On Sun, 23 Apr 2006 15:24:21 -0600, Roy Smith wrote:

I've got a Unisaw that I want to attach an extension table to the rear
of.
There's two holes (approx 3/8" diameter) already drilled in the rear
flange
of the cast iron top (it came from the factory that way), but they're not
tapped; just through-drilled. They're a little too small for clearance
of
a 3/8" bolt; it would be nice if they were whatever the tap drill
diameter
for a 3/8 UNC is supposed to be, but I haven't measured them exactly, so
I'm not sure.

I suspect the easiest way to attach something would be to tap those two
holes and bolt on a piece aluminum angle, to which my plywood table would
get attached. How difficult will it be to tap these holes? I've tapped
holes before, but never in cast iron. Does it go easy? Is there any
risk
that I'll damage the top? What if I end up having to drill some
additional
holes in the flange?

Cast iron taps fairly easy, but it clogs the tap, so back it out to clear
the chips, then tap anouther 1/4 - 1/2 turn or so.
DAGS comes up with this site for drill sizes:
http://www.newmantools.com/tapdrill.htm





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