I had not run across microns as a measure of vacuum.
A micron is a millionth of a meter, or a thousandth of a millimeter. One inch is 25.400 mm so 1" is 25400 microns; atmospheric pressure is about 30" of mercury (Hg) so atmospheric pressure is about 762,000 microns.
For vacuum degassing you need about 29"Hg of vacuum which is equal to about 25400 microns so a pump that can reach 50 microns, theoretically is more than enough.
Do you have a good vacuum gauge and have you tested your Harbor Freight pump just with the gauge, blanked off so you know there are no leaks; rig up an adapter to fit the gauge directly to the pump inlet.
I have successfully degassed RTV silicone at around 26" Hg which should be within reach of your pump provided there are no leaks.
Incidentally I think microns for vacuum is a totally hokey measurement; it sounds more technical than inches of mercury but doesn't conform to any recognised system of measurement.