"Michael Koblic" wrote in message
...
Drilling 1/4" holes 0.075" apart is well beyond my skill level.


Did you mean .075" apart or .750 inches apart?

If you wanted the slot .250 X .325 then what you do is to center drill
and
drill an under size hole, swap to the end mill (2 flute or 4 will work
fine
and enlarge the hole to size.

Next unlock your table, turn your crank .010", Loch the gib and plunge.
Repeat toll you get to the end and then use a smaller diameter end mill
to
cut off the little tits between the plunges.

This should yield a perfect slot even with a shaky machine.

Worth trying.
Do you feel that there is an incremental benefit in this method rather
than
just making 8 passes of 0.075" from the initial hole increasing the depth
by
0.050" each time?


Since you don't have a very rigid set-up, you have to avoid doing the things
that promote flex. To start off with a center drill spots the beginning of
the hole as close as possible.

When you drill the hole under size, it removes the bulk of the material yet
still permits a bit of wandering to occur.

When you then switch to the end mill to size the end of the slot, you are
not removing very much material and even on a non rigid machine you get very
little walking if the end mill, so your hole will be as true as you can get.


Now when you offset one axis by only .010", that should allow enough
rigidity to keep the cutter from walking on you.

When you then switch to an undersize mill to clear the tits, the tendency of
the cutter to walk will be deflected into the waste area of the slot, and as
material is removed the spring in the cutter relaxes and straightens out the
slot wall.

By milling shallow passes you are going left to right and then back so you
are getting two slightly different feed paths and increasing the amount of
walk and flex that will widen the slot on you.

The question is if on your machine the end result is acceptable to you, is
one of practical application.

You can try it both ways and see what the limits of you machine are. I have
done some pretty close work on some really tired old machines and have got
**** poor results on great machines and it seems that the key to getting the
good result consistently is to work within the limitations of what you have
got to work with at the time you are doing the work.

When you think about all the forces Murphy has to botch up a project, you
are always well advised to limit the degree of mischief he can cause.


--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.