Author Topic: A new cannoner (Read 8593 times)

accuratemike · « **Reply #60 on:** October 10, 2007, 06:29:34 AM »

I haven't been following this thread from the beginning, but I read it today. I had a look at the Lassen hoop stress calculator mentioned/linked above. Handy link. One question, I plugged some numbers into it and got a little confused. I used an ID of 2.913", wall thickness of 2.0435" (like a "light 3pdr") and pressure of 20,000psi.. The thin wall calculator gave a hoop stress of 14254.95 and the thick wall calculator came out at 28377.82. Why would the thick wall formula result in ~2x the hoop stress of the thin wall? Just curious. MIKE

Cannon caster · « **Reply #61 on:** October 10, 2007, 08:36:47 AM »

Quote from: Artilleryman on October 10, 2007, 02:56:12 AM

Another problem with crimping. How do you clean the "breech face"? This would be a good place for an ember that could ignite the next charge.

I always fill the cannon with water after I fire it.

Double D · « **Reply #62 on:** October 10, 2007, 08:40:19 AM »

We have had discussion on hoop strength before. But no one has yet explained if any releationshipe exists between hoop strength pressure and transducer or Copper crusher pressures. Transducer and copper crush pressures are not of the same value. Where does hopp strength fit in?

Double D · « **Reply #63 on:** October 10, 2007, 08:44:15 AM »

Quote from: Cannon caster on October 10, 2007, 08:36:47 AM

I always fill the cannon with water after I fire it.

I am beginning to wonder of you are building a cannoin or a pipe bomb. You seem more interested in rationalizing your actions than learning how to make a proper and safe cannon.

Further if you have tube thin enough to crimp it certainly isn't strong enough to be a cannon to start with.

Cannon caster · « **Reply #64 on:** October 10, 2007, 09:05:37 AM »

Quote from: Double D on October 10, 2007, 08:44:15 AM

Quote from: Cannon caster on October 10, 2007, 08:36:47 AM
I always fill the cannon with water after I fire it.

I am beginning to wonder of you are building a cannoin or a pipe bomb. You seem more interested in rationalizing your actions than learning how to make a proper and safe cannon.

Further if you have tube thin enough to crimp it certainly isn't strong enough to be a cannon to start with.

In this case a I am building a cannon. And I am interested in learning how to make a proper and safe cannon. Now that we have access to a lathe we will cast a large cylinder and drill it. But I had to improvise. Yes the pipe cannon is not safe and that is why I always retreat to a safer distance (I never stay next to the cannon) because I know that any time I fire it it can explode.

Artilleryman · « **Reply #65 on:** October 10, 2007, 09:34:59 AM »

You say you always retreat to a safe area after lighting the fuse because you know that the pipe may explode. First if I had a cannon that I thought might explode the next time I fired it I would fill the barrel with concrete and use it as a yard decoration. Second, you sure are putting a lot of trust in how fast the fuse burns. Sometimes fuses flash through. I know of a case years ago when a teenager was firing a pipe cannon, and his fuse flash through and when the "cannon" went off the pipe failed and blew a piece of it through his chest killing him. There is no sense in risking life and limb for a noise maker. Third, what is a safe distance? Fragments can travel quite a distance with potentially lethal results.

Improperly made cannons will fail, it is just a matter of when. There is a lot of information on this board and else where. Please take the time to learn as much as you can. There are no shortcuts to this.

Cannon caster · « **Reply #66 on:** October 10, 2007, 09:41:15 AM »

You are right fuse can flash. Even the commercially made. And I have been using a very unsafe fuse (a line of slow burning black powder and then a firecracker fuse down the vent).
And yes improperly made cannons will explode. One of ours already has.

Now that a lathe is within our reach safer cannons can be made.

GGaskill · « **Reply #67 on:** October 10, 2007, 11:35:24 AM »

We have had discussion on hoop strength before. But no one has yet explained if any releationship exists between hoop strength pressure and transducer or Copper crusher pressures. Transducer and copper crusher pressures are not of the same value. Where does hoop strength fit in?

Hoop stress is measured in the same units as chamber pressure (psi) but it is caused by chamber pressure. The relationships are stated in the Hoop Stress Calculator page. Chamber pressure is one of the independent variables (along with chamber diameter and wall thickness.)

Strength is a characteristic of the material--steel has more than brass or aluminum or cast iron, for example. When you are designing something using the numbers, you typically want the stress to be some relatively small fraction of the strength so you have a safety factor for unknown quantities such as actual material strength versus nominal material strength, fabrication mistakes or flaws, fatigue, etc. When you are reviewing an existing design, you are looking to see how close to material strength the hoop stress is. You want to find out that you have a lot of cushion.

accuratemike · « **Reply #68 on:** October 10, 2007, 11:47:26 AM »

Why would the thick wall formula result in ~2x the hoop stress of the thin wall? Just curious. MIKE

Inquiring minds want to know. Any ideas? I still haven't fingered it out. MIKE

Cannon caster · « **Reply #69 on:** October 10, 2007, 12:06:39 PM »

We are going to cast a brass cannon. Since we have access to a lathe we can easily drill the bore. It will be 35 cm long and 52 mm in diameter. It will be made from 80:20 brass. As a mold we are going to use a steel pipe closed at one end with pressed plaster. I have 2 questions. First would it bee a good idea to substitute 5 % of the zinc with lead to improve machinability (it will be drilled easier)? Or would another amount of lead be better? And what would be the largest bore diameter that would be safe to use with metal (lead and steel) balls and black powder?

GGaskill · « **Reply #70 on:** October 10, 2007, 03:54:29 PM »

Why would the thick wall formula result in ~2x the hoop stress of the thin wall? Just curious.

Don't hold me to this but the reason I recall from engineering classes 40 years ago is that in the thin wall cylinder, the stress is all from the hoop tension but in a thick wall one, there is also stress from the perpendicular force (the pressure.)

Any qualified engineer who knows this stuff is invited to step in here and correct this statement if it is wrong.

GGaskill · « **Reply #71 on:** October 11, 2007, 02:52:36 PM »

First would it bee a good idea to substitute 5 % of the zinc with lead to improve machinability (it will be drilled easier)? Or would another amount of lead be better?

I would say forget the lead entirely. Brass is pretty easy to machine and the lead will weaken the material.

Double D · « **Reply #72 on:** October 11, 2007, 06:38:37 PM »

Quote from: GGaskill on October 10, 2007, 11:35:24 AM

oop stress is measured in the same units as chamber pressure (psi) but it is caused by chamber pressure. The relationships are stated in the Hoop Stress Calculator page. Chamber pressure is one of the independent variables (along with chamber diameter and wall thickness.)

Yes they the same units of measure but are not directly comparable. Pressures taken by copper crusher method are not equivalant to and will not be the same as pressures taken by transducer. I am asking what the pressures reported by hoop strength measurements are based on--what type of verification; transducer, crusher, mathamatical?

What type pressures are we talking about. Static, gradual increase, variable along the surface distance.

Are hoop strength pressures based on a universal peak pressure the full length of the tube?

What effect if any does fact the peak pressure may be localized in one spot and variable in other spot the length of the tube.

Does the hoop stress pressure mean this is the pressure which the tube will always fail? Will the failure be instantaneous?

I don't know much about hoop stress and I have a lot of questions. Quite frankly in some 25 years in the business I have never seen reference to hoop stress test in relationship to gun barrels and it sure seems like it should be. But then it pretty well established what steels work for gun barrels and what doesn't.

GGaskill · « **Reply #73 on:** October 11, 2007, 09:35:10 PM »

DD,
I'm not quite clear what you are asking. Is it for a discussion of the strain gage system used by Oehler? The equations of the Cylinder Stress page use the chamber pressure determined by either copper crushers or electronic strain gages as an input variable, along with the chamber dimensions, to calculate the stress in the metal surrounding the burning powder.

The Oehler Personal Ballistic system uses a strain gage on the outside of the chamber to measure the actual stretching of the metal when firing occurs and then calculates chamber pressure from the strain (stretch of the metal), the chamber dimensions and some characteristics of typical barrel steel.

Double D · « **Reply #74 on:** October 12, 2007, 08:12:22 AM »

No I what i am trying figure out is what is the origination of the pressure measurements in in the hope stress formula. How are these measurment determined.

Were they determined mathmatically or by some sort of physical mesearment such as pressure transducer meseaurements. If so what type of measurements?

GGaskill · « **Reply #75 on:** October 12, 2007, 09:23:25 AM »

...what is the origination of the pressure measurements...

It is whatever your source of pressure measurements is. Switlik's experiments, your own testing, your own estimates, whatever rings your bell. The hoop stress formulas don't supply or compute chamber pressure, they use it as a parameter to calculate the material stress caused by a chamber pressure of the value you supply.

Cat Whisperer · « **Reply #76 on:** October 16, 2007, 11:56:27 AM »

Quote from: Cannon caster on October 10, 2007, 12:06:39 PM

We are going to cast a brass cannon. Since we have access to a lathe we can easily drill the bore. It will be 35 cm long and 52 mm in diameter. It will be made from 80:20 brass. As a mold we are going to use a steel pipe closed at one end with pressed plaster. I have 2 questions. First would it bee a good idea to substitute 5 % of the zinc with lead to improve machinability (it will be drilled easier)? Or would another amount of lead be better? And what would be the largest bore diameter that would be safe to use with metal (lead and steel) balls and black powder?

These are VERY good questions. I hope you realise that unless you are 1) experienced and 2) trained as a mechanical engineer or metalurgist that it will be easy to come to an overly simple conclusion that COULD have catestrophic results.

Most folks are somewhat to very experienced in MACHINING; a few folks are experienced in DESIGNING CANNONS. The forces are different than what anything else provides. Be VERY carefull to look at how the metal acts under repeated stress - work hardening - brittleness - and such. Charpy notch test is just one of several tests that will lead you in the right direction; but your BEST bet is to look at other folk's designs that work and have been proven to work many times (lots of cannons) over a long period of time.

Musketeer · « **Reply #77 on:** October 18, 2007, 02:03:41 AM »

I am interested in the torched used to melt the brass, is it a commercial (bought) torch or modified, if modified please let me have details how to build it

Quote from: Cannon caster on September 19, 2007, 12:22:36 PM

Hello. My name is Jugoslav and I am 14 years old. I am very interested in making small model cannons. Me and my friend made 6 cannons. I am also interested in metalcasting. You can see the cast brass cannon firing here: http://www.metacafe.com/watch/794729/firing_a_homemade_cannon_using_whistle_mix/ It is small but it is our first cast cannon. We casted it solid (the mold was a steel pipe close by pressed plaster at one end). Here you can see our furnace: http://www.metacafe.com/watch/744893/how_to_making_and_casting_brass/ Here is one of our stainless steel cannons: http://www.metacafe.com/watch/821548/firing_and_shooting_with_homemade_black_powder_cannon/ We made ths one by crimping the steel pipe at one end, heating it and striking it with a hammer to close it better, put a piece of lead in it and melted it in the cannon. When it soldified we drilled the hole or the fuse. So what do you think? We made our whistle mix and black powder ourself. Also has anyone here cast his own cannon? If yes can you please give me some advice about it? We casted our cannon solid and then drilled the bore but we can do it only with small cannons (we use a hand drill and dont have a large drill bit). I was thinking about using a steel pipe closed at one end (weld a plate or crimp) and use it as the core. The walls of the pipe would have to be thick enough to not to warp from the heat. Also is copper (I have melted it many times and it is easy.) a god material to cast small model cannons from it? I know that it is soft but with enough wall thikness maybe it can work?
Sorry if it is too many questions.
Thanks in advance.

Cannon caster · « **Reply #78 on:** October 22, 2007, 08:10:24 AM »

The burner can be bought at hardware stores for 20-30 dollars. I didn't modify it. You can find a lot of informations about metalcasting here: http://backyardmetalcasting.com/forums/

Cannon caster · « **Reply #79 on:** November 03, 2007, 04:23:12 PM »

We have started making brass for our 20 kg cannon. The mold will be a steel pipe standing on a steel plate and all that will be covered with sillica sand. The brass is 85% copper and 15% zinc. The cannon will be bored on a lathe. If you are interested you can see our brass making video here: http://www.metacafe.com/watch/901662/how_to_making_and_casting_brass_2/ We make the brass in 2 kg batches.

GGaskill · « **Reply #80 on:** November 03, 2007, 06:40:21 PM »

We make the brass in 2 kg batches.

Hopefully you can melt all 20 kg for the cannon pour at once. Making small batches will cause you to lose some of the zinc to burn out because you will be remelting it. It would be better to make it when you are going to pour it.

cannonmn · « **Reply #81 on:** November 03, 2007, 10:01:57 PM »

Quote

The brass is 85% copper and 15% zinc.

Interesting, I've never heard of anyone casting brass cannons (as opposed to bronze,) but then I haven't been around people making small cannons.

My one question I guess is, since most original nonferrous cannons made for military purposes were made of a bronze alloy of about 90/10 copper/tin, why would you not use that alloy instead of what you are doing? Would real bronze be that much more expensive?

Cannon caster · « **Reply #82 on:** November 04, 2007, 02:46:52 AM »

I can't find any tin and I have a lot of copper and zinc.

We will be able to melt 20 kg. We will use a larger furnace and crucible than the one we use in the video. And yes some zinc burns of so we will add some in when we melt the 20 kg.

Tropico · « **Reply #83 on:** November 04, 2007, 10:11:43 AM »

Quote

Would real bronze be that much more expensive?

Yes !., Copper is Pure Money ., even better than money . next time you find a pre 1981 penny and then any one made newer ., file the edge a bit and have a look.

I just bought another stick of 4" X 26" ., it topped 9 Benny's !!

Quote

I can't find any tin and I have a lot of copper and zinc.

You are lucky !

Cannon caster · « **Reply #84 on:** November 04, 2007, 11:34:22 AM »

Quote from: Tropico on November 04, 2007, 10:11:43 AM

You are lucky !

GGaskill · « **Reply #85 on:** November 04, 2007, 07:49:16 PM »

I can't find any tin ...

Did you check your hardware store for lead free solder?

Cannon caster · « **Reply #86 on:** November 05, 2007, 11:57:02 AM »

No.
Ups. I forgot that. I will check.

Cannon caster · « **Reply #87 on:** November 07, 2007, 10:11:53 AM »

Now as we are preparing the brass for the large cannon I was thinking of casting a small cannon as I am in the "cannon-making" mood and don't want to wait until we make enough 85:15 brass. I also like to cast various metals. Lead, solder, zinc, aluminium and copper are not good cannon materials. Brass and bronze are. Is aluminium bronze a good material to cast a small cannon with it? The mold would be a steel pipe standing on a steel plate and all that covered in sand. So is Al bronze a good cannon material? and what would be the best ratios of Al to Cu?

GGaskill · « **Reply #88 on:** November 07, 2007, 11:29:07 AM »

So is Al bronze a good cannon material?

Aluminum bronze is a strong material but it does not cast easily. Check out the Anchor Bronze website for lots of information about copper alloys.

Cannon caster · « **Reply #89 on:** November 07, 2007, 12:00:54 PM »

Thanks for the website. Lots of good information.

I have noticed that most of the Al bronzes contain iron. How is iron added to the alloy? Is solid iron added in the molten mix of Al and Cu or is there some other method?