nick2354 Posted June 18, 2009 Posted June 18, 2009 I have managed to obtain many thin wall cardboard tubes, that im going to make into mortars. I just have a few questions. The tubes diameters are 9cm (3.5"), 10cm (4"). The problem I have is that they are spiral wound and only have a 4mm wall. 1. Will it be strong enough to launch 1 break Cannisters from it? They are obviously unplugged, therefore I need to plug them, but I dont have any wood of that size. 2. Can I just put about 4 nails through the tube and then cement the bottom up? I dont think it will be unsafe in anyway, but I just want confirmation. I have read a few methods of coating cardboard mortars that include a mixture of sodium silicate (which I have) and calcium chloride (which I dont have) to just dipping them into varnish or polyurethane. 3. Has anyone had any experience with either method, or knows where to find Calcium Chloride?
Chris Posted June 18, 2009 Posted June 18, 2009 5mm walls is not what I would consider safe. The tube might stand the lift charge, but a shell failure would result in a disaster. I would advice you to laminate the tubes with epoxy impregnated fiberglass fabric . It is cheap and easy(though a little messy) to do, and will drastically improve strength.
Arthur Posted June 18, 2009 Posted June 18, 2009 With 4" tubes 4mm wall is seriously under strength for paper but OK for well made GRP . Paper tubes are fine IF they are thick enough in fact the manner of destruction of a paper tube is lots of confetti size pieces so probably the best tubes because the shrapnel is least damaging. My 3" tubes are spiral wound BUT they are about 15 mm thick walled. Unless you have all the tools and a supply of the optimum size of tube then please buy your tubes from a fireworks place. Tubes to regs and plugs to regs. Proper GRP mortars with integral plugs are so much more convenient and so much lighter.
nick2354 Posted June 18, 2009 Author Posted June 18, 2009 (edited) With 4" tubes 4mm wall is seriously under strength for paper but OK for well made GRP . Paper tubes are fine IF they are thick enough in fact the manner of destruction of a paper tube is lots of confetti size pieces so probably the best tubes because the shrapnel is least damaging. My 3" tubes are spiral wound BUT they are about 15 mm thick walled. Unless you have all the tools and a supply of the optimum size of tube then please buy your tubes from a fireworks place. Tubes to regs and plugs to regs. Proper GRP mortars with integral plugs are so much more convenient and so much lighter. The tubes are strong enough to stand on. 15mm wall is overkill for a 3" mortar. Do you think you are launching nuke? I think I may have to make a shell up, and put one upside down inside it, to see if the mortar can take the force, of a shell going off inside. Edited June 18, 2009 by nick2354
Pretty green flame Posted June 18, 2009 Posted June 18, 2009 My 3" tubes are spiral wound BUT they are about 15 mm thick walled. I would have to agree with Nick, 15mm is way overkill, i've launched rounds shells, canister shells, double break canisters, from a 3" tube with 5mm walls, no damage to the tubes. Ofcourse the tube would not survive a shell going off in the mortar. Some people underestimate the toughness of spiral wound carboard tubes.
Richtee Posted June 18, 2009 Posted June 18, 2009 (edited) The tubes are strong enough to stand on. 15mm wall is overkill for a 3" mortar. Do you think you are launching nuke? I disagree. Well- you may get a couple launches. but my 20 MM 3" tubes have been thru dozens... And 200 gram shells once in a while... 15 G BP. Well, back when they were mine. Sigh. Edited June 18, 2009 by Richtee
Arthur Posted June 18, 2009 Posted June 18, 2009 The tubes I have were FREE so they are the right thickness they are thick enough and more. You could use thinner tubes but You should have some good reason to trust them as a tube failing would ot be nice! Plugs: In paper tubes I simply pour an equal mix of warm dry sand and polyester resin, Guess/calculate the volume of resin needed to make a plug about 2/3 of the bore of the tube.
mike_au Posted June 19, 2009 Posted June 19, 2009 I have used the sodium silicate + calcium chloride inside and linseed oil outside method to coat my mortars, seems to be holding up OK so far although the linseed oil dissolved the liquid nails and made a horrible mess which took days to dry :/ Next time around I will do the linseed coating before cutting and plugging. Calcium chloride can be bought at Bunnings as "Damp rid" in the storage isle.
scrappy Posted June 19, 2009 Posted June 19, 2009 (edited) i have an endless supply of 3" cardboard mortars. At the moment i have about 25 and would trade 12 ( i get about 2 a week and have done for the past 3 months and will do until i don't want any more ) the specs are.... 75mm ID , 98mm OD ( 11mm wall ) 515mm long, ( 20 1/4" ) ....no end plugs.. if you are interested Pm me... oh yea Nick.. how about an up date on the bulk order Edit :- this is mainly directed to those in Au, appologies to those whom are not Edited June 19, 2009 by scrappy
nick2354 Posted June 19, 2009 Author Posted June 19, 2009 i have an endless supply of 3" cardboard mortars. At the moment i have about 25 and would trade 12 ( i get about 2 a week and have done for the past 3 months and will do until i don't want any more ) the specs are.... 75mm ID , 98mm OD ( 11mm wall ) 515mm long, ( 20 1/4" ) ....no end plugs.. if you are interested Pm me... oh yea Nick.. how about an up date on the bulk order Edit :- this is mainly directed to those in Au, appologies to those whom are not The order: Everything has been made and paid for but they still havent sent it out yet, because I need to tell them a Notify party and a Consignee (I think I will be the consignee).If anyone knows anything about importing could you please PM me. I have finished exams and Im thinking of using my dads company as the Notify party. Your 3" tubes im very interested in, how much for each?
Bonny Posted June 19, 2009 Posted June 19, 2009 I use ~3"ID 3/8" (9.5mm) wall mortars all the time for 3" ball and single break cans weighing up to about 1lb. I haven't treated them with anything, and after about 10 firings, the inside has lost only about 1 layer of paper. I'm not worried as I have an endless supply at work, so when needed I'll just remove the screwed in wood plugs and replace. I also just tested some 1/4" wall (6.35mm) tubes with ball shells only and they seem fine. I don't think I'd fire heavier cans from them though.
Mumbles Posted June 19, 2009 Posted June 19, 2009 I'd at least bury the tubes. It's amazing what a little earth around the mortar can do to reinforce a mortar. I've fired 3" shells out of 3" ID mailing tubes before in a pinch. They lasted through 4 or 5 shells. It then got rained on, so it's hard to tell the damage it sustained as it was shredding from being so wet.
nick2354 Posted July 14, 2009 Author Posted July 14, 2009 (edited) I decided to test the tubes out, after so much criticism of the tubes and their strength. I made up a 3.5" shell and put it upside down in my 3.5" mortar to find out how devastating a shell going off would be. The mortar took the shell really well, although the wall of my fire pit that it was facing had been completely knocked over. I have a video, I will upload it soon. EDIT: here is the video, skip to the 40 second mark. Edited July 15, 2009 by nick2354
Plasm7 Posted July 15, 2009 Posted July 15, 2009 I decided to test the tubes out, after so much criticism of the tubes and their strength. I made up a 3.5" shell and put it upside down in my 3.5" mortar to find out how devastating a shell going off would be. The mortar took the shell really well, although the wall of my fire pit that it was facing had been completely knocked over. I have a video, I will upload it soon. EDIT: here is the video, skip to the 40 second mark. nice videos on your youtube account. If you dont want to worry about the tubes just put a few in a 5gallon bucket and fill it with sand and it should solve alot of problems with the tube
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