Trunnion attachment on a mortar?

[Doc Brown.]

Is there anything better or worse between these two ways to put the trunnion bar on a mortar. One is welded on. The other is screwed on. I have seen it done both ways and don't know what the real difference is.
 


 
Also is the radius necessary in a mortar or does it just help shoot balls farther. Thanks.
 

[Cat Whisperer]

The radius is a really GOOD design feature.  If the inside 'corner' was sharp, all the stresses would be concentrated there - making it a likely place for metal fatigue - i.e. failure by cracking.  The radius spreads the stresses over a wider area.  ALWAYS include a radius inside.  Smaller isn't as good as larger, but a sharp corner should be avoided.

GOOD questions!

[Doc Brown.]

 Would it help if this part im pointing to had a radius. This would be easy to do before it goes in the tube.  Thanks.
 

[GGaskill]

Outside corners do not compromise the design; inside corners create stress risers which can cause fatigue problems.

[flagman1776]

You could machine a hemisphere in the breech end of the tube end, then machine a matching pocket in the trunnion bar with a ball end mill.  Then weld. 

Note:  I'd already turned off some old cuts that were in the piece when I got it.  Otherwise a larger hemisphere could have been made.  The trunnion shaft is stock I had from the same source, somewhat over scale but since we were going to cut into it, perhaps that was a good thing. 




The pieces mated nicely.
 
 
Prior to finish grinding.  Note:  the brass shaft welded strongly but not as pretty as we'd hoped...  testing showed the propeller shaft cutoff to be C462 Naval Brass with no welding specs listed. (Hmmm)   
I won't take credit for this idea, another member thought of it, I readily agreed & did he the machining to complete my project.  Thanks!!  (He knows who he is.  These picts are his.) 
 

[armorer77]

I cut a trunnion diameter groove into the base of the mortar . Seat the trunnion into it then weld . Ed

[Cat Whisperer]

Would it help if this part im pointing to had a radius. This would be easy to do before it goes in the tube.  Thanks.
 

Yup, that's one of the two places.  (Inside bottom of the powder chamber is the other.)

[flagman1776]

On the brz shaft mortar, the barrel piece was very limited.  I had the chamber well into the base of the tube and I didn't want to compromise the 1 caliber around the chamber by drilling into it which the hemispere design does not.   
 
You could machine a hemisphere in the breech end of the tube end, then machine a matching pocket in the trunnion bar with a ball end mill.  Then weld. 

Note:  I'd already turned off some old cuts that were in the piece when I got it.  Otherwise a larger hemisphere could have been made.  The trunnion shaft is stock I had from the same source, somewhat over scale but since we were going to cut into it, perhaps that was a good thing. 




The pieces mated nicely.
 
 
Prior to finish grinding.  Note:  the brass shaft welded strongly but not as pretty as we'd hoped...  testing showed the propeller shaft cutoff to be C462 Naval Brass with no welding specs listed. (Hmmm)   
I won't take credit for this idea, another member thought of it, I readily agreed & did he the machining to complete my project.  Thanks!!  (He knows who he is.  These picts are his.)