Buildup welding is quite common on repairs to large axles and shafts as the cost of replacing the entire part is expensive. The idea is that extra material is welded onto the shaft, often by spray welding and then it’s machined to the new size.
I decided to use this technique on a small project for a friend. He wanted a tool to fit the tails for some new valves on domestic radiators. You can see the tails being fitted here using a large radiator allen key.
His problem is that there’s not enough space next to the radiator to get an allen key in place. We discussed the options and came up with a small gadget where one end could be slipped into a socket set and the other into the radiator tail.
I took some hex bar of the required diameter and then built up weld around the middle of it. The welded part was then machined in the lathe producing the results above. Obviously if you had a mill and dividing head you could do this the other way around and machine the hex flats onto a larger bar but I have to work with the tools available.
Since completing this I spotted the following “drain plug keys” in Glickman’s hardware store. These are actually for use on car and bike oil drains but you can see how they are quite similar to the design I came up with.