Archive for August 11th, 2014

Kenmore 158: Pulley Form Tool FAIL

Mulling over how to add a 1/rev sensor to the sewing machine motor, it occurred to me that simply drilling a hole through the pulley would provide a clean optical path and a convenient 2/rev output signal.

However, the OEM pulley doesn’t extend beyond the end of the shaft:

Kenmore 158 - AC drive motor - overview

Kenmore 158 – AC drive motor – overview

Rather than drill a hole in the shaft or (attempt to) affix something onto a pulley that spins at 10 kRPM, I figured I should make another pulley and mutilate that.

Because this will surely call for more than one new pulley before I get everything right, a lathe form tool seemed in order. Introducing a suitable blank from the Bin o’ 1/4 Inch Bits to Mr. Bench Grinder produced a likely looking candidate, with an included angle of about 35° (a skosh over 17° on each side) and sized just a wee bit narrower than the pulley groove.

From the top:

Pulley form tool - top

Pulley form tool – top

From the side:

Pulley form tool - side

Pulley form tool – side

Skim the surface of a 5/8 inch rod to match the pulley OD, plunge a cutoff tool to make most of the cut, insert bit in holder, align perpendicular to workpiece, line up to center of cut, slobber on more cutting lube:

Pulley form tool - prepared blank

Pulley form tool – prepared blank

Plunging the tool slowly into the cut produces … no chips … nothing … smoke?

Come to find out that the Bin o’ 1/4 Inch Bits contained not just lathe tool bits & blanks made from tool steel, but one length of 1/4 inch square key stock made from ordinary soft steel:

Pulley form tool - damage

Pulley form tool – damage

I should have known that from the type of sparks flying off the grinding wheel, right?

You knew that just from looking at the first picture, because a real lathe bit blank wouldn’t be all beat to shit…