Thank you
@firemaker76 for explaining the details for the 4140 steel material approach, I'll look into those bits and pieces... Your right, it does sound counter-intuitive.
I know you need to be careful with abrasives around your lathe, after protecting the bed and other key surfaces would it be possible to do the final rounds of surfacing with an aluminum oxide abrasive? Just thinking out loud. Maybe that is a bad idea, I don't know enough at this point. I haven't seen anything where folks are using abrasives on their lathe in this way to reach the final tolerances and get a nice surface too. Although I do know abrasives are used in high precision surface grinders.
Since I have a Sherline 4410 CNC (I ordered a PM-1340GT and that baby is scheduled for delivery in Aug/Sept, with a DRO of course
), I was thinking to practice first with 6061 Al manually unless you have a suggestion for a better/different material to use. Not sure if the 4410 lathe would take well to the 4140 material. I looked up 4140 on Wiki, they mention chromoly which is a term I heard before on the Extreme-4X4 and other car shows I watched and they use it for roll-cages among other things. I would imagine the 4140 is tough enough out of the box and is why machinists use it to make this kind of tooling. I wonder if there are other steel options that may be easier to machine and get a nice surface, then do a casehardening process to it at the end, like carburization. (I do intend to learn to process 4140 steel, when the time is right & I do think it would be a good skill to acquire.)
Recently I looked into the Al anodizing process and was absolutely amazed that it makes aluminum oxide on the outer surface of aluminum and increases the hardness to 60-65 Rockwell C (this happened because I was looking into Air Bearings for a project, which would be cool to make!, and I found this video
).
So the idea would be to machine 6061, get it hard coat anodized (optionally with some color), then use this for tooling. There may be some downsides to this. Where I live there is a company that does the anodizing, I don't know if it is expensive. Also, using steel may just be stronger (stiffer) and won't yield as much as Al for milling operations, don't know.
Phil