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Indexing Wheel for PM 3520B

An indexing wheel attached to the lathe spindle can be an invaluable aid in laying out equally-spaced lines on a turning.  The lines might locate the feet to be carved on a vessel, the waves on a wavy-edged bowl, or the elements of a geometric pattern to be carved or burned into the wood.  

Most lathes have at least a limited indexing capability.  In the case of the Powermatic, the indexer is rather complicated and time-consuming to use.  Many turners have rigged up their own indexing systems; I’m one of them.    

I used an indexing wheel from Iron Fire Innovations (www.IronFireLLC.com) that has evenly spaced holes drilled around four concentric circles.  There are 60, 48, 36, and 14 holes in the respective rings that allow a total of 20 different equal angular spacings.  

The wheel is sandwiched between the bearing surface of the spindle and the chuck or faceplate holding the workpiece.  There is no mechanical connection between the disk and the chuck or spindle.  You must build a simple fixture to receive the indexing pin (provided) and lock the wheel at the desired angular position.  I turned a knob for the pin to make it easier to handle.

A simpler design, used by many turners, consists of an L-shaped bracket clamped to the ways of the lathe.  Holes drilled in the bracket accept the indexing pin.  However, I like the design described here.

The base of the fixture.   A piece of 3/4” plywood mounted vertically against the headstock housing forms a base that holds the indexing-pin block.  A single bolt screwed into the existing hole at the top of the spindle housing holds the plywood in place.  The bolt steadies the base at the top and forces the bottom of the base against the ways of the lathe.  The bolt is 5/16” x 18 tpi.


The hole cut in the base should not be a tight fit around the spindle housing.  The base must be able to move downward ever so slightly so the bolt can force the bottom of the base against the ways.

The Powermatic 3520 Model A uses a different design for the spindle housing.  The base must be clamped to the ways of the lathe by a clamping block as shown in the drawing.  

Block for indexing pin.  Holes for the indexing pin are drilled in a small block glued to the base.  The thickness of the block (1/4”) is just enough so that it very nearly touches the back of the indexing wheel.  

Clamping surface.  The indexing wheel (and workpiece) can be held in any position by clamping the indexing wheel against the clamping surface using one or more spring clamps. A rectangular piece of 1/4” plywood glued to the upper right corner of the base prevents the wheel from being deformed by the clamp.

Drilling the holes in the pin block.  A hole must be drilled for each ring of holes.  With the indexer set up on the lathe, I clamped the disk in a position so that a hole in the outer ring was centered on the block.  Then, using a drill bit that fit the hole exactly, I drilled through the hole in the disk just enough to mark the location of the hole.  I did this for each ring of holes on the disk.  The disk was then removed so the holes could be drilled to their full depth without the risk of enlarging the holes in the disk.

Using the indexer.  First, install the base on the lathe, then slip the indexing wheel over the headstock spindle. Mount the workpiece, which can be held by either a faceplate or scroll chuck.  

Before tightening everything down, pin the indexing wheel at the starting position and orient the workpiece as you desire relative to the wheel to establish the starting position.  

The indexing procedure is straightforward.  For example, if you desire 9 equal segments, select the ring with 36 holes (because 36 is evenly divisible by 9).  In this case, to advance from one position to the next, you move forward by 4 holes.  

If you want 5 equal segments, use the ring having 60 holes and move forward by 12 holes to advance from one indexed position to the next.

Spindle extender.  If you would like the workpiece to be separated a greater distance from the indexing wheel, you can buy a spindle extender from Packard Woodworks that will move the workpiece out 3” to allow more space to work between the wheel and the workpiece.

(www.packardwoodworks.com)

Note: Ironfire LLC is now Flute Master LLC. This change is due, in part, to three new products: the Flute Master makes it possible to cut straight flutes on a curved surface while the Spiral Master will cut spiral flutes on a spindle or curved surface. Also, a pin holder is now available for purchase that does the same job as the fixture described in this article.

Demonstrations of these new products can be seen at

www.flutemasters.com
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