80 replies to this topic

[Chaz]

Salvaging tubes from professional multi shot devices like cakes can do quite nicely. A single cake will last me for ages, although typically the tubes are a little too wide for rockets or roman candles, and too small for shells.

I did take a row of 5 tubes from a cake, which handily already have 2 fuse holes at the bottom, to make a 5 shot aerial maroon cake of my own. The video is on my site if you would like to see it.

[sizzle]

So far I have bought tubes from Pyrotube.com but it costs and awful lot of money to have them shipped over here to the UK, where can I get hold of some relatively cheaply in the UK?

[karlfoxman]

So far I have bought tubes from Pyrotube.com but it costs and awful lot of money to have them shipped over here to the UK, where can I get hold of some relatively cheaply in the UK?

Depends on what tubes you want, most tubes can be scavenged from places that make use of anything with a cardboard tube thorough the middle. If your after mortar tubes for shells then a quick search will give you the answers. Oh and is it really that hard to roll your own?

[sizzle]

Oh and is it really that hard to roll your own?

For me it is as my main interest is rockets and I need thick casings for that, plus I am an impatient person, I need any size I can get really. Not mortar tubes just normal pyro tubes. I got some from a carpet shop but their thinest was a little too wide (1.5" ID).

[karlfoxman]

For me it is as my main interest is rockets and I need thick casings for that, plus I am an impatient person, I need any size I can get really. Not mortar tubes just normal pyro tubes. I got some from a carpet shop but their thinest was a little too wide (1.5" ID).

Being in this hobby whilst being impatient is not a good thing as it implies cutting corners, cutting corners leads to dangers and very bad things. Thick cases can easily be rolled with kraft paper, when done properly they will be hard as rock and very tough. I know essextubes.co.uk supply to the pyrotechnic industry so give them a call.

[sizzle]

Being in this hobby whilst being impatient is not a good thing as it implies cutting corners, cutting corners leads to dangers and very bad things. Thick cases can easily be rolled with kraft paper, when done properly they will be hard as rock and very tough. I know essextubes.co.uk supply to the pyrotechnic industry so give them a call.

I'm not THAT Impatient, I never cut corners in pyrotechnics because of obvious reasons, I don't know any stores that sell Kraft paper near me. I will try essextubes.co.uk

[Creepin_pyro]

It shouldn't be very hard to find kraft paper - it doesn't nessicairily need to be "kraft" either.

IIRC, Essex Tubes' smallest tube is a 52mm pre-plugged mortar - you might be able to get them to make custom sizes though...

[Pretty green flames]

I'm not THAT Impatient, I never cut corners in pyrotechnics because of obvious reasons, I don't know any stores that sell Kraft paper near me. I will try essextubes.co.uk

Steve's Inoxia.co.uk sells rolls of 90gram craft.

[paul]

And with this calculation, you know exactly how long the paper strip must be to get a certain diametre, wall thickness or whatever:
This may be very usefull if your tubes for rockets have to have all the same strenght.



L= lenght of the strip you?ll need
w=desired wall-thickness of the tube
p=papers thickness
d=diametre of the rod you roll your tube on

[karlfoxman]

And with this calculation, you know exactly how long the paper strip must be to get a certain diametre, wall thickness or whatever:
This may be very usefull if your tubes for rockets have to have all the same strenght.



L= lenght of the strip you?ll need
w=desired wall-thickness of the tube
p=papers thickness
d=diametre of the rod you roll your tube on

Nice one Paul, thats now in my black book!!!

[paul]

The credit for that goes to a friend of mine I needed a calculation for this once and he needed a fair amount of time to calculate it

But it works out great. Tested it up to 0,5mm cardboard.

Greets,

paul

[BigG]

don't wanna dump water on the calebration, buy finding paper thickness is going to bit of a task....

Edited by BigG, 14 October 2005 - 12:37 PM.

[alany]

Indeed, but you can get a reasonable figure with a pair of calipers (or better a micrometer) and averaging several measurements in different places. You can also measure the thickness of a ream or a folded strip to multiply up the dimensions to something easier to measure.

The contribution of the paste and shrinkage are non-trivial effects too, making the basic formula an approximation at best, but none the less a very useful one. For the lazy (like me) I wrote a calculator for it:

http://www.vk2zay.ne...s/paperTube.php

[paul]

alany is right. This way you can get quite acurate values. I used that method, too and as the lenghts the calculation gives me give EXACTLY the calculated result I?m sure the measured values were right

[JamesH]

Just to expand a bit on alany's post. Averaging the paper thickness from several points is a good idea since the thickness will vary slightly.

The point I want to make is that these small variations in thickness, while having a minimal effect on the calculated length of paper required for a smaller, thinner tube, will have a greater effect in larger diameter tubes with thicker walls. The thicker the walls become the less accurate the calculation will be, not only because of the multiplling variation in paper thickness but also due to the amount of airspace between paper layers.
A thicker wall means more layers of paper, more possible airspaces between layers and multiplied variation in paper thickness.
These factors coupled together will result in the actual length of paper required being considerably less than the calculated.
A short reference to this effect can be found in David sleeter's book "Amateur Rocket Motor Construction" on page 231.

But as alany says it is a very useful aproximation that will work well for the sizes of tubes commonly hand rolled, since most of us dont roll very large, very thick tubes!

Hats off to your friend paul for working out that formula!