The Home Machinist!

I did a final finish cut machining the rear with a higher speed, small depth of cut and a fine feed using the round nose tool. This gave a good finish.

I machined the boss down to final diameter. While doing that, I found that the hole in the back of the chuck actually has a slight taper. I used a bevel protracter and measured it at 86 degrees. I set the compound to 86 degrees and cut the boss on a taper until I got a snug fit where the chuck just barely didn't bottom on the backplate. That way the bolts should snug it down tight. I could just barely see light through the gap.

By the way, while checking the fit, I put the chuck on a holder I made so that I won't ding the ways if I drop it. If you don't have one of these, you should, particularly is you have large, heavy chucks.

I used the compound to undercut where the boss and the back meet, so as to not have any dirt or swarf prevent the chuck from seating.

Now that the face is finished, I need to locate the 6 bolt holes. The bolt circle is 5-1/2". I used a pointed tool in the toolpost to scribe the circle. First, I needed to line the tool up and zero the cross slide.

Then I backed the cross slide up one-half the bolt circle diameter and scribed the circle. Of course, I forgot about the 1/2", and did it wrong. I set the cross-slide up again and marked the circle. I checked the circle with dividers set to 5-1/2.

Next, I needed to mark off where the bolt holes go. A 6-hole layout is actually easy, as you can just set a caliper to the radius and use that to mark from one hole to the next, as the radius is equal to the chord between each hole.

Instead, I chose to use something I never thought I would have a use for when I got my lathe: an indexing pin. The Atlas has 60 holes in the bull gear, and a pin that holds the bull gear locked on one of the holes.

To be sure I didn't screw up anything if I forgot to release the pin and turned the lathe on, I unplugged the lathe and released the bull gear from the spindle (as you would in backgear). This also made it easier to turn the spindle.

I used the pointed tool to make a mark on the circle by moving it back and forth. Then I counted out 10 holes and did it again. I repeated this until I got back to the original mark (whew!). You can see some of the marks in the picture. I checked the marks with calipers set to the radius.

Next, I will center punch and drill the holes. Then I need to counterbore from the rear for the socket head cap screws.