Author Topic: One of my half scale mountain howitzers (Read 7563 times)

GGaskill · « **on:** March 15, 2005, 05:57:02 PM »

This is one of my half scale bronze mountain howitzers. I cast it in silicon bronze in a Bronze Casting class in a community college and machined it at Lassen College during one of their summer sessions. It is on a steel carriage I designed for test firing the various sized guns that we make in my cannon class (when it has been held.) The cheeks move apart to hold different width barrels and the trunnion holes are oversize for sleeves to match the trunnions of the barrel in question. It is bored for 2 lb spherical sinkers, which I think will give too much recoil but we will see (not fired yet.)

I finally fired this gun and the recoil is less than I expected.

machinehead · « **Reply #1 on:** March 15, 2005, 06:41:28 PM »

That is a great looking tube. I would love to cast my own out of bronze. im looking to do a half scale mountain howitzer next. The largest pwice of stock i have is 4" 4130 and naval brass. Im finishing up on my first artillary peice right now, a 1/2 scale coehorn.

CU_Cannon · « **Reply #2 on:** March 17, 2005, 06:50:54 AM »

Good looking work. I like the carriage more pictures would be nice. My next project will be a 1/3 to 1/2 scale mountain howitzer. It will be a while before I get the wood carriage built. Something like you have would work great.

GGaskill · « **Reply #3 on:** March 17, 2005, 08:54:53 AM »

The stock trail is made of 3" square steel tubing with both ends closed by welded pieces. The bottom is a separate piece of 1/8" on a diagonal for the friction plate and the front end is the top layer of the tubing bent down to parallel the ground (side material cut away to permit this) with a small filler piece to close the remaining hole. The cheeks are 1" aluminum plate bolted to the trail with 1x2x3" steel blocks behind them welded to the trail to transfer the recoil force from the cheeks to the trail without going through the bolts. There are washers between the cheeks and trail to space the cheeks for whichever barrel is mounted. The axle is 3" square oak with a groove in the bottom for a 3/4" steel axle.

I can post drawings or send a dwg file if you can read it or a paper print if you prefer.

GGaskill · « **Reply #4 on:** March 17, 2005, 09:18:31 PM »

Here are a couple of closeup pictures of the steel carriage.

Note the 1x2 steel blocks welded underneath and behind the cheeks. These are there to take up the recoil forces instead of the bolts holding the cheeks and axle. Also note the robust trunnion caps. It needs a quoin or elevation screw but that hasn't made it high enough on my priorities list. :-)

CU_Cannon · « **Reply #5 on:** March 18, 2005, 05:01:51 PM »

Thanks, that should be enough to come up with something of my own. I should be able to scrounge enough stuff together to build one. It will be dangerous going to the junk yard. You can never tell what will follow you home.

Out of curiosity how much was the bronze and what kind is it? IÂ’m not sure if I want to cast the barrel or machine it from solid. I would probably go with steel if I go solid stock.

GGaskill · « **Reply #6 on:** March 18, 2005, 08:32:38 PM »

It is silicon bronze (6% silicon, 94% copper less impurities) and casts very well (great for sculpture, very fluid when melted) but not the strongest possible alloy. But for a half scale tube, it should be strong enough assuming the operator stays away from anti-aircraft duty. It has a 1" diameter chamber.

As I recall, it was $2.20 a pound and the raw casting plus gates and sprue weighed about 95 pounds. I actually cast four of them, the first three in petrobond sand and the last as an investment casting. The finished weight is only 28 pounds so a lot of it becomes chips, but they can be remelted so they aren't totally waste.

The advantage of casting is less waste and integral trunnions but the process is expensive or time consuming (make pattern, make mould, melt bronze, set up foundry for casting, pour bronze, clean up, yada yada yada.) But a bronze version of a bronze gun really looks nice.

CU_Cannon · « **Reply #7 on:** March 20, 2005, 03:59:42 PM »

I've wanted to try casting for a while. My dad picked up the foundry from the local high school metal shop a few years ago. The school was phasing out the metal shop and most of the tools went for cheep (also got a 9" south bend for $120). I plan on getting the foundry set up this summer if I have time. I believe the largest charge is 10 lbs of brass. It not much but I may try some small barrels.

I have also considered finding a foundry that would casts iron to do the barrel. It probably would cost more than machining from solid and around the same if not more time. I might be able to defray some of the cost if I have a few cast at once and sold the extras. They would most likely be sold un-machined to defer liability.

I have a list ten feet long of other projects that should come first so it will be a while.

Cat Whisperer · « **Reply #8 on:** March 21, 2005, 01:26:19 AM »

Quote from: CU_Cannon

.... I have also considered finding a foundry that would casts iron to do the barrel. ....

There are many around. We're down to one from the two that were active in Radford, VA. But I know the guy who runs Pattern Services.

That's an interesting idea - if we could get together on one design to have several made .....

Double D · « **Reply #9 on:** March 21, 2005, 05:38:48 AM »

Something to keep in mind NSSA requires that "all reproduction and original barrels failing inspection must be lined with a bore liner of extruded steel tubing of a minimum ANSI standard and a minimum 3/8 wall thickness. The liner must be closed closed at the breech end with a steel breech plug, sweat fitted into the liner and welded."

NSSA rules goes on to describe the breech plug shape and minimum dimensions. NSSA also requires pictures of the the liner before and after welding.

These are safety regulations. I suggest you follow these regulations even if you are not going fire your gun in NSSA competition, they might just keep you from being injured or killed.

Cat Whisperer · « **Reply #10 on:** March 21, 2005, 06:45:19 AM »

Quote from: Double D

Something to keep in mind NSSA requires that "all reproduction and original barrels failing inspection must be lined with a bore liner of extruded steel tubing of a minimum ANSI standard and a minimum 3/8 wall thickness. The liner must be closed closed at the breech end with a steel breech plug, sweat fitted into the liner and welded."

NSSA rules goes on to describe the breech plug shape and minimum dimensions. NSSA also requires pictures of the the liner before and after welding.

These are safety regulations. I suggest you follow these regulations even if you are not going fire your gun in NSSA competition, they might just keep you from being injured or killed.

Not a bad idea. Since the quality of the barrel cast is at least somewhat dependant upon the quality of the process - based on experience.

Double D · « **Reply #11 on:** March 21, 2005, 08:10:03 AM »

Another thing...does anyone know the correct composition is for the alloy ordnance bronze?

Probably wouldn't matter with a sleeved bore, but it could be an issue in an unsleeved bore.

GGaskill · « **Reply #12 on:** March 21, 2005, 08:19:53 AM »

Civil War era bronze was traditional tin bronze; more or less 10% tin, 90% copper (about the same as C90700). Modern practice has separated copper alloys into brasses and bronzes by the presence of zinc. If the alloy contains zinc, it is a brass. If not, it is a bronze. So the alloy I used is a bronze even though there is no tin in it. Aluminum bronze is a very strong material but it doesn't cast as well as silicon bronze.

There are also some alloys called "gun metal" which are quite strong and cast well. I don't have my bronze casting book at work to look up the details but can update this when I get the chance. (This may be C94800 [internet search]; will still check for book tonight.) C94800 isn't it; it is most like a proprietary alloy called Nicomet.

By the way, I have a match plate (pattern) for the half scale mountain howitzer.

CAV Trooper · « **Reply #13 on:** March 21, 2005, 09:08:50 AM »

From the Cannon Ltd web page:

Quote

Naval gun bronze is a mixture of 88 parts copper, 8 parts tin and 4 parts zinc. Bronze tubes are not cheap; in fact, casting costs alone are 3 times as much as iron. On the other hand, overall appearance and safety may be consideration in making your decision on a particular tube. Our bronze tubes are twice as strong as iron tubes.

Cast gray iron tubes have a pressure rating of about 40,000 pounds per square inch; mild steel tubes have a rating of about 60,000 pounds per square inch and Naval bronze tubes have a rating of 65,000 pounds per square inch. So, as you can see, bronze tubes are the strongest, not to mention the most attractive.

GGaskill,

That's a really sweet howitzer you have. You should be very proud of it. There's just something about a bronze tube that makes people drool. I'm dreaming about the day I can get my own bronze cannon. Maybe a nice 3 pound Verbruggen.

GGaskill · « **Reply #14 on:** March 21, 2005, 09:29:50 AM »

The price differential is substantial; the raw casting cost about $200 just for metal. A steel equivalent would cost about $60 for new metal and less for surplus (you never find surplus bronze cheap.)

CU_Cannon · « **Reply #15 on:** March 21, 2005, 10:46:02 AM »

If price was not an issue bronze is defiantly the way to go. I'm not sure which would be easer to find though, a shop set up for bronze or for iron. Many of the larger iron foundries have a minimum. It might be possible to find a sculpture shop that would be willing to cast a bronze barrel.

Since cost is an issue I will most likely have to go with steel until I can save up the money for a bronze barrel. Then again I could win the lottery.

GGaskill · « **Reply #16 on:** March 21, 2005, 11:48:24 AM »

Check your local community colleges for an Art Dept that does bronze casting, then go talk to the instructor. Tell him you are not really interested in sculpture but in the foundry work. It helps to have metal working skills such as TIG welding as that is a commonly used procedure to repair or join bronze pieces. I cast four of the half scale howitzers, two about half scale Coehorns (the first was flawed so we melted it and cast a second one), and 4 quarter scale Coehorns (1.5" bore, primarily desktop conversation pieces.) I also did a lot of TIG welding that the instructor would have otherwise done (brownie points.)

A quarter scale Coehorn mortar.

Calamity Jane · « **Reply #17 on:** March 24, 2005, 02:46:06 AM »

Unlined barrels give me the heebee-geebees! (Too long in engineering, I guess. . .)

CU_Cannon · « **Reply #18 on:** March 24, 2005, 06:55:22 AM »

That is one cute mortar. I'm not sure if I would shoot anything from it. It would make a neat fire cracker mortar. I'm not sure the size but you might find some Styrofoam balls to shoot.

I now have access to a foundry furnace. It can melt a 20bl change of brass. I need to run some numbers to see if it would melt a big enough charge to cast a 1/3 scale mountain howitzer. I guess I'll need to work on some pattern making skills. Then I need to track down some bronze.

GGaskill:

Original cannons were poured with out a core vertically. Did you use this method or did you pour it horizontally? Would it even make a difference on a cannon this small? How would one go about pouring a tube vertically with a split pattern?

GGaskill · « **Reply #19 on:** March 24, 2005, 08:17:48 AM »

The Art Dept foundry didn't have any flasks big enough to pour a 1/2 scale mountain howitzer so I built my own. It was designed for pouring from the end instead of the top so I could vertically pour the castings. My 2 pounder mortar was cast horizontally and suffered from shrinkage defects (not catastrophically though) and it is only 8" long (the problem was in the top and a couple more vents would have probably taken care of it; the shrinkage was where there were no vents.) A 1/3 scale MH would be a little over a foot long which would make for a relatively easily handled mould (filled with Petrobond sand, the mould for the 1/2 scale weighed over 200 lbs and we lifted it with the crane.) But I would make the effort to do a vertical pour with at least 4" of shrink feeder at the muzzle (notice the extra long shrink feeder and gate at the top of the shrink feeder.) Here is a picture of the match plate (pattern) for the 1/2 scale MH so you can see the sprue and gating I used.

Half scale Coehorn matchplate

<<< How would one go about pouring a tube vertically with a split pattern?
>>> You need one end of the flasks partially open so you can pour through it; you may have to make an end pour flask. Here is a picture of the flask. The two loose pieces sitting on the edges are bolted in the ends during ramming and removed after the mould has been positioned upright. The black stuff is charred wood from molten bronze spills. The angles are stiffeners to keep the sides from bowing out under the pressure of the ramming.

A raw 1/2 scale bronze mountain howitzer casting

CU_Cannon · « **Reply #20 on:** March 24, 2005, 01:24:26 PM »

I found a 1/2 scale howitzer from Hern Iron Works. It is cast of iron un-bored. I would most likely bore it out my self and sleeve it. The price is $162 which doesn't seam that bad. I can't imagine that it would be any cheaper to have it cast.

I think the cheapest way to go would be machined from solid. I may have to go that route until I can save up the money for a cast barrel.

Powder keg · « **Reply #21 on:** March 24, 2005, 05:41:54 PM »

Hello, I have a 3/4 scale Mtn Howitzer machined from solid steel. I'll post some pictures tomarrow. I'm considering getting the barrel brass plated.

Cat Whisperer · « **Reply #22 on:** March 25, 2005, 01:46:38 AM »

GGaskill

WOW - having done some casting, the pictures tell me of all the work and planning you've done. Gutsey. It shows a genuine committment (addiction?) to the process.

GGaskill · « **Reply #23 on:** March 25, 2005, 08:21:19 AM »

I have to say that making stuff from liquid metal is an engaging process. The main problem, beyond the need for a foundry, is the need for assistants when making large stuff. This is an inhibition to a serious home foundry.

CU_Cannon · « **Reply #24 on:** March 28, 2005, 08:22:06 AM »

Thanks for the pictures. They answered a lot of the questions I had. How much extra did you add to the pattern to allow for machining? Once I can get the time I'll make the patterns and cast a test one from aluminum (much cheaper than bronze, free in fact).

GGaskill · « **Reply #25 on:** March 28, 2005, 10:23:27 AM »

When you make a casting pattern, you have to make two enlargements (called allowances)--one for shrinkage and one for machining. The shrinkage factor you look up in Machinery's Handbook (different for each metal); the machining allowance primarily compensates for distortion in casting. I increased the length from a finished 18.6" to 19.27" and the diameter from a finished 3.8" to 3.94". For aluminum, I am guessing you should about double those numbers.

Powder keg · « **Reply #26 on:** March 28, 2005, 01:16:53 PM »

Hey GGaskill, Can you explain something? how does a matchplate work? I get the first step, place the drag over and ram the sand around it. what do you do for the cope? Won't the two be reversed when you put them togather? Thanks,

GGaskill · « **Reply #27 on:** March 28, 2005, 01:27:57 PM »

The matchplate goes between the cope and drag. You assemble them all, fill and ram cope or drag, put a moulding board over the filled half and turn the whole thing over. Then fill and ram the other side. Cover with the other moulding board. Perforate the mould through the cover boards for gas escape paths; be sure not to penetrate to the pattern. Separate the upper half from the match plate, then remove the match plate from the bottom. Fix any imperfections and reassemble with moulding boards. My flask is held together with seven pieces of allthread, washers and nuts on each end. Rotate end up and remove end pieces to reveal pouring cup.

Powder keg · « **Reply #28 on:** March 28, 2005, 02:23:02 PM »

So does the matchplate protrude on both sides? Or just one side? This is where my confusion is I think.

GGaskill · « **Reply #29 on:** March 28, 2005, 03:02:02 PM »

Yes, half of the pattern is on each side, although the sprue and gating is on only one side with the mountain howitzer matchplate. That is why you have to use both cope and drag when ramming.