Toolmaking
September 1, 2007
Entry Details
 

# 499
George Salt
Maple Ridge, BC
Dimensions (inches):  
  Width:   12
  Height:   17
  Depth:   2
Materials:   12" x 12" x .5" white UHMWPE
2" X 4.5" white UHMWPE
5" square of tempered hardboard
2 steel rods 4MM Dia. x 2"
Misc. hardware including 6 1/4X20 1.5" bolts
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.
 
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.
 
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.
 
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".
 
Just to prove that it all works. Here is the mantel that I made with fluted ionic columns.
 

Judges Comments
CS : Great solution to a construction problem. The jig is accurately made and spins nice and free.
Clarence : Handy for indexing. Should be very accurate.

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