I didn't do any prep work other than the acetone bath, to remove every bit of the machining oils. The stuff sticks like nuts to the metal after baked, so I can't imagine needing to improve that part. I had reason to turn down on the lathe a little bit by the yoke where a bit of excess had got past me, and it cut away the same as the metal did... meaning it did not chip off.

You could tape them off, but the thing to remember, until this is baked on, the powder is on there, just barely. If I took a deep breath, and blew on it after shooting it, I'd blow half of it back off. For that matter, you could just wipe it off with a paper towel with just a couple swipes.

Be careful not to get the gun too close, or it will 'arc', like a mini arc welder would. It does no damage to the part, but the spark disturbs the even layout of the powder. That happened a few times on me, and I would wipe/blow off the powder and recoat it.

Since you can't touch it without disturbing the powder, plan ahead on how you will hold the parts, and how you can get them into the oven, without disturbing the powder.

Good luck on it,
Lance