A stealth cannon class at Lassen College

[GGaskill]

I am up in Susanville for part of my annual vacation and had intended to take two weeks of machine shop but when I got here, they said I had already taken it 8 times ( ) and couldn't take it again.  So I enrolled in a couple of other classes and can wander into the shop when I want to.

I found, however, that my reputation had preceded me the first time I went into the shop when I was button-holed by someone who had been in a previous cannon class and by another student who asked if he could make a golf ball mortar from the odd-shaped piece of scrap he had brought.

So I eventually took his scrap to measure and designed a freelance mortar that combines themes from the 1841 seacoast mortars and some much earlier bronze mortars.  I will put up some prints later tonight and some photos once some progress has been made.

[Cat Whisperer]

"attitude"


 

[keith44]

 

Too funny!  Please post pics of the piece of scrap, and finished mortar.

[gunsonwheels]

It realy IS a disease to which others are easily infected!!     

[Cat Whisperer]

You might check to see if you can 'audit' the class.

[GGaskill]

I might have to pay the non-resident fee then.   

OK, I didn't have my camera in the shop before we started cutting on the piece of scrap but here is a drawing of it:



The top view would be a 4" diameter circle. 

I have been planning to make a golf ball scaled M1841/44 10" seacoast mortar to use with the Fox steel golf balls since it is heavier duty than a Coehorn so that is where I started with the design.  But that conical section seemed to present a problem for making a curved breech so I decided to keep the cone and do a breech treatment somewhat like Gary's Smee.



So this is how I fit the bore and chamber and breech and trunnion into the funny shaped piece of scrap.



Once the student had bought off on this idea, I made some additional drawings to explore options.



The first dolphin idea was modeled after the lifting lug on the seacoast mortars but then I thought I should present a sample with two dolphins.



The student has turned off the outer cone and has the breech to diameter.  the metal is really freecutting and I think it will work well for this project.  Hopefully it is not leaded steel but we will see.  I will take my cameras in tomorrow and get some pix.

The middle two pix are a little bigger than the forum default so click them for larger versions.

[GGaskill]

So here are a few pictures of the mortar under construction.  By the time I got a camera to the shop, the breech cylinder had already been turned and the piece turned around for drilling.



The bore drilling proceeded through the usual series of smaller drills until we reached Big Daddy.



And this is the current state:



As you can see, Big Daddy left a rather rough bore so the student is going to take a skim cut with a boring bar to try to get a smoother bore.

All images are links to larger ones.

[Victor3]

...they said I had already taken it 8 times ( ) and couldn't take it again. 

 Methinks you got off easy, George.

 The Dean at El Camino College (my boss at the time, when I was teaching there) said that "The State" had already fulfilled its obligation to me years hence via my AA degree. I would have had to pay the equivalent of out-of-state tuition for ANY class. Maybe I should have claimed I was an illegal alien from Finland. Seems to work for darker-haired individuals around here...

[Cat Whisperer]

Perhaps an illegal alien from Iowa?
 

[GGaskill]

He took a light cut but it wasn't deep enough to get rid of all of the grooves and he didn't want to enlarge to bore any more so he will have some grooves to keep clean.  While making my own M1844 seacoast mortar, I decided that the drill needed sharpening and after sharpening, my bore has no grooves.  So we should have sharpened the drill before we started.

We needed to make a fixture to hold the barrel while cutting the trunnion groove and that turned out to be a show stopper for this week.  But he is local and can make the fixture and come back and cut the trunnion groove later.  We drilled the vent so he would have a shooter by making a special mount.



The proud possessor and maker of a new golf ball mortar.



The M1844 on the left and the freelance one on the right.  I didn't have enough data on the drawing to do the hemispherical breech so that will have to wait until I get back to my own shop.  Obviously the trunnions will be sunk into the rear of the tubes.

[keith44]

I like the profile of the "freelance" mortar.

[dan610324]

sharp tools should always been used when doing some prcission work
another very good idea is to drill the hole 1 mm smaller than the finished diameter first
then drill it to the correct diameter with a new sharpened drill that you grind a small radius on at both the corners between the cutting edges and the steering ridges of the drill
without any angled corners there you can never get any grooves

[GGaskill]

Vacation has ended (this one, at least) and I am back home and in my own shop.  I adjusted my computer program to calculate the X and Z offsets for the hemispherical breech using .005" increments in the X direction and printed out several pages of moves.  Feeding in at .005" per step means a lot of steps (1.260" total infeed) although I did the last dozen or so at .010" and .015" per move since the Z cuts were getting less than .005".

The benefits of this tedium are very little filing is needed to finish the curve and the curve is very close to true.  Here's where it stands as of now:



The little tail is because I cut the piece too long.  It will go away when I cut the trunnion groove.

Next I am going to make some taller jaws for my mill vise and then bore the trunnion groove.