Anyone with a modicum of chainsaw expertise can accomplish what you want, no jigs necessary. If you require absolute dimensional perfection, a cutoff saw will be necessary to make the crosscuts you desire (be it a circular or band saw).
A typical saw mill, either commissioned or rented, isn’t capable of making the cross cuts that you need. They are intended to make longitudinal (rip) cuts along the length of the log, not across it, as you want.
Ignore the advice of utilizing professional or rented sawmills, unless they have the capability of making 18" deep cross cuts…less the notion of (easily)planing such rounds. Nearly impossible without special jigs and the expertise to use them.:smack:
I was at an antique shop today and outside they had a large trunk filled with freshly cut discs like you want. They were only about 8"-10" though. A buck apiece. So if you are near Medina, Ohio…
planing such rounds. Nearly impossible without special jigs and the expertise to use them.:smack: