How is Kubota B5200 steering spindle constructed?

[Agvg]

Quite sure it's forged in one piece.

 

[rScotty]

I was lucky enough to find a new spindle on ebay, which fit. It took a wheel puller to get the bearings off the old taper. I used a 3 ton arbor press to set the bearings on the new spindle's tapered axle, but I think you can do it by threading the castle nut too.

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The original question is, how is this thing constructed? The corner is cast. The kingpin and axle taper are pressed in. The end of the kingpin is protected by some material, maybe epoxy. It could be welded, but it cut easily on the drill press.

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Glad to see you got a new spindle. Yes, the way you are describing the construction is typical.
Welding anywhere near a bearing can make them hard to get off. Depending on where the ground lead is connected and the resulting current path, the bearing can even get welded right to the spindle. Welding heat usually shortens bearing life because it anneals (softens) the metal.

The fit of the steering arm around the top of the kingpin is critical. So is the fit of the key and the arm is probably clamped by a special high tension clamping bolt as well. If any of these things have seen welding heat they probably need replaced. But that's all easy stuff to do.
The kingpin bushings are doubtless shot as well. It would be hard to twist the kingpin like the DPO did without affecting the kingpin diameter. And even with the kingpin softened by welding heat it is stronger than a bronze bushing so it wallows them out.

I'd replace the bushings myself, but it's a judgement call as the kingpin bushings affect how nicely it steers more than how long it lasts.

Most important thing is to make sure that steering arm stays tight to the top of the kingpin. You don't want to wallow out that keyway on either part.
Good luck with it,
rScotty.