Making spolette timing fuse

[deer]

I have several questions regarding making one. I have 7 and 10mm PVC tube rolling cores, but only 10mm Aluminium rod for ramming. I plan to use 80gr kraft paper to roll them with 2:1 PVA glue to water.

• Which one would work better and can I maybe use BP+Dextrin putty to fill the 7mm without the need to ram?
• How thick the wall must be so it contains burning and fire doesn't escape prematurely?
• Does it need to be processed additionally for fuse use (e.g. soaked in sodium bicarbonate solution)?
• Do I need true milled / wet mixed BP for this? Wouldn't coffee grinder C+S+Saltpetre mix work (ground separately OFC) - I'm hand milling my BP with mortar and pestle, so I prefer making minimum needed actual BP.

P.S. Off topic question - why would someone choose cut or rolled stars? IMHO basic level rolling seems simpler and more consistent than cutting. Where is the main difference?

 

Edit: duh, confused crossette with spolette. No wonder google search was weird..

Edited May 28, 2015 by deer

[nater]

Spolettes are the only time I use commercial meal-d. This is because reliability and consistent timing are essential to them.

 

There is no reason why you cannot use your own powder, although I would use milled and finely granulated BP. You want the BP to be reasonably fast If you get your BP to burn just under 3 Seconds per inch, you can use all the published timing. If your BP burns too slow, you risk not being able to press a column tall enough to withstand the pressure while burning and still obtain the proper burn time.

 

It would be wise to make an amount of BP and use it only for spolettes. This way you can test your burn time, label the powder and trust it when you need to use it. Otherwise, test each batch of BP you use for spolettes to ensure you have proper timing.

 

You can use your rod for ramming as the former to roll your tubes. The commercial tubes I use have walls about 1/8" thick.

[deer]

What about the internal diameter? I'm leaning towards the 7mm one. Even while I don't have aluminium rod, I think one can get copper wire in that size.

IMHO, pros:

*Cheaper (less paper, BP, etc),

*Less prone to blow-out,

*Causes smaller "irregularity" in shell,

 

Cons:

*Probably less consistent

*More difficult rolling

 

Am I missing anything?

[mikeee]

Copper is lot more expensive material than aluminum. For rolling your own tubes you should be

able to find wood dowels the correct size for less money. You want to ram the powder to gain a

consistent grain density which provides a reliable/repeatable burn time. Either size would work

fine for a spolette. A larger diameter tube will provide more surface area when attaching/gluing

it to your shells. The spolette entry point to a shell needs to be sealed well, or your lift charge

can breach the seal and ignite the contents of the shell.

[schroedinger]

Spolettes are very reliable and as consistent as your bp ist.

 

6-8 mm is a good size. Smaller then 6 mm is a pitty to work with, bigger doesn't give any advantage. A 6 mm spolette gives enough fire to ignite a normal burst charge or flash made with dark al. (Don't know about flake al).

Additinally you can add some blackmatch and nosing.

Dor priming normally scratching the surface is enough. Sometimes blackmatch is also tied over the spolette.

[Arthur]

Spollettes are like 1/4" gerbes without the clay plug! 1/4" is a good tube bore and you can press increments of good fine powder to get the required delay time. If your tubes are a bit long then you can push a little black match in either or both ends.

[nater]

Typically a spolette is rammed with one end flush to the ramming surface and the other left open. Using 5/16" ID tubes, I ram or press in 1/4" increments. I add one extra increment and then drill the open end back with a 1/8" drill bit with the spolette held in a jig on a small drill press. This lets me set the drilling depth to a precise amount. The small drilled out core helps with flame propegation and it also helps lock the powder column in place much like a bulkhead in a rocket. Finally the open space in the tube is filled with several sticks of black match. This bundle of match is nosed and tied off. A small hole is pierced in the nosing to allow the gasses from the spolette to escape into the burst in the event the black match fails for some reason.

 

After the shell is finished and ready for the lift wrap, the flush end is scratched with an awl to roughen the powder and scrape off any paste. A small dap of BP / Nitrocellulose lacquer slurry is added to half the flush end of the powder. A piece of black match is folded like a top hat or rabbit ears and tied off with tarred or pasted twine.

 

I have some spolettes for insert shells to finish tomorrow when I get off from work. I will post pictures of the process if anyone is interested. There are other ways to do this and some take shortcuts. This is how I was shown to make them by a very talented builder. It is the traditional Italian-American method as has been passed down to other pyros and rarely fails.

[Twignberry]

I've just posted up a collection of photos for the way I do my spolettes in the tutorial section.

 

It's mostly inline with what nater has posted

 

I haven't drilled out my spolettes with a drill press before but I will be now . Sounds like a great way to get perfect consistent timing.

 

When I am nosing with the black match, I just wrap one turn of tape and lightly crush it around the black match.