11 replies to this topic

[italteen3]

Here is the situation.

Have some 6" length 1" ID 1.5" OD tubes I am using for mortars. The small 2g titanium salutes I am shooting up are double fused with green falling leaves fuse for a rising green tail. I have seen many single shot aerials before, but they utilize a plastic base that the mortar fits snugly into.

At first I hot glued the mortar to a square wooden block. First test shot went almost perfect, second one the hot glue seal broke and shell was underlifted. Proper precautions were taken so even the low burst was not a problem, except to my feelings . Third one I doubled the lift to about 3.5 grams(The shell weighed total 14 grams approx, this is commercial FFg, figuring it was the BP. WOW was I wrong. Third one shot up way too high and the tail was not to be seen accept on the way down where it went off right above the ground and the mortar's seal was not gently broken off, it flew off.

Do most of you press a clay plug, then glue to a base? Screw it in then glue? Epoxy?(bit to costly for me though )

I was thinking of first get a sturdy mount and use about 1.5-2 grams of lift, which hopefully shouldnt blow the fuse out.

[Richard H]

I would suspect that ramming a slightly recessed clay plug and then gluing to the base would be a good idea. Alternatively use a cork or wood dowel. All of these are used in commerce.

[Jerronimo]

Why not make a hole in the wooden block, the same size as the o.d. of the tube and then glue it in place with some construction or wood glue.

[Flashy]

I managed to drag myself out of bed to quickly knock this up. The dowel is 1" and is easily availiable, at least it is at this side of the pond.




The dowell is just drilled and then countersunk to allow the screw head to be recessed into the dowel. The tube can then either be glued in place or just slotted over. Depending on what type of fit the tube is to the dowel. My tubes have a tight interferance fit so there is no need to glue them.

Edited by Flashy, 19 March 2005 - 12:00 PM.

[italteen3]

Thanks both RichardH and Flashy for your help! Jerronimo, I tried doing it before but dont have a drill bit that large and getting a hole that big accurately is not too easy. Thanks for dragging yourself out of bed to help a fellow pyro!

[Chaz]

I used a large amount of plaster of paris to plug the bottom end of my 44mm ID mortar. Theres about an inch of it down there. This gives it a bit of weight, so the mortar can stand up on its own quite easily. I usually trap the mortar between 4 bricks to keep it steady, but it would be a good idea for me to take a large piece of wood for a baseplate and drill a hole the same diameter as the OD of the tube like Jerronimo suggested.

You could just plug the bottom like I have and then glue the tube to a flat baseplate, the bond wouldent have to be very strong because the stress is between the tube and whatever is plugging it, and in my case an inch of plaster is plugging it.

[pyromedic]

All the professional tubes that I use have a wooden plug at least 2" thick screwed from the outside in with fairly heavy screws. I don't have anything as small as 1" but i presume a 2" length of 1" dowel would do the job of plugging the tube. For setting up we use a length of builders rebar banged securely into the ground at the correct angle with a piece of 3/4" ply for the tube to rest on. The tube being lashed to this to stop any movement. This serves 2 purposes... It stops your tube being buried as you fire. I think some bloke called Newton gabbled on about acions having equal and opposite reactions.
Secondly it reduces the amount of dampness that your tube will absorb from the ground.
Not sure I like the idea if a tube just being supported with 4 bricks. If the tube were to blow for any reason, your nice soft (reasonably) card would be intermingled with the occasional half brick CHAZ. Enough to really upset your day!!!

Also you need someting with a posative fixing to the tube ie screws or nails. As a rammed plug on card or plastic tubes will come loose fairly quickly as the tube does expand a fraction as the shell is fired. Alot of time could be wasted re-ramming tubes after every firing

[italteen3]

I screwed the tube to the base with two brass screws both opposite of each other. Then I used a little hot glue to seal any possible gap, none was visible though.

For lift the 1/10 weight for lift rule was used. The 2g salute was lifted perfectly. Green falling leaves fuse provided a nice tail on the way up into a nice snowball of sparks and a decent bang.

For future multi shots utilizing the same tubes I believe I will be using the methods you gus described earlier. Thanks again everyone for the help. If you would like to see a video let me know and I will host it. It is not high quality visually due to my lack of a firewire card for best transfer rate.

Edited by italteen3, 14 April 2005 - 07:03 PM.

[italteen3]

Finally got my custom tubes in about a week ago. They are so sexy. Ive been spending most of my time working on small shells and building up some 1, 3, 5, and 10 shot racks/cakes. Doing some tuning and trying to master a time fuse for small shells with only visco without a prime, unless absolutely necessary. Thought I would share some pics.

First pic

Second pic

Third pic

The tubes are 1 1/16" ID and a 1" OD was screwed on to the wooden base. A ring of hot glue was placed inside the mortar and the mortar was then slid on the dowel. They are very sturdy, but I decided to go with 2 pieces of 1/2" plywood screwed into each other. One piece has 1 1/4" holes drilled in them and then sanded slightly(OD of tubes is 1 5/16") for a nice tight fit. 1/2" dowel pieces are glued into the mortar so when the tube is placed in plywood the bottom is flush with where the dowel rod is glued in.

The 10 shot rack, not pictured, is meant to be reloadable. I just dont know how to get the fuse back through?

[1145climber]

On the subject, i am making a 2 inch PVC mortar, and was also curious about the mounting. The directions on pyrotechnix's site say to just glu the pvc with some strong glue to a wooden base, using glue like liquid nails. I originally used liquid nails, but it didnt seem strong enough, so i ripped it off and re-glued it using plenty of gorilla glue. This stuff feels and looks strong. so i was wondering:

is just glue-ing the PVC to the wooden base enough? do i need to have a dowel or clay end cap of some sort? any suggestions appreciated.

[italteen3]

First off I wouldnt use pvc as a mortar. If you have a strong shell break in the pvc, you will have A LOT of nice sharp shrapnel flying everywhere. I would recomend highly to use only cardboard, hdpe, or fiberglass mortars. Steel should not be used unless buried or you have plenty of fallout area. Your better off just playing it safe and not use pvc or any metal.

If you just glue a mortar to a base you probably will experience the mortar blowing the glued seal out. There will almost always be tiny small sand-grain sized air gaps the lift stress will blow-out. Better off finding a 2" OD wooden plug and screwing it into the mortar THEN gluing it to a base. Make sure you mark the height of the plug on the outside of the mortar if you are going to side fuse it.

I had problems with a 1" mortar and just gluing it to the base. You can figure out the rest .

[Phoenix]

Anything much larger than 30mm or so is best plugged with, as italteen3 says, a cylinder of wood about 1 tube ID long, glued and/or screwed or nailed in place. If you've got a blade the right size, this can be cut with a holesaw minus the pilot drill (using a drill press) or turned on a lathe. Obviously the former is dependant on having the correct sized holesaw.

As an experiment, I have used used ordinary brick-laying mortar (no pun intended) to plug a 40mm tube. I drilled three holes at the base of the tube, so that I could insert nails into the plug whilst it was still wet. The plug was about 60mm long. The mortar is still alive and well after about four firings. I have seen 40mm Cat. 3 mines plugged in this way.

IMHO, the best way to support a single mortar tube (ie not a big rack of them) is to bury it in the ground up to within a few cm of the muzzle. This may be impractical if you're using a lot of mortars in racks, but it does offer excellent stability and protection from shrapnel should one burst. It would be a very wise precaution if you are using PVC. I wrap paper mortars in plastic bags before burying them, so that they aren't in contact with damp earth. It's a good idea to put a firm base (such as a plank of wood) under a buried mortar, as they can drive themselves into the ground from the recoil. However, this is not something I've ever experienced (though I've only shot 4" and smaller single break shells).