GEM 500 Milling Machine

Hi group,

After getting back from a needed vacation last week, I brought home
the new baby (GEM 500 Milling machine) yesterday. I had to
disassemble it to be able to carry it downstairs into the basement,
plus to I wanted to inspect all the parts, and measure them for 3D
modelling. The machine breaks down into managable sized parts,
enough that I handled all but the cast stand myself with a dolly
cart. I will list the good and bad things I found below about the
design/manufacture of this machine.

Good things:
Good to excllent casting quality - no porosity I can see on
the unpainted surfaces inside the sections.
All the running ways are frosted - I don't know if that means
hand scraped or they have a machine to do that.
All slide ways have oil path grooves on the traveling face.
It will be easy to mount drive motors on all 3 axis, as there
are already flats and some tapped holes for the current screw
supports.
Tapered gibs on all axis with a cinch bolt on both ends of
each gib. Dovetails are 60°.
Gear levers work smoothly - I haven't powered it up yet to
hear it run.
LOTS of travel available - twice the Y travel on my
mill/drill.
5" of quill travel, 3" Dia. quill with R8 taper.
HEAVY duty structure - the mill base and column are ribbed
internally to support all the structural zones.
Wide slide surfaces to distribute the load, though this
increases "stick".
Wide dovetails - 6 3/4" tip to tip on X and Z axis, 8 5/8" on
the Y axis.
Coolant drain on table and cast stand.
Lots of room for ballnuts on the Y and Z axis. X axis will
be tighter under the table.
I estimate that the cast stand is 400lbs, so the rest of the
mill is ~1000lbs.


Bad things:
The Y axis nut has no positive drive pin or stud to mate to
the Y saddle. It is only relying on the one bolt in single shear to
move the table in Y direction.
All 3 screws use the same bearing sets (probably for cost),
but the setup was sloppy as I received it. It would take some
careful shimming to take the thrust slop out of the screws.
The X axis nut has 2 large holes for the mount bolts - with
small bolts through them (way too sloppy), again with no positive
drive pin or stud.
No lock washers on any of the bolts from 8MM on down (screw
bearing mounts, screw nuts, motor mounts).
The main table has no ribbing underneath, though that can get
in the way of a ballscrew nut setup.
I found copper shims under the column front edge, and under
the mill base between the cast stand.
The pivot zone for the rotating head doesn't have as much
face area as I would like, though it will just be set and stay set.
When I transported it home with the head on its side, the top
bearing on the spindle leaked oil.
The switches are pretty cheap (just actuators on the
contactor pins, and the white cover is held only by friction, so it
could pop off).

So far it looks like it will be my "ultimate" mill for home shop
CNC. Plans for a 3ph 2HP motor with VFD, and A and B rotary tables
for 5 axis are swimming in my head. The plan for now is to model it
in solids in CadKey, then start designing the conversion.
Most of the bad things are easily cured during a conversion to CNC.
I have placed a ZIP file of 10 photos on the Files page (GEM 500
Mill.zip) = 260Kb, which shows the mill as I received it, and partly
stripped down.
If there are questions, post them and I'll try to answer.

Allan