I machined a new adapter plate for a 5” diameter 4-Jaw chuck for use on my 7” swing lathe. The adapter was made from 0.75” thick by 6 “ diameter hot rolled steel plate custom cut and available through eBay Buy-It-Now. There were challenges with machining the adapter: 1) six inch diameter steel is at the outer limit of the lathe’s capacity and 3/4 horsepower; and 2) the steel plate was cut out with a plasma cutter which left a very hard slag crust; and 3) the wavy plasma cut edge produced an interrupted cutting surface. I used TiN coated carbide inserts of the TT222 style for my cutting tool. If I had to do it again, I would have started with a brazed carbide-tipped tool bit with a C5 grade to handle the interrupted cuts and switched to the carbide inserts. Getting through the slag when the lathe could only handle 0.005” depth of cut was difficult. I used the product Energy Release P011 Cutting and Tapping Fluid for this hard material and then switched to using Rapid Tap Heavy Duty Cutting Fluid. After removing the slag, the cutting was very easy and the “rough” cuts had almost mirror-like finishes as shown in the photos. I do not know the steel alloy except that it machines extremely well. The adapter spindle recess and chuck boss on opposite side were machined to within the 0.0005” limit of the lathe precision but I did this to allow taking the chuck on and off with the parts left in the chuck for other operations off the lathe. The adapter plate attaches to the lathe spindle with hardened M6X1 screws and the chuck is mounted into bottom taped holes using 5/16X18 bolts.