How do I solve this problem? Also: 1876 Centennial Exposition

[Ubarch]

So I've moved on to aluminum from iron (I'm very happy with the iron piece and have taken pictures that I will post one day). The process requires a 1" deep, .74" diameter hole to be bored in a 1.3"x2"x3" block of aluminum along the 1.3" dimension, and the remaining 0.3" to have a 0.64" hole along the same center. I've faced the block as best I could, using a fly cutter and covering myself in festive holiday tinsel.

1.3" is slightly deeper than anything I have on hand can cut, except drill bits, and .74 is far wider than any drill bit I have. However, I /do/ have a mill boring tool. Now, here's where I do something stupid: I figured, "Well, as long as I'm using a boring tool, I should start it off with the largest drill bit that I can hold". This, of course, is a drill bit whose flutes just barely fit into the Sherline collet that uses a set screw. I drill a starter hole (using a center, then the huge drill bit), and then began boring. The bored hole is visibly off center from the starter hole. I don't know what caused the error. Worse yet, I dont know if it's the bored hole, or the drilled hole that is off. I re-center the boring tool with respect to the edges of the block, and finish the 1" deep hole. Now, the 0.64" flange remains to be cut. The stater hole may, or may not be off. I can't figure out a way to measure it. I could drill it based on the same way I measured the bored hole, but I would rather calibrate the mill with respect to the bored hole itself, rather than the edges of the block. Any ideas?


Also, the 1876 Centenial Exposition had a "Hall of Machinery" which was powered by a massive Corliss steam engine. It was 3 stories tall and had a 56 ton flywheel that provided 1400 horsepower. This is clearly the coolest thing ever. Why don't we do these thing anymore?

[Genguy]

Put a dial test indicator in the chuck and dial in the bore.
Once your centered on the bore, you can find the location of the bore relative to the rest of the block by using an edge finder on the sides of the block.

[Mcgyver]

there are some great corliss engines still being built, but more stuff would fit on a desk rather than fill and exhibit hall. they were they most efficient steam engine made (iirc) and very interesting to look at - complex valving. The why is pretty simple, cost, both capital and operating, while they were efficient for steam they don't compare to internal combustion.

on the hole, you've confused me. genguy is right, you use an indicator to pick up the bore, but I’m not following what you did, how the set up lost concentricity and why the starter hole is still and issue. - how about some diagrams?