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When building oak columns for my fireplace mantel, I found my lathe was limited to indexing in 10 degree steps . A column in the Roman Ionic style has 24 flutes. This requires indexing to 5 degrees. The lathe index on the back of the pulley would not take any more holes so I had to come up with an external indexing wheel that would allow 5 degree steps. This is what I came up with. It is a 12" Dia. wheel made of UHMWPE with 72 holes drilled around the circumference. That is every 5 degrees. However by using a selector plate with holes spaced every 6 degrees it is possible to index right down to 1 degree steps.The principle is the same as the vernier caliper.
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Here is the index mounted on the outboard side of the headstock spindle. The hub is turned from a short piece of 4.5" UHMWPE rod and is threaded 3/4 x 16 Left Hand thread. Each of the holes in the wheel is a 5 degree step while the holes in the selector plate are spaced 6 degrees apart.
From any point where the 0 hole in the plate, lines up with a hole in the wheel, it takes 1 degree of rotation to make the next wheel hole ( 5 deg ) to line up with the next hole in the plate ( 6 deg) That hole is marked 1 deg. on the plate. It takes 1 more degree of rotation to make the second wheel hole (10 deg ) line up with the next hole in the plate (12 deg ) That hole is marked 2 deg. on the plate. The same applies for the 3 and 4 deg holes. The 5 degree hole requires no rotation. The wheel holes are spaced at 5 degrees so whenever the 0 lines up, the 5 will also line up. The only reason for having the 5 degree hole in the plate is to align the arc of holes in the plate with the arc of holes in the wheel, when attaching the plate to the lathe.
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The rear of the hub does not rest on the shoulder of the headstock spindle. The plastic is too soft to stop on such a small step. Instead, the hub is recessed to allow contact with the 2" dia flat side of the drive pulley. This allows the wheel to be tightened enough that a set screw to the spindle is not required.
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Here is my complete setup for fluting columns. The index wheel is on the left . A small router is addapted and mounted on top of the tool holder of a universal copy attachment which is mounted to the stand rather than to the ways of the lathe. On the right you can see the bed extension I added to increase the length from 36" to 52".
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Just to prove that it all works. Here is the mantel that I made with fluted ionic columns.
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