Re: [CAD_CAM_EDM_DRO] Help Understanding Grizzly Mini Mill Specs

1/2" drill capacity means that the machine has enough power (under
certain conditions) to drill a 1/2" hole in a certain thickness of mild
steel. These specs are VERY broad. It is just a way to roughly
estimate the power of the machine. In other words it has about as much
Umph as your average drill press. The amount of power needed to cut and
drill varies all over the place (type of material, sharpness, type of
cutter, dry or lube, speed and feed, etc. etc.) and you "usually" won't
run into power problems in the home shop (that you can't work around).
I have drilled many many 1" holes with a 1/2" capacity drill press. 1"
face means the same thing referring to a 1" face mill or fly cutter. I
guarantee you can use a 3" fly cutter.
Quill travel is what you were asking about. Any decent machine will
have about 3" more or less of quill travel. This means you can move the
quill 3" before it stops, it doesn't mean you can't drill deeper holes
than 3" (although it takes some tricks).
The other spec to worry about is the throat. The distance from the
center of the drill point to the edge of the column. Many manufacturers
will measure this distance differently so you have to be careful. If
this distance is 9" then you can drill to the center of an 18" disk, and
this is frequently how it is specified. (I have seen it both ways, 9
and 18) Or they might measure to the "center" of the column, which of
course you can never reach, so you loose 1.5" or whatever. This is the
"swing". The swing, divided by 2, minus half the column width is the
throat.
Next problem on MiniMills is the height of the cutter head. Most
minis are "tree mills" (vs "knee mills" on the big boys). Not to be
confused with TREE (the manufacturer) We'll just call them column
mills.
You may be able to raise the head 18" but you loose rigidity as you
go up. The closer the head to the work the better, which is true on any
machine, but much much worse on a column mill. Whatever max height they
advertise subtract 3-4" for a small vise, 1-2" for the tool holder, plus
tool length, and then whatever quill travel you need.
I assume you are talking about the G8689 MiniMill, which I just read
the specs on. The thing that stands out to me is the MT3 spindle
taper. Just be aware that you will have less flexibility and will have
to pay more for your toolholders, etc. MT3 with the threaded hole for a
drawbar just ain't all that common.
One more thing, Electronic Variable Speed means LESS power for any
given machine. I know some guys on this list will argue with that, but
that is my experience. AND, if it goes bad you will pay out the butt to
get it replaced. The way the G8689 is configured you have little option
for belt drive if something fails.

Good Luck