Re: [CAD_CAM_EDM_DRO] Dumb question on the drilling of holes

Marv Frankel wrote:

>Jon,
> Thanks for your input. My spindle is tight, so are the bearings, and
>the 1/4" end mill is held in a pretty new collet. When I tried plunging the
>end mill through an 1/8" wall aluminum extrusion, I could feel resistance on
>the quill. Then I realized that, as the cut started, the chips built up
>between the end flutes, and caused some galling and hole distortion, since
>the chips, unlike a fluted drill which gets rid of it's own chips, had no
>place to go. I'll try to do some testing, and document my findings, to
>arrive at the best solution.
>
>

Well, there is an optimum feedrate, that varies depending on material
and the particular
way the end of the cutter is fashioned, that makes for the best cuts.
It is the center of the
cutter that develops the most force. One trick is to use a smaller
cutter first, then follow
through with the desired size. I often use end mills to countersink
through holes for
socket head cap screws, drilling the through hole first, and the results
are very good.

Aluminum extrusions are generally horrible, plastic alloys, unlike the
wrought aluminum
that machines well. You may have to use lots of cutting oil, and lift
the cutter to clean the
flutes with a brush. Harder alloys, like 2024-T6 or 6061-T6 will flow
up through the
end mill's flutes nicely. But, I avoid machining of extrusions as much
as possible.

My best formula would be :
Drill through with a 1/8" solid carbide end mill, and then orbit the
machine to produce the
correct size. Use a water-based flood coolant system. When these
extrusions get even mildly
warm, they plastic-flow and gum up on the cutter, and that is a
disaster. Only flood coolant
will prevent that.

Jon