I mentioned this jig in another thread. A gent on the site asked if I would post a photo, so here it is. Basically, I took a short section of scrap wood and attached two sides to it to form a corner. This is placed in a vice on the drill press. I use a clamp to keep the blank verticle in the jig. In addition, I'll keep a hand near the top of the plug to secure it. To do the actual mouth, I'm using a full round rotar bit. Center the bit over the front of the plug and slowly lower the bit into the wood and drill to the depth you want. Instant popper mouth
I used to use the same jig to keep my blanks verticle when thru-drilling on the drill press.
Jigman