When I purchased the ScanTek 2000 Scan Mill (A rebranded Denford Micromill) from a surplus supply house, the spindle motor was at an odd angle and the drive belt had frayed (probably due to the angle).

When   I took the motor off, it was clear that the problem was a bent bracket.

Since I needed to purchase a new drive belt ( Sherline PN 40040   – $9) I decided to just buy a new Sherline spindle motor support bracket (PN 40020 – $7 ) at the same time because it was relatively inexpensive.
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In part 1 of this series I showed how to get the X/Y/Z steppers moving. In part 2 I hooked up the home and estop switches. In part 3 I got the spindle go relay working so that I could turn the spindle on (at full speed) or off. In this post, I will show how to get PWM speed control of the spindle working.

The Balfor NextMove ST card has an output (SOUT & SGND) line that provides an isolated 0-10 volt signal (at low current) suitable for controlling a spindle motor driver board. (0 volts is stopped, 10 volts is full power) In the bottom left of the picture below you can see the small blue and red wire leading away from SOUT & SGND.

It does this by using a DC/DC converter (NME0512D) to provide an isolated (floating) 12 volts, referenced to the SGND connector. A TLC272C OpAmp chip integrates a PWM signal (taking into account an offset adjustment from R35, the boxy blue variable resistor near the SGND/SOUT pins) into a 0-10 volt signal.

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Now that I have the hardware in place, I’m working on the software side of things. I installed and configured LinuxCNC to control the Mill. (Mach3 was easier to get set up and running initially on the trial license, but they do require you to run windows…and the GUI is a bit garish.) In this video you can see the mill cutting out a circular pocket (in the middle of the air, as I’m testing CAM software, software limits, etc as well.)

You might notice that the belt has been removed between my spindle and spindle motor. When I purchased the machine the spindle motor was at a slight angle, which I traced to a bent spindle motor bracket.   As a new bracket costs under $7, I decided to buy a new one instead of trying to bend my existing one back into shape. The replacement bracket appears to be machined slightly better overall anyways. Until it arrives, I don’t have the spindle hooked up.

In part 1 of this series I got the stepper motors for the 3 axes moving. In part 2 I hooked up the home and E-Stop switches. In this post I will describe getting the spindle motor to turn on (and off!) controlled via the parallel port break out card (I’m using Pin 1).

You can watch the video here, or read the text and see the photos below:

To enable the spindle motor, two things have to be done. First, the Spindle Go Relay (SGR) must be turned on, which provides 120 volts AC to the spindle driver board. Second, the spindle driver board input needs a 10 volt input to turn on the output (to the spindle motor) at full blast. The photos below are of my Dispatch Date 2005 mill, but other mills from Denford are similar in their general operation. [If you have an earlier dispatch date mill, you may have a DIN rail of relays mounted individually instead of this custom PCB of relays. Check out this post for a few photos and info about the SGR in that situation.]
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Part 1 told how to make your computer output commands to the 3 stepper motors controlling the X,Y,Z axes of the mill so that you could jog them around under computer control.

This post deals with getting input from the switches on the mill to your computer.

I am interested in getting input from 4 switches on the mill. First, the Emergency Stop button on the front panel is great to have operational!

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I was trying to figure out what the series of   E 5 L- o P letters on the 7 segment display was trying to tell me ( E, S   o, L   and P are all valid messages, but the L combined with a dash was throwing me. Turns out the 5 was an S and the L- was a T….) A sharp eyed viewer (who wasn’t constrained by having a table of all the possible error codes) commented that it looked like it was spelling out “EStoP” or Emergency Stop, which wasn’t listed in the table.   Sure enough, it turns out that the front panel key switch generates an E-STOP (just as the main E-Stop switch does).

After defeating the keyswitch, the machine gave a single “dash” – on the display, which is a standard “Servo Power Off” state. Continue reading →