Re: [CAD_CAM_EDM_DRO] Re: knee mill router

george_barr wrote:

>Jon,
>
>I did not mean knee mill. What I was referring to is using a drill
>press and converting it to cnc (hobby stuff). The X & Y table is all
>metal using dovetail grooves to slide back and forth (usually comes
>with hand turnable handles). I already have a self made gantry and
>found the gantry moves alot. I will limit my projects to just wood
>projects for my gantry cnc. As for metal projects that require more
>precision, I plan to build another cnc using a drill press and X&Y
>tables (dovetail groove style). I know the aluminum extrusion of the
>non moving gantry system will bend, but I plan to build mine using
>mild steel. I am hoping I can get as nearly the same precision for
>the fixed gantry as compared with the drill press conversion.
>
>

Many of the really cheap drill presses don't even have a hollow spindle,
so you have little choice but a jacob's chuck, which is terrible for
milling.
If you have at least a Morse taper, you can get collets or end mill holders
to properly hold the cutters.

Then, the quill of a drill press is much too light to support the side loads
of milling, and many head castings are so loose that the quill wanders
around. This all causes pretty bad problems.

There are many round-column mill-drills, drill presses, etc, that give you
trouble when changing from a small end mill to a large drill bit in a
jacobs chuck, for instance, where the quill travel is not enough to use
both. You have to either elevate the head, or raise/lower the table,
which knocks your X-Y axes out of alignment with the part coordinates.
A knee mill doesn't have this problem.

Having actually tried to mill on a fairly decent drill press at work, it
was quite apparent it was a horrible idea. We had a Palmgren X-Y table
that was pretty stiff, but the drill press head was just WAY too flexible.

Jon