Begginer needs material guidance and a few inital pointers

[KEM]

I want to try building a beer can mortar as my first project.
I have seen several plans on the forum and they use various sizes of round stock.
What kinds of steel do you recommend and how much should I expect to spend.

Once I start building, I can handle the outside lathe work.
I have never bored into a large chunk before.
1st question: Would using a large drill bit be appropriate to start the hole?
2nd Question: The powder pocket looks to be the hardest portion to me.
Most people use a taper. How do I do this taper?

[Cat Whisperer]

KEM  -

WELCOME to the board!

Good questions.  Let me address with a few comments; others will certainly chip in too.

Beer can caliber is a good place to start.  Concrete filled is the norm, other materials are good too.  The modern ones are MICRO thin and oft times will be ripped off in flight.

Bore diameter should include 1/40 the diameter as "windage" (read total clearance) as a good rule of thumb.

Outside shape is your choice - simple, like the confederate style or more conoured as many other styles are.

Powder chamber - about 1" diameter and 1" deep.  Some others will comment here.  Longer/smaller diameter will give higher and focused pressure.

Wall thickness (around the powder chamber) should be at least as thick ALL the way around (all sides and behind) as the diameter of the powder chamber.  Wall thickness of the tube can be much reduced as the pressure has peaked by the time the round is moving up the tube.

Drilling?  I would use as large a bit as I could safely handle - to reduce the boring time.  My first was cut with a 3/4" bit which became my boring bar (didn't have anything else).  SPADE drills come big, but require lots of HP and gripping.

Taper can be cut a number of ways, I even did it a little at a time with the 3/4" bit!

Again, welcome, and keep the questions coming!

[GGaskill]

I start with a drill that is chamber diameter and drill to the bottom of the chamber first.  Then I use the largest drill I have that is smaller than the finished bore diameter.  Boring is a very slow way of removing material and should be relied upon only for ensuring roundness and centering of the finished bore.  If you want a tapered chamber, set the compound rest at the desired angle and cut the taper with the boring bar.  You probably should make the final cut of the bore and the chamber on the same pass.

Mild steel (1018) is plenty strong enough for this kind of service, and it welds easily which is my recommended way of attaching trunnions (cut a shallow cavity and press the trunnion into it, then weld all around.) 

A Coehorn style mortar for beer cans can be made from 4" round stock which is not too expensive and not too hard to manhandle.  A full scale one is 8.65" in diameter so a 4" one is a little less than one half scale.  Mine is made from 6" round (you can see the muzzle in my avatar) and has gotten almost too heavy for me in the last ten years. 

[Victor3]

"What kinds of steel do you recommend and how much should I expect to spend."

 A 12" piece of 4" round 1018 is ~$50 from my local supplier.

[GGaskill]

You'll need about 7" of 4" round and 6" of 1.25" round for the trunnion.