Shikano53- That's a 5/64" bit...I use it and the file to funnel the slot at least 1.25" deep. The other side is drilled to within .75" of the button with a taper bit. Tends to be a very open draw...what size bit do you use to drill the airhole at the button? Or put another way, what size bit are you using shown in the picture where you are working on the slot?
There are a few- I use Buckeye Engraving- http://www.buckeyeengraving.com/Where do you get custom stamps at?
Imagine the slot tapering into a funnel shape- that's the part that is 1.25" deep. I think you are thinking about the height of the slot..I'm probably misunderstanding something here; but did you mean 0.125" not 1.25" for the slot depth?