Makeing My First Coehorn Mortar (Golf ball)

[warf73]

I found the Mortar I want to make. It's at the very bottom of the link.

http://www.geocities.com/mikefinch24060/artillery/artillery.html

I really like the looks of this Mortar. I think the cap for lighting it is nice touch.

Here’s were I stand.

I will be making this Mortar myself. Machinist by trade I have a vast array of machines at my disposal. So the labor is not an issue.

The material for the cannon its self can be made out of what? What are my metal choices? Would mild steel work with this?

The carriage will be 3/4" plate steel. I really don’t want to mess with wood.

I’ve got an idea how to make everything just need little help along is all :grin:

This will be a work in progress (winter project) Ill try to post pics as it comes together if you all like?

Just to let you all know I’ve been reading this forum for well over a year and can’t stand it anymore I have to make me a cannon.

Thanks Warf

[warf73]

This is thinking out loud.
If the final OD of the cannon is 6".
A golf ball dai. hole which is aprox. 1.75".
I would have a  2" wall thickness aprox.

Would that be a safe wall thickness if I used mild soild steel stock.

Or would I need to something stronger?

Warf

[Cat Whisperer]

You will have much more than enough.  For golf balls 3/8" of an inch should be enough - I'd go more than 3/8" or stronger because someone might put a lead ball in it.

By mild steel, I assume you mean something like CRS, 1018.  Strength of it is what 60k lbs tensile?  4140 prehardened is more like 100k give or take.

Golf balls give very little resistance.  If it's 6" in diameter you might want to consider a larger bullet.  Although I've got a 5-3/8 diameter hunk of metal that will look like the dictator with the golf-ball diameter bore on the lathe right now.

The issues I have are trying to figure out how to get that huge chunk of iron held securely.  It's a little rough on the OD and my steady rest will only go up to about 4" diameter, the 3 and 4 jaw chucks are big enough.  I do have a couple of face plates available.  So I may try to bolt it to the face plate.

Suggest drilling the biggest hole you can first - that eliminates a LOT of boring.

[warf73]

How much ya want for that chunk of hog iron :grin:

Warf

[CU_Cannon]

I have a chunk of 4140 for my eventual coehorn.  It measures 3 7/8 by around 6 1/2.  I got it off ebay for around $15 with $8 shipping.  I figured it wasn't a bad price considering the piece of 1018 I bought for my last cannon cost $23 locally.  

I chose 4140 because I plan on shooting golf balls and lead with it.  I figure a large factor of safety is never a problem.  

I will hopefully be starting on it this weekend.

CW,
Have you considered making your own steady rest?  I think I remember reading in live steam about a guy that maid his own.  He used a plate of 1/2 aluminum with three slots machined radial from the center of a hole.  The slots were to hold bars with bearings on the end of them that ran against the work piece.  If you don't understand what I am saying I can draw something up to make it more clearly.

[CAV Trooper]

Machinist by trade I have a vast array of machines at my disposal.

I'm jealous!   :mrgreen:

[Cat Whisperer]

CW,Have you considered making your own steady rest?  I think I remember reading in live steam about a guy that maid his own.  He used a plate of 1/2 aluminum with three slots machined radial from the center of a hole.  The slots were to hold bars with bearings on the end of them that ran against the work piece.  If you don't understand what I am saying I can draw something up to make it more clearly.

Hot dawg!  Yes, I was considering parting out one of the two identical ones I have, BUT your idea is ideal - I have some 3/4" - 16" diameter disks of 6061 and handfulls of bearings - just a matter of fitting the disk to an ell bracket and 3 slots for the shoulder bolts!

Thanks much for the design!

[Cat Whisperer]

I have a chunk of 4140 for my eventual coehorn.  It measures 3 7/8 by around 6 1/2.  I got it off ebay for around $15 with $8 shipping.  I figured it wasn't a bad price considering the piece of 1018 I bought for my last cannon cost $23 locally.  

I chose 4140 because I plan on shooting golf balls and lead with it.  I figure a large factor of safety is never a problem.  

That's about what I pay for scraps from a local machine shop.  (The shop does lots of piece work for local industries and has a steady supply of mill ends.)  

Sometimes you can find odd pieces of steel at yard sales.  I found a 5" x 20" piece of mystery (probably CRS) steel that was used for rolling down vynal tile.  $5 was paid in haste!

[warf73]

I found a nice peace of 4" round stock.

Now I need to find my drill bit. :grin:

Do you guys think 7075 T-6 Aluminum would be ok for carriage?

Thinking about 1" think.

Thanks Warf

[Double D]

That aluminum will work for a carriage, but it would depend on how you use it.  The carriage needs some weight to add stability to the gun or it can  flip on its back.  

Field carriage have a long trail sticking out the back.  That trail serves two purposes.  One to serve as a connecter to the caisson for transport and second for stabilization when fired.  

Mortars have large flat beds that intersect the line force from recoil of the gun when fired  keep them from flipping.  

Naval guns are different.  they need weight and they need to be tied down.



You would be better off not making a an aluminum truck if you were building a naval gun.