With the spindle upgrade the 3" 3 and 4 jaws self-centering chucks were resting for some time, as well as the faceplate.
I'm keeping the 3" chucks also for indexing on a mill, but decided to make an adapter backplate to use both the chucks and the faceplate on the mini-lathe with the 4" spindle. After a visit to my metal supplier at the end of the day, I got back to the shop with a piece of steel for this project.
After facing the piece, it was center drilled and drilled with 6, 12 and 16mm drills. Then, with the small Glanze boring bar, the center hole was enlarged to 17mm, as that's the bore size of my 3" chucks.
The register for the spindle was made with 72mm diameter and 4.25mm deep, and all that rust has gone. After that all the edges were chamfered.
After some calculations to mark the studs positions, it was drilled, taped M8 and deburred the four taped holes.
It was faced down, removing all the metal until the final dimension.Then started turning down the register for the 3" chucks.
Then I found that I wasn't having on shop neither blue ink or even a single sharpie pen in good condition. With a sharp threading tool, scribed a line on a 66mm circumference for drilling the holes. To do this the toolbit tip must be indexed first. With a piece of round stock of a known diameter on the tailstock chuck and the dial indicator base on the lathe bed, it's easy to find the lathe center. Then removing the tailstock and, without moving the dial indicator, bringing the toolbit tip to measure it's position and adjust it until it is on the lathe center. Then the cross-slide was advanced toward the front by 33mm.
After that, the 6 holes needed for mounting a 3 and a 4 jaws chuck were drilled using a computer generated template to locate holes positions. After drilling, holes were taped M6 and conterbored on both sides.
Modified chucks for front mounting
As I'm keeping these chucks for use on a mill, with a rotary table or indexing table, for mounting a chuck for such work a front mounting chuck makes all the work a lot easier. And makes it usable on a lathe with a larger spindle flange.
The chuck was drilled and counterboed to 11mm, 6mm deep for the SHCS. Screws are M6x60mm, now with 56mm after cut on the lathe.
Here is my good "old" 3 jaws chuck ready for use, front mounted on the chuck backplate.
Later did the same modification to the 3" 4 jaws self-centering chuck. And made another backplate to use it on the 4" mini-lathe spindle and on the 8-1/2 x 16" lathe.