Author Topic: 12 pdr coehorn project (Read 5807 times)

CU_Cannon · « **on:** November 19, 2005, 02:25:30 PM »

IÂ’ve finally started my big mortar. ItÂ’s a 12 pdr coehorn scaled from the 24 pdr. It will be machined from a 7Â” x 12.5Â” piece of 1018. That doesnÂ’t sound that big until you try to pick it up. I ordered it from a distributor online. It said 134# on the shipping label. Shipping was high but it was still cheaper than getting it locally. IÂ’m not sure that the delivery man liked it much though.

Here what it looked like starting out.

I started by facing off one end and drilling a center. Then I roughed out the trunnion end. IÂ’ve found it is easiest to rough it out now. The rest of the profile and the bore can then be finished in one chucking.

This is as far as I got today. IÂ’ll see if I can get the reinforcing rings finished and the bore roughed out tomorrow. Its starting to look like a mortar.

It will be interesting to see how much weight is remove by machining.

Double D · « **Reply #1 on:** November 19, 2005, 03:10:12 PM »

Who was the online distributor who sold you the steel?

Cat Whisperer · « **Reply #2 on:** November 19, 2005, 03:49:09 PM »

Holding a 7" chunk of ir'n like that looks like no watch-maker's lathe!

You're off to a good start!

GGaskill · « **Reply #3 on:** November 19, 2005, 07:45:21 PM »

Gotta say that working that big stuff is fun (although lifting it is not so much fun.) (-: 2.25" bore.

CU_Cannon · « **Reply #4 on:** November 20, 2005, 04:21:02 PM »

This is the biggest piece of steel IÂ’ve worked with so far. It is a lot of fun but you are right about the weight.

I purchased it from speedy metals; they do a lot of business thought ebay. The steel cost $117 plus $80 shipping. The cheapest I could find locally was well over $200.

I accomplished a little bit more today. I have the outside profiles finished and the bore drilled. So far I have around 8 hours into it. It is starting to get lighter but not by much. On to the boring.

At some point IÂ’d like to build a siege mortar. I was thinking something in the golf ball to beer can scale.

Powder keg · « **Reply #5 on:** November 20, 2005, 04:35:49 PM »

Lookin Good! How are you going to cut the slot for the trunion? I have built a special flycutter for each diff. trunnion dia. I do. I can post a picture if you want. Keep up the good work and progress.

Later, Wes

Cat Whisperer · « **Reply #6 on:** November 21, 2005, 12:40:54 AM »

Is that a spruce/white-pine steady-rest?

Cool way to think outside the box!

freddo · « **Reply #7 on:** November 21, 2005, 04:35:09 AM »

cu cannon
Thats a lovely piece of steel.I take it the shipping costs were not airmail and I hope the delivery man was not hunched over and hobbling when he left.
I have to haul my steel for my 6 pounder field piece to night school every time I go It is surprisingly heavy.For reasons that I won't go into here I actually have to haul two pieces of steel.I think the back of my car may be striking sparks off the road surface
The school has big lathes with taper turning attachments and they have a copy turning lathe so I was able to make a wooden model and turn the muzzle swell on that.It made it quite easy to do the job and learn a lot also.
For the same reasons that I have to do two I will not be able to cut the holes for the trunnions at school so I am very interested to see the fly cutters that Powder keg mentions .
Powder Keg.
If you would post the pictures I would be most grateful.
Regards Freddo

CU_Cannon · « **Reply #8 on:** November 21, 2005, 06:10:13 AM »

The pieces of pine are just a cradle to make setup easier. The picture was taken right before I took it out of the lathe. I would have liked to get all the machining done in one chucking but it will be a while before IÂ’ll have time to work on it again. A wood steady rest might be a novel idea though. I may have to try that on one of my next projects.

I plan on having the trunnion welded. So my idea is to mill away half of the trunnion piece in the region of the barrel and then mill a corresponding grove in the barrel. Once everything is welded together it should look like it was cast. The other mortars IÂ’ve built have groves cut with fly cutters. I didnÂ’t like how it limits the powder chamber depth.

Powder keg Â– How are the trunnions attached on your mortar? Are they set into pockets or contoured to fit the barrel?

GGaskill · « **Reply #9 on:** November 21, 2005, 06:31:45 AM »

Freddo,
The easiest way to cut trunnion pockets is to start with a two flute end mill and plunge cut to the final depth. Once you have removed the center, you can open the hole with a fly cutter or a boring bar in a boring head.

Dictator · « **Reply #10 on:** November 21, 2005, 11:51:16 AM »

that's a cute looking seige mortar G. What's the story on it? It's always neat to look at what you guys are working on, There's some nice talent out there.

Cat Whisperer · « **Reply #11 on:** November 21, 2005, 12:22:42 PM »

Quote from: CU_Cannon

The pieces of pine are just a cradle to make setup easier.
....

Even if it's not a "poor-man's steady rest" being a setup aid is GOOD!
I'll bet it keeps a few more nicks from occuring on the ways.

GGaskill · « **Reply #12 on:** November 21, 2005, 04:00:51 PM »

It was made from a piece of 6" scrap I had in my shop. It was built as a favor for another board member who had done me a favor. It is bored to the same diameter as his half scale Napoleon so he could use the same shot in both. He built the bed for it.

freddo · « **Reply #13 on:** November 23, 2005, 12:16:18 AM »

Thank you G Gaskill
Fly cutter,boring bar,-up goes the learning curve again.

CU_Cannon · « **Reply #14 on:** December 02, 2005, 06:08:08 PM »

I got a little bit more done tonight. I forgot how long it takes to open up a hole like this. They donÂ’t call it boring for nothing. After about 3 hours the bore is up to 2.5Â” from 2Â”. I may end up making a bigger boring bar so I can take a heavier cut. The 1Â” I have doesnÂ’t flex all that much but starts to chatter if I try to take too heavy a cut.

IÂ’m kicking my self now. I was at a flea market this summer that had a guy selling a 2.5Â”, 3Â” and 3.5Â” drill. I think they were around $20 each!

Cat Whisperer · « **Reply #15 on:** December 03, 2005, 02:34:22 AM »

Quote from: CU_Cannon

....
IÂ’m kicking my self now. I was at a flea market this summer that had a guy selling a 2.5Â”, 3Â” and 3.5Â” drill. I think they were around $20 each!

That's about what I pay by watching ebay. A lot of the really big stuff is not 'high-demand' material.

CU_Cannon · « **Reply #16 on:** December 04, 2005, 02:36:53 PM »

I got some more boring done today. IÂ’m up to about 3 1/8Â”. I actually did end up using the wood cradle I made for set up as an impromptu steady rest. I was hoping I could get away without building a steady rest but the chatter was starting to get out of hand. It was a combination of boring bar chatter and the piece its self vibrating. With the cradle in place with some oil and a brace on the bar it worked chatter free. I guess I can hold of on the steady rest for a while longer. The camera wasnÂ’t handy so I didnÂ’t get any pictures but IÂ’ll get some next time.

The weight is down to 105 lbs. IÂ’ve lost almost 30 lbs so far. It is still darn heavy though.

Cat Whisperer · « **Reply #17 on:** December 04, 2005, 03:38:49 PM »

One kind of hates to see all those pounds of steel just turn into chips; but the result is worth it!

The tube and trunion of my 4.5" mortar weigh in at 103 lbs. I don't want anything heavier to lug around than that!

CU_Cannon · « **Reply #18 on:** December 09, 2005, 12:27:45 PM »

IÂ’m almost to the finished bore size. The bore is currently a little over 4Â”. I have about 10 hours total in boring so far. I figure around 5 more will finish the bore.

john pike · « **Reply #19 on:** December 09, 2005, 12:35:38 PM »

Quote from: CU_Cannon

IÂ’m almost to the finished bore size. The bore is currently a little over 4Â”. I have about 10 hours total in boring so far. I figure around 5 more will finish the bore.

whats your turning speed,
are you getting any chatter?
and are you greasing that chunk of wood?

just curious
johnp

CU_Cannon · « **Reply #20 on:** December 09, 2005, 04:52:00 PM »

The speed is 68 rpm at around a .02Â” cut. IÂ’m not sure what the feed is. I generally just play around with the levers until I get a feed I like. I may have some time tomorrow to get some more done, IÂ’ll check then to see what the feed is.

I have been battling with chatter on and off. I think IÂ’ve found a good combination of fed rpms and tool shape. The boring bar is 1Â”. IÂ’m thinking now it would have been worth it to make a bigger one. You can see in the right of the picture a block of wood bracing the boring bar. It helps to dampen out the chatter. The trick is to avoid getting greedy with the cuts.

The wood is oiled up. It is not the best setup I admit but it seams to work quite well. It also saves me the time of building a steady rest. I think if it was a little better designed it would work as well as a conventional steady rest. The wood also doesnÂ’t mar the work as much. I may try this method again in the future. I would put much more thought into it though.

john pike · « **Reply #21 on:** December 09, 2005, 06:35:09 PM »

The wood is oiled up. It is not the best setup I admit but it seams to work quite well. It also saves me the time of building a steady rest. I think if it was a little better designed it would work as well as a conventional steady rest. The wood also doesnÂ’t mar the work as much. I may try this method again in the future. I would put much more thought into it though.[/quote]

i tore my bronze/brass tips all to hell, and it was on polished metal, on my steady rest,

im thinking of making an adjustable rest using skate-bearings, doubled up,

johnp

CU_Cannon · « **Reply #22 on:** December 10, 2005, 05:06:32 AM »

I wonder how some of the new plastics and ceramics would work for fingers. Since many of these materials are self lubricating they may not mar the work as much.

Cat Whisperer · « **Reply #23 on:** December 10, 2005, 06:31:55 AM »

Quote from: CU_Cannon

I wonder how some of the new plastics and ceramics would work for fingers. Since many of these materials are self lubricating they may not mar the work as much.

I'd give my eye-teeth for Delrin for this application.

http://www.upchurch.com/TechInfo/matDelrin.asp
http://www.boedeker.com/acetal_p.htm

I've used it for rails that supported traveling fixtures that held brake pads going through a grinder (establishing a true surface on the pad). Talk about abrasion resistance! Slick, tough and long-lasting!

You can get it 'filled' with PTFE (teflon)!

CU_Cannon · « **Reply #24 on:** December 11, 2005, 04:32:33 AM »

This is where it stands so far. I have the bulk of the bruit force machining done on the bore.

The bottom of the bore will be hemispherical. I have built a follower that IÂ’m somewhat confidant will work. IÂ’ll post pictures once I get machining the profile. The hole in the center is for the powder chamber. It will be the same profile as the original.

The weight is down to about 90 lbs.

Cat Whisperer · « **Reply #25 on:** December 11, 2005, 07:12:19 AM »

Wow - 44 lbs of perfectly good iron ending up in chip city!

CU_Cannon · « **Reply #26 on:** December 11, 2005, 01:40:10 PM »

IÂ’ve already thrown enough away to build a beer can mortar. I think the result will be worth it though.

Tropico · « **Reply #27 on:** December 19, 2005, 10:32:53 PM »

CU Whats happening with "The Big Mortar" ? Are you working on the Breach yet ?

Cat Whisperer · « **Reply #28 on:** December 20, 2005, 12:13:47 AM »

If you're referring to the 1/4" bore little one that was on top of the powder can - I gave it away. I cut a small base of aluminum on the mill and gave it to a friend (who's going through cancer treatment). We'd shot mortars at his place several times.

There will be more. Most of what I build are learning exercises where I try things out.

TexasReb · « **Reply #29 on:** December 21, 2005, 07:54:23 PM »

CU Cannon,
If you don't mind me asking, which shipping company did you use and how much did they charge? I just bought a 12lb Confederate Coehorn Mortar in Virginia and need to get it to Texas.
Thanks,
Matt G.
'TexasReb'