Step 4: Dialling in a cube
Now. lets get started on the actual project! I've seen some fancy cube holding jigs and fixtures on the lathe, but I didn't want people to have to use those if they wanted to make this. So I made this in an independent 4 jaw chuck.
Before we do anything, we have to dial in the cube. It's not so hard.
1) Place the cube in the jaws, use shims. Keep the shims flush with the jaws, so there is room to use the dial indicator.
2) Set up the dial indicator so it rests in the centre of the cube
3) Rotate the chuck side to side slightly, to see the needle moving side to side. It should start dropping, hit a low number, then start rising again. Note what that low number is.
4) Lift the dial indicator needle so it doesn't get hit by the cube, and rotate the chuck 180 degrees. Find the low number again, on the opposite side, and calculate the difference. Now it becomes the same as dialing in a round piece. Tighten and loosen the jaws, keep checking both sides, and get the low spots to be equal (or as equal as you want them to be, I usually get them to within 0.001 of each other.)
5) Rotate the chuck 90 degrees, and repeat to align the next pair of jaws on centre.
It's good to draw a X on the face of the cube, so you know roughly where the centre is, then you can test-align your centre drill once you think you are dialled in. The first time I dialled in the cube, I was 0.100 off on both axis, but I thought I was dead on. So when I drilled the centre drill, I was off. No need to do this every time, just once to make sure you're good and know what you're doing.
I wish I had more pictures, but no such luck. I don't even know what pictures I could get.... Maybe I'll try for a video one day.