IH Mill VFD & CNC Spindle and Coolant
The work required to control
the mill spindle from Mach3 is not terribly hard, but there are a lot
of details, so I've split it off to a different page to make it easier
to follow this subsystem.
Controller Board Selection
Given the Smoothstepper and
Geckos handle the 6 axes worth of motion, and the safety circuitry is
covered, the next thing is what's needed for spindle and coolant control.
Controlling the spindle typically means outputting a 0-10V DC signal that
controls speed and having 2 signals that control spindle on/off and forward/reverse.
Lots of ways to skin this cat,
but my favorite is the PMDX-106, because it has front panel overrides
for spindle on/off, direction, and speed. Sweet!
That's a lot of Doh-re-me for
essentially just the extra front panel controls. There's also a Safety
Charge Pump interlock, which is nice and could be daisy chained into the
E-stop circuit, but there is a much cheaper alternative. Homann Designs
has a board called the DigiSpeed SD that's only $30. You get the variable
spindle control voltage and 2 relays for start/stop and direction. I've
got no charge pump circuit, so I'd have to rely on some other means of
shutting down my spindle in the event of an E-Stop. It can't be too hard
to put something in series with the spindle on/off output though, so I'll
noodle on that and plan to use the Homann board.
Alternatively, the CNC4PC Variable
Speed Control Board is pretty similar to the Homann Digispeed also, and
Coolant control is easy, I
just need 2 relays controlled via the breakout board outputs. The CNC4PC
dual relay board fits the bill nicely for $18. I'm thinking a couple of
IES sockets for power cords on the rear auxilliary panel will complete
the coolant control.
Variable Speed Control Board $32.50
A breakout board to allow point
to point wiring for a Smoothstepper.
Designs DigiSpeed SD $30
0-10V DC control signal for
VFD plus 2 relays for on/off and direction.
Spindle Control Interface $89 - $109
- Works with 0-5V, 0-10V, and
potentiometer interfaces to the VFD to control spindle speed.
- Optional front panel potentiometer
and switches allow forward, reverse, and variable speed overrides of Mach
3 along with LED indicators.
- Full isolation works with
- Filter can limit speed ramp
for sensitive controls
- Charge pump safety interlock
- Needs either 7-9V unregulated
DC or 5V regulated DC power supply
- Takes a direction input,
PWM input (generated by Mach on an output pin), and charge pump in.
Dual Relay Board $18
2 x 10 amp relays either AC
VFD Mounting and Wiring
about chips or coolant getting into the VFD's cooling slots, so I'm doing
quite a bit of agonizing over just where to mount it. Most people mount
their VFD's up high on the mill head, but this seems exposed to an errant
chip. Another possibility is to mount mine on the NEMA enclosure along
with the rest of the electronics. Unfortunately this would put it even
closer to where chips are being slung that if I stuck it on top of the
is I will mount the VFD in a box either on the mill (most likely) or on
the wall behind the mill. If I build a flood cooling enclosure for the
mill, I may move the box onto the outside of the enclosure.
Based on the VFD
manual, I need a box on the order of 9" wide x 13" high x 6"
deep. I will likely provide a receptacle on the box for the motor, a 5-pin
connector of some kind for control signals back to the CNC enclosure,
and a cord with twist lock plug back to the existing receptacle I use
for the mill. This box is quite a big larger than the VFD to provide room
I wound up buying
this little NEMA enclosure on eBay from seller electrical_parts for $50:
smaller than the desired dimensions, but not by much. I need to decide
whether to put a fan on the box too.
I'm running a
L200-015NFU VFD. It's good for up to 2 HP motors, and cost about $200.
Rumor has it my CNC4PC motor control board will put out a little voltage
even when Mach3 hasn't commanded it to run, but that the VFD has a programmable
parameter to deal with that. The answer is to select the active portion
of the analog input voltage range. Set parameter A013 to say 1volt (this
is set in a percentage) and set parameter AO15 to 0Hz (this should set
the frequency to 0 Hz when the cnc4pc is outputting any voltage less that
1 vdc (the AO13 value), and turn off the motor. I'll need to remember
to do that when I set up the VFD!
VFD delivers full torque over a 1:10 speed range, so for example with
a 1700 rpm motor I can still get full torque at 170 rpm. The output frequency
range is 0.5 to 400 Hz, so in theory, I could run my motor quite a bit
faster than its rated speed. The problem in doing that for any time is
the motor's bearings are probably not rated for it. The accuracy is 0.1%
of the maximum frequency.
The input signal
is a 0-10 VDC signal, a forward run/stop signal, and a reverse run/stop
signal. This is very compatible with my CNC4PC motor control board which
will output all 3.
1. Make sure the
TM/PRG dip switch is set to TM to accept control from the input terminals.
2. The motor wiring
should be AWG12.
0-10 VDC output
from CNC4PC: Terminal "O"
Ground for 0-10
VDC from CNC4PC: Terminal "L"
CCW1/NO from CNC4PC:
VCC from CNC4PC:
CCW2/NO from CNC4PC:
Since the connections
to run foward (Terminal "1") and backward (Terminal "2")
are NO, and the relay has to close to trigger the spindle, we can assume
that E-stop cutting the power to the motor control board will open the
relay and thereby stop the spindle in the event of an E-Stop.
Here is the overall
schematic for how the VFD is controlled by the system:
and for informational use only. Do not use as a plan for your CNC machine!
I'll be using
22 AWG shielded 6 conductor cable to route the VFD control signals back
to the VFD NEMA enclosure.
Useful VFD Links
Installs a VFD on his Enco Bridgeport Clone
Article on Wiring a VFD to a Mill
One Stop Buy VFD Cable by the Foot