Author Topic: new cannon/mortar (Read 2682 times)

Bornsouthern34 · « **Reply #30 on:** May 03, 2009, 03:53:33 PM »

Quote from: Cat Whisperer on May 03, 2009, 03:02:09 PM

I ASSUME that the 4130 was preheated before welding to the recommended temp.

I cannot make assumptions about that. I do know however that the welds are much better than anything I could do with my welder here at the house. However, I follow Double D's thinking on the barrel. It is more for directional purposes than any real pressure.

Cat Whisperer · « **Reply #31 on:** May 03, 2009, 04:22:19 PM »

Good looking welds are a good sign. Did the welder know it was 4130? Was the welder certified? If so, then it likely was done right.

Victor3 · « **Reply #32 on:** May 04, 2009, 12:55:19 AM »

Quote from: Double D on May 02, 2009, 04:25:09 PM

No the wall thicknes rule of thumb is the wall should be the same thickens as the diameter of the bore. Bore in a mortar being the powder chamber. If you have a two inch diameter powder chamber you need the walls to be 2 inch thick also. 2 inch chamber your minimum safe recommended diameter would be 6 inches.

I didn't see where the material for the chamber was described as 4130 here, but I'll assume that it is since CW mentioned above that it is.

Not to take anything away from the wall thickness rule (I think it's a good one that assures over-building for safety) but is it really necessary for safety in all cases? Material strength and barrel design, not just thickness need to be taken into account.

An example...

A grey iron cannon barrel, 6" OD with a 2" wall would have a bursting pressure of ~13000 psi (using Barlow's formula, a 20000 psi tensile strength and assuming the tube was cast correctly). Let's throw in a 3/8" wall 2.75 OD steel liner that adds 24000 psi to the total strength of the bbl (accounting for the ~6000 psi loss via removal of 3/8" wall thickness of cast iron needed to add the liner) 13K + 24K = 37000 psi. I believe this configuration is acceptable per N-SSA rules.

A 4" OD 4130 (condition N) 1" wall tube would have a bursting pressure of ~45000 psi., and would most likely stand up to repeted firing better than a sleeved cast iron barrel.

Also, the design of this mortar provides a rapid and significant drop in pressure as the ball moves off of the chamber face, which will reduce material fatigue in the chamber material.

Double D · « **Reply #33 on:** May 04, 2009, 04:51:09 AM »

Victor,

You are absolutley right the one wall thickness rule is not an absolute. You can indeed use much thinner material safely. It's done every day in modern gunmaking.

Here on this board were have folks with different skills and knowledge levels. I know you been around here long enough to know some of the folks here are quite highly skilled in shop practices and others are extremely knowledgable in the engineering. Some folks even have both skills. I'm not sure where I fall, prorbably with the third group who just have desire.

Because everyone who comes here does not have the same skill set and knowledgeable base we have had find a base line to assure people are safely building cannons and aren't building bombs. It is our policy to point to the safety guidlines of the North South Skirmish Association and the American Artillery Association. The quidelines are clearly and simply written, readily understood and readily available on the net. The engineering theory is not.

If I read the pulse of the board correctly most are coming here to build or shoot a cannon. The found a piece of steel or a chunk of pipe and they want to build. Most are just hobbist, not professionals.

We need a starting baseline so we fall back on N-SSA and AAA rules. As you say those guidlines provide for over building. These guidlines are a good starting point for those who not knowledgeable Engineers.

Is there room for deviation in those quidlines. Sure there is. There must be, a Napolean made to orignal specifications can not comply with the guidlines.

We have to be real careful in our discussion here to make sure people understand what they are working with. So unless it's very clear to me the person posting has a good knowledge in the Engineering I am going to point to the safety guidlines.

When you guys who have the advanced skills do discuss these thing, I ask you to keep in mind who is reading what you write. Could you inadvertantly be leading someone to believe what they are building is safe, if they miss a detail in your discussion?

For advanced design you very right. But for some guy who just wants to build a basic gun to fling golf balls and bowling balls out in the hay field, the N-SSA guidlines are all they need.

I think Tim got his posts confused. The 4130 is in a different post and a different cannon build.

Double D · « **Reply #34 on:** May 04, 2009, 04:56:27 AM »

Victor,

I think I just found a better response to your question.

Quote from: Victor3 on May 03, 2009, 09:20:53 PM

The best designer I ever worked with was a Russian guy. Leonid told me that the first thing they were taught in engineering school in the USSR was "Make it simple, make it strong, make it work."

carronader · « **Reply #35 on:** May 04, 2009, 10:28:18 AM »

DD,
could you get that guy round to sort out my wife,she's a damn Russian and she fails all of those tests.

carronader · « **Reply #36 on:** May 04, 2009, 11:07:56 AM »

forgot to post this,have you got this DD?

Bornsouthern34 · « **Reply #37 on:** May 04, 2009, 12:18:40 PM »

Double D,

Thanks for keeping guys like me safe. Although I am very mechanically inclined and supposedly pretty smart (that's what they say anyway), I am by no means and engineer. However, I do want to have fun with it and although there may be the occassional YouTube idiot show up, I believe most of the guys on this forum take safety pretty seriously.

Victor3,

Thanks for numbers, guys like me need pointers from both sides of this discussion.

As for my mortar, I came across a set of 6 inch diameter pieces of round rubber. They have a 1 1/2 inch hole in the middle. I thought about boring it to 2 inch and pressing them onto my trunion on each side as a damper between the trunion and the carriage. What do yall think? Think it may take some of the brunt off the axles?

GGaskill · « **Reply #38 on:** May 04, 2009, 12:57:09 PM »

I thought about boring it to 2 inch and pressing them onto my trunnion on each side as a damper between the trunnion and the carriage.

Assuming that the rubber will bear on the web of the wide flange and not the edge of the flange, it should help some.

Victor3 · « **Reply #39 on:** May 04, 2009, 11:18:24 PM »

Quote from: Double D on May 04, 2009, 04:51:09 AM

We have to be real careful in our discussion here to make sure people understand what they are working with. So unless it's very clear to me the person posting has a good knowledge in the Engineering I am going to point to the safety guidlines.

I ask you to keep in mind who is reading what you write. Could you inadvertantly be leading someone to believe what they are building is safe, if they miss a detail in your discussion?

DD,

Good point. I'll be mindful of it in the future. Thanks.

Bornsouthern34 · « **Reply #40 on:** May 13, 2009, 12:07:22 PM »

Ok guys, I promised the video when I finished this project and here it goes. It should also answer some of the questions about the wheels on the carriage. Enjoy!

http://www.youtube.com/watch?v=hE1GX5se6GE

Double D · « **Reply #41 on:** May 13, 2009, 12:22:32 PM »

That worked good. Rolled back out of battery quite nice. I like it! The ringing as the gun went out of the picture, what was that?

You need to look at the post on how to make quill and linstock. That way you don't have wait while the fuse burns down for the cannon to fire. Lighting the quill with a linstock while you are standing next to the gun gives you the full "ambiance" of firing.

Bornsouthern34 · « **Reply #42 on:** May 13, 2009, 03:08:13 PM »

The ringing was the barrel but if you listen real close you can hear the whistle of the finger holes in the ball as it descends. That was a 650 yard shot and it landed out past the white building at the end of the video.

Bornsouthern34 · « **Reply #43 on:** May 13, 2009, 03:11:34 PM »

Oh I forgot, I am working on a design to use a 209 shotgun primer for ignition. It would let me use a pull rope and stand back a bit. Not to mention the instantanious light versus a fuse. I posted another video of my golfball mortar and thought the dog was going to stick his nose down the barrel. Very tense moment. Once that fuse is lit, there is no going back.

dominick · « **Reply #44 on:** May 13, 2009, 04:27:37 PM »

Quote from: Bornsouthern34 on May 13, 2009, 03:11:34 PM

Oh I forgot, I am working on a design to use a 209 shotgun primer for ignition. It would let me use a pull rope and stand back a bit. Not to mention the instantanious light versus a fuse. I posted another video of my golfball mortar and thought the dog was going to stick his nose down the barrel. Very tense moment. Once that fuse is lit, there is no going back.

You may want to install a deflector plate behind the vent. Without a shield, the primer will eject to the rear at a high velocity.

Here's a set-up I used.

Victor3 · « **Reply #45 on:** May 14, 2009, 02:49:05 AM »

Quote from: Bornsouthern34 on May 13, 2009, 03:11:34 PM

Oh I forgot, I am working on a design to use a 209 shotgun primer for ignition. It would let me use a pull rope and stand back a bit. Not to mention the instantanious light versus a fuse. I posted another video of my golfball mortar and thought the dog was going to stick his nose down the barrel. Very tense moment. Once that fuse is lit, there is no going back.

Joe,

You might consider installing a nipple for a #11 cap. A 209 is pretty big and stays together after firing. A cap is less substantial, so safer as far as a secondary projectile goes. Easier to make one go off too.

Bornsouthern34 · « **Reply #46 on:** May 14, 2009, 02:05:31 PM »

I am not sure which way is best. I want what is safest but at the same time be able to put enough flame into the powder to get a better ignition than with a fuse. The quills seem good but at this time I would have to buy what I needed. Too many other projects going on.

Double D · « **Reply #47 on:** May 14, 2009, 02:38:27 PM »

Quill is the way to go.

I made this one to day just to see if I could. It's a 16 incher...and it does burn end to end.

I made it with some flax string and spray glue. Had to use a darning needle to thread it. Tried it with double sided sticky tape. The furthest I could push the tape was 8 inches.

Works good, hope the neighbors didn't call the cops...

Cat Whisperer · « **Reply #48 on:** May 14, 2009, 04:14:23 PM »

What are you shooting that has a 15-16" wall thickness ?

Cornbelt · « **Reply #49 on:** May 14, 2009, 04:22:48 PM »

Any of you guys use cut-offs from Nonel Primadet lead-in for ignition? Substantial flash, can be ignited w/rifle, pistol, or sgn primers, and can be unrolled whatever distance you want. No cap, just the plastic tube. And they get thrown out for the guy in the right place.

Bornsouthern34 · « **Reply #50 on:** May 14, 2009, 05:02:51 PM »

Quote from: Double D on May 14, 2009, 02:38:27 PM

Quill is the way to go.

I made this one to day just to see if I could. It's a 16 incher...and it does burn end to end.

I made it with some flax string and spray glue. Had to use a darning needle to thread it. Tried it with double sided sticky tape. The furthest I could push the tape was 8 inches.

Works good, hope the neighbors didn't call the cops...

Double D,
How fast does it burn? I have been using fuses out of oversized bottle rockets that are about 3 inches long. They burn slower than I want though. I have found a site that sells cannon fuse but I am not sure what burn rate would be appropriate for me if that is the way I choose to go. Ideas?

Double D · « **Reply #51 on:** May 14, 2009, 05:33:19 PM »

Quills are half a heart beat slower than instantaneous. Go through all four pages of this post for details.
http://www.gboreloaded.com/forums//index.php/topic,95774.0.html.

Here is a post with the quills being fired in a Mortar.

http://www.gboreloaded.com/forums/index.php/topic,166412.0.html

Scroll past the stills shots and watch the videos.

Bornsouthern34 · « **Reply #52 on:** May 15, 2009, 04:58:27 PM »

Yeah, those quills are much faster than my fuses. The videos are good too. However it will take me some time to build up enough courage to stand next to a mortar firing a 12-14 lb bowling ball with 750 grains of powder using a quill.

Perhaps I can practice with my golf ball mortar.

Cat Whisperer · « **Reply #53 on:** May 16, 2009, 04:45:09 PM »

Quote from: Cornbelt on May 14, 2009, 04:22:48 PM

Any of you guys use cut-offs from Nonel Primadet lead-in for ignition? Substantial flash, can be ignited w/rifle, pistol, or sgn primers, and can be unrolled whatever distance you want. No cap, just the plastic tube. And they get thrown out for the guy in the right place.

They in all likelyhood work well, but that's a bit out of the leage of what we cover here - Pre- 1898 vintage (and replicas) in order to be well within the parameters of both the law and the scope of blackpowder cannons and mortars discussed on our forum.

Bornsouthern34 · « **Reply #54 on:** May 16, 2009, 06:38:52 PM »

I took some new videos today. I will be posting soon but should be worth the wait.