Homemade fiberglass mortars

[LiamPyro]

I was thinking about constructing a small mortar for some ball shells I'm going to make. The shell

hemispheres are about 1 3/8 inch diameter, so the finished shells will be a bit more.

I happen to have a bunch of fiberglass cloth and epoxy resin in my garage, and was thinking about using it

for the tube. Anything I should know before I make it? Obviously I will wait until one of the shells is complete so I can make it the right size. What would I use for a plug? I was thinking of something strong and non moisture-absorbent such as caulk or epoxy. Thanks!

[taiwanluthiers]

Seems that shell's finished diameter should be about right for a 1.75" mortar. You can always find ways to increase the shell diameter by overpasting it, wrapping it in additional layers of paper, etc. but I just don't know if I trust homemade mortars. I suppose it will work if you make it at least 1/4" thick though but I'd complete a shell and see how big it is before making your own mortar. There are problems like roundness that could happen with homemade mortars. I've made one out of paper and it works, however it was slightly oval.

 

Plus 1.75" fiberglass or HDPE mortars are cheap so why bother?

[psyco_1322]

Use a wooden plug, at least as tall as it's wide. You could just buy a gun too.

[Respirator]

I just recently made my own 2" fiberglass mortar and used treated pine for the plug, epoxied into the tube

 

... but I just don't know if I trust homemade mortars. I suppose it will work if you make it at least 1/4" thick though but I'd complete a shell and see how big it is before making your own mortar. There are problems like roundness that could happen with homemade mortars. I've made one out of paper and it works, however it was slightly oval.

I personally trust my mortars if made properly with fiberglass cloth that can at least make 1 full revolution around the mortar along its full length. If you only have thin strips of cloth, try overlaying them, otherwise it is most likely to fail at the seams.

 

Providing that you have a dowel or mold to base your tube on, I doubt roundness to be a problem with fiberglass. Paper/cardboard tubes can deform during drying and storage but fiber tends to keep it's shape, especially is you only remove the former when fully dry.

 

 

Plus 1.75" fiberglass or HDPE mortars are cheap so why bother?

Well, some governments take pyro bans further than others. LiamPyro, where are you located?

Edited May 9, 2014 by Respirator

[LiamPyro]

I'm in California, unfortunately. Anyways, I think I'll try using a homemade mortar first, and if it doesn't work I'll buy one.

[LiamPyro]

Mortar tubes and most chemicals can be shipped here, but the shipping is usually outrageous because most of the companies are based on the easy coast.

[Thezoranator]

I do have a 1.81 inch HDPE mortar like I told you and I probably will be able to give it to you and even though the shell is a tiny bit smaller it would probably still work. I suggest you use either some gummy or kraft tape and make it a bit wider, just so it would fit better.

[Arthur]

If you really must make mortars then think about the mould or former, it needs making carefully to enable you to get the moulding off a core with a small or zero taper. Maybe the tube will be plugged in the forming process, maybe you need air pressure in the core to force the tube to release the moulding, maybe a DIY mortar will cost more in trial and error than a professional mortar. Commercial shrink wrap film often comes on 2" or 3" bore tubes of great strength, keep looking to a tube that you can repurpose, just remember that a card mortar needs to have walls of great strength, and a suitable plug.

 

As you will be reusing this tube hopefully perhaps you could spend a little on the tube and get a good one by economy courier. remember that a mortar failure is usually BAD and people may get hurt, so this is one bit you must get right first time.

[LiamPyro]

Good point. I think I'll measure my shell when it's complete and either find a cardboard tube the right size or order

something online. If I used cardboard, I would probably want to wrap it with additional paper to strengthen it and

coat it in some sort of sealer like polyurethane, right?

[Arthur]

My 2" card mortars are wound paper about 6mm thick and plugged with timber glued in and nailed -some have polyester resin poured in to make plugs.

My 3" card mortars are about 15mm wall thickness, plugged with wood or resin.

 

My 2 and 3" mortars made from HDPE (yellow gas) pipe are plugged with timber.

[Bobosan]

Cardboard mortars will serve you well with proper preparation. With thick walled spiral tubes, glue down loose ends and dip the entire tube in a wood hardener such as Minwax. Minwax is a bit expensive but I have read that clear polyurethane mixed 50/50 with acetone is close to the same. I usually glue, press in place and staple/screw the wood end plugs before dipping in the Minwax.

I also reinforce the lift charge area of the tube with fiberglass strapping tape.

 

Edited May 11, 2014 by Bobosan

[ivars21]

If you are considering cardboard tubes - http://www.amateurpyro.com/forums/topic/7748-cardboard-tube-mortars/ my topic might be useful.

[psyco_1322]

Once you get to the point that the lift is tearing apart that thick cardboard tube, a few wraps of tape is not going to stop it. It's practically useless.

[Bobosan]

Once you get to the point that the lift is tearing apart that thick cardboard tube, a few wraps of tape is not going to stop it. It's practically useless.

 

Yup, that's the point it gets tossed out. The wrap helps to keep the tube from bulging and weakening to an early failure.

[schroedinger]

That cardboard mortar looks beautifull.

I woulnd't dare to use a homemade fibreglass mortar. If you know what you are doing build it, and use with some barricade. If you look at industrial fibreglass mortars, you will see that those are often not made that accurate and often seame like most mass cheap mass gods, ok but not that superrior. A homemade one by sm1 who know's what he is doing and using the same materials will properbly much stronger

[ddewees]

Has anyone ever made rocket support sleeves out of fiberglass? Is it rigid and strong enough for that?

 

I find myself wanting support sleeves for so many different applications... but don't have the money or capability of having them machined. I'm also not a fan of the pvc/hose clamp devices either.

[schroedinger]

Have a look at youtube the movie of tom rebenklau posted by displayfireworks1, he show how he uses just a plain metall tube

[jessoman]

I was just watching that T.R video, for the plethora amount of times... He's so inspiring. That sleeve he uses is great, any machinist could turn it up providing your using a consistent OD tube.