Most of the cheaper motors are LH threaded. Hold the other end of the motor shaft in a bench vise, grab the flywheel in both hands and turn it clockwise. That motor looks like a nice one that I put on my lathe which is definitely 1/2-13 LH threaded. I built a 2 step polyV pulley for it and bought a tap for the internal threads. Also put a screw in the end of the shaft as extra insurance against the pulley threading off.
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View attachment 319749
I've also done it as FanMan shows above, turning down the original polyV pulley part of the flywheel and slipping a regular V pulley over it. I've also made a top hat stub shaft to attach an original stepped V pulley to (for the mill) so I could use the original spindle pulley.
If you were to make a jackshaft, I'd suggest keeping the original flywheel/ pulley and match it to a treadmill roller shaft pulley. The output of the jackshaft can be whatever matches up to the pulley on your planer. Pretty sure I have one of those treadmill roller shaft pulleys around - you're welcome to it for the price of postage.
