Quick and easy does it
Old File Recycled as Form Tool
© Frank Ford 2006; Photos by FF

Not long ago  I bought a used Themac tool post grinder from "the usual Internet source."  About the time I first decided to use it, I discovered that one pulley was missing.  , I suppose anybody who would buy a used tool post grinder would have the lathe and wherewithal to make a simple pulley.  So that's what I did.  It was the smallest one, and since they are used in pairs and I had the other pair and the mate to the needed pulley, I was able to calculate the size I needed without too much brain strain.

My new pulley was to be .856" at its maximum diameter, and crowned to track the flat belt well with its mate.  There's enough belt adjustment that I wouldn't need to be too exact with the diameter, but I did want to get the crown to match nicely, so I thought I'd concentrate my effort on that part of the project.

I had a piece of 1" W-1 drill rod in my scrap drawer, so I stuck it in the lathe collet and got to work. First I faced the end and drilled, bored and reamed a nice concentric 3/8" hole for the drive shaft.  Then I turned the O.D. to .856" and ran my 1/8" parting tool in about an eighth inch to establish the width of the pulley:

I must admit I didn't actually measure the width - I just held one of the other pulleys up next to it as I moved the lathe carriage to the left.  When the ends felt flush, I figured I was good to go.  After all, this isn't rocket surgery.  And, to be absolutely sure of concentricity and balance, I did all the work without loosening the collet.


Now for the fun part.  I thought of about a half dozen ways to turn that convex crown on my little pulley, and finally came up with what I think was the easiest and quickest way.  I rummaged around the shop and found a seriously dead Nicholson "Handy File."  So, I called on it to volunteer for this assignment. Not high speed steel, for sure, but this would be a one-use tool, and I could afford the time to hone the edge a couple of times if I needed to as I went along.

I introduced the file to Mr. Bench Grinder, and roughly ground a concave radius (the radius of the grinding wheel, of course) in its end.  I approached the wheel at an angle to create a bit of clearance for my new form tool:


The end of the file now had a smooth radius and a good clearance angle, but the radius was too great to match my pulley, so I'd have a bit more work to do on it:


Before correcting the radius, I ground off the file teeth on the top side, so I'd have a smooth cutter.  My 1" x 42" belt sander was just the ticket:

After interviewing all my various sanding and grinding machines, I discovered that they were either too small or too big a radius to match the crown in the pulley, so I chose the upper wheel of the belt sander to adjust the radius on my form tool:

It was a smaller radius, but by carefully and gently touching the belt, I was able to reduce the radius on the tool until I could hold it up to a pulley and see a nice match:

The entire grinding process took around five minutes - less time than it took to shoot the pictures.


A couple of strokes with a medium grit diamond pocket hone, and I had a right sharp form tool:


Here's the file-tool, clamped in a double tool holder with the least overhang I could manage:

This file wasn't very thick, so any extra overhang would have produced a nasty chatter.  I noticed that while my freehand grinding did a nice job of reproducing the radius of the pulley crown, I hadn't managed to align the radius exactly on the centerline of the file.  No problema - I loosened all the setscrews on my tool holder, and ran the tool right up to the work.  Then I angled the file until both outer corners of my "blank" touched the curved end.  Clamping down all the setscrews, I was certain that the curved portion would approach the new pulley quite squarely.

To get the file into the holder I had to remove the central stabilizing screw, which allowed a bit of flex in the holder but not enough to be a problem.  I think now that I like this file tool technique, I'll make myself an extra beefy holder just for files.

A view from the Sky Cam as I ran the tool in to form the radius on my little pulley:

Parting off, after a bit of polishing with 600 grit waterproof paper lubricated with kerosene:


Done - nice and neat, quick and easy: