What is the smallest drill that the Drill Doctor will reasonably sharpen? What is your experience (as opposed to what the company advertises)? And all those odd leftover sets and odds-and-end bits I have in my shop from who-knows-how-long-ago, are they worth trying to sharpen? Or just start over fresh here? Maybe the leftovers can provide good practice material? And I saw an ad for a spring-loaded centering punch tool. Worth the money? Or just use the traditional punch granddaddy gave me and whack it with a ball peen hammer the old fashioned way?