Author Topic: 1/2 scale mt howitzer (Read 2949 times)

sseib · « **on:** September 16, 2010, 08:11:22 AM »

I have been wanting to build a mt howitzer since I started reading this board. I have AOP plans #12 & #25. For my first build I am wanting to try a half scale as I have a 2-5/16 spade drill for the bore and either some 1018, A572 Gr 50, or 4130HT solid round bar drop for the tube. I have two safety issues I'd like some input from those who have been there before, the reduced powder chamber size and shape.

For a half scale the tube dia at the chamber is 3.15 and the only drills I have available are 1-1/4 or 1-1/2. The scaled chamber as drawn would be 1.67 dia x approx 1.6 long with a volume of 3.5 cubic inches and a wall thickness of .74, that's approx 60% of a caliber thickness. If I go 1-1/4 dia x 2.5 long it will get me 3" volume with a wall thickness of .95, approx 75% of a caliber. The only way to get to one caliber wall is to go to 1-1/32 drill which I don't have in the required length. The other option I have come up with is to go 5/8 scale on the outside 3.9375 dia at the chamber and stay 1/2 scale for the bore as I said before I have a drill for that. Now the 1-1/4 drill will give a wall thickness of 1.34, over one caliber. My material selection is limited for the 5/8 scale verses the 1/2 scale but it would give more room to seat the trunions. Does this sound like a better solution than staying to the 1/2 scale based on my material is as stronger as an original bronze would have been?

Now the shape of the bottom of the chamber and the bottom of the bore are going to be as drilled - 130 deg point for bore and 118 deg for chamber, no radiuses or tapers per the original drawings. I have seen mortar drawings on here designed this way and I understand rad's would be better, and for loading powder charges the taper would be better but I am using company tools and the 1-1/4 drill is a twist drill for a specific job we do and not to be modified. If I were using the 1-1/2 drill, it is a spade and we have a bunch of dull inserts I could regrind to any shape I wanted. So, is this a deal breaker or ok?

I have many more questions about full size tubes, projectiles, ignition systems, etc.., maybe another day. I could e-mail my CAD layout if anyone needs it to help answer the above issues.

Thanks,
Steve Seib - cannoneer wantabe

Double D · « **Reply #1 on:** September 16, 2010, 08:33:44 AM »

It is our policy to recommend the one caliber rule for safety. We are well aware that it has a large margin of safety built into it. There are ways around that rule--safely. If you choose to not use these safety recommendations and consider other issues, you only need to be prepared to justify how you built the gun if there is a failure in the future.

If you wish to stay faithful to the the scale you will have to learn how to use the scale safely--it can be done. But on the other hand you are not staying faithful when it comes to drilling holes .

The issue with with drill bit form is the square corners, those corners need round corners to reduce stress points. Instead of drilling holes to finish size, drill them under finish size and the bore or reamed them to size. Then make a one time use form cutting tool for the radii.

Cannoneer · « **Reply #2 on:** September 16, 2010, 10:05:34 AM »

I know that George G. cast a bronze reduced scale Mt. Howitzer barrel, but another member had a good thread on his (half scale?) Mt. Howitzer build; he machined the barrel out of steel, and he made a realistic scale reproduction prairie carriage to mount it on. Unfortunately the memory is blank on the member's name; I think the thread would date from around four years ago.

GGaskill · « **Reply #3 on:** September 16, 2010, 10:22:01 AM »

My bronze mountain howitzers have a 1" diameter chamber. A cheap way to drill that deep a hole with a regular Morse taper drill is to get a Morse taper extension socket and drill the chamber after the bore is finished. Look at the master catalog page at the bottom right for details.

Also, keep in mind what you are going to use for projectiles when deciding on bore size.

bpsteve · « **Reply #4 on:** September 16, 2010, 11:05:53 AM »

Steve,
I replied to your PM but if it didn't go through just email me @ bpsteve@cox.net
Steve R.
AZ.

dan610324 · « **Reply #5 on:** September 16, 2010, 12:13:22 PM »

corners without a radius is an absolute no no in this specific case
first of all when you design a barrel is to think about safety
the howie is already under dimensioned as it is in original to meet modern safety thinking
back then and it was war , it doesnt matter if a few people died because of an exploding cannon .
but today we think a bit different , at least I hope you will .

its very complicated to know where to draw the lines here between safety and scaled dimensions .
but you already taken a hugh step from the original by building in steel , so why not go all the way and make it a safe shooter instead of a scaled down copy ??

try to find an old drill bit that you can regrind to a safe shape

the 5/8 scale sounds like the perfect solution for me

Cannoneer · « **Reply #6 on:** September 16, 2010, 12:34:39 PM »

Holy guacamole, that was one heck of a search, and what do I find when I return to the present? bpsteve is still alive and well, thank goodness!

Eureka!

http://www.gboreloaded.com/forums/index.php/topic,93541.0.html

http://www.gboreloaded.com/forums/index.php/topic,95401.msg1098233039.html#msg1098233039

http://www.gboreloaded.com/forums/index.php/topic,102175.msg1098287818.html#msg1098287818

Zulu · « **Reply #7 on:** September 16, 2010, 01:34:17 PM »

Quote from: Boom J on September 16, 2010, 12:34:39 PM

Holy guacamole, that was one heck of a search, and what do I find when I return to the present? bpsteve is still alive and well, thank goodness!

Eureka!

http://www.gboreloaded.com/forums/index.php/topic,93541.0.html

http://www.gboreloaded.com/forums/index.php/topic,95401.msg1098233039.html#msg1098233039

http://www.gboreloaded.com/forums/index.php/topic,102175.msg1098287818.html#msg1098287818

Wow!
Neat stuff. A whole lot of names I don't recognize. I guess I'm still a "newbie" after more than one year.
Zulu

Victor3 · « **Reply #8 on:** September 16, 2010, 04:46:46 PM »

If you use 1018 and keep the one cal wall thickness, there's really no need to machine the huge radii of the originals. You want some radius at the corners, but not a lot is needed.

If you grind a .187 R on the drills, it'll be enough. Seeing as how you're using company tools, the polite thing to do would be to resharpen them after use. You could grind them back far enough to remove the radius when you do so.

Cat Whisperer · « **Reply #9 on:** September 16, 2010, 05:19:16 PM »

Steve --

WELCOME to the board!

There is a pleasure in using spade drills - fast removal and good finish. I accidentally burned the corners of one of my 1" bits and reground it to a 1/8 radius. Best thing that could have happened. I then used a new bit for most of the next bore and finished the last 1/2" with the one with the radiused bit. The cost of one spade bit is well worth it to make a custom bottoming drill for any bore.

sseib · « **Reply #10 on:** September 17, 2010, 05:51:10 AM »

I want to thank everyone for the responses and bpsteve for the pictures and other info. I'm trying to stay with material and tooling on hand here at the shop. I saw a peice of 5" OD x 2-1/2" ID A182 GR F11 tube 101" long and am looking for the cert's to verify it is seamless. That would make a 2/3 scale tube with a finished bore of 3.080 and then weld the chamber in, if it is not seamless then I will drill and bore a solid bar from both ends and send it to a hyduralic cylinder shop and have them finish bore and hone to size. I was trying to stay one peice with welded on trunions for my first project but in the interest of safety it is worth getting the weld tech involved. I have the BuckStix plans, I actually bought them before I started reading this board and found the AOP plans. Is the BuckStix design considered a safe design as far as welding the breech plug? I can change the chamber shape to fit the recommended one caliber wall thickness.

For a little back-ground on me, I am the designer, detailer and CNC Mill programmer at a job shop that supports a fabrication shop and a field installation division. Our focus is the power and chemical industries so welding pressure vessels will be something the fab-shop welders and tech's are familier with. We have a turning center with 12" chuck and 70" between centers or a vertical lathe that will turn 70", vertical mills up to 33" x 108" and horizon boring mills to 20 feet x 6 feet plus a manual shop with all the standard bridgeports and Leblond lathes plus one large lathe I'm guessing would go 24" chuck by 12 foot bed. I make knives as a hobby and most the guy's in the shop have one of them so I have a few favors I can call in to get this done.

Thanks,
Steve Seib

Double D · « **Reply #11 on:** September 17, 2010, 06:14:43 AM »

The buckstix design has some issues and I would be reluctant to use his it. Breech plug show shrink fit not slip fit. The trunnion he uses are weak. There much better ways to do this.

All that welding he does in the rear bothers me. With the welders you have available to you they should know how to make thos weld and not leave brittle sections.

The less welding on the cannon the better.

A bigger problem that you haven't addressed...projectiles, what are you going to shoot in it?

sseib · « **Reply #12 on:** September 17, 2010, 08:13:43 AM »

For projectiles I was going to start with aluminum round bar one or one and a half calibers long, haven't checked on 3" steel balls or what ever scale bore I finalize on. I have a friend who cast zinc projectiles and balls for his cannons and motars ranging from 1-1/2" up to 4-1/2", which reminds me he may have a mold for his 3" Parrotts - he has a pair of reproductions he takes to re-enactments but I don't think they are rifled. Guess I need to get over there with a calipers and check them.

We freeze shafts into bearing all the time with liquid nitrogen, that is how I presume you would prefer on the breech plug then weld. For the trunions I have seen on the board here a better method with the larger step of the trunion being fit to a bored pocket in the barrel then welded rather than the 1/4" dowel and welding. Is it common for the tube to shrink at the trunions when welded?

The process I'm think would be something like this:
- finish the OD of the tube and rough the bore
- weld the trunions on
- finish the bore
- shrink-in and weld the breech plug
- turn the welded end square and to length
- weld the Cascabel flange on
- turn the radius where the flange welded on

Again, thanks everyone for the input and don't be afraid to hurt my feelings if you see a safety issue or know a better way let me hear it. I'm not trying to re-invent the wheel here I just want something safe based on everyone's collective experience and please, try to be specific if you have a better way.
Steve Seib

Cannoneer · « **Reply #13 on:** September 17, 2010, 08:27:55 AM »

Quote from: Zulu on September 16, 2010, 01:34:17 PM

Wow!
Neat stuff. A whole lot of names I don't recognize. I guess I'm still a "newbie" after more than one year.
Zulu

Zulu,
You may not have known about this place in 06, but this place knew about you!

I ran across this while looking for the Mt. Howitzer build yesterday.

http://www.gboreloaded.com/forums/index.php/topic,90488.0.html

Zulu · « **Reply #14 on:** September 17, 2010, 10:15:25 AM »

Quote from: Boom J on September 17, 2010, 08:27:55 AM

Quote from: Zulu on September 16, 2010, 01:34:17 PM
Wow!
Neat stuff. A whole lot of names I don't recognize. I guess I'm still a "newbie" after more than one year.
Zulu

Zulu,
You may not have known about this place in 06, but this place knew about you! I ran across this while looking for the Mt. Howitzer build yesterday. http://www.gboreloaded.com/forums/index.php/topic,90488.0.html

Cool!

Zulu

dan610324 · « **Reply #15 on:** September 17, 2010, 12:16:17 PM »

that sound safe enough for me

Victor3 · « **Reply #16 on:** September 17, 2010, 04:09:20 PM »

Quote from: sseib on September 17, 2010, 08:13:43 AM

Is it common for the tube to shrink at the trunions when welded?

I don't know if it's common, but when I welded a trunnion ring on my 1" bore cannon it did cause a slight constriction of the bore at the welds. However, the wall thickness at the welds was only 1/4", so that was at least part of the reason.

sseib · « **Reply #17 on:** October 21, 2010, 04:10:24 AM »

Well the stock size and design has allowed me to go with 2/3 scale now.

Here are the basics.

The turned tube getting ready to mill the trunion pockets, no bore yet.

Trunions in and ready to weld.

Breech plug will have .010 freeze in fit and welded.

After the trunions are welded in we will drill and bore the tube, more soon.

Steve Seib

Cat Whisperer · « **Reply #18 on:** October 21, 2010, 02:44:57 PM »

GOOD LOOKIN' TUBE!

GGaskill · « **Reply #19 on:** October 21, 2010, 03:16:14 PM »

That plan should work well.

sseib · « **Reply #20 on:** October 30, 2010, 08:16:23 PM »

Well good news on the progress and bad news on the plans.

Drilling the tube to 2.75 dia, half way from each end.

Horizontal boring mill over-kill, 20 feet of X and 6 feet of Y travel and a drill only 12 inches long.

The hole goes all the way thru now.

Turns out the .010" freeze in fit was a bit too much, would have been fine on the full scale bore but we are only going to get about .008 - .009 shrinkage on a 3 inch bore.

sseib · « **Reply #21 on:** October 30, 2010, 08:27:54 PM »

Setting up to bore to 3.080.

Steady rest view.

Rough bored, just a little over-kill on the lathe also.

Tube has been bored to 3.080, c-bored and weld prepped. We will most likely hone it a few thousands over size and set-up the breech plug and turn it to get about .005 to .006 freeze fit. Now I need to fab up a carraige to test fire it.

Steve Seib

Double D · « **Reply #22 on:** October 31, 2010, 03:44:08 AM »

with Machines that big why didn't you just bore a blind hole and not fuss around with shrink fitting and welding?

moose53 · « **Reply #23 on:** October 31, 2010, 06:24:02 AM »

Man I'm jealous now , with machines that big you can make the real thing .

GGaskill · « **Reply #24 on:** October 31, 2010, 07:42:44 AM »

With a space that big, one could have a really big shop.

Cat Whisperer · « **Reply #25 on:** October 31, 2010, 09:12:01 AM »

Overkill?

How about fire-cracker cannons next?

GOOD PIX, Even though we're jealous, it's good to see the how-to pix!

sseib · « **Reply #26 on:** October 31, 2010, 02:12:28 PM »

Double D,

I was trying to work that out at first in a half-scale, I just couldn't work it out without having to buy tooling or modify existing company tools. The shop has the equipment, material, just lacks tooling for cannons. My cost for this is zero right now, for a second full sized cannon I will consider buying or building the deep hole drills and boring bars to make it happen. I just want to get number one under my belt and see if this is hobby I truely want to invest more time and money into.

As luck would have it, the fabrication shop just rebuilt a ball mill at a power plant and there is a pile of rusty old slightly under three inch diameter steel balls out in the parking lot. If I make sabots for them, will it hurt if they are 2.950 and out of round as long as they are not over 3.000?

Thanks

Double D · « **Reply #27 on:** October 31, 2010, 02:19:51 PM »

Make a ball guage for them. If they pass gauging, shoot them.