Welded and machined works if you can true up all surfaces true to the center bore and balanced
That takes some order of operations and work holding thought.
Would you have to use a mandrel ? I'd love to see how you do it if you do.
I don't see an advantage of 4130 over 1018
Thanks for the feedback.
Order of operations is everything.
You could turn it mounted on a mandrel, and if that mandrel was cut in that setup without being removed from the spindle you'd probably get good results, though I might get chatter cutting a 9" disk mounted on a 5/8" mandrel.
I'd most likely start with a machined disk with a pocket cut into the back and a machined solid shaft that would press into that pocket and be TIG welded. The welded assembly could be mounted in a chuck from the outside of the disk so the OD of the shaft could be turned accurately relative to the disk. You might dust a little off the back face at this point.
Then the disk could be held from the OD of the shaft
and both the bore of the shaft and the face of the disk would be cut in the same setup to assure precision between the working surface of the disk and the bore that mounts it to the motor shaft. When you can, you order your operations like this so the important surfaces are all cut in the same setup to eliminate run out caused by imprecision between setups.
Advantages to chromoly steel is that it is harder to dent and ding than 1018. Also, 1018 and A36 are gummy steels that don't finish well when I turn them. 4130 is weldable and finishes well in addition to being more durable. It costs a little more, but in the grand scheme it might be worth it.
As far as balancing is concerned, parts that are nearly geometrically perfect can still have variations that mess up their balance. I look at things like machine tool spindles that are precision ground to very high levels of precision that still require balancing to eliminate vibration. So I wonder if something like this should be precision balanced?
