7 replies to this topic

[wjames]

hi guys.

got a few questions - im just looking for other people's advise.

I have rolled my own tubes in the past...both for rockets, and reports.

i found that although the looked the part, i had a much higher incident of cato's from my own tubes....hence i went back to mass produced tubes.

how many of you guys make your own, and upto what size....what type of paper do you use....

how do you make end plugs....i made mine using thin card, 2 bonded layers, made twice the dia of the tube, then feathered...they worked pretty well.

and lastly....whats your choice of glue for rolling tubes....i know most people use PVA - although some use heat glue sticks for tubes.

i have been using impact glue, pre-applied to the paper ( prior to rolling ) at small intervals.


any advise welcomed !

[digger]

hi guys.

got a few questions - im just looking for other people's advise.

I have rolled my own tubes in the past...both for rockets, and reports.

i found that although the looked the part, i had a much higher incident of cato's from my own tubes....hence i went back to mass produced tubes.

how many of you guys make your own, and upto what size....what type of paper do you use....

how do you make end plugs....i made mine using thin card, 2 bonded layers, made twice the dia of the tube, then feathered...they worked pretty well.

and lastly....whats your choice of glue for rolling tubes....i know most people use PVA - although some use heat glue sticks for tubes.

i have been using impact glue, pre-applied to the paper ( prior to rolling ) at small intervals.


any advise welcomed !

I roll a few tubes for various things, mainly for custom sizes to suit custom tooling. I make all of my rocket tubes and no CATO do date. I simply use 160gsm coloured card (this is important as it soaks up the glue and can be had very cheaply) with PVA + 10% water wrapped around a stainless steel mandrel.

Even with very small wall thicknesses my small rockets (21.3mm ID 37.5g of BP) will lift 200 grams to a very respectable height. However I use a core burner and the rocket is pressed to 5 tonnes so initially the fuel adds to the structural integrity of the engine.

I use the same technique for producing non standard size tubes for candles with no failure to date.

All of my end plugs in these applications are either straight bentonite or mix of molochite 80 & 40 mesh / bentonite / wax. These are simply rammed in (no good for salutes, but there is no need for a strong end cap in salutes from my experience).

Edited by digger, 07 October 2008 - 02:13 PM.

[wjames]

my rolled tubes sound similar to yours....i use 130gsm matt paper, but no PVA.......perhaps i'll try it out....

i think it comes down to my lack of a press.....i ram my powders home using a slide hammer......hard to guess what tonnage it equates too.

i didnt mean endplugs for rockets....more for reports.....i also use bentonite for plugs, sometimes with a little bonding agent added.

i used to use pre-made tubes...that were rolled at an angle.....theyre pants.....they very often split open.

[digger]

my rolled tubes sound similar to yours....i use 130gsm matt paper, but no PVA.......perhaps i'll try it out....

i think it comes down to my lack of a press.....i ram my powders home using a slide hammer......hard to guess what tonnage it equates too.

i didnt mean endplugs for rockets....more for reports.....i also use bentonite for plugs, sometimes with a little bonding agent added.

i used to use pre-made tubes...that were rolled at an angle.....theyre pants.....they very often split open.

Before I got a press I used to hand ram and I still had no tube failures, I did however blow out a couple of nozzles.

For reports I use bentonite at the fuse end with tooling that makes a plug with the fuse through it, at the other end I just glue in a a bit of card that has scrunched over a dowel into a tube. There is no need for strong confinement with reports using flash in my experience (tried a few variations with no change in volume).

The type of card used is critical to the strength of the tubes I make, white card simply does not end up at the same strength as it is thinner for a given weight which does not allow the glue to penetrate it in the same way.

Edited by digger, 07 October 2008 - 05:11 PM.

[bigtonyicu]

I think the slide hammer is the big part of your problem; it delivers a sharp high energy blow, but the duration is way too short as soon as your powder starts compacting it's more then capable of absorbing the blow with out compacting any further.

What happens is your first hit or 2 produces a small plug leaving under it some uncompress powder the subsequent hits don't have enough energy to push that plug further down, a 1 lbs dead blow mallet would deliver easily 10+ times the force.

The only way you should be getting reliable motors with the slide hammer is if your max layer thickness (each installment of powder) was less then half the grain wall thickness

Example: 1lbs motor
3/4 ID
3/16 core

(ID-core)/2 = Grain wall thickness
0.28125 = Grain wall thickness

Grain wall thickness/2 = max layer thickness
0.140625 = max layer thickness

so a 6.25 inch long powder charge would have to be done in 44 layers

I think that your rocket that survive happen to do so due to very very strong tubes and a nice helping of luck (and don't get me wrong, I love luck.... but in pyro I try to make sure I don't need it)

[wjames]

hmmm


i see where you are coming from...give me some time to try with different paper...and a large hammer........

i'll post my results up.

im sure nasa didnt get it right first time !!!!

now that i'll be using a hammer to ram my bp home....i presume a wooden dowel is a good option for a ram ?

thanks once again....i like the way i get advice here, as opposed to people telling me im useless !!!!



As for containment with flash......what differences is there in burn rate between Perc based flash, and Pot Nitrate based flash.....i use Pot Nitrate and powdered magnesium....very very fine.....it burns pretty quick...id say it self confines around 2 grams.....by that i mean 1 gram goes poof....2 grams goes pop....3 grams goes bang.....

[starseeker]

[quote name='wjames' date='Oct 7 2008, 08:47 PM' post='49454']
hmmm


i see where you are coming from...give me some time to try with different paper...and a large hammer........

Not just a big hammer mind,
as Bigtonyicu said,a 1lb dead blow hammer,which is a rubber mallet filled with lead shot.I ordered mine at my local hardware store for about £6.As opposed to a lump hammer,this hammer gives a softer ramming action.

[wjames]

yeah, also gives a longer blow, with less recoil.


a great tool.