DIYbanter - View Single Post

In article .com,
says...

... I am attempting to
get a handle on the *physical* reasons why so many here say that a
drill press shouldn't be adapted to mill use.

The foremost reason is physics.

Basically it has to do with friction.

Bear with me.

Drill presses mostly use a morse taper to mount the chuck to the
spindle. Morse tapers are ordinarily considered to be 'self holding'
which means the tangent of the taper angle is *smaller* than the
coefficient of friction for the materials involved. Here this
is of course steel on steel.

What this means is that for axial loads the taper will not come loose
from the socket.

You can drill all you want and the forces that try to extract the
taper shank of the drill chuck will not do so.

Note the preceeding explaination involves axial loads.

Milling imposes *radial* loads, or side loads to the taper. At this
point the relevant angle one compares with the friction coefficient
is no longer the taper angle.

Simply put, under radial (side) loads, morse tapers become self
releasing. The drill chuck arbor will self-extract from the
spindle under side loads.

The other reason one does not mill in a drill press (namely, the
absense of a draw bar to prevent the arbor from extracting) is that
it typically involves putting and end mill in a drill chuck.

Again the physical sciences rear their ugly heads and the problem
here is that the end mill is *harder* than the jaws of the drill
chuck. Aside from ruining it for precsion drilling work, an
end mill, no matter how tightly cranked down in the chuck, will
never be secure for extracting under axial loads.

So what to do? Buy a drill press and modify it to accept a draw
bar, and some kind of collet perhaps. By the time you are done
you could buy an R8 spindle mill-drill and be done with the
thing.

Jim

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