Pilot Shaft Counterbore

Whilst looking for chucking reamers, I stumbled across this on the Enco website

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=948457&PMAKA=368-6080

While expensive, this appears to be an interesting variation on the pen mills. The mill head has a 1/4" shank that is chucked rather then the 3/16" pilot shaft. These counter bores are used to mill the holes for socket head cap screws.

One frustration I have had with traditional pen mills is that as the drive force is applied to the pilot shaft, one is really at the mercy of those tiny socket head grub screws.

Anyone ever use these instead?

when I use a pen mill it is one of these, I have turned pilots from corian to fit most tube sizes.
mostly I square the ends on the lathe.

Eric,
For a fun time, and to see if it would work out, I bought a 3/4" end mill with a 1/4" pilot. I had some 1/4" drill rod laying around and use it when I need to face a pen barrel. The 1/4" drill rod was so I could ensure level. The ends of the PSI interchangeable pen mill work in it as well. For larger tubes just turn the proper diameter of some scrap wood on a 7mm tube and away you go. As easy as a thermodynamics exam after a weekend bender, or so I'm told.

I have made a couple of pen mills out of these. Used letter D drill rod to make the pilot. Good quality HSS, better than what most pen mills are made of.

Yup - that works -- the mandrels I have are D sized (0.244 to 0.246) and as 1/4 inch (0.250) rod will not fit into a standard 7mm brass tube for me.

If you seldom or never use 7mm tubed materials and use sleeves, 1/4 inch holes work well with these.

I hope the steel is better -- Daniel sells replacement pen mill heads for about $5 and these are $35

Paul - I presume you will sharpen these also??