I ordered a Grizzly 6 jaw set-true chuck and D1-4 backplate last week and they arrived 2 days later; great service. A set-true chuck uses setscrews to align the chuck on a backplate with a raised surface area to fit inside a pocket in the chuck body. The backplate ordered for this chuck has a flat surface so an adapter was required to use the set-true feature.
As received the backplate had 0.015" run-out and I discovered that the backplate couldn't be mounted with repeatable results. Examination revealed that the D1-4 taper and thru-hole was undersized on the backplate. Some layout die and careful scraping of the backplate spindle mount resolved the spindle mount repeatability issue. The backplate face and thru-hole were turned for a uniform surface and measured to be true within one ten-thousandth inch with repeatable mounting results.
I found a piece of screw stock in my scrap pile to make a backplate adapter for the chuck. The adapter consists of two 0.625" thick diameters, one 3.120" diameter to fit the chuck pocket and a 2.387" diameter for a 0.002" interference fit (press-fit) inside the backplate's 2.385" thru-hole. Final diameters were turned after boring a 1.5" hole through the adapter for stock to pass-through the spindle. The adapter was pressed onto the backplate, surfaced true in the lathe, and turned in diameter for a sliding fit with the chuck's pocket. The chuck's mounting hole locations were marked with a transfer punch, drilled and tapped 1/4-28" for mounting capscrews, and reduced the raised backplate diameter 0.005" to allow room for alignment.
Ready for my next project.
Airguns are a gas