Step 9: 4 Nested Cubes
We'll start with the calculations. The cube began at 1.900 after milling, and I wanted 4 cubes. I decided to keep it simple, and make the difference between each cube 0.500 (as opposed to 1.900/4 = 0.475 difference). So the cubes are 1.900, 1.500, 0.900, and 0.400.
For the bore sizes, I drew the 4 cubes on Google Sketch up, drew an X to find centre, and then used the tape measure to find the corner to corner distance of each. I then just drew circles (make sure to keep the diameters of the bores less then the corner to corner distances.) until I thought they looked good. In hindsight, I would have made the bore diameters closer to the corner to corner distances, I think it would look cleaner. Maybe I'll make another. Since the difference between cubes is 0.500, the bore depth is half of that (so 0.250).
The cubes are 1.900, 1.400, 0.900, and 0.400. The bores are 1.700 x 0.250, 1.100 x 0.500, 0.500 x 0.750, and the hole through is a 13/64th drill bit.
- Now we can begin! Put the cube in the 4 jaw, and dial it in.
Note: On one side, I tightened the vice too much, and there are now indents along the side of the cube. It was the 5th side I did, I believe. 5th or 6th. So be careful when tightening, keep it tight for safe machining, but don't tighten it so much that you crush the aluminium.
- Centre drill, drill 13/64th's 1 in deep, drill 7/16's so the tip is 0.750 deep, drill 1 1/16th so the tip is 0.500 deep, and drill 1 5/8ths so the diameter just appears. (I'll say this now, I never quite worked out exactly how far to rough with the drill bits. If you put the tip to the bore depth, you will never screw up (because the drill point angle will go into the smaller hole, so the diameter you are making will not be to depth.). You may have more boring to do, but that's fine. Experiment and find out what works.)
- Get the boring tool set up, set it to centre height, and touch off on the face of the cube (use the paper!)
- Set up the dial indicator on the ways, and move in to your first bore depth. Don't leave extra room for undercutting, all we're doing is boring. It doesn't matter if you do biggest to smallest, or smallest to biggest, since we're not undercutting, and the cubes will always be attached. I did biggest to smallest, because after roughing with the drills, it looked weird. (Again, when roughing, always make the drill hole smaller/shallower if you're having doubts. It's better to have to bore more, then to have a too big, rough hole.) So if you're doing the 0.750 bore first, then move in 0.753 (remember the paper width!) and set 0 there.
- Begin roughing out the bore depth, getting to 90 on the dial indicator (save the final depth cut for last!). Then rough out the diameter of the bore. As before, on your final diameter pass, go to 0 on the dial indicator (full depth) and make your facing cut, so that you have a nice smooth transition between the diameter and the face.
- Repeat for the other 2 bores.
- Chamfer if you like, I didn't for this one because I'm going to throw it in a steel shot tumbler to try and polish it, and that will break the corners. Also, I knew that it would be wicked hard to file the edges of the inner cubes, since they are still attached, and I figured that it would look funny if the outer cubes and the bores were chamfered, and the inner cubes were not. So I left the corners sharp for now, the tumbler will smooth them off a bit (and hopefully smooth them equally).
- Repeat on the other 5 sides (remember to do opposite sides, think of a dice! Do 1 then 6, 2 then 5, 3 then 4)
And you now have 4 nested cubes! I think the nested ones look better in pictures, and are nicer to look at, but the free floating cubes are cooler/more mind blowing/better to play with.
I didn't take many pictures, there is not much to see. Just imagine all the pictures from previous steps, but think of 4 cubes, not 3, and forget the undercuts. I wish I took a picture after all the roughing drill bits had gone through, so you could see what it looked like, but oh well.