Author Topic: Bowling Ball Mortar Help (Read 2058 times)

Ernest T · « **on:** February 09, 2008, 08:00:26 AM »

I am new to this board but have been reading it for several weeks. I have decided to build a bowling ball mortar. I borrowed a high pressure nitrogen bottle from work and cut it off 20 inches the bowling ball fit perfect. With 1/16 to 1/8" windage. Could someone help me with a couple of questions. I do not want to shoot over 400 yards. How small of a powder chamber can I go with. The powder chamber will be on the outside like the Florida Bowling ball mortar. When I cut the valve end of the tank should I cut it off where the curve of the tank ends or where the shoulder above the curve end on the valve side. How do I need to tell the Certified Welder to weld the powder chamber (rod to use etc). What is the best metal to use for the powder chamber. Thanks for any help I can get with this. I have already read every post I could find on this board but these are questions I could not find the answer's to. If anyone could send me pictures that would help too. Pm and I will send you my email address. Thanks again Trent

Cat Whisperer · « **Reply #1 on:** February 10, 2008, 03:45:53 AM »

Earnest T -

WELCOME to the board!!

I have just a minute to write this so let me be BRIEF.

You'll need ABOUT one to two ounces of powder. (DO a search through the threads on 'bowling ball' and you'll find other folks' real-life examples.

Suggest something like 1018 steel - 3 or more inches in diameter with a 1" diameter 2" deep powder chamber. (rough guess). Powder chamber takes the high pressure, tank walls just guide the ball after the pressure peak.

SLEEPY BEEPER · « **Reply #2 on:** February 10, 2008, 12:33:49 PM »

Hi Ernest T, I don't have all the answers for you but I hope this helps. Max load for a bowling ball mortar should be 2 ounces. So a chamber that holds 2 ounces when sitting at a 45 degree angle would work. Mine is bigger. 1 1/8 X 3 inches deep. This is a little to big. I fill the extra space with rice or Cream Of Wheat. This protects the plastic bowling balls from pitting when the burning powder goes off. The valve end should be cut off so the outside cut off area. Is the same width as the piece your welding on (5 inches wide?). The person doing the welding should be good enough to tell you how the welding should be done. If he cannot. Find a better welder. I under cut the outside face of my powder chamber. So a much deeper weld could be built up (J-weld). Also weld the inside. To keep powder residue from getting in where you cannot clean and oil it. I second the use of 1018 steel for the powder chamber. There are other steels that weld well. But make sure you know what it is. Don't use something that is in question. Good luck.

Ernest T · « **Reply #3 on:** February 13, 2008, 12:35:05 PM »

Thanks for your help. I found a piece of 4" round steel. Is there any way I can tell what type it is. It seems to be very hard steel with red sparks when I grind it. Is there any way I can tell if it would be safe for the powder chamber. Trying to cut cost but I know safety comes first.

dominick · « **Reply #4 on:** February 13, 2008, 02:39:25 PM »

If you have a large quanity of 4" stock you plan to use, your best bet is to find a local metallurgist lab and ask for a "numerical designation by composition" test. This will determine the AISI number [1018, 1026, 4130, 4140 etc...] average cost of the test is usually 40 to 60 dollars. Sounds like you may have high carbon steel, not good for welding. There are many other steels that are in the not easily weldable to un-weldable range. For example, 1100 and 1200 series are re-sulfurized [not good]. The Kaiser Liberty ships of WWII had steel with a high sulfur content. The high sulfur content metal along with a design flaw caused those ships to break at the welds and sink in minutes when exposed to the cold and rough Atlantic. Also, the last two numbers are the point percentage of carbon ie, 1018= .18% carbon, 4130= .30% carbon. You want to stay with low carbon for welding. My opinion is it would be best to find a piece of 1018. Dom

Cat Whisperer · « **Reply #5 on:** February 13, 2008, 03:29:34 PM »

Good advice.

KNOWING the type of steel for THE critical part (the powder chamber) is smart.

Grinding and evaluation of the sparks will give you an indication of the carbon content. You should KNOW the type.

Ernest T · « **Reply #6 on:** February 14, 2008, 01:15:42 PM »

Thanks guys for your help. I have fond someone that will make me a powder chamber out of 1018 steel. About the size of the powder chamber, the Florida Mortar id is 2x2.5 deep but the id that are recomended here smaller. What kind of altitude and distance do you get with a full powder chamber 1 1/8x3". Thanks

SLEEPY BEEPER · « **Reply #7 on:** February 15, 2008, 07:29:03 AM »

Hi, A 1 1/8 X 3 powder chamber will send a bowling ball close to a 1/4 mile. But unless you give a lot of thought to adding weight to your barrel. And carefully designing your base. The base will not survive more then a couple 1/4 mile shots. Barrels made out of tanks end up light. This is good for transportation. Bad for shooting distance. If you think you need to shoot long distance. You should be planning a heavier barrel.

Ernest T · « **Reply #8 on:** February 16, 2008, 01:05:19 AM »

Again, Thanks for your help!. Sleepy Beeper I use the pic of your mortar for a guide. I have changed several things thanks to every ones recommendation's. My powder chamber size will be 4x5 long od and 1 1/4 x 2 1/2 deep id and it will be out off 1018 steel. I have a friend that inspect welds for piping in power plants that is going to weld it up for me. What welding rod is used to weld the 1018 to the barrel did you use. How do you go about putting the bands on the barrel. I think this adds to the look of the mortar. Thanks

SLEEPY BEEPER · « **Reply #9 on:** February 16, 2008, 05:14:41 AM »

Hi Ernest T, You asked me 2 very good questions. And I'm going to side step them. Here is why. Welding is half equipment and half experience. What works for me and my equipment. May not work for your welder. Let him make the welding decisions. I would ask him what he wants for welding undercuts (J-weld). So you can pass this information on to the person machining the chamber. Most common welding practices will work with 1018. This is why it was selected. As for putting bands on. It is a lot of work. And can be done last if you still want to do it. I would practice on your cut off piece of barrel. Bend a ring out of flat iron. Cut it 1/16 in short. Weld the seem. Heat it almost red hot. Slide it over the barrel. And get out of the way. If the weld is bad. The band can break and go flying. This is real high on my scary meter. Don't let my answers detour you. You are doing a good job of working through this.

Cat Whisperer · « **Reply #10 on:** February 16, 2008, 05:24:08 AM »

You could get lucky and find a short length of steel pipe that is just the right size, or could be inside machined to JUST smaller than the tube OD.

There are folks here that have done it - on smaller tubes and have posted pictures of the process of heating it up and shrink-fitting it - LOTS of fun at this size.

Cat Whisperer · « **Reply #11 on:** February 16, 2008, 07:42:15 AM »

WHOA! Stop the press!

The beauty of having a discussion is that over the course of the conversation MANY aspects of design considerations are brought up.

OUR FIRST concern here is safety. So lets get back to Principle #1. Use a design the MANY other folks have used over a LONG period of time successfully. [Notably see the requirements for N-SSA and AAA competitions AND SWITLICK's volume on the Complete or More Complete Cannoneer.]

Of concern here is what happens to the tube when one shrink-fits a band around it. (The example I referred to was for a golf-ball caliber mortar - in a MUCH different class when it comes to pressure!)

There is ample evidence that two things happen when shrink fitting a band to a tube: a) the tube is reduced in diameter (inside), and b) there may well be a change in the metallurgy of the tube due to heat. (The pressure in the tube certainly is much less than in the powder chamber; but the characteristic of importance is that of ductility - resistance to hardening after many flexings (firings). Unknown turf.

There are folks that have posted here about shrink-fitting trunnion bands onto a cannon with 1-1/2" wall thickness and SERIOUSLY reducing the ID of the bore (Ellsworth ?).

Consider the alternative methods of securing the bands. (Take heed to the "scary meter" readings.)

Let me repeat from the past - when you light the fuse YOU have to KNOW whether it's a cannon or a bomb !

We are going to be as safe as possible when we do good research and listen for concerns from those 'in-the-know' around us. Don't hesitate to ask nor to speakup! (And T. THANKS for the call ! )

Terry C. · « **Reply #12 on:** February 16, 2008, 12:28:49 PM »

I may be able to help a little here. I've designed a few high-stress parts that required parts to be shrink-fitted.

In this situation, the large diameters of the tube and bands are a definite plus, but we'll get back to that later.

First of all, most people go way overboard on the shrinkage. It's surprising just how little interference it takes to securely lock two pieces together. Excess shrinkage does not add security, it only imparts stresses on both the band and the tube.

When planning the fit, consider the minimum interference fit that will keep the piece secured against the forces attempting to move it. In this case it's just the recoil and that isn't going to move a band with a good, clean interference fit of as little as .005". I would consider .010" the absolute MAXIMUM for this application.

Expansion is greatly influenced by circumference. That's where the large diameter of these pieces is a plus. For the same desired expansion, a band with a large circumference will 'grow' in diameter with much less heat applied than one with a small circumference.

In the case of these bands, the concerns about heat altering the metallurgy of the tube are pretty much a non-issue. It won't be necessary to get the bands that hot. Significant expansion occurs well before the steel gets red hot, Afterward expansion slows to the point that it takes a LOT of heat to make it continue to expand once it's glowing red.

Only parts assemble under very controlled conditions can be heated to this level and recovered intact. I've done it with very heavy fits (.025"-.030" @ 5" diameter), but it isn't easy.

So that's my contribution to this discussion. Take away from it what you will.

Cat Whisperer · « **Reply #13 on:** February 16, 2008, 05:49:50 PM »

Thanks for adding the numbers to the equation!

My only experience with shrink fitting was taking the ring gear off a 1964 MGB flywheel - about 12" in diameter - cutting it with a hacksaw (about 1/8" kerf) opened up to at least 3/8" when cut through - right much stressed.

Heating a ring up that's 8-9" in diameter to gain .010 interference shouldn't be too radical - but will take a bit of planning to do it right. Handling it could prove to be a game.

Victor3 · « **Reply #14 on:** February 17, 2008, 12:45:34 AM »

Terry C. said...

"First of all, most people go way overboard on the shrinkage. It's surprising just how little interference it takes to securely lock two pieces together. Excess shrinkage does not add security, it only imparts stresses on both the band and the tube."

I would (respectfully) take issue with that statement as it relates to the strength of a cannon breech.

As Dom and others here have noted in researching the historical design of multiple-sleeve cannon barrels, the stress (hoop stress) imparted by the shrinking of one sleeve over another has indeed been found to "add security" above that of an un-stressed sleeve. Therefore, it is desirable to impart some measure of hoop stress here.

It's been scientifically demonstrated that adding thickness alone does not necessarily add additional resistance to bursting pressures UNLESS there is some significant stress applied to the outer banding of a chamber.

Locking two sleeves together so that they can't slip apart is easy to do with a very slight interference fit, but that isn't the primary engineering principle concerned in sleeved cannon barrel design.

Terry C. · « **Reply #15 on:** February 17, 2008, 03:03:41 AM »

Poor wording on my part, and maybe some misinterpretation of what's being done here.

I was under the impression that these bands were for appearance only. And this tube will be thin and easily distorted in the areas covered by the bands.

The strength of a breech was never in question. The chamber will be a solid and substantial piece of machined steel.

Hooping a cannon breech was never mentioned.

BTW: I've done this type of heavy shrink fit (as I stated) but this is another animal altogether and the planning and execution are far removed from anything being discussed in this thread. And if you research farther, you will find that the amount of shrinkage required to impart HUGE stress is less than many people think.

I (respectfully) withdraw my suggestions, as I obviously haven't been paying attention.

[edited to remove the word "most"]

Cat Whisperer · « **Reply #16 on:** February 17, 2008, 03:09:00 AM »

I'll side-step the issue of "most" or not.

There are two distinct applications for the process of adding a band - one for strength and (here) the other is to LOOK like a different style. (The O2 cylinders with a good powder chamber are in common use unadorned with bands).

The design needs to be appropriate to the application, where, as before (I may not have mentioned that the band in question that did the restriction of the bore was to attach the trunnions). Certainly a different level of stresses applied to the band.

(and as I post this Terry C. just posted his comments)

Great discussion!

Victor3 · « **Reply #17 on:** February 17, 2008, 08:38:41 PM »

Oops.... I guess my reading comprehension skills need some work. I went back and read again, and I see I totally missed the part about these bands being only decorative. My bad.

Step right up folks, poke the dummy (me) with a stick! Only 25 cents!

Cat Whisperer · « **Reply #18 on:** February 18, 2008, 12:40:45 AM »

Nope - no poking!

This has been a MOST interesting post from two aspects.

First, it has brought together a little more knowledge about the purposes of and what happens when about heat shrink fitting reinforcing bands.

Second, it has got to be one of the MOST polite (initial) disagreements on record!

I heard on the radio the other day, it is not the difference of opinion that causes conflict it is the polarization that is at fault.

I have the highest respect for folks that can discuss in a civil manner different perspectives in life - especially via the internet.

Ernest T · « **Reply #19 on:** February 23, 2008, 01:42:06 PM »

Thanks for everyone's help again. I am trying to design my base to copy a coehorn mortar but I would like to put a screw adjustment under the bottom of the barrel for a height adjustment. Does anyone know of a model of mortar that had this that dates before 1899? That I can use for a guide.

GGaskill · « **Reply #20 on:** February 23, 2008, 02:21:50 PM »

10-inch seacoast mortar, Model of 1840.
Total length, 46.0 inches; weight, 5,575 pounds;
total production, 33; known survivors, 5.

This model has been discussed on the board.

SLEEPY BEEPER · « **Reply #21 on:** April 28, 2008, 12:56:31 PM »

Hi Ernest T, How is the mortar build going?