I'm going to order some media blast from Harbor Freight for my ST90 project. I have no experience with this, but I've heard that sand is very harsh on the parts. Harbor Freight has Soda Blast, 80 grit Glass Beads, 40/70 grit ground Glass, fine Walnut and coarse Walnut. What should I get that would be effective but won't damage the parts resulting in unnecessary work? Thanks!