On 2016-01-16, wrote:
On Sat, 16 Jan 2016 13:40:12 -0500, Ned Simmons
wrote:

On Sat, 16 Jan 2016 10:20:28 -0500, wrote:

[ ... ]

The slot depth is the full 1 inch thickness of the stock, and the
length of the slot is 1 3/8"

O.K. Slots cut across the end and 1-3/8" from the end of the
workpiece to the end of the slot.

The mill doesn't have a DRO. It is old but lightly used and well
maintained. Being a 3/8" mill holder, it is almost impossible to buy
an end-mill smaller than 3/16 with a length of 1/2" or more,

There is a reason for short lengths with small diameters. They
tend to break easily when longer.

Now -- you say it is a "Bridgeport type" mill -- and never say
that it is truly a Bridgeport, so I may interpret that as meaning a
vertical spindle mill of unknown size. If it is truly a Bridgeport, or
a clone of the Bridgeport (there have been many), it should accept
alternate end mill holders and not be stuck at 3/8" diameter. End mill
holders or R-8 collets are both options -- and not that expensive to
purchase for your friend if he does not have them.

which is
required to cut the full slot, cutting from both sides. Our local
machine tool supplier doesn't carry them, but an old machinist friend
has a 5/8" long cutter from a box of cutters he bought at a close-out
auction over 10 years ago - brand new never been used, that he has
given me.

You will probably do better with an adaptor arbor to accept
horizontal milling cutters. Typical arbor diameter is 1", though there
are smaller and larger diameter. A 1" arbor had clamping rings 1-1/4"
diameter (and a key to keep the cutter from spinning on the arbor). It
fits into the R-8 socket in the spindle of the mill. This produces a
horizontal cut, so you will need the workpiece sicking out the side of
the vise.

Now -- for 1-3/8" depth of cut, we need to take half the
diameter of the clamping rings (0.625") and add to that at least the
depth of the needed cut (1-3/8") which brings us up to a 2" radius (4"
diameter) thus eliminating the smallest common cutters, which are 3"
diameter. The other size which I normally see is 6" diameter, which
would be plenty for your task.

Good Luck,
DoN.

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