Instructables

Step 5: Roughing the bores

This step is just drilling a lot of holes.  It goes by quick.  You need to figure out how big of drill bits you want to rough your bores, and how deep they should go.  For the numbers we calculated earlier, we need a 1.500 bore, and a 0.750 bore.  So the roughing drill bits should be smaller then that.  I used a 1 7/16 (1.4375) and a 23/32 (0.719).  And the 9/32 hole for the middle.  The easiest way to know how deep you should drill, is just draw a line with a marker on the drill bit.  These are roughing operations, so all you need is to get it close.  This will minimizes how much material you need to bore.  If in doubt, make the hole a little smaller/shallower, it's better to bore more then to go oversize.

1) Centre drill (Picture #1)

2) Drill the first drill bit (9/32) halfway into the cube (cube is 1.875, drill about an inch deep) (Picture #2)

3) Drill the second drill bit (23/32) just less then the depth of your deepest bore (the bore is 0.625 deep, drill so the tip goes ~ 0.630 (You go a little beyond, because the tip of the drill bit is angled and will drop into the 9/32 hole)) (Picture #3)

4) Drill the third drill bit just less then the depth of your next bore (bore is 0.313, BUT you have a 23/32 hole in already, so the tip of the drill bit will go a lot deeper before you actually hit your depth.  This make take some trial and error, or careful measuring.  Using the 1 7/16 bit, I drilled until the diameter of the drill bit just appeared.  Had maybe a 1/64 deep 1 7/16 hole, the rest was just the drill point angle.) (Picture #4)
 
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