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1/3 scale Coehorn project.

10K views 70 replies 15 participants last post by  Fredstaple 
#1 · (Edited)
Actually this is a them, as I'm building a pair. One to keep and one as a gift for a friend.

I'd never built a mortar before when I started my first golfball project, so I just looked at my piece of stock and said "It will be this big." Turns out it was seriously overbuilt, with a chamber that could almost put a GB into low earth orbit. But it's been a lot of fun.




Over the years and other mortar projects of varying calibers, I've come back around to the golfball. This time in a more compact package.








I've had this on the boards for awhile now (a long while), and I've had the steel blanks sawed for months. I didn't want to start a thread until I had actually done something.

A few days ago I went to the shop and turned and faced one end of each. Then went back this morning and bored and chambered the first tube. It will probably be next weekend before I can get back up there to bore the other one.






In the meantime I will start making handle parts and assembling my soldering fixture.

I bought 3/16" brass flat for the handles, the brass rod I already had.




I will be constructing a bed for mine, the other will be sent with all the instructions and measurements and he can take it from there.

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#32 ·
Thanks!

Vents are drilled. Still a little dingy from the cutting oil. The camera perspective makes them look off-center but they actually turned out pretty well.

The vents are drilled 9/64", roughly 3/16" dia. at the top of the chamfer.




Mine (left) could use a little more cleanup, but the other will be on it's way to Alaska soon.

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#37 ·
OBTW: I'm in Georgia not Florida.

It's only 40 miles due south to the FL line. But you can't get there from here, swamp's in the way. :tango_face_grin:

The majority of the Okefenokee Swamp (and all of the Okefenokee National Wildlife Refuge) is in Georgia, starts here and heads south the the state line and beyond. The part of the swamp that crosses into Florida borders the Osceola National Forest.

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#40 ·

The majority of the Okefenokee Swamp (and all of the Okefenokee National Wildlife Refuge) is in Georgia, starts here and heads south the the state line and beyond. The part of the swamp that crosses into Florida borders the Osceola National Forest.



I was confusing Lake Okeechobee with the Okefenokee, although the way the USPS works, something you mail locally might get ultimately shipped from an FL location.
 
#41 · (Edited)
Now that you mention it, everything I mail from this Post Office goes to the regional hub in Jacksonville, Florida (75 miles away) as its first stop.

The mortar was mailed from GA, but it went to FL before heading to AK. :tango_face_wink:

It's "Out for delivery" in Alaska now.

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#42 · (Edited)
It's official, there is not a single 15/16" Forstner bit in any store in this town.

Plenty of 7/8" and 1" but nothing in between. I could get a 15/16" hole saw but that doesn't work for me.

Shopping online, 24mm gets the nod. It's only .007" larger and I always ended up sanding a little relief anyway. Plus it was the best price, free shipping, and closest location. Supposed to be here Monday.

Hurry up and wait . . .

-------

Eta: Just got notification from USPS that the package has been delivered in AK.

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#44 ·
I found plenty of 15/16" bits, but I went with the 24mm because I felt it was better deal for me. Especially of the seller live up to their promised delivery time. I'm hoping the extra 0.007" will cut down on some sanding.

Locally there just wasn't anything. 7/8" or 1" but nothing in between.
 
#45 · (Edited)
Slabs of red oak, 1" and 3/4" thick, rough cut about 1/8" over on length and width. The 1" slabs are built up but I cut them so there are only two pieces in each slab and I will stagger the seams.

The 3/4" slabs for the sides are solid, for appearance. 1/2" on the sides have come out a little narrow so I will build it up with the 3/4" and trim away the excess.

I also got my new carbide Forstner bit in the mail (need to round up the others, they've gotten scattered), but I had already put everything away and cleaned up by that time. Maybe tomorrow . . .

 
#46 ·
Not a lot of time today but I did get the holes drilled. I checked them for alignment with my wooden mock trunnion.

Next step is to shave off the extra 1/8" from the width, that will bring the top level with the edge of the holes. I don't like drilling right to the edge, even with a new bit, so it's worth the extra step to me for the drill to have full support all the way around:




After that, I'll drill the tiebolt holes and glue these four pieces together, then use the table saw to cut away the tops of the holes to make a groove. The shallow blind holes in the outside slabs will be opened up by hand to match the groove after they are glued on.

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#47 ·
The core. I made the metal mock trunnion in the photo and did the glue up with it in place, something I did not do on the poolball mortar and that resulted in a lot of extra sanding to get the mortar trunnion to fit down in the goove. A little misalignment really shows.

I sanded the excess glue from inside the holes and I think this one will turn out better and easier. The trunnion slides all the way through easily from either side . . .

 
#48 · (Edited)
Groovy . . .

Top of groove cut away, sides glued on and opened up to match, bed narrowed to the proper width, and the ends trimmed. Trunnion groove still needs a little cleanup but I'll do that after inletting:



Test fit of the handles. Hole spacing and rod length checks out:



The rods I used to glue up the bed were some cheap zinc-plated all-thread I bought just for that purpose, since they would need to be cut long. The stainless was already cut to finished length and wouldn't fit until the block was the correct width.

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#50 · (Edited)
I'm about 55 miles inland, and hopefully the last track will hold. It will hug the the coast as it curves back out to the northeast.

I got food, water, and two full vehicles. I'll get soaked for sure, and some high winds, but I'm on some of the highest ground in a very low area and I have good runoff, I should be okay.

I'm on the northwest side of town so if I do have to put some miles between me and the storm I can take the backroads out and not have to deal with the mess coming down the corridor through town.

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#51 · (Edited)
Sorry for the lack of progress or updates. This project was pushed to the side for a while due to health issues, but my New Year Resolution is to get this done in a timely manner (although nothing is ever truly "done").

So over the past few days I've been chiseling and sanding on the inleting, and today I cut the profile on the ends of the bed and got them roughly sanded round.

It's not my best work, especially on the inleting, but my vision and muscle coordination have seriously declined over the past months. To the point that I was genuinely afraid of the table saw, but I couldn't put that step off any longer. I did my damndest . . .






It's downhill from here, some rough spots needs to smoothed out, then a good finish sanding and a couple of coats of Danish Oil.
Then buff and blue the steel, I've left it in the white until now because of all the handling while fitting it to the bed.

More to come . . .


PS: I always jokingly say that every one is "The last one." "Never again! And then the next one starts . . .

This time I don't think I'm joking.

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#55 ·
With what program did you create the several drawings to which you've treated us along this journey? I see using it to draw wildcat cartridges...
 
#56 ·
It's an old 2D program called CAD Pro (descended from the Softkey CAD programs). It's pretty lightweight compared to some of the more sophisticated programs I've used, but I know it like the back of my hand (learned on KeyCAD) and it does what I need. And it could run on pretty much any old junker.

Although I did run into some unexpected issues when I first got this new laptop. I finally I figured out that this laptop has a default resolution of HD1080p (1920x1080) and scales up the display to 125% to be more readable (which only makes sense when you're watching full HD movies).

This meant that nothing displayed, or more importantly, printed at the correct scale. Drawings that I'd used many times before would no longer print anywhere near the correct size, which was not good since many of them are templates. Setting the scale to 100% fixed the print issue but the program was difficult to use at that resolution. Everything was too tiny.

Changing the resolution to 1600x900 at 100% fixed that and everything once again looks and prints correctly.

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#60 ·
Thanks for the Kewpie!

It was test fired once (blank, no GB) before final cleaning and polishing. I wasn't planning to fire again until after it was blued (which unless something comes up I will do this weekend).

If it were just an ornament I'd leave it polished and buffed 'in-the-white.' But it would be hard to keep it that way after it's fired a few times.

Early on I'd considered a bronze powdercoat, but right now that's not an option I can realistically pursue. Maybe sometime in the future.

There will be pics, and hopefully video, soon.

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