I got a used Bison 5C collet chuck, plain back mount, bought a threaded adapter from little machine shop, it showed up about 6.5in diameter. I also bought a Bison 8inch 3 jaw, im waiting for the cast iron slug to show up from speedy metals to do that one, the 8inch is a direct mount d1-6, so im gonna have to turn a taper on the cast iron to fit the chuck, the CI I bought is 7in oversize, so it will finish machine to 7inches diameter. I got both chucks for about 200 bucks off craigslist.
first picture shows the adaptor for the 5c on the lathe, and the plastic wrap
here is the chuck and plate, I had taken an initial od skim
here is where I started to fit the boss, I don't know anything about this tool other than its a Hertel brand, I just wanted to try it out
drilling and tapping the bolt holes
and done! I ended up with about .0006 runout, I checked the taper to a hardinge collet with some highspot while gripping a tool and it makes full contact, I clocked all three holes and its the same. I may at a later date redress the taper to get it a little better on my centerline, reason is I checked my original 6in 3 jaw and it has .0004-.0005 runout with the same end mill I was checking against.
here is the 8inch Bison setup just to get idea of how it will ride this one out. it will have no hub length to keep the jaws as close to the bearings as possible. it will have about the same stickout as my 6in 4jaw does.