Advice on a joint needed

[Perry Owens]

I need to butt weld a 150mm length of 50mm x 6mm mild steel bar to the edge of a 200mm diameter x 12mm mild steel disc in such a way that the finished assembly is the shape of a table tennis bat. What would be the correct way of prepping the joint to get the best strength, eg radius the end of the bar or grind a flat on the disc, bevel edges, leave a gap etc? The largest rods I can run are 3.2mm.

 

[Fazerruss]

Butt weld wont be as strong but then the bar is only half the thickness of the circle so should get a weld down each side. The best way is the tennis bat method. The stem of handle is either slit down the shaft or ground flat on one side then that overlaps the circle. same would apply for steel I would only say you need to overlap a distance equal to the diameter of shaft then weld.
Or you could drill/ mill the edge of circle and insert the shaft and weld.
Suppose all depends on what its for and how strong it needs to be.

 

[Andrew55]

If I understand your requirement, the main thing is a pair of mating edges, either by a flat on the disc, or curve on the bar end. Flat on the disc is easier. After that bevel the edges, and allow a slight gap. You are aiming for a weld that penetrates just over half way through, with a following weld on the other side that will complete the fusion of the joint right through. Main thing is to produce a weld, which if cut through should have no visible un-welded patch in the centre.

 

[PTvor]

I think the requirement is for a target where the weld is going to be subjected to enormous shock routinely and the disc has to be a near perfect flat circle. No question of welding the flat onto the surface of the disc or the tennis racket approach.

I wonder whether the 6mm section would put up with being hit anyway. There will be misses.

 

[Perry Owens]

It's for a duelling tree and will be hit by pistol-calibre bullets with a muzzle energy around 800ftlb. The targets pivot around the end of the "handle" when hit so do not have to absorb the full impact energy.
I was trying to reduce costs by using what I have to hand but I am thinking that maybe I should get some 12mm bar and dowel pin it into the edge of the disc before welding.