On 2011-09-03, Wild_Bill wrote:

[ ... ]

I assume that you're aware that countersinking thin materials/sheetmetal can
be a little troublesome since common cutting tools will tend to lift the
material, making consistent countersink dimensions problematic.

Using a multi-flute countersink cutter which doesn't have any, or little
cutting edge relief angle (like dressing a drill points' relief angles for
drilling brass) so the cutting forces are more like that of a reamer -
scraping away the metal.. should eliminate lifting of the thin materials.

Another tool which is nice for thin metals is the tool made for
aircraft sheet metal use. The Microstop countersink cage, such as this
one on eBay:

Auction # 280731984065

It chucks in a drill press or a hand drill. It uses special
piloted countersinks which screw into the spindle. It will push down
with the cage until the preset depth is reached (adjustable in 0.001"
steps), at which point the ball bearing will stop the advance with the
cage in contact with the workpiece. IIRC, it has a certain amount of
spring travel before it hits the stop, but I may be mis-remembering that
part.

It would be nice if the eBay auction came with some sample
countersink bits, but this one does not have them.

O.K. This one has two cages, and four bits of different sizes:

Auction # 190569970965

Some bits, such as this one, are drilled for a pilot but you
put your choice of size pilot in and secure it by a setscrew in the body
of the countersink.

Auction # 230633535081

The search term to see several styles and groupings is:

Microstop countersink

Good luck,
DoN.

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