Author Topic: Newbie post and a word about my project (Read 972 times)

AaronH · « **on:** April 26, 2006, 09:30:12 AM »

Howdy all! I've been stumbling around the net for information about mortars. Specifically any dimensional data about the 13". I ran into this site and by the looks of things I have a lot of reading to do. I've got this chunk of 3" dia. x 3.4" brass that's sitting on the corner of my desk begging to get thrown in the lathe. Depending on the mood I'm in I might gently put it in the chuck, well see. I've decided to turn it into a scaled version of the 13". Looking around the net I have found a very small amount of info on it. Basically, I found one site that said it was 56.5" long and weighed about over 17,000 pounds. Not sure where the measurements were from, but that's what I've got. So, I printed a number of pictures from various sources and scaled them using the 13" bore figure and the 56.5" length number. Here's what I've come up with: The muzzle dia. is somewhere around 43", the trunion dia. is about 17" and the trunion centerline is a few inches behind the center of gravity of the mortar (can't think of the actual number right off). If you're familiar with the 13" there is a lug on the top side of the mortar with a hole through it. This is used to hoist the mortar into the carriage. That lug is dead nuts on the center of gravity of the mortar. I figured this out based on a picture of one being set on display at Fort Hamilton a couple of years ago. I was originally going to bore it for 50 cal so that I could use pyrodex pellets, but to keep any sort of a scale it was going to remove a lot of material from my stock. I'd like to maximize the chunk of brass I have and get the most bang for my buck, so to speak. So, I have been playing around with scales and decided upon 17-1/3 scale. I know that's a stupid number, but makes for some decent dimensions to work with. With some slight rounding it produces a muzzle dia. of 2.25", 3.25" long with a .75" inch bore. The trunion works out to about 63/64" and centered roughly about the midpoint of the length. The center of gravity will about about 1/8" ahead of the trunion centerline. These numbers are off the top of my head, they're written down at home, but I think I've got it pretty close. Does anyone have any hard data on the 13" that they can confirm my scaled picture dimensions? Also, any idea of how the fuse hole is drilled? I've been looking for a nice cross section of this type of mortar design, but so far no luck. Thanks in advance for any info you guys might have on these 13" mortars.

Aaron

GGaskill · « **Reply #1 on:** April 26, 2006, 09:53:40 AM »

The next step in your project should be getting the AOP plan folio for this piece. See the AOP (Antique Ordnance Publishers) Artillery Plans list thread below for a link to their catalog sheet. The one you need is No. 41.

The originals were cast iron and I think you would be more satisfied with a steel version than a brass one unless it is strictly for display with no shooting planned. Even then, it is the wrong material for this kind of piece. Save the brass for a Coehorn.

Cat Whisperer · « **Reply #2 on:** April 26, 2006, 03:01:35 PM »

Aaron -

WELCOME to the board.

Great project!

I'm too far behind in CAD drawings now, but when I get caught up (note that, Wes) it is a relatively simple matter to generate the 3d solid and figure center of mass (to verify positioning of the lug). Also, the drawing takes little time if the dimensions are readily at hand. Once drawn, scaling is a simple matter, and if done in 3d solids, making working drawings in 2d is a mere transformation.

Keep us up on your progress!

AaronH · « **Reply #3 on:** April 26, 2006, 06:00:25 PM »

I hear ya. I've got the barrel modeled in Solidworks. Just need to finish the fine tweeking then do the carriage. It's looks sweet even just on the screen.

Cat Whisperer · « **Reply #4 on:** April 26, 2006, 11:38:14 PM »

Excellent move to put it into Solid Works - Do you have an FEA program?

AaronH · « **Reply #5 on:** April 27, 2006, 11:24:36 AM »

Yeah, we've got COSMOS which is bundled with Solidworks. I've used it some for bending loads. I assume it would handle pressure loads, but you know what they say about "assume".

Cat Whisperer · « **Reply #6 on:** April 27, 2006, 12:28:10 PM »

I am a FIRM believer of knowing the details of the calculations if one is going to trust the results of a program, such as FEA. BUT to run the program and to observe the relative stress levels around inside corners, powder chambers and fuse holes would be absolutely fascinating! For example, to see the difference between a rounded end of a powder chamber compared to one simple drilled with a standard drill bit; or to see the differences in stress around a fuse hole drilled straight vs one at a 15 degree angle!