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I've been making some lazy susan shelves for my corner cupboards. I have a pilot hole in them from machining them round to start with but I needed to enlarge the hole to 1" for the pipe column that the shelves are supported by. The pilot is only 3/16". I also need to keep the hole centered so that they turn true inside the cabinet. My original plan was to take them to the drill press and chuck a 3/16" bit in the DP and then with the bit in the pilot hole I would clamp the shelf to the DP table and tehn replace the 3/16" drill with a 1" Forstner. Except when I got to the DP I found out that the throat depth on it wasn't wide enough. So I had to come up with a way to do it by hand. It me a few minutes to devise a plan and around 45 minutes to carry it out but it worked well and some may find it useful.
The plan became drilling 2 guide blocks on the DP with one matching the 3/16" pilot hole and the next matching the 1" hole I needed for the pipe column. By clamping a fence and stop on the DP's table I could insure that I was drilling centered at the same spot on both blocks. I marked both blocks so that I could be sure that I kept the same orientation from one block to the other. I never bothered measuring where on the block I drilled. I only needed to make sure that I could keep both the same.
From there I laid a backing panel on one of the lazy susan shelves and clamped it.Then I put a 3/16" drill bit in the pilot guide block and into the pilot hole in the shelf. With that block in place I hot-glued two stops to the backing panel so that I had something to register the guide blocks against. Then it was just a matter of replacing the pilot block with the 1" block. The last picture shows the shelf with the pipe in it. I did need to smooth the hole a bit with an abrasive sleeve on a drill to get the pipe to slide though easily plus give me enough clearance in the hole to make sure the pipe could sit vertical. I'm guessing that even with that step at the end that I'm no more than 1/32 off dead center, 1/16th at the worst and that is plenty good enough for this application.
The plan became drilling 2 guide blocks on the DP with one matching the 3/16" pilot hole and the next matching the 1" hole I needed for the pipe column. By clamping a fence and stop on the DP's table I could insure that I was drilling centered at the same spot on both blocks. I marked both blocks so that I could be sure that I kept the same orientation from one block to the other. I never bothered measuring where on the block I drilled. I only needed to make sure that I could keep both the same.
From there I laid a backing panel on one of the lazy susan shelves and clamped it.Then I put a 3/16" drill bit in the pilot guide block and into the pilot hole in the shelf. With that block in place I hot-glued two stops to the backing panel so that I had something to register the guide blocks against. Then it was just a matter of replacing the pilot block with the 1" block. The last picture shows the shelf with the pipe in it. I did need to smooth the hole a bit with an abrasive sleeve on a drill to get the pipe to slide though easily plus give me enough clearance in the hole to make sure the pipe could sit vertical. I'm guessing that even with that step at the end that I'm no more than 1/32 off dead center, 1/16th at the worst and that is plenty good enough for this application.
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