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How to connect mortars in cakes?


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#1 MinamotoKobayashi

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Posted 07 November 2019 - 09:47 PM

Hello forum.

I tried to make my first cake with nine cardboard tubes used like small mortars.

I found the right burst charge and the right diameter of the stars, but .. only the first mortar was ignited!

At the bottom of every tube, just over the surface of the pressed bentonite, I created small holes where I passed

and connected the tubes thru small pieces of normal fuse.

Then I putted 10 grams of granulated hot BP and finally the cylindrical stars.

Well, none of the fuses were ignited: the first detonation do not ignite the following fuses.

I had the same issue when I make 2" shells placed inside bigger shells: the main detonation do not ignite the fuses connected to the

small shells.

Anyone know how to ignite a fuse from a detonation (mortar or shells?)

 



#2 pyrokid

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Posted 07 November 2019 - 09:58 PM

What do you mean "normal fuse" ? I have dissected many Chinese cakes and most of them are fused with some type of visco fuse. Visco fuse is the type with a powder core contained by spiral threads coated with lacquer. There are some important points: I have observed that fuse used in cakes has a thinner coating of lacquer. Waterproofing is not such a necessity in cakes, and lacquer impedes ignition. If you used "cannon fuse" or some other such off-the-shelf visco fuse, the heavy lacquer coating could have caused poor ignition. It's also possible that the violence of lift is destroying the fuse, but this seems unlikely. In all the cakes I've made, passfire from tube to tube has been the least of my concerns.

 

Some recommendations:

 

1) Cut the fuse at an angle to expose a larger cross section of powder.

2) Prime the fuse at both ends to improve ignition and maintain integrity of the powder core.

3) Adjust timing to allow for the use of black match between tubes.

 

An interesting aside: While the Chinese DO use different speeds of visco fuse to control timing, they also know that variation in timing can be achieved with fuse of a constant speed by varying the angle of adjacent tubes to one another, such that the length of fuse between tubes is varied. Constant speed fuse with different lengths between tubes gives different shot speeds.



#3 SKC

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Posted 08 November 2019 - 12:11 AM

After a nice failure of 15shot cake made by standard fuse for fireworks like fountains shells made me understand that cake pattern requires different quality of blackmatch. All the shots got ignited simulteniously & it was a pure CATO(lol). I felt slow fuse has to be used. Still I don't have access to visco soI was wondering how people successfully used to make cakes before invention of visco. An old & kind pyromaker has helped me giving a composition of slow fuse & some other specifications for building a cake. I'll share that in this forum when I give that a go.

#4 kaotch

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Posted 08 November 2019 - 10:49 AM

Did you make a video ? Looking back frame by frame might discover the problem. Possibly your fuse to the second mortar was blown out!



#5 BetICouldMake1

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Posted 08 November 2019 - 12:30 PM

I'm with kaotch, sound like the lift from the first shot probably pulled the fuse out. Were the fuses glued or taped in place? I like using hot glue around fuses when I make or modify cakes, but masking or foil tape also works well. In term of the shell of shells not working that sounds like a prime/match issue. Inserts need to either be cross matched if using time fuse, or slurry primed, especially if the shell is hard breaking. 

 

In terms of timing without using visco, you can use distance between tubes to control ignition rate. This could be done with blackmatch, or even just a powder train. You could also use something like a mini spolette between shots, but that would be a lot of work. Unconfined blackmatch burns relatively slowly, the hard part is keeping it isolated from the lift so it doesn't all light at once, but not having it confined. 



#6 SKC

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Posted 08 November 2019 - 02:43 PM

No Kaotch, no chance for a recording. The xxxl length-sized match only saved me. I didn't even got the chance to look back. All got set off at once. But just hold on, cool down your glue gun & keep foil tapes at bay.Very easy & non instrumental techniques are involved. But I need some time.

#7 MinamotoKobayashi

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Posted 09 November 2019 - 08:08 PM

Thanks Pyrokid, cutting the fuses at 45° has 100% solved my issue! No need to prime the cutted extremity and not need to glue the fuses.

BUT .. since I want to reuse the cardboard tubes many times (it is a pity to trash all the integer cardboard tubes everytime),

I was forced to pass the fuses externally to the cake. In that way I can reload the tubes and reinsert easily new fuses without unglue everytime all the tubes.

The solution works well but the ignition between the mortars becomed too slow because the fuses had more lenght.

So I used the green fast Visco fuse (not the white superfast one), but all the mortars were ignited almost istantly.

Not a bad show, but slowing a little bit the ignition could be much better.

It seems that I will be forced to build my own fuses to reach the right burning speed.


Edited by MinamotoKobayashi, 09 November 2019 - 08:10 PM.





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