolled+shots#70aab6618a1aa20b

 

The method described in Fulcanelli part II is the traditional Italian
method and is the best in my opinion. The stringing of the hole shots
as described is an art. The dried shots are cut apart and the string
ears overlap the cavity end of the crossette star and are held in plase
by the pasted paper crown when finishing the loaded star. The string
keeps the shot from falling through the burned open cavity as the comet
is spinning through the air. I cheat a little and use 3" gummed paper
tape to roll the shots using a 4 point crimp to close one end before
punching and fusing.
For the 1-1/4" comet shots I take a 5/16" diameter piece of wooden
dowel (mandrel) which is about 4 to 5" long and waxed by rubbing with a
candle stub to avoid the paper's sticking to it. One end of this
mandrel is bored dead center with an 1/8" hole about 3/8" deep. The 3"
gummed kraft paper tape (std. 60# weight) is cut into 3" lengths to
give three turns around the mandrel. (One 3" strip gives 5 finished
"hole shots". A piece of this paper is placed gum side up with the
mandrel squared and centered on the edge nearest you. With thumbs and
forefingers the first turn of paper is laid on the mandrel and held
tightly against the rolling board with the fingers of the left hand (if
you're right handed) grabbing the damped sponge and wiping the
remaining pasted side of paper to activate the glue. The thin casing
is formed with a push of the palm of the hand and rolled firmly back
and forth the round and tighten the 3" long tube. The damp tube is
slipped up about 1/8" to 3/16" past the drilled end and with athin
awl, a 4 point crimp is started on the overlapping paper. (12:00, 3:00,
6:00 and 9:00 o'clock positions. The mandrel with the overlap crimp
end is smashed smartly down on the rolling table which folds the 4
point crimp down on the end of the mandrel. While the mandrel (crimped
tube end) is held tightly against the table the mallet is taken and the
mandrel is give two or three quick raps to "set" the crimp closed. The
awl is taken and a hole punched in the center of the crimp to allow for
the insertion of the fuse later.
The case is slipped up on the mandrel again and with sharp scissors is
snipped off (into a small box) so you have a shot tube with one end
open , one end crimped closed and with a fuse hole in the center of the
crimp. This is repeated 4 more times and the another 3" paper strip is
rolled and so on till you have 100 "shots" or however many you need.
This sounds like it is time consuming but I could have rolled ten shots
in the time it took me to type this.
I use either specially made thin fast match or chinese firecracker
(tissue) fuse which is cut ahead of time into 3/4" lengths: the fuse is
inserted through the hole in the crimp of the shot leaving about 1/4"
projecting outside the crimped end. The shots are all fused first and
then loaded. A number of 1-1/4" pcs of thin cotton or flax string are
cut (one per shot). First, a shot is taken and a piece of the cut
string dropped into the open end of the shot tube with the tag end
hanging out.
A scoop of dark report comp. (50/50 mix of KClO3 and Antimony Sulfide)
is added to the open end of the shot. A pinch of fairly coarse sawdust
is added on top lightly pressing in with the forefinger (string still
hanging out.) Lastly a good smear of white glue (PVA) is run across
the sawdust (keeping the string end out of the way). Set them aside to
dry. When the shots are loaded into the star cavity the string lays
across the comet end. The comets get a 1-1/4" very thin chipboard disc
on the end (holding the string) before the kraft pastewrap is pleated
down over the shot end. (The chipboard disc helps keep the paste from
soaking into the star). There are many method and tricks to cracking
crossettes and this is just one way I find convenient and workable for
me. There is no "correct" technique except the one you find reliable
and feel comfortable with. Flash powder (70/30 KClO4 to blackhead or
similar fine flake aluminum) will work fine with these shots too. I
only use the black antimony and chlorate to avoid the bright flash'

John

From 6/13/06, same source and acquisition date

 

Hi Tes. When I "star crimp" small tubes like these, I simply use the
pointed 1/2" or so of an awl or ice pick. I've made little awls by
taking the sharp ended pivot pin from a cheap metal compass and turning
a little wooden handle on a mini lathe. Drill a hole in the handle use
good 2 part epoxy cement to secure it. I use the same awl to crimp the
tubes and ream the hole for the fuse in crossette shots (don't have to
switch hands or tools). This is how I've made 1/4" or 5/16" bore
bottle rockets since the mid 60s as well. I posted the method 6 months
or so ago on how to make those with strips of gummed kraft tape. The
"core" is formed by simply twisting and pushing the awl point about a
half or 5/8" through the center of the star crimp and into the rammed
fuel core. Quick and easy and they work great with "chrysanthemum 6"
fuel. If the hole shots were a bit larger in diameter, I could use a
.410 shotshell crimp starter die but it's so quick with the 4 point
"crimp and slam" technique that I don't worry about it.

John

[lloyd]

Mumb,

The only problem I see with that plan is that 3/4" crossettes have - at most - a 1/4" square cavity (sorry.. 1/4" diameter... MINE are square). So the size will need to be scaled to fit.

 

Lloyd

Edited June 22, 2017 by lloyd

[Mumbles]

Sorry, I thought that much was common sense. Smaller comet/cavity will require a smaller shot. For my 3/4" crossettes made with Wolter tooling I found using a 3/16" or 7/32" former for the shots was about right. The taper of the cavity combined with the cruciform shape almost made the "ears" obsolete. A shot will friction fit into the cavity and be held in place.

[lloyd]

It IS common-sense, Mumbles. But we're dealing with folks who don't have any experience doing it. Ya' never know.... <grin>

 

Lloyd

[Sparx88]

John Reilly gave an alternative method for making shots that doesn't involve tying. If anyone is interested I'd be happy to post my notes. Encasing 70/30 in a shot can help a bit over loose in some cases. This is more for jetting vs. not jetting, but may help a little bit for a more concentrated explosion.

 

Edit, I decided to go ahead and post it.

 

Originally posted on 6/6/06 by John Reilly

 

http://groups.google.com/group/rec.pyrotechnics/browse_thread/thread/ad1938a90753687a/70aab6618a1aa20b?hl=en&ie=UTF-8&q=John+Reilly+rolled+shots#70aab6618a1aa20b

 

 

Good stuff thank you.

 

I couldn't help pointing out the date John Reilly Posted that.... (twilight zone music) That's a date that gladly happens only once a lifetime!

 

Lloyd also thank you for your help on that.