pipemakersforum.com

Does anyone know where to get a counterbore with an 7mm pilothole?
I an located i Denmark and we use 7mm delrin tenons.
It would be nice to have a tool so I can face the shank and drill at the same time:-)
Anyone?

I turn my pilots from tool steel on a lathe. The hole in the counterbore is 3/16” and the pilots are 3/16”, 1/4”, and 5/16” which are standard for American pipe makers. My process involves drilling slightly undersized, reaming, then using the counterbore to face the shank, all on the drill press. I get my counterbores and pilots from MSC direct, but don’t think they deal in metric sizes. The counterbores that drill and face at the same time come from a boating supply firm -Jamestown Distributors, or Vermont Freehand but again, these are inch sizes. Plus, I think that these particular devices are not that precise and you might wind up with a loose mortise.
Generally, the maker/supplier of the counterbores has the pilots available, but mine tend to be missing when I need them.
If you don’t have a lathe and can’t find commercial pilots, perhaps you have a skilled friend who owns a lathe.
DocAitch

You'll get cleaner cuts if you use one process for facing and a different for drilling.