Iron Mule, Broke the boom off.

[old-iron-habit]

Well so far this has not been a good winter for my old working toys. The other day I was finishing up hauling firewood out, using the Iron Mule forwarder since the skidder went lame. When I went to pick a grapple full I heard a loud snap, a real loud snap. A investigation revealed that the shaft that is the head and boom support snapped. It is a 4-1/2" shaft. It has the turning gears below and a brass two piece shim it pivots on. I found a piece of 4140 shaft locally that I can get to replace it with. It has to have the turning gears welded on with the upper mounting bracket in place making preheating tough. At the top of the head it has a plate welded to the top of the pin and to the head holding the pin up and also turning the head. It snapped off a inch below the top weld. Heat stress from the original weld, overwork, who knows. My question is this. The welding standards say 4140 should be heated to 400 degrees and then cooled slowly. I have talked to two welders whom weld hi tensile steel often. One deals with 4140 often. They both tell me that they heat until the moisture is out and then weld, taking care to not over heat it with the weld. I appreciate your thoughts . I'm concerned a softer steel will bend at the swivel point.

 

[old-iron-habit]

Couple more pictures.

 

[Theweldor]

They are on track working with 4140. The gears might add a little more time as welding around a 4140 shaft without putting a lot of heat to takes a little time. Have you touched it with a file to some what determine if it is actually not just 1018 colled rolled.

 

[old-iron-habit]

They are on track working with 4140. The gears might add a little more time as welding around a 4140 shaft without putting a lot of heat to takes a little time. Have you touched it with a file to some what determine if it is actually not just 1018 colled rolled.

I have not put a file to it. The machine shop that has the shaft in both 1018 and 4140 told me that they felt 1018 would have bent some before snapping, I will put a file to it. That is a good idea. The gears only have to be stitch welded in a few spots as they only control the swing on a 14 ft boom. It would have to rip the welds length wise. To you think air arcing the gear welding off will harm the gears hardness? Maybe I have to go in short bursts and let it cool in between?

 

[ianjoub]

That greasy firewood won't smell too good if you plan to burn it inside.

 

[Theweldor]

Air arc should work well to clean the welds off.

 

[old-iron-habit]

Thought I would update this post. Got it all repaired a couple of weeks ago. A local technical school analyzed the broken shaft and determined it to be mild steel. We had thought so from a file test but it was good to know for sure. I got new bushing as close to size as I could and had them machined to fit. A local machine shop had a 4-9/16" diameter piece of shaft in the scrap pile that was 1" longer than I needed. They turned it down to 4-1/2" and fitted the bushings to it for a cheaper price than I could buy a new piece of shaft for. For the flat bushing that the boom pivots on I used a piece of space age plastic looking material that the power companies use for heavy duty similar applications. I also added a piece of 1/2" plate to the existing 3/4" on the head that it pivoted on so I had a nice new flat surface for the head to pivot on. The existing one was slight worn or bent on the outer edges so it would have added stress to the pin. I welded it all the way around to the 3/4" one so I got double strength now. You can see it in the photo.