Guide for Building a Bowling Ball Mortar.

[Double D]

Those cylinders are like hens teeth here, tough to find on the cheap!

I could buy one for 375 bucks...... But I dont need one that bad! 

Are you sure?

 Are you talking about presserized gas cylinder or are you talking about a DOT  3AA2400?

Some of use have been looking for one of these tanks for years with out luck.

Not just any pressurized tank  can be used.  The only one that will work is the DOT 3AA2400.

[DarbinCo]

Yea I seen a whole dock full of them today, well there was 8 to 10 of them sitting there anyways. 3AA2400 I could have had one for 475.00 at that place.

[KABAR2]

I think most people use ones that have not passed inspection with pressure testing to the companies that fill them they are worthless,

But if it's a good usable tank they will probably cost ya.

[DarbinCo]

I think most people use ones that have not passed inspection with pressure testing to the companies that fill them they are worthless,

But if it's a good usable tank they will probably cost ya.

Tomorrow I will be talking to the guy that does this work in this area. I will know more then but I found out today that these tanks that dont pass testing are mostly repaired and retested and certified again or sent off to larger shops for the work to be done. Most of the tanks that have been deemed unusable have been arced on the sides from a welder. These 2400 tanks just dont go bad...


What about finding some large dia. seamless pipe and doing up a big breach plug?

A bowling ball is 8.5" dia right?   

[Double D]

Yea I seen a whole dock full of them today, well there was 8 to 10 of them sitting there anyways. 3AA2400 I could have had one for 475.00 at that place.

Great, what gas was in them?

You don't want a new one you want one that failed testing.  Ask for it and tell them you prefer one with bottom or neck removed...they may speak to you then.

[RocklockI]

Yea I seen a whole dock full of them today, well there was 8 to 10 3AA2400's of them sitting there anyways.  I could have had one for 475.00 at that place.

If they are rare enough to have had people looking for oline for years , I'd grab as many as I could . BE THE SOUCRE for 3AA2400's sell two or three and recoup your cost .

This aycettyenne stuffage sounds like fun ................ you's guys say it is really ,really twitchy ..........

How can an empty tank not be empty ? If you fill it with an inert gas ....is it still explosive ?

Like into the pours of the steel explosive ? I'm missing something ?

Tracy it seems like we need to get some acytelylenne gas , I believe it rates futher studies under close supervision of an adult . Do you know any adults ?

Gary

[DarbinCo]

DD
Oxygen was in them. I'll get ahold of this other guy tomorrow. They all talked to me, I told them I wanted one that was out of cert or damaged etc.. One guy on the phone said.... I bet I know what your going to do with it! I said you think? his reply was "your going to make a device to hurl bowling balls arnt you" We both laughed, he was the most helpful of them all and had the best price on a used tank for me!   

I also found a 3AA1800 tank I could get for 75 bucks, like new.... I might see what it would take to trade that one in and upgrade to the 2500, might be a cheaper way into one..

I may have also found some 10" seamless pipe that has an OD of 10.75 and 1.00 walls, that would be a 8.75 ID......

[Double D]

I had the following question on this subject via email.  It's a good question and I'm sure others may also have the same or similar questions so I decide to share it with everyone. I did edit the quote to protect the anonymity of the person sending the email

I have a question on the powder chamber on the BB mortar.

I see one person says to use 6  in. OD breech and weld it to the butt on the outside of theCly. using a 2 in. X 2 in. powder chamber.
    
Another person  says us a 4 in. ODX 6 in. long  with the powder chamber in it, 2x2 in. This breech plug is  on the inside of the tank and the fuse hole is made  with a rod like fixed to the inside, The butt end of the  4 in. has the tunnion weld to it.

I have a 3AA2400 tank now.   I like the 4 in. steel  pipe on the inside  as it make the wt. less on the unit. But if I have to I will use the  6 in. steel, The 4 in. x 6 in. long is $24.00 will the 6 in. is $50.00, And the wt. is more,  I will put a 2 in. to 2 1/2 in powder chamber in the steel and use fuse,   I would like your idea on it. I think I perfer the 4 in.  Thanks for you time

Here is my response.

Yours is a perfectly legitimate question and if you have the question then I can assure you, others do also.  Your question is better asked on the board but I do understand the reluctance to post.

First you want too cut the bottom off the tank and see if a bowling ball will indeed fit.

Whether you put the powder chamber inside or out side is strictly your call.  I would build mine inside.

Here the rule.  The thickness of the chamber wall should be the same thickness as the diameter of the bore. The 4 inch diameter with 2 inch powder chamber is to small and not safe.

If you have a piece steel you are considering using as chamber and want to know what size powder chamber to make in it, divide the diameter by 3. The will give you the maximum safe powder chamber  diameter  for the piece of steel.  6 in/3=2 in powder chamber.   4 in /3 = 1.33 inch diameter.

To determine the length, you need a piece of pipe with the same inside diameter as the purposed powder chamber. Figure the maximum powder charge for the bore.  Lets say for the example you use the 6 inch piece.  Your powder chamber diameter is 2 inches.  The rule of thumb  is 2 oz of cannons grade black powder per inch of bore. So for 2 inch bore,  4 ozs is you maximum powder charge. Pour 4 ozs of cannon grade powder down a 2 inch ID piece of pipe and measure how long the column of powder is. What ever this measurement is add   the diameter of your chamber to it for wall thickness.  Lets just say for example the 4 oz powder column is 3.75 inch long. you will need a breech plug that is 6 inches in diameter and 5.75 inch long.  Your powder chamber will be 2 inches in diameter and 3.75 inches deep.  Warning this is just an example to explain the theory.  Do not use these numbers.

I would go for the heavier weight and the 6 inch piece. You need all  the weight you can get to dampen recoil from shooting a 16 lb bowling ball.

[dougrunnels]

As I have stated here before, I still have the unused bottom of the cylinder that I used to build my BBM and would be happy to donate it someone who is serious about building one.  The inside bottom in not concave like the top but a person could still install powder chamber into it allowing the BB to rest on top.  I am in the Houston area (Spring) but I have no idea what shipping for this would cost.  I haven't weighed it but it maybe be under that 75 lbs limit.  Might have to be cut off again to make that or to fit the box.  Bowling balls fit it.  It just needs a new home.  And it's free!  If you come get it!

dougrunnels@sbcglobal.net

[DarbinCo]

On this page
http://www.fedsteel.com/products/catalog_carbon_106.aspx

They list a 10 inch boiler and pressure vessel pipe with a 10.75 OD and 1" wall thickness, that would bring the ID down to 8.750. One could open it up to the required windage if needed.

I bet its expensive though.....


Dougrunnels
Did that come from a 3AA2400 tank

[dougrunnels]

DarbinCo,

Yes it did.  I have pics of the stampings on the cylinder also, although the DOT pic is blurred due to the flash.
But the BB fits and it shoots wonderfully and whistles and makes a great thump 600 yds away to everyone’s amazement. It's tons of fun.  The hard part is getting replacement bowling balls.

[dougrunnels]

I just went to a small welding supply store that had "stored bottles" in the back.
Talked to the guys and they let me look over what they had.  The first cylinder I got and cut in half would not work.  Too small.  I went back and measured the circumference to get the proper cylinder.  It just so happens the the DOT 3AA2400 was it.  They had one and gave it to me when I told them I was gonna make a cannon.  I don't think they believed me but I got the cylinder.
"You will never get anything for free unless you ask for it"

[Double D]

Drawings:

 


 

I have been thinking about this design. 

I no longer feel that it is okay to weld the chamber to the bottom of the barrel .  Welding the chamber to the bottom of the barrel puts a weld right at the mouth of the powder chamber.  Because welds have porosity they are not good in cannons.  With the weld right at the mouth of the chamber  pressure and heat will  blast powder residue right into the weld.  The corrosive effects can quickly weaken the weld and the weld can fail.

A better way to do this is to weld the chamber to a trunnion, insert the chamber into the bottom of the tank and weld the tank to the trunnion.  It will also look like a mortar when you are done.

[DH2]

I have been thinking about this design. 

*snip*

A better way to do this is to weld the chamber to a trunnion, insert the chamber into the bottom of the tank and weld the tank to the trunnion.  It will also look like a mortar when you are done.

That'd make a good amount of sense to do it like that, but you'd wind up with one heck of a fill weld. Now that might not be too much of a problem, but it could present a few from a production stand point. If you only recessed the breech into the tube by a half inch or so you can protect the welds by keeping them out of the initial blast from ignition, as well as using a smaller size fill weld to reinforce the joint.

The other option that occurs to me is to take off the top of the tank right under the valve stem and turn out a recessed space in the end of the breech plug. By placing the convex top of the tank into the concave space on the breech plug you make a much stronger joint by taking away all of the perpendicular forces acting on the welds. You can also round off the breech plug for aesthetics. The down side is that this would require a lathe.

Pic to follow when able.

(Sorry for such a blast from the past with this thread resurrection, but Basic and Ordnance School have kept me slightly busy and out of the loop)

[jamesbeat]

We have two gas cylinders at work, one full of helium, and one empty one that an old supplier never bothered picking up. I might be able to have the latter one, because the store is moving to new premises and they are just going to leave it behind.

The full one is a 3AA2400, but the scrap one is 3Asomething (I didn't write it down)
I googled it, and a chart told me that it should be 7" dia. but I measured the circumference of both, and calculated that there is only 1/2" difference in diameter, which is around 9".
A little research has led me to believe that the specs refer to things like filling pressures etc, and that dimensions can vary a great deal.
The orphan tank is from 1944, so maybe new ones are 7" diameter, but this one certainly isn't.
I left my measurements at work, but I believe that as long as the walls are about 1/4" thick, a bowling ball will fit with adequate windage.

So, don't just go by the number, take some measurements.

EDIT: it's 3A2015

[Double D]

The dimensions are from the official  specs of the tank and the only tank that will work is the 3AA2400.  The others are two small. 

Cut the end off and see.

[jamesbeat]

DD, I don't mean to be obtuse, but it's not as simple as that.
If you go here:
http://www.dla.mil/dlaps/dlai/i4145.25.htm
You'll find some government data about gas cylinders.
If you scroll down past all the stuff about gas and get to the part about cylinders, you'll see what I'm talking about.

It explains that over the years, actual dimensions have varied as much as 2" in OD.
'3AA' appears to refer to the specs of the steel the cylinder is made from.
It even mentions that you should pay attention to this variation in size if you need a particular size cylinder to fit into a specific fixture.

The specs say that my cylinder should be 7", but it's definitely way bigger than that.

For a modern made cylinder, the specs probably are standard, but an old cylinder might not obey the rules.
I'd hate for someone to spend a load of money on one only to discover it's no good...

As you rightly point out though, the only way to know for sure is to cut the thing open

[Double D]

Do be obtuse, if you find some data that helps find the right tank, we are listening.

Here is the chart I refer to http://www.taylorwharton.com/assets/base/doc/products/cylinders/TW1102_StandardHighPressure.pdf

We have it listed in the stickies by the way.  If you look a the  chart you will see you will need at least 9.25 inch diameter.

What is the number of this 1944 tank?

[jamesbeat]

Yes, I think I remember seeing that document when I was looking up the code for this cylinder.
 There's no 3A cylinders listed on that one at all, they are all 3AA.


The tank is marked 3A2015.
I measured the circumference and it was 74cm, which works out as an OD of 9.3"

The other tank at work (which is in on hire from the helium company so I can't have it) is marked 3AA2400.
Circumference is 75cm, which is equivalent to an OD of 9.4"

I didn't bother getting an accurate height measurement, because it's irrelevant for cannon purposes, but the 3A2015 is somewhat shorter than the 3AA2400

From what I understand, wall thicknesses tend to be in the order of 1/4".
Providing the wall thicknesses of the two cylinders are equal, the 3A2015 should be less than 1/8" smaller in
internal diameter.


Just for giggles, here's another pdf spec sheet that lists the 3AA2400 as 9" OD, and the 3A2015 as 7"OD, which is 2" less than the 3A2015 I have physically measured:

http://www.google.com/url?sa=t&source=web&cd=4&ved=0CCkQFjAD&url=http%3A%2F%2Fwww.airgas.com%2Fdocuments%2Fpdf%2FCylDimension.pdf&rct=j&q=3a2015%20cylinder&ei=i_iBTrT2H4Hq0gH9-523AQ&usg=AFQjCNFL6sB_SBIVICko3D1Z2MwMofcM_Q&cad=rja



I'm not going to worry about it too much at the moment anyway. My main priority is to try to get this 5' tall 140lb cylinder home before the store closes down and I lose my chance.

I don't even have the equipment to cut it yet, so I won't be building a mortar any time soon.
I just don't want to miss the opportunity to get my hands on a free cylinder while I have the chance.

[Double D]

I had that Air Gas saved some where before, but never used it as it does no include internal measurements.

Pull the valve out of that tank fill it with water and then get you hacksaw our and start cutting...report back in 4 or 5 days and let us know if the tankl is the right ID and did your arm fall off. 

[Cat Whisperer]

I had that Air Gas saved some where before, but never used it as it does no include internal measurements.

Pull the valve out of that tank fill it with water and then get you hacksaw our and start cutting...report back in 4 or 5 days and let us know if the tankl is the right ID and did your arm fall off. 

I cut mine with a 4-1/4" angle grinder.

But if you only need to know the ID, a small hole drilled in the side will allow a wire to be inserted to measure it.

[jamesbeat]

Fill it with water?
Is that in case of flammable gas, or or some other reason?
The tank held helium, so no worries on that score.

I was actually considering the hacksaw idea, just cut an inch a day until it's done. It would also be a good workout

[Double D]

yeah fill it with water, to keep the heat down when hack sawing... It was hydrogen that got the Hindenburg, wasn't.  Helium makes you talk like a duck.

[jamesbeat]

Ducks can talk?!
Now I feel really guilty for eating them

I might still do the water thing, I have a pretty fast hacksaw arm...

[smokemjoe]

3AA2400 DOT300CF tank Dem. are,  outside 9.180 or 9 1/4, or Cir.29 1/4, inside ID 8.610, wall thickness .274,   I had trouble getting a tank, I had a machince shop call the place that sell gas, told them they needed a reject tank that size to make wheels from and they were made of chrome moly steel that was needed, I had one the next day, cost me $15.00 for tank at junk steel price and 3 cases of beer.
  I used the top part for my  1st. mortar and just got a 2nd. one done using the bottom part  and welded the chamber up inside, I have pics. to post  after this week in shoot. Joe

[Winger Ed.]

I cut mine with a 4-1/4" angle grinder.

That's what I used on mine also, and it does a great job.
I wrapped 2" masking tape around the cylinder to have a easy to follow guide.
 
If you go that route, I'd suggest ya bundle up. 
When running a cut off wheel on a angle grinder:
I wear a leather jacket, heavy arc welding gloves, full face shield and ear muffs.
 
While cutting the tank for my mortar, the wheel got in a bind and shattered.
Even hitting the leather jacket-- I still got a bruise on my chest. 
Then the same large chunk of the disc crawled on up,,,,,,,,, and 'trenched' the full face shield,
bouncing off the face shield- it stuck in the sheetrock ceiling of the shop.
 

[smokemjoe]

DH2: Something that may helps you out is not to mill a flat  1 in. deep into the trunnion, I went about  3/16 deep and cleaned up the area that sits on the bottom of the tank. 1 in. deep weakens the 2 in. piece and you have to inlett the bottom of the tank in the the wood  more to get your elevation. I put a 3/8s chamfer  on the bottom of the piece for weld, fitted it to the trunnion so it was center and wil not move.  Pics. also. Hope this helps. Joe

[mooke]

I started looking around for the materials to build me one of these. I went to the local welding supply shop and asked for a 3AA2400 tank that failed. Two days and $20 later I had one in my possession. The bad news is right on the tank was written BV for bad valve, and (2) L Cracks........Junk. The guy I got it from says they usually mark the problem area and there was no marks. I rigged up an adapter to pressure test, ran it up to 80lbs and sprayed with soapy water. Only leaks I found were on my adapter and the air compressor tank itself. I understand they normally fill to 2000-2400lbs and test higher. I went ahead and cut it apart and of course a ball fits with about 3/16 to spare (lol).
I'm a little leery of using this. Does anyone else worry about why their tank failed? Would magnafluxing be an option?
Maybe I will make it into a bell.

Dave

[Double D]

Keep in mimd the tank is an expansion chamber and ball holder, the powder chamber is where the pressure is.  The neck doesn't matter as you are cutting it off anyway,

[mooke]

Is it the neck that usually fails?