Hoping some people can give me their input on this:

I have always made keyseats in shafts by cutting the entire depth in one
pass using the correct diameter slot drill for the keyseat. For example: I
would use a 1/2" diameter slot drill for a 1/2" keyseat, touch the top of
the shaft with the slot drill, raise the table until the slot drill cut its
full diameter on the shaft and then go another 1/4" deep. This has always
worked for me in the past.

The foreman of the facility where I work said this was incorrect. He said
what I should have done was go in with a smaller cutter first, such as
7/16", and then finish with the 1/2" slot drill.

After all, slot drills are made to a minus tolerance. I believe by taking
two cuts, you run the risk of creating an oversize keyseat.

Just wanted to know what other people's thoughts were.

Thanks,

Ted



According to Machinery's Handbook...............


For milling keyseats, the total depth to feed cutter in from outside of
shaft to bottom of keyseat is M + D, where D is depth of keyseat.
For checking an assembled key and shaft, calliper measurement J between
top of key and bottom of shaft is used. Where J=S-(M+D)+C

The page shows a diagram of a shaft and key and the following
annotations are made.

C = height of key
D = depth of keyseat (or the wall height of the keyway)
E = width of key
J = distance from bottom of shaft to top of key
M = the distance between the top of the shaft and a line passing through
the upper corners or edges of the keyseat
S = diameter of shaft

M is calculated using the formula M=1/2(S-sq.rt.(S^2-E^2))

However an easier approximation to give M within .001" is

M=E^2/4S

As M varies with shaft diameter it is hard to say whether or not your
method is correct without knowing the diameter of the shaft in question.

What I can say though is that I personally have never heard of using two
sizes of cutter to cut a keyway in a shaft and when I was an apprentice
(many moons ago) I was taught the same method as you for a down and
dirty 'shop method'. If the keyway was large (i.e. around 2" wide) I
would probably have taken it in a couple of cuts rather than hogging it
all out in one pass.

--
Larry Green