15 replies to this topic

[RFD]

Hi all,when i am putting two halves of a small shell together(2in mostly) i always manage a bit of spillage,(two left hands possibly)had contemplated using a layer of clingfilm or foodwrap in the states i think its called over one half and then it can be inverted on the other half without any disturbance or spillage,quistion is will it prevent the flame proagation between the halves and end up with half a shell being blind,possibly a bit of a dim quistion i know but would rather ask for some opinions rather than fire shells off and be disapointed.

[Brakkie]

Instead of using clinfilm rather use 1 layer of tissuepaper. You know the tissue- and toiletpapers these day's have several layers? Get some normal tissuepapers or some fancy (thin) toiletpaper and take off only 1 layer. Put it one side of the shell and it will burst just fine.

I don't know about the clinfilm, it might work, it might not. The tissuepaper works that's a proven fact.

[phildunford]

Given the wall of flame & heat you get inside a shell, a bit of cling film is not going to stop it!

[digger]

I agree cling film won't harm. Use whatever is at hand within reason. On larger double and triple petal shells I end up using lots of layers of strong tissue (the stuff used on model airplane chassis) and have not had a fire block problem yet.

You could even use the polythene bag method if you are random filling. I.E. you could cut a little hole in the bottom of a food bag put it over the internal fuse fill it with stars and burst to approximately the right level tie it off with a bit of string and test fit the top hemi. You can then adjust the amount of filling and refit to get the perfect amount in there.

Edited by digger, 03 December 2008 - 05:53 PM.

[Bonny]

On my 3" shells I use a layer of "tissue paper" although I've never been able to figure out what is meant by that for pyro use. I use the crispy thin stuff that often accompanies new clothes and gifts packed in gift bags. In IPP it recommends punching some holes (with a pin or something) to aid flame passage. I have made shells with and without pinholes and have noticed no difference.

[pyromaniac303]

I use the tissue paper sold in gift shops for wrapping presents.

I cut a square piece of tissue paper which will take up approximately 4 identical hemispheres in, for example, a 5" shell this would be 10" by 10". I then push the centre of the paper into the centre of the hemi without fuse hole, and flatten it until it conforms to the shape of the hemi. I fill in the normal way and fold the remaining flaps in over the shell contents, and trim if it seems excessively thick in places. I repeat this for the other side, but with the added modification of cutting a fuse hole in the paper. Although there may be up to 3 or 4 layers of tissue paper in places, this has never caused a problem for me.

I prefer not to simply put a layer in between the 2 hemis, without first surrounding the contents as this doesnt allow a 'bulging' fit, the tissue would tear if the hemi was slightly overfilled and caused outward pressure on it.

Also that tissue paper makes great touchpaper when soaked in saturated KNO3 solution.

[Bonny]

I use the tissue paper sold in gift shops for wrapping presents.

As noted in my earlier post, that is what I use too, but can someone elaborate on exactly what "tissue paper" is when commonly referred to as "tissue paper" in pyro? gift wrap tissue? Toilet tissue?

[spanner]

Who’d have thought there were 165 styles of tissue paper to choose from at one site?
http://www.papermart...CFQ-bnAodUGyQjw

Anyway, the tissue I’ve seen used most has been the white “crispy”, thin (.0125 mm) type that is found as wrapping paper.

It works for flash paper, nosing, Senko Hanabi and the like.

[pyroduck7]

no, i couldent ever do that either, (i can now, but i still sometimes make mistakes) what i did was i took a peice of paper, put it on one shell hemi, inverted it then put it ontop of the other and then slided the paper out - it works every time!

[Mortartube]

I would suggest that tissue paper may be safer. Plastics can generate static.

[knackers]

i have never fired a shell from a mortar, but have fired many shells on rockets, but am ready to give it a try, , i have 2.5", 3" and 4" round plastic shells and 2.5" cylindrical cans,...... visco fuse is unavailable but i have plenty of black match,,,

how can i launch a shell with black match as a fuse in the lift cup without it going off to early or in unison with the lift charge,

i tried spiral wrapping blackmatch with a cotton string then coating it in nc laquer to hold it in place but it burnt like a slowed down quick match,

any ideas would be great thanks

[pyrotrev]

Not easily is the answer I'm afraid Phill 63. To get a consistent burn rate the powder in your time fuse needs to be compacted. Try doing a search on "spolette" and you should find some advice on how to make something reliable.

[digger]

i have never fired a shell from a mortar, but have fired many shells on rockets, but am ready to give it a try, , i have 2.5", 3" and 4" round plastic shells and 2.5" cylindrical cans,...... visco fuse is unavailable but i have plenty of black match,,,

how can i launch a shell with black match as a fuse in the lift cup without it going off to early or in unison with the lift charge,

i tried spiral wrapping blackmatch with a cotton string then coating it in nc laquer to hold it in place but it burnt like a slowed down quick match,

any ideas would be great thanks

If you can't get time fuse how about using a spoulette instead. You should be able to get very accurate timing.

If you don't already know a spoulette is a fuse made by ramming a composition (usually meal) in a narrow tube of around 6mm ID (usually). It effectively burns like a mini end burning motor.

Have a look at the wolter pyro tools web page under shell tooling to get an idea of the tools needed to make them.

D

Edit you beat me to it Trev

Edited by digger, 24 January 2009 - 12:08 AM.

[cooperman435]

spoolettes are your friend here.

I'm not sure what fuse holes are in the shell cases you have so this will be a brief description of what I did when in your situation.

For the purpose of this I will work on a time fuse hole of 12mm IE the hole the time fuse goes into is 12mm Id so your fuse would be 12mm OD.

Find a few pieces of 8mm OD stainless steel rod around 150mm long (aluminium is OK but a little soft for this size I find but brass is fine too) it can be anything in reality from 5mm up to 10mm but wants to be smaller than the ID of the fuse hole.

Use one of them to roll tubes about 30mm to 50mm long around preferably using a few wraps of sticky tape around the rod first so the tube made is just slightly loose on an unwrapped rod. The tube wants to be rolled so its OD is that of the fuse hole when dry so this may take a few attempts depending on shrinkage. The tubes want to be hard when dry to allow ramming of composition into them. If using an 8mm rod the tube will have a wall thickness of 2mm.

Once a reasonably tight fitting tube has been made and can be reliably reproduced take a few and ram 10mm of BP into it, another can be done with 20mm of powder and 30mm and 40mm etc. When test burns of these are done time them as accurately as you can.

Use the mm/seconds to calculate the powder needed for a given time delay IE if it works out .5seconds for 10mm and 1 second for 20mm and a 3 second delay is wanted then 60mm of BP is needed. (time is in reality about 1second per 10mm btw)

When ramming be sure to consolidate the powder well to avoid gaps and you shouldn't have any problems. Ideally a small piece of wood with a short length of the rod inserted into it pointed on the end so as to create an indent in the base of the powder when ramming a tube supported on it will aid ignition as there is a greater flame at the end of the burn from the spoolette.

[knackers]

"Thanks for your help guys" very much appreciated
spoulettes it is, i've got 4 days off so i'll give it a go