Crossette problem

[Merlin]

I just test fired a 1.75" crossette made of D1 comp. It was completely dry and it attained a respectable altitude. I didn't put flash in it but used BP so I didn't expect a break. It went up and back down and the BP popped at about 100 feet. It came on down and burned out on the ground.

I can only think that D1 must be long burning or I used too much pressure. Assuming that I had them over pressed thus too dense, can anyone tell me at what pressure they should be pressed?

[Carbon796]

What is the correct pressing force to use, will vary by who you ask. Just adjust the timing on them to burst at apogee.

[calebkessinger]

How much length was between the shot hole tit and the end of the comet?

 

 

Most people want anywhere from 1000-1500 psi on the comp. adjusting to their liking depending on what comp, binder and moisture.

[Merlin]

Hey, Caleb. Think I have it figured out. Carbon said adjust the timing. I don't have the patience to weight each aliquot of comp so my crossettes come out different lengths. So I am back drilling the fuse hole (slowly and carefully)to allow precisely 1/2 inch of comp burning before it reaches fuse. May have to adjust to get burst at top of flight. Thanks for the ball park pressure. I was probably over pressing. Edited May 19, 2017 by Merlin

[lloyd]

I ran all my hundreds of thousands of them at about 1600psi. Depending upon the timing requirements, I've made them with as little as 1/16" between bottom-flat and tit-bottom.

 

When I was making BP-based crossettes, I did not prime them. As a result (as Shimizu shows), they burned in a 'conical' fashion, with the outside edges taking ignition first, and the inner flat burning more slowly.

 

As a result of that, I could reliably get as short as 1-second delays on properly-pressed crossettes. This was only for either lightly-lifted ones, or ones intended to burst on rise, so as to give a "fleur de lis" pattern in the air. We did all sorts of varieties of lift-to-burst timings to suit special needs.

 

On average, though, the thickness of the 'web' beneath the former tit was about 3/16" to 1/4", suitable to getting a 22mm crossette to about 400' before bursting right at apex.

 

Lloyd

[Merlin]

Thanks Lloyd. I should have mentioned these will be fired from a mortar. Do you think 1/2 inch of D1 is too much base to fuse? They will go 400 or higher.

Hundreds of thousands? I know you mean commercially but that's a lot of comp!

Edited May 19, 2017 by Merlin

[lloyd]

Yeah, Merlin, it was a LOT of comp... about 70-170lb per week during that episode of my life. During peak periods (and with some shop help), we could do 250lb of 22mm crossettes in a week.

 

That included drying time and loading them with burst -- and loading/finishing took as long as pressing. We loaded 64 at a time in a special 'jig' that gave uniform loads. Then, of course, each one needed to be cavity-sealed, 'encased' to fire-proof the sides (not paper wrapped, but the same concept with similar performance), and counted/packaged.

 

I'm not sure what you mean by "they will be fired from a mortar". ALL mine were fired from 'mortars', either single-fire guns sized to the single crossettes, or 5-11 at a time from 3" to 4" guns, sometimes mixed with colored stars.

 

I'm also not clear on what you mean by "1/2 inch of D1". Do you mean the thickness of the base below the shot tit? IF that's what you mean, yes; I think that's way too much. D1 is considerably slower-burning than the comps we used, which were designed so the branches of the 4-segment crossettes (square cavities) would go out before drooping too far. They were supposed to burn out so as to make only a 'gentle curve', not a 'drooping willow style'.

 

Somewhere, I have a photo of them being shot at World Golf Village in Jacksonville, FL. If I can find the photo, I'll post it.

 

Lloyd

Edited May 20, 2017 by lloyd

[Merlin]

What I mean by fired from a mortar is I am under the impression that smaller diameter crossettes could be used like cavity stars in large shells

The Wolters pumps can be pretty large. Mine is in the middle at 1.75 so I paste it to fit snugly in a 1.91" mortar..

I will drill back to.25" as you recommend. My largest shells are single break 4" cylinders which I use with 3/8 and 1/2" stars so I will never use crossettes in them. It's no wonder my test crossette came all the way back down!. At least I took the precaution not to load the flash cavity with anything but BP. However long I have on earth I will still be learning when the end comes.

Thanks much for your expertise.

[lloyd]

Merlin,

EVERY day is a 'learning day', if you haven't wasted it! No matter how much of this I've done, there's a new formula, new method, or a 'twist' on an old one that I haven't yet learned.

 

If you love the art, you love the learning, even when it makes you feel 'dumb' for not having figured it out yourself!

 

Just keep in mind that although I've done (literally) tons of crossettes, many other techniques besides mine are in use with good success. So far as the timing between base and shot-cavity... well, that's a 'physical constraint', and everyone deals with more-or-less the same issues, and in the same ways.

 

Lloyd

Edited May 20, 2017 by lloyd

[OldMarine]

I have an 1½" crossette pump I haven't tried yet but just did a quick measure and it seems to leave just shy of ¼" of comp above the tit on the end of the shot hole former. This might be a bit small for a consumer mine but I plan on trying them on a piston. Think it'll work?

[lloyd]

My guess would be 'yes', Patrick. In fact, that sounds like 'about right'. Just make sure every crossette gets enough fire to ignite all-around. The 'bane' of crossettes is "ignition on one side, only".

 

 

 

Lloyd

Edited May 20, 2017 by lloyd

[gregh]

Merlin, I make 4" cylinder shells with 3/4" crossettes. I do three layers of 11. They seem to work just fine. Go to 5:37.

https://m.youtube.com/watch?v=qBN3CHUyuIw

Edited May 20, 2017 by gregh

[OldMarine]

One more question n the subject (Yeah, right!): Will sali whistle burst a crossette? I'm still not ready to mess with flash if I can help it but if I need to I will.

[Merlin]

One more question n the subject (Yeah, right!): Will sali whistle burst a crossette? I'm still not ready to mess with flash if I can help it but if I need to I will.

Funny. I am chicken to make whistle but not so much flash. Well not afraid to make it but chicken to press it into rockets! I bet Spanish flash will work or even "safer" TPH flash. I have never used whistle but from what I have read it is quite powerful. Lloyd will know.

[Merlin]

Merlin, I make 4" cylinder shells with 3/4" crossettes. I do three layers of 11. They seem to work just fine. Go to 5:37.

https://m.youtube.com/watch?v=qBN3CHUyuIw

I know that will work but right now I only have a 1.75". Nice video!

Merlin, I make 4" cylinder shells with 3/4" crossettes. I do three layers of 11. They seem to work just fine. Go to 5:37.

https://m.youtube.com/watch?v=qBN3CHUyuIw

I know that will work but right now I only have a 1.75". Nice video!

[Carbon796]

Merlin, your crossette pump should have some sort of stop. So you can trim your comets to the exact same length every time. With out having to weigh out your comp for each one. Does your pump not have a stop ?

 

Also you don't need to paste the crossette to fit snugly in a 1.91" mortar. It should already fit nicely with just two paste wraps.

[lloyd]

Patrick,

 

I've made - in just the last four years - probably 100lb of Saly whistle mix, and can't ever recall trying it in a crossette, or even trying to make a firecracker out of it -- just whistles.

 

My guess is that it _might_ work, but would need to be heavily pasted-in to get a good explosion. It might also need an effective way to prevent caking, since saly whistle is pretty hygroscopic. For saly mixes, you might also need a longer shot-tit in order to offer more containment on the bottom end.

 

On my little 3/4" crossettes, not even ordinary 7:3 is enough (because of the small cavity size), unless I paste them in with several turns - about 4 turns of 30lb. Since we try to avoid paper-pasting tiny effects like that, I had to resort to a house-blend of one of those magnesium 'hyper-flash' formulae that had enough explosive force even un-contained (or at least lightly-so) to explode them well.

 

That particular mixture scared me to make it. I'd make my peace with the Lord, kick everyone out of the mixing room, and mix a minimum of 5lb of it per batch. If it went off, I didn't want to know it happened. And that, because 0.3g in an open (un-contained) pile would explode with a loud report! Five pounds might not sound like a lot in a production environment, but it was more than enough for about 15K units... so anywhere from a week to three weeks of production.

Oddly, after 'tuning' that mix as well as we could, it turned out to be too strong and would shatter some crossettes. So then, we ended up diluting the whole mass 50/50 (by volume) with Cab-O-Sil. And even though it made the explosive force less brissant and damaging, it had the surprising effect of making the ignition and its tendency to explode more-sure.

Over more than 10 years of making many tens-of-K of those per year, we averaged something less-than 0.05% failure rate (no, not five percent, five ONE HUNDRETHS of ONE percent -- less than one in every 2000 items fired). Even that figure was hard to really put a finger on, because they failed so infrequently, you nearly always weren't even watching when they did fail.

 

And even when they failed, they still burnt, 'flashed', and did something interesting in the air... just didn't split into the 4 nice pieces we desired.

 

We had one stage-effects competitor (whose name many of you would know) who made 3/8" and 1/4" crossettes!! (Yeah, really). They were fired at almost point-blank range (about 15-25') directly AT an actor, and they had to burst before striking him. For those, he used a tiny dab of one of the metal fulminates applied right to the bottom of the shot-tit. Not me, man! (To be clear, the actor was wearing protective gear... but still!!!)

 

Sooo.... that whole diatribe was just to say that I suspect salicylate whistle mix probably will not be the ideal burst for tiny crossettes; but it might work OK in ones larger than, say 1-1/4" o.d.

 

Lloyd

[Merlin]

Merlin, your crossette pump should have some sort of stop. So you can trim your comets to the exact same length every time. With out having to weigh out your comp for each one. Does your pump not have a stop ?

 

Also you don't need to paste the crossette to fit snugly in a 1.91" mortar. It should already fit nicely with just two paste wraps.

I hot glue a end disk on the crossette (break charge end) and put 1 layer of masking tape and two layers of kraft tape. I prime the bottom with nitro cellulose and 4FA.

There is a pin protruding from the side of the former ( inside cylinder) which aligns with a slot in the outer sleeve but during pressing when it reaches the slot I quit pressing and eject the crossette. If I continue pressing past the slot opening the fuse pin on the former will bottom out. I thought the beginning of the slot in the outer sleeve was like a no pass line on rocket tooling. I don't see any pin above this pin to indicate a "fill" line. I guess I should scratch a line for the fill line at some point above the no pass piN?

I tried to paste a picture but I don't know how on iphone.. It is a Wolter tool.

FullSizeRender.jpg

[OldMarine]

Is this it?

 

[Merlin]

Yes. That's the same model.

[OldMarine]

I think on that one the stop to the top of the tube is the depth stop and the groove is just for ejection. I have a similar one I haven't tried out yet.

[lloyd]

Patrick, that's usually the case; but it's not the 'pressing' depth-stop, it's the stop for "cutting off". One always presses slightly over-length in that sort of mold, then presses the grain out to the stop, and trims the end. Then you rotate the pin to the slot and eject the finished, trimmed comet.

 

All of ours are made that way, with the exception that we have a few with a 'stepped' top on the tube, so we can use different cut-off heights for different tip-to-end spacings, for different timing.

 

Our bulk-pressed small crossettes were always pressed-to-length (not trimmed). We pressed up to 64 at a stroke.

 

Lloyd

[OldMarine]

The other pump I have uses a shot hole former on the base and it looks pretty useless to me. I just use it for solid comets using a paper disc to cover the hole in the base. I'm going to order the 1.75" multi-pump with spinning crossette from Caleb today I think. The few I've tried with my current setup have done pretty well as standalone comets except for my weak bursting.

[Merlin]

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? Of course with the crossette pump the pin has to be aligned with the slot during pressing and ejection to avoid deformity of the crossette cavity.

[Carbon796]

Thats correct. Though I thought Wolter's crossette pumps had a removable pin for ejection. Or you can clock the pin 180° from the slot for pressing/trimming. Then rotate 180 for ejection. " Possibly "