I bought a used industrial machine (a huge pipe threader).
It is a super nice machine in all respects and was rebuilt in 2007.
However, the reason why it was sold for nothing is that the cast iron
transmission case in it is cracked due to a past accident.
The picture, with the crack highlighted, is here:
You can visualize this as a rectangular casting with one corner broken
off. The three highlighted areas are in fact one crack separating only
The size of this is about 1x1x2ft.
What I need to do is put it back together. Put in funny terms, I could
take these pieces, clean them and "glue" them together, the question
Real glue, obviously, would not work.
Nickel welding would likely not work well either.
It would seem that the pieces could be taken out, really cleaned up,
pushed together, heated red hot, and brazed with brass.
Does that make any sense?
What would be the best approach?
If you can get it out and apart, I would try drilling and tapping some holes
and bolt it back together so you don't have to worry about thermal stresses,
more cracks, heat treat, keeping it square and aligned, etc. In the picture
the bottom crack would need bolts perpendicular to the shaft with the gear
but each hole would only total about 2" or 2.5" deep. For the upper crack
the holes will be parallel to the gear shaft and the non-threaded holes are
going to be 3" or more, then the shorter threaded holes, so not trivial but
maybe you can find someone who owns a big mill :-) :-). Maybe someone can
recommend something better but I'd use bolts that are 1/3 to 1/2 of the
plate thickness when you go into an edge, so 3/8 or maybe 1/2" bolts if your
casting is 1" thick. Counterbore and use socket head cap screws if you
don't have clearance for hex heads on the surface. Grade 5 bolts just to
avoid the horrible variable quality of anything less, thread engagement of
double the bolt diameter since the bolt material is stronger than the cast
iron, and torque with a torque wrench in a couple of steps.