I am building a tool post grinder based on the idea of the GENIUS Mark Frasier. He used drillrod for the grinding stone arbours so I am going along with that idea.
He is a very helpful man and I am praying for his health.You can see his plan on this forum. I only made a few tweaks here and there to suite my lathe.I am just not sure how much yeald the1/2 inch rod used for the internal grinding stone will give at longer distances. I think I must ask him how his machine performed.
I had a quick look at the thread with Mark's build description, and I think that you will be able to get away without using tool steel (O-1, W-1, Silver Steel). As Mark mentions, he has the option of hardening the drill rod, but if you harden it, then you will have to grind it afterwards to ensure it remains straight.
Keep in mind that hardening the arbor will not reduce the amount of deflection under load; hardening does not change the modulus of elasiticty of the steel, which will remain about 200 GPa.
My suggestion would be to go with the EN8 steel, and leave it soft.
If you really want a more durable arbor, then I would recommend EN19 steel. You can buy this in heat-treated form, which means it has already been quenched and tempered, usually to somewhere around 40 HRC, which I had no difficulty turning (with carbide inserts), or drilling/threading using HSS.
Using either the EN8 or the EN19 will be slightly more work for you, since it is not usually supplied in ground form (around here).
-F
