just thought i would try to explain a little better, i assumed for some reason you were making a decent quantity but irrespective i would still tackle the job the same way, set up your length of bar in 4 jaw with jaws reversed, clock it at the chuck end then the tailstock when both running true and chuck nice and tight centre the bar and secure workpiece with revolving centre. Turn the OD down to 80mm, working from the tailstock to the chuck set the parting tool 2mm thicker than the required finished width your disc,go in with the parting tool but leave 30mm remaining to support the bar as you continue parting your items to said 30mm depth, even if the parting isn't brilliant you will be able to clean it with a file after you have sawn the blanks off(by hand) then 3 jaw with reverse jaws face off both sides to finished thickness, yes you can do it on your lathe if it's in reasonable condition, only tricky bit might be the parting, in that case as i said earlier just go in as far as you are comfortable with(just means a but longer on the hacksaw but you still have the reference of your parting attempt. No soft dogs required, jobs a goodun.
Mike