My first pop can mortar build

[DarbinCo]

Well I finally got my lathe in and set up a week ago. The first order of business was to build a mortar. I have a few pics of the project under way.

Heres a pic of the mortar barrel itself. I used the chamber plug method with a gracious shoulder for the plug.


Chamber plug, chamber is 3/4 x 1.25" should be enough chamber I think? 


Plug installed, waiting for the welder


The trunnion,
I have a piece of 2" 1018 that I want to mill the center out like a saddle so the back of the mortar will fit into it and cover the weld of the chamber plug. I will have the trunnion TIG welded to the barrel for strength. It will add an inch to the back of the chamber area which is already 3/4...... the diameter of the chamber. With the extra on the back, it makes me want to increase the chamber size to 1" dia unless you guys think the 3/4 x 1.25 will be enough?

I think I'll put it in a plain sled, nothing fancy. I might use some rough cut timber from a local saw mill. 

[RocklockI]

Looks good to me ! that chamber plug sit on a coresponding lip in the barrel .

[Double D]

Doesn't look good to me.

The theory behind the drop in breech plug is that it can be removed for cleaning. 

In order for your plug to work correctly it needs to be shrink fit at least and then welded. A two diameter breech plug is going to be difficult to shrink fit properly.

[Cat Whisperer]

Even slip fit, providing the tube has enough thickness at the bottom holding in the powder chamber, it looks like it'll be strong.

So, if there is clearance around the major diameter (after welding at the back on the smaller diameter) one could seal the gap (from corosive elements of combustion) with solder, silver-solder or such.

Perhaps not conventional, but worth a try.

[DarbinCo]

Looks good to me ! that chamber plug sit on a coresponding lip in the barrel .

Yes there is a matching shoulder in the bottom of barrel to match the chamber plug. The fit is so tight the plug wont fit when its hot. I had to cool it in the freezer to room temp to get it to fit.

Heres that pic

[Double D]

Looks good to me ! that chamber plug sit on a coresponding lip in the barrel .

Yes there is a matching shoulder in the bottom of barrel to match the chamber plug. The fit is so tight the plug wont fit when its hot. I had to cool it in the freezer to room temp to get it to fit.

Heres that pic

Still not a go for me.

You need some way to stop molecules of powder fouling and water from getting between walls of the tube and plug and if they do some way to remove the plug and clean it.

I am not as enthusiastic about time idea of soldering as Tim is.  That's not saying it won't work. That's just saying I am not as enthusiastic about time idea of soldering as Tim is..  It might work and we can use term sweat as we are more accustomed to.

Before you round the end of the tube,  machine a round groove 1/4 to 1/2 the depth of the diameter of the trunnion in the bottom of the barrel to seat your trunnion.  The trunnion should be a least 2 inches in diameter.  Drill a hole through  the trunnion into the plug to suck it tight.  I'm not real comfort

I know you copied my idea from golf ball mortar.  The base of my plug is a larger diameter with a small shoulder. I am able to use two screws and pull the breech plug against the plug seat.   You might get by with one screw...let us know.

[RocklockI]

Shrink fit and welded it is ! Now it looks really good to me .

This is my opinion only as I am NOT the committe of saftey here ........

Mortars are low pressure propositions . Yes ,you will prolly get some weepage in between the plug and the barrel .

Is there any way you could make a new plug a bit bigger ? Then thread it (single point) ,ditto with a boring bar for the ID on the barrel ?

Honestly I dont think you'll have an issue as is , but then agian ..... I AM not the committe of saftey around here .

MT used a sealer on the monster mortar for the same issue , it might be worth a try ? But it does degrade after abit . ....at least when using 1 lb charges .

YMMV GARY

[Victor3]

 There's a simple way to 'cheat' on the fit if you feel it's necessary....

 Chuck the chamber piece up in the lathe with the open end out. Use a hard steel hammer to peen the face at the OD to bring it up to a slightly larger diameter. Turn the OD in the peened area to the correct diameter for a heat-shrink fit. Should be ~.002 - .004" larger than the bore in this case.

 If you don't have a sturdy enough lathe and/or chuck, you can do the peening separately in a vise.

 Or, if your welder is capable of getting to the bottom of the bore, just have him fuse the chamber piece the bore. No need to use any filler (rod/wire).