First Cannon

[keithinvestigations]

Hi all I'm new here. I just sent off a check to Hern Iron for their Coehern mortar. I've been surfing here for a little while but still need some direction. I am very green here so please be patient with me. I am very familiar with modern firearms, but I've never loaded, fired or know squat about cannons.

I understand that I am going to have to get the vent tube drilled. Are there any instructions for this? I plan on taking this to a machine shop but I think I need some kind of direction instead of, drill me a vent hole as I doubt they do that often.

I also ordered the hardware for the sled and am going to get this built. Is there anyone here who could build this for me for a reasonable price? I'm not a woodworker but I guess I could try! lol

Where do I learn about type of powder, how much and basically how to fire this thing. Hern builds these but from what I gather you are on your own to figure everything out.

Thanks.

 

[kevthebassman]

Welcome to the site!

I'm no cannoneer, but my bosses do seem to think I'm a machinist. (I'm really not, by training, but one has a way of picking up a few things, then getting thrown into the deep end of the pool.) You've come to the right place, to be sure. Someone will be along shortly to give you a better run-down than I possibly could.

Drilling a vent hole isn't a very complicated operation so long as you've got a drill press and a vise, if you can find a small shop willing to do it for you it shouldn't cost you very much at all. If you wanted to make things easier on everyone involved I think it would be best for you to show up with two of the proper diameter and length drill bits.

The carriage shouldn't give you much trouble. Let me rephrase that, the carriage wouldn't give me much trouble, but I'm mechanically inclined. Likewise, balancing a check book shouldn't give a normal person much trouble, but I'm totally inept at it.

My best advice would be to sit down with it in front of you and visualize and write down everything that would have to be done to make it complete, then determine if you have the skills/confidence to try it. If the "to be done" list dwarfs the "confident enough to do" list, I'm sure that somebody here can help you out.

 

[TheDoubleD]

Well a vent liner hole isn't just a thread hole drilled in the side of the barrel. It's a bit more complicated than that, but not much.

It needs to be drilled at a slight angle rearward so the center of the vent liner comes out at the back of the powder chamber.

The hole is threaded and then upper portion relieved for the unthread portion of the liner. The depth of the relief helps control the over all depth of the liner. You don't want the vent liner protruding into the powder chamber.

Be sure to grease the threads of the liner so it is easier to be removed.

 

[kevthebassman]

DD, what kind of angle should our friend be needing? 5 or 10 degrees?

And a good coating of high temperature anti-seize on the threads would definitely be a smart thing to do.

 

[matt denison]

Why a vent liner? Couldn't he just drill for a fuse? All the morters I've seen in action just fired via a fuse in the touch hole. Easy, safe. I drilled mine straight down into the very back of the chamber so that the prick punctured the very back of the tin foil cartridge of powder that I used. Worked great, did it with a hand held drill and long 1/8" drill bit IIRC.

By the way you may find that a commercial machine shop will refuse to be complicit in the drilling of an ignition system of a cannon. Then again you might get lucky.

 

[TheDoubleD]

The gun he has is getting is cast steel out side steel liner inside. He has to protect the intersection of the liner and cast steel from the introduction of black powder fouling. The junction will erode and corrode making a weak spot which over time can and will fail. The vent liner seals the hole and prevents the fouling from getting to the junction.

Original guns had them to repair eroded vents. Here's one on an original Mt.Howitzer on display at the Big Hole Battle field.

In more modern times where in the interest of safety we use barrel liners, they have been adapted to protect the liner seam.

I looked at the official drawings for the Federal 24 PDR. The Vent is angled but the drawing does not give an angle.

I checked the drawing for the Confederate 24 PDR coehorn and the angle is 11 degrees.

Comparing the drawings the angle look the same.

 

[keithinvestigations]

Regarding the Coehorn mortar from Hearn Iron Works, should the vent be drilled in the middle of the indentation that is on top of the barrel?

 

[TheDoubleD]

You will need to do some measurements to be sure.

 

[mazo kid]

It's good that you are asking your questions now....above all, you want to be safe! Here is a picture I saved off an on-line auction site for future reference.

The workmanship looks great!

 

[keithinvestigations]

Yes, I saw that one on gunbroker. That thing is HUGE and weighs 300 lbs I think.