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Many of our projects benefit from variable speed. My approach is to use a spring loaded pulley that changes the speed simply by moving the motor to change the pitch of the pulley and change the speed. The trial pulley shown here was machined from a piece of 3 1/2" diameter by 5 1/2" aluminum bar stock and over the shelf hardware. |
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A center drill is used on a metal lathe to start a hole that is bored and reamed to 1/2" for the motor shaft. The aluminum stock is held in the lathe chuck jaws for all the lathe machining steps to insure a smooth running pulley. |
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This photo shows the pulley with finished diameters, a groove has been cut for an external snap ring and is ready to be separated with a cut off tool for both sides of the pulley. A bull nose live center is used in the tailstock. |
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After parting off one side of the pulley, this side is bored to .755 so it will slide easily over the .750 shaft. This piece is turned and held by it's hub and a 9 degree taper is machined to fit the contour of a 4L belt. |
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A 3/16" x .190" deep x 1.2" long is milled for the 3/16" key. The slot is made .003 over depth so the other pulley side will slide easily over the key. This keyway serves two purposes, to hold both sides of the pulley together and allow movement. |
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The keyway is cut with a broach in two passes for 3/16" wide by .187" deep. The second pass is made with a shim since it would be difficult to remove this much metal in one pass. The broach is pushed with an arbor press. |
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To hold the spring, this photo shows an end cap being bored to .755". Notice the 1/4" groove near the edge, it's purpose is to support the top of the spring. |
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