| I made this tool so I could clearance my cylinder heads for some JWT solid lifter cams - it allows me to use a cordless drill to machine the slots concentric to the cam bearing bore... it took less than an hour to do two heads. Basic construction is 0.750" drill rod with 0.250" hardened drill bushings pressed in to pilot the 0.250" end mill. An adjustable stop is installed onto the end mill and sets the depth of cut when it hits the top of each respective drill bushing. I narrowed some old cam caps and added Al-Ni bronze bushings for the shaft to ride within so it's not wearing on the head's bearing surfaces. A thrust adjuster on each end allows me to move the shaft over to machine the full width of the clearance slot in four passes. The only trick is remembering to always roll the drill/cutter so it's a conventional cut vs. a climb cut which could kill such a small end mill used like this. Interestingly, the OE machining was not concentric to the cam bearing bores (several lifter bores had very little material removed on one side while the other side removed about 0.050"). I can't imagine setting up to do this in a Bridgeport or by hand grinding. 
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More VG cylinder head-related stuff... big cam clearance - 
