Re: MSC Knee Mill

Converting that mill is certainly do-able.

Depending upon the type and accuracy of the existing feedscrews, you
may not need to change them immediately. Consider the precision and
accuracy your work requires and evaluate the actual backlash in the
system when properly adjusted. Remember, once ballscrews are
installed, the mill is no longer really suitable for manual milling
as the forces transferred by the cutting tool to the workpiece will
probably be able to move the table at least a small amount, maybe
enough to scrap your part or damage the tooling. See for
yourself...If you push on a ballscrew nut along the screw axis
direction, it will "roll" along the screw with little resistance but
if you push on an ACME Nut, it won't move at all.

Also, for a mill that size, I would certainly choose SERVOS over
STEPPERS. Servos retain almost all of their torque up to their top
RPM while steppers fall off the faster they go. You would need huge
steppers to have adequate power to achieve decent rapids especially
in the X Axis.

You can leave the DRO in place as well as the Mitutoyo quill kit.
However, the scales will probably not be useful for CNC as most
servo systems include encoders on the motors and feedback in the
drives. Steppers rely on the step counts actually sent to determine
distance moved, and if a step is "missed", there is no feedback to
notify you. Advantage SERVO.

Although many are available, I have preferences in servo drivers.
First, since I am using some Sanyo Denki P5 AC Brushless Servos, I
chose RUTEX drives which can drive almost any brushless servo motor
including AC Brushless. Other than that, if you limit yourself to
just DC Servo motors, GECKO drives are also very good.

Now to your Z Axis issue...Driving the knee is possible, but would
take a huge motor. A nice gearmotor would be convenient for manual
up/downmotion, but for CNC, I would definately drive the quill.

When driving the quill, you always have the option of programming
with constant Z position so the quill can be locked for rigidity,
but on smaller cuts or detail work, I think you will want it to be
active. I would use a ballscrew drive cantilevered off to one side
driving the lower plate that rides with the quill.

You should also consider a VFD for the motor, not only to gain
variable speed, but also to operate a 3-phase motor on single phase
if applicable, and particularly so your CNC drive setup can
potentially control spindle power/direction/RPM via software.

Sounds like a great project, so good luck!

Tom

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tyson" <timbercutter@...>
wrote:

>
> I have the opportunity to aquire a 16 speed, 2HP, 9x42 vertical

spindle

> knee mill, it's an asian import Bridgeport Clone. Does anyone have
> experience with these? I am interested in doing a CNC conversion

to it

> someday, at least a 2 axis cnc with manual Z. It has a 2 axis

Mitutoyo DRO

> and the little Z axis caliper looking thing DRO. I guess I would

need ball

> screws and mounts, steppers would be OK with me. Does it sound

doable?

> or waste of time/money? Here is the catalog link for it:
>
> http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=1408&PMCTLG=00
>