The big issue with sharpening lawnmower blade is not to over heat the metal. I originally thought about connecting the vacuum in the reverse "blower" direction to air cool the blade while sharpening. This proved not to be necessary. I should mention that unless you have a spark arrester attached to the vacuum, I would not use the vacuum in this application. Too high a risk of fire. Thanks for you positive comments and suggestions.
A little bit off subject. The other day I was routing out Russian Birch plywood 3/4 inch using 1/2 inch bit, 1400 with CT22 and MFS. I was creating a round mirror frame with a 30 inch interior groove to receive the mirror. I was taking off 3 mm of material at each pass so not to overheat the bit. I was finishing the second pass when I notice the saw dust left in the groove was smoking in one spot. I lifted with my glove hand the dust and there was a 2-3 mm piece of material burning like hot coals.
I was wondering if anybody had this experience before, would it have started a fire in the CT22 bag and what is a spark arrestor for vaccum.
Bruce