An Index Plate for the Taig Lathe

An indexing plate by itself seems to have limited use on a lathe. It's fine for anything that can be done with a toolpost mounted cutter like scribing divisions on a dial. But for drilling or milling, you need a rotating tool and, therefore, something like a milling spindle mounted on the cross-slide. For light work perhaps a Dremel or flexible shaft would do.

But the Taig design makes that uneccessary. If you think of a second

The indexing values I wanted were relatively few, - 2,3,4 and 6 for general use; 25 and 50 for dials suited to leadscrews with 20 or 40 TPI. But even this minimum needed at least two rows of holes and a detent movable from one row to another. In addition, I already had a couple of attachments which overhung the pulley so that ruled out any plate which would extend above the top of the headstock.

From these considerations, I decided on two rows of 50 and 36 holes respectively drilled radially into a 5/16" thick, 2 1/4" diameter plate. This allows index values of 2,3,4,5,6,9,10,12,18,25,36 and 50, more than

Fig 2.1: Pulley and Index Plate Assembly

The index plate is made first so it can later be used as a gauge when machining the pulley. Start with a 3/8" length of 2 3/8" diameter 12L14. This should be long enough to get a finished length of 5/16" even if the initial

Fig 3.1.1.1: Index Plate Blank

Mount the blank in the four-jaw chuck, face one side, turn it around, and indicate it true ready for thicknessing and boring.

Fig 3.1.1.3: Index Plate Drilled for Boring

Drill out the index plate with the largest drill you can manage in preparation for boring to final size.

To machine the pulley it must be chucked as the working piece so a second pulley  is necessary  to drive the spindle. If  you have a mill you can borrow

Fig 3.1.2.1: The Pulley Mandrel

Because of the reduced bore through the smallest sheave, a special mandrel must be turned to hold the pulley for machining. The chucking part is 3/8" diameter. The mandrel part is 5/8" diameter and should be a fairly snug fit for a wobble-free rotation of the pulley.

Fig 3.1.2.3: Boss Turned on the Pulley

The index plate is located radially by fitting the hole previously bored in it to a boss turned on the pulley. Turn the boss down axially to within 1/64" or less of the shoulder on the largest sheave.

The index plate is attached to the pulley with 4-40 socket head cap screws. Almost any pattern would do but three screws is kind of elegant and really easy to do with a simple setup on the drill press.The Taig spindle nut is a natural index plate just needing a rotation stop and a spindle lock to produce 2,3,or 6 divisions. The following Figures show how the spindle

The pilot holes are drilled 1/2" deep to take 3/8" long 4-40 socket head cap screws. The plate is 5/16" thick so, after a 1/8" deep counter bore, the thread depth is about 3/16". For blind holes in aluminum, I use a #36 pilot

Maximum concentricity is achieved by finishing the plate with the pulley mounted in its final position on the lathe spindle shaft. Taig pulley bores seem to vary quite a bit in diameter. Some are tight and some loose. In this case, I had to wrap the shaft with .001" brass shim stock to get a good fit.

Turn the headstock end for end and mount the spare pulley outboard in the three jaw chuck reversing the previously made machining adapter for use as a mandrel. Use the topslide to be sure the tool can travel right up to the headstock, especially if you have bed wipers installed on the carriage.

True up the plate diameter and reduce to a size you like. In my case, it only had to be enough so that it was below the top of the headstock.

Both rows of index holes will be drilled with the pulley in this position so it can now be regarded as more or less permanently installed.

I've seen quite a few references to improvised indexing techniques using circular saw blades but have never found a detailed how-to description. The following describes how I did it on the drill press but it should work equally well using a mill.

Fig 3.2.1: Mounting Platform

From scrap plywood or particle board, make a platform with a base extending well beyond the headstock mounting and with risers to get the spindle 6" above the base. This provides a surface for clamping to the machine table and enough height to swing a 10" saw blade.

Fig 3.2.3: Locating the Plate Axially

Scribe lines on the index plate 5/64" in from each edge as center lines for each of the two rows of index holes. Shift the headstock on the mounting plate to center the drill chuck over one of the two scribed lines and tighten it in place.

Mount the blade on a mandrel made with a couple of nuts on a short, headless 5/8" bolt held in the three-jaw chuck. Incremental rotation of the blade is controlled and locked with the simple device shown in Fig 3.2.6. The rubber band driven detent is very positive but the blade can still move

Here is a detailed look at the Detent/Lock Assembly.

The frame is made from scrap 3/4" plywood. The detent lever is bent from a 3" flat corner brace. It's pivot is a 10-32 socket head cap screw self-threaded into a 5/32" hole. The stop and rubber band anchor are #8 wood

Figure 3.2.9: Drilling the First Row of Holes

Now the first row of holes can be drilled. Select and lock each tooth of the saw blade to rotate the index plate to each successive hole location. Use a #1 center drill, but only deep enough to come about half way up the 60° countersink. This gives about a 3/32" target cone for the detent.

Here is the finished pulley and index plate.