Author Topic: Homemade thinwall, surprisingly strong (Read 1832 times)

jonaddis84 · « **on:** December 15, 2006, 03:40:16 AM »

www.geocities.com/jonaddis842003/mortarpage.html

Me and a buddy just fabbed this up out of boredom. Weve shot up to 500grains out of it with lighter ammo, and the most strain on it was a 425 grain pyrodex FFG charge with a 1.25lb lead slug, have mic'd the barrel several times with no deformation.

We cut small 1-2" pieces of the same material as the bore and pour lead slugs with them. At 25yds (the closest we have hit the target so far) those slugs penetrate ~13" of treated wood.

Several pics/video on the webpage.

Were new to this, so what does everyone think?

Rickk · « **Reply #1 on:** December 15, 2006, 04:55:53 AM »

I'll save my comments on the construction. as there will be others that have more experience there.

The powder choice is a a bit fine. 1F or Cannon grade BP would be safer.

jonaddis84 · « **Reply #2 on:** December 15, 2006, 05:16:10 AM »

I should say we didnt build this knowing that it would work flawlessly and safely, I just had the tubing laying around and thought wed give it a shot, if it blew up we wouldnt be out anything. I would rather have a thicker wall so that I could stand next to it and not be worried about losing a leg, but I am quite shocked at how its stood up. We are using such large charges and faster burning powder to see what it can take, believe me we arent anywhere near it when it goes off.

We originally shot it with just the inside tube (1-1/2" x .095 wall) and were putting 500-600 grain charges in it and lead slugs, I mic'd the barrel after those shots and it was identical as before!

No matter how many times it holds up though I will never stand right next to this cannon, if a slug gets stuck in the barrel I know it will blow up.

Double D · « **Reply #3 on:** December 15, 2006, 06:44:14 AM »

Jonaddis84 Welcome to our Black powder cannon and mortar board. From what you have posted you clearly will fit in on this board. It's very clear you have the skills to build a cannon, just not the knowledge. We can help you there. We have both the skills and the knowledge here, a couple of felllows even have both. Unfortunately your cannon does not fit with in the rules of this board.

I suggest you start at the top of the board in our BPM&C Board Rules, FAQ's, Posting Pictures and Safe Loads and Cannon plans posts an read all the links--tons of information there. You will find very quickly that your loads are gross overloads and your tube walls are dangerously undersized. After you read the Board rules and FAQ's then please read this post as a summary Read and Heed

Don't dispair, your tube can be made safe relatively simply by reducing your loads to a safe level and by reinforcing the chamber area. The fellows here will tell you how.

Artilleryman · « **Reply #4 on:** December 15, 2006, 12:51:38 PM »

I watched your must see video. I hope that you have plenty of down range area, as you may have shot your projectile a mile with the elevation that you gave the barrel. If the barrel were to fail, lighting a short fuse and running away will not take you out of shrapnel distance. Having the "carriage" come apart is due not only to the construction, but not being able to recoil freely. I am sure others will make additional comments. I like to see more people involved in cannon shooting, but any accident could cause a problem for all of us.

jonaddis84 · « **Reply #5 on:** December 15, 2006, 01:32:03 PM »

Quote from: Artilleryman on December 15, 2006, 12:51:38 PM

I watched your must see video. I hope that you have plenty of down range area, as you may have shot your projectile a mile with the elevation that you gave the barrel. If the barrel were to fail, lighting a short fuse and running away will not take you out of shrapnel distance. Having the "carriage" come apart is due not only to the construction, but not being able to recoil freely. I am sure others will make additional comments. I like to see more people involved in cannon shooting, but any accident could cause a problem for all of us.

Yeah, lots of range, and theres a shed slightly out of camera angle behind the cannon to protect us if it exploded.

All a moot point though now, the barrel/frame finally failed today. Ill post pics of what happened later. It was a relatively light charge, loose projectile, carriage wasnt anchored. Bent the heck out of the frame, broke a few welds, and bulged the combustion chamber area of the barrel. It did however still have the power to take out two 2" pine tree branches after it missed the target, and still made it 150yds back to the woods. The carriage was not held to the ground, and recoiled over 10ft backward and ran over the camera tripod.

In conclusion, we definitely underbuilt and overcharged this cannon, we did however get more use out of it than either of us expected being such a thin-wall. The frame takes an enormous amount of abuse from the recoil. The rear strut rod bent a grade 8 pin into a U shape. The 3/4" x .058 tubing I used for the framing was far too weak, and there were a few welds that I couldnt finish do to the angle.

Our next endevour will be a larger barrel, both bore size and wall thickness. It will use at least 1-1/4" x .083 4130 for the frame. It will have more than 10 min of research and design time go into it. And Id like to try using a coilover shock I have for the strut rod to try and absorb some of the shock instead of it all going into the frame. We could easily just build a fixed position mortar like most are, but I like being able to shoot it at targets or in the air, so adjustability will remain.

Maybe someone will be able to benefit from our poor design.

Rickk · « **Reply #6 on:** December 15, 2006, 01:39:50 PM »

I watched the videos.

Pyrocreations is having a fuse sale this weekend.

I would stock up and use way-more-longer fuse.

I don't scare easily, but I would be scared.

Seriously, 1/2 seemless tubing (minimum) is what you want.

We don't know anything about your breech plug, but it is aimed in the direction that you appear to be running.

A more massive base would help recoil. Make the gun wiegh about 100 - 150 # and you will be where you should be.

Put it on a naval style carraige and you will be closer to a "pre-1898 design"

Cannon grade powder would keep pressure lower. Pyrodex is not recommended for bores that big.

You are running from it, so you know it is dangerous. Go safer, and make your life less stressfull and live long and prosper.

Rickk · « **Reply #7 on:** December 15, 2006, 01:41:01 PM »

My post was ten seconds after yours, but apparenlty a few hours too late anyway

jonaddis84 · « **Reply #8 on:** December 15, 2006, 02:18:37 PM »

Ok i posted the new pics

Double D · « **Reply #9 on:** December 15, 2006, 04:31:36 PM »

The cannon seent you a message to today, I hope you heard it. This picture says a lot.

You cannon is very unsafe and doesn't appear to replicate any pre1899 cannon I am aware of. You loads are very unsafe. Do you wish some help in being able bring this cannon into safe parameters?

If not please tell us the name of your local newspaper so we can monitor it and add your story to the cannon accidents posting...theway you are that's what is going to happen next.

Read you PM please!

Cannon building and shooting can be fun, but if not done safely can be deadly!

GGaskill · « **Reply #10 on:** December 15, 2006, 08:02:23 PM »

Looks like the inner tube failed and the outer one barely contained the gas. Cannon building to minimum material condition needs to be done by an engineer who does all the calculations before putting match to fuse. SOP (seat of the pants) cannon building can be done using the "chamber walls the same thickness as the bore diameter" rule. While the barrel will be heavy for its bore, it will be safe. Check the dimensions of the old timers and you will find most of them are pretty close to that rule.

The easiest way to deal with recoil is to put the barrel on some kind of wheeled carriage so the carriage can absorb the recoil as kinetic energy instead of elastic (and plastic) deflection. You could use the French 75mm Gun of 1897 as a model of gun that used a hydraulic recoil mechanism.

Double D · « **Reply #11 on:** December 16, 2006, 12:52:17 AM »

I would like to see that bulge sectioned length wise with a band saw. I think it would serve as a good example of why you shouldn't do it this way.

I'm with you George, the inner tube failed. It appears the inner tube is welded to a piece of CRS, then an outer tube is slipped over that and welded to the CRS. My guess is that a small section of the inner tube weld failed allowing the gas to vent and make the bulge.

Here is how the North-South Skirmish Association recommends you build a breechplug.

Quote

The liner must be closed at the breech end with a steel plug, sweat-fitted into the liner and welded. The breech plug must have a radius of at least 25 percent of the bore radius and be at least 1 inch thick at its thinnest point.All reproduction barrels manufactured after March 1, 1986 must have pictures of the liner and breech plug before and after welding. No reproduction barrel shall be approved after March 1, 1986, which does not have one caliber's thickness of metal surrounding the bore at the breech.

Cat Whisperer · « **Reply #12 on:** December 16, 2006, 03:28:53 PM »

Excellent series. Good example of how metal will stand excessive forces repitively - for a time. The metal stretchs, returns to form (and gets a little harder each time) and then it fails. The question obviously is when.

DD - good rules of thumb on the dimensions. Proven to withstand reasonable loads over time by a BUNCH of folks over a number of YEARS.

GGaskill · « **Reply #13 on:** December 16, 2006, 04:16:16 PM »

Not to pick too many nits with the N-SSA drawing but i have a couple of quarrels with it. First, the welds as shown are impossible to achieve. The drawing implies that the weld is between the liner, the plug, and the breech of the lined barrel, which is impossible. Second, any weld metal projecting from the rear of the liner will prevent seating the liner flush with the bottom of the bore, which I consider to be a bad thing (not seating flush.)

Clearly what is needed is a weld between the plug and liner with deep penetration such that there is a wide fusion zone. But the back of the plugged liner needs to be flat (or maybe shaped like the point of a twist drill if that is what the bottom of the bore looks like.)

Double D · « **Reply #14 on:** December 16, 2006, 04:29:15 PM »

George,

The picture is an illustration not a techical drawing. Here's the rule in writing.

Quote

All reproduction barrels and those original barrels failing inspection must be lined with a bore liner of extruded seamless steel tubing of a minimum ANSI standard and of a minimum 3/8-inch wall thickness. The liner must be closed at the breech end with a steel plug, sweat-fitted into the liner and welded. The breech plug must have a radius of at least 25 percent of the bore radius and be at least 1 inch thick at its thinnest point. (See figure 10.1). All reproduction barrels manufactured after March 1, 1986 must have pictures of the liner and breech plug before and after welding. No reproduction barrel shall be approved after March 1, 1986, which does not have one caliber's thickness of metal surrounding the bore at the breech.

GGaskill · « **Reply #15 on:** December 16, 2006, 05:15:14 PM »

Any idea what "sweat-fitted" means? Shrink fitted? The only thing I have ever heard of referred to as "sweat" something is sweat soldering which seems completely inappropriate in this context.

Double D · « **Reply #16 on:** December 16, 2006, 05:36:21 PM »

George, how does Machinery Handbook define sweat fitting?

Don Krag · « **Reply #17 on:** December 16, 2006, 05:41:28 PM »

Wow...under a 1/4" wall for a 1.25" bore!!!??? I often use multiple sleeves to build up layers, but I always start with about 1/4" DOM seamless tubing. My 1.12" bore ones start with 3/16" DOM, then get 3/8" of bronze, followed by 1/4" of drill casing for the entire barrel. I then shrink on some 1/4" thick wrought iron bands over the breech area both for added margin of safety as well as looks. My original one is the smallest with 3/8" DOM as the main barrel with 3/8" wrought iron over the breech and periodic barrel bands down the remaining length. I don't thread my plugs. I press-fit a 1.5" long plug, then pin in both X and Y axis using 1/4" steel rod. I'm relatively new to this and I'm no expert. Mine tend to be heavy and overbuilt, but If you're interested, I can put together a "how-to" for you. There's tons of cool info through the pages here. I think I've learned more in the last week here as I have in the last year on my own!

I was shooting some patched 0.80" steel balls with about 1/4 oz loads of Swiss Fg out at 75 yards (have some video of it). I was quite suprised at the power the projectiles had. Green spruce pinecones shot at a 45* angle with much less than that would go ~200 yards. Blasting a 1.25" lead slug with 500 grains...I hope yo have a LOT of space out in front!

Estes model rocket igniters, 100' of speaker wire, a 9-volt battery and a wide oak tree serve as my "barrel proofing" set up. I set up a video camera behind 1/2" thick ballistic lexan shield at about 10 yards. That way if it goes kabloohey, I get some cool video.

copdoc · « **Reply #18 on:** December 16, 2006, 06:37:32 PM »

I don't know what "sweat fitting" is but I built my first cannon using a breech in 1975-76. We tuned the plug a couple of thousandths larger than the diameter as the inside of the bbl , cooled the breech in the freezer, heated the bbl, then knocked it in with a 5 lb sledge. We turned the plug and welded the ring. I'll put up some pics later. It is solid. Proof testing was with a 2" dia 6" long steel projectile and 4 Oz of FG. Now I know that is too much and can stress a bbl causing it to fail later. I use estimated 10% overpressure for proof tests now. We dug a hole with a post hole diigger in the side of a ditch to mount it. It was about the loudest report I have ever heard. We had to dig the bbl out of the dirt. I would expect it to split at the flash hole if it ever failed. That cannon has shot about every thing that can be shoved down the bore. I don't think the weld really adds that much to the strength. I have fitted a few other pieces of metal this way and it is almost like having one piece. All the other cannon I have made are drilled from solid stock.

I have thought about sectioning the breech to look at it after 30 years of use, but I hate to take it apart. If i do I'll post some pics.

Does anyone know the reason for the radius at the breech. Is the idea that it increases adherace to the bbl like a hollow based bullet?

Double D · « **Reply #19 on:** December 16, 2006, 08:38:46 PM »

The radius is to facilitate cleaning. With square corners it is possible for embers and debris to gather and not be accessible to cleaning tools.

CU_Cannon · « **Reply #20 on:** December 17, 2006, 01:10:11 AM »

The curve also helps make the barrel stronger by avoiding stress concentrations. Inside sharp corners can increase the stress to 2 or 3 times that of the surrounding area. If you look at ordinance drawings there are never any sharp corners in the bore this is why. It is much easer to make sharp corners but rounded corners are a better design.

copdoc · « **Reply #21 on:** December 17, 2006, 02:11:08 AM »

Both of the above make sense. thanks.

Cat Whisperer · « **Reply #22 on:** December 17, 2006, 02:51:54 AM »

Quote from: copdoc on December 17, 2006, 02:11:08 AM

Both of the above make sense. thanks.

Those are clearly true. I would guess also that the taper on the inside of the plug would add to it's ablitiy to seal; but it should be shrink fitted into place so that may just be academic. (Considering the corrosive effects of the products of combustion.)

jonaddis84 · « **Reply #23 on:** December 20, 2006, 05:33:16 PM »

DD you can delete this if you want, it doesnt matter to me. I only posted all this up because we had already built it, if I had found this site before we built it we wouldve never gone through with it, but I figured people would find it interesting, and it seems they have, I think its a good learning experience what not to do.

Like someone above said I find steel amazing in the fact that it can stand so much, and then all the sudden it will just fail. We honestly were shooting probably close to 600 grains out of the inside barrel! That is .095 DOM! And it stood it about 5 shots, then we added the outside sleeve and it took about 30 shots varying anywhere from 100grains to 425grains a lot of them the carriage was fastened pretty tightly to the ground, then it failed on a relatively light 250grain load when the carriage was not fixed at all.

Looking back I know it was just a pipebomb in disguise waiting to explode, luckily it never did, but we never gave it a chance to hurt us, always behind something and nowhere near it....the camera on the other hand, would have been destroyed it it blew. almost got destroyed by the 10ft recoil of the final shot.

It did make for some pretty cool videos though huh?

Cat Whisperer · « **Reply #24 on:** December 21, 2006, 01:07:22 AM »

Jon -

This is a KEEPER. It is a great example of why we 'overbuild' things - because you CAN get away with it for a while, until ....

When I look at design, the factors of that peak of pressure and the exercising (causing fatigue) steel are complex enough that just being a metalurgist or a mechanical engineer aren't enough - it takes that plus experience in the field. Even then, design is done AND the prototypes are TESTED to prove the design.

The DOCUMENTATION of what you did and how long it lasted are what's of value. As the metal gets thicker and thicker the tube will last longer and longer. That's the gamble - how thick is ENOUGH?

I maintain that the best way for us to design is to look at other designs that have been in USE for long periods of time, make them stronger and do that. At the same time, the two best organizations to observe are the AAA and N-SSA - to look at their rules - they've been around for some time and FOLLOWING thier rules has provided safe competition. (It's hard to argue with success.)

Thanks for posting this! Great documentation. It appears that you were safe enough in procedures to still have all fingers and toes and no pucture wounds - that's the best part. You echoed my saying - you've got to KNOW if it's a cannon or a bomb when you light the fuse.

Double D · « **Reply #25 on:** December 21, 2006, 05:52:31 AM »

Jon,

CW says it well, this post is a keeper. This is a good post. Your build is good. You got some great feedback on how to correct your defaults.

You are miles ahead of my first cannon and my second and third one also. Mine were far more dangerous than yours far far more.

You got some good learning from what you did all around. You learned that seamless has its limits, how to setup a website, how to film cannons.

So the next step is to build a better cannon. You have the entire board sitting waiting to advise you and guide you, so get busy start designing. Tell us what you have in mind. If there is a problem we'll let you know. If you have a good idea we'll steal for our selves and take full credit.

Get to work!