Step 6: Finishing the Bores
Now we'll get to use that beautiful boring tool we made! You can use power feed for this, and just face off by hand (power feed Z axis, hand feed X axis). The dial indicator will tell you when you are getting close, and you can finish off the last ~0.030 by hand on the Z axis. 0.005 per revolution is a good feed to use in aluminium.
Note: X axis is for facing cuts, Z axis is for turning/longitudinal cuts.
1) Put the tool in the tool holder, and set it to the proper height (centre)
2) Using the carriage hand wheel, move the tool right near the face of the cube (don't touch it yet! Just get close)
3) Place a piece of paper on the cube face, and use the compound rest to inch (to thousandth of an inch, actually) closer, until the tool tip is barely touching the paper, and it (the tool) holds it (the paper) to the cube face. Now you know that the tool tip is the width of a piece of paper (about 0.003) away from the cube face. (Picture #1)
4) Move the tool to the side, so you don't crash into the cube or the jaws when you move in ( Picture #2)
5) Place the dial indicator with a magnetic back on the ways of the lathe, and set it to 0. (Picture #3)
6) Move the carriage in about 0.618 (watch the dial indicator). We're roughing the depth of the bore, and the bore should be 0.625. Leave about 0.010 for the undercutting tool, so if your bore is different, make this cut 0.010 less then the depth of bore you calculated. Don't forget to compensate for the 0.003 that is the paper width! (Picture #4)
7) Don't move the carriage now! Remove the dial indicator, and set it to 10 when it's not touching anything (neutral). (Picture #5)
8) Press the indicator against the carriage, until the needle reaches 0. Make sure it makes less then 1 rotation, so you should be moving it approximately 0.090. Now, you may move the carriage away. When you move the carriage back, you'll hit the dial indicator, and the needle will show you when you reach your depth of 0.615 (or whatever you set it to) as it approaches 0. You'll have a 0.090 countdown (should be at 10 when it hits, then travel around until it hits 0), and remember to use the carriage hand wheel (turn off the power feed) for the last ~0.030.
9) Now bring your tool back to the face of the cube, and begin roughing the deepest and innermost bore. Focus on depth first, get it to within 0.010 of the final size (90 on the dial indicator) then make one little (0.010) cut to clean up the sides. Now you can cut the sides, and get them to size (0.750). When you are making your final cut on the sides, go to full depth on the dial indicator (cut off that last 0.010, get to 0!) and face off the back. Now your first bore is complete! (Picture #6)
10) Do the same thing for the next bore. Touch the tool off on paper, reset the dial indicator to the next bore depth (0.313 - 0.010 = 0.303) , rough the depth to within 0.010 (90 on dial indicator), finish the width (1.500), then finish the depth with your last width cut. (Picture #7)