Tools - Spin Index

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Spin Index - Modification, Accessories, and Use

[Nov. 13, 2013]

Note: For other links related to this topic, go here (scroll down to "Spin Index").

[Note: I borrowed a lot from the work of "Bogstandard," whose work can be seen in one of the links referenced above.

Purchased from Wholesale Tools (Type PF70/5C, cat. #1709-0010) at a discounted price of $41.65. Regarding the quality of this spin indexer: I have seen comments on some machinist forums to the effect that the quality of this particular make/model is not good; I did not find that to be the case. The base casting is well made and solid, and the bottom of the casting is quite smooth. The ends of the casting are not as smooth as the base (they appear to have been simple milled flat, and the milling marks are evident), but these are not critical surfaces. The crank handle on the draw bar is solid and firmly attached. The spindle sits firmly in the casting with no wobble or play.

The photo below shows a 5C collet installed (purchased separately, NOT included with the spin index)

Documents and drawings related to the PF70/5C are located here:

Scanned copy of the manual for the PF70/5C [PDF] : https://drive.google.com/file/d/0Bykt5WZ092aWN2hqV09lNlJ3dkU/edit?usp=sharing
Measured drawing [PDF] : pending
Measured drawing [LibreOffice Draw] : pending

The information below is taken from the manual:

Main technical specification

Center height of spindle: 70mm (2.756")
Min. indexing degree: 1°
Indexing accuracy: 4'
Parallelism of center
line of spindle
to base surface : 0.02mm (0.00079")
Radial run-out of spindle: 0.02mm (0.00079")

Dis-Assembly

Dis-assembly of the spin index is necessary to prepare the base for milling mounting slots. Dis-assembly is simple. Refer to the photo at left for a parts list (left to right, top to bottom):

Collet draw tube with crank handle
Spindle
Base
Locking collar for index plate
Spindle collar with three set screws
Aluminum set screw (to lock down spindle)
Index pin
Index plate

The collet draw tube simply pulls out (note that the crank handle on the draw bar can also be removed, but I did not bother to do this). Next, remove the index pin and the locking collar for the index plate (requires a pin spanner - see below); unscrew the locking collar and remove the index plate. Unscrew the aluminum set screw. Loosen the three set screws on the spindle collar and remove. Remove the spindle.

Below are some additional photos of the base with parts removed, as well as the bottom of the base.

Front end of casting - milling marks are clearly visible.

Rear end of casting - a bit smoother but also showing milling marks.

The bottom is quite flat and smooth, and appears to have been ground flat.

Pin Spanner

Complete dis-assembly of the spin index requires the use of a pin spanner, which is not included with the spin index. Since pin spanners tend to be rather expensive, and as I did not have one available, I fabricated one out of rectangular steel bar. Making the pin spanner only took about 30 - 40 minutes; I simply traced the outline on a piece of steel stock (3/16" x 2" rectangular bar, hot rolled steel), cut out the rough shape with my bandsaw, and then used a bench grinder and files to finalize the shape. I finished up with a wire wheel to smooth out the surface and edges. A template for this pin spanner is included in the measured drawing above.

Completed pin spanner

Closeup of "business end"

Mounting on a Milling Table

Spin indexers are primarily designed for magnetic mounting on a grinder table, so there are no mounting holes, slots, etc. The simplest method of mounting on a small mill table is simply the clamp down the base. While this works, it has several disadvantages: The clamps take up more space, and only fit well on the rear of the casting, as the front end of the casting is mostly blocked by the index plate. Consequently , a variety of other methods have been used.

The measured drawings linked to above show how I positioned slots for mounting on my mill (a LittleMachineShop Model 3900 HiTorque Mini Mill). This may not be appropriate for other milling machines, so make adjustments to fit your own mill as necessary. As noted previously, I borrowed many ideas from "Bogstandard," though I had to make some modifications due to my smaller mill. Also, if I had it to do over, I would use the alignment bar method of SBWHART - easier to do, and easier to adjust.

The photos below show the un-modified spin index sitting on the table of my mill (a LittleMachineShop Model 3900 HiTorque Mini Mill). This shows the first problem - the spin index is very large relative to my small mill. This is not an especially big problem for using the spin index, but it is a much more difficult problem for milling modification to the index.

Closeup showing mill base relative to mill table.

Bad idea: To the left you can see my initial idea for milling the edge of the index base. This did not work well; it was very difficult to adjust the position of the mill, and when I cut the slots they would have come out square instead of rounded. Also, it would of course have been impossible to mill the slot for the alignment bar this way.

Better idea: Initially I used a v-block below the index, but this had two problems: It was too high, and the block edges cut into the finish of the mill. I replaced the v-block with a small oak block with a circular section cut out of it. While I would not normally use wood for work holding, I felt it was justified in this case as a temporary expedient, and that it would be stabkle enough for the short time I would be using it.

In addition to the oak block, I used a steel bar through the spindle ("cushioned" with small pieces of aluminum underneath to prevent it from gouging the inside of the spindle). Tightening the clamps on either end of the bar allowed for adjusting the sideways tilt of the base.

Finally, jack screws on either side of the base allowed for adjusting the back-to-front tilt of the base.

With this arrangement, I had just enough space to position a dial indicator against the quill or the top of the base to adjust the position to squareness.

With the spin index clamped in place, I first milled the side of the index base, in case I should ever want to clamp the index in a vise. This step was likely unnecessary, as my small mill does not really have room for this type of mounting.

Next, I carefully milled a slot on one side. I started with a shallow cut (10 thou) and continued with cautious cuts of no more than 50 thou until the slot was completed. Note that with this clamping arrangement, there was only room to mill a slot on one side. In order to mill the slot on the other side, I had to turn the index around and redo all of the clamping.

The photo to the left shows the spin index turned around in preparation for milling the second slot.

At this time I also milled the slot for the alignment bar (already completed in the photo). I then clamped down the already prepared alignment bar and drilled and tapped the alignment bar screw holes. Following this, I milled the second side and slot as shown above.

Note also in this photo the use of the jacking screw. This is slightly different that shown in the previous photo, as I modified the method to provide a bit more clearance. I simply created a sort of jack stand using parts from my clamping kit (with a large washer underneath to protect the surface of the mill table). It was necessary to improvise in the was because there was simply no room for a typical jack stand.

The photos below show the (almost) completed modifications. At this point the index is useable, but the runout is greater than I like, so some adjustment will be necessary.

Bottom of the spin index.

Milled slot - left side.

Milled slot - right side.

This page is a work in progress

Other Modifications and Additions

A minor modification to improve the readability of the vernier numbers and index pointer: The recesses were filled with orange acrylic paint by putting a large dollop of paint on one end of the vernier section and scraping it along the top with an index card. This fills the recesses with paint, and leaves only a thin film of paint on the rest of the surface. When the paint dries, the thin film of paint on the surface can be simply wiped off with a rag.

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