The CNC software

The software for driving the mill was chosen as Mach3. This has all the standard features to be expected plus a few more. For a few extra pound of outlay a series of Wizards can be bought that will do a range of cycles without first having to draw the part.

There are a number of video tutorials that can be seen on the suppliers web page and these are excellent to the newcomer for setting up and driving the software at its basic and intermediate levels.

A screen shot of the test piece in Mach3

The software needs to be configured to drive the electrics and the main steps are:

Chose the units of working, inch or millimeter,

Assign the pins that will carry the step (pulse) and direction signals from the computer to the breakout board, and

Tune the motor drive characteristics to get smooth running.

The choice of working units is only done the once and will probably be decided by the machine being driven whether it's a metric or imperial leadscrew as this will determine how the stepper motor revolutions and therefore steps relate to actual movement. (Although it is possible with micro stepping to get a metric leadscrew to work in inches to reasonable accuracy)

The assignment of pins can be altered at any time but once set are unlikely to change. The pin numbers are those relating to the 25D parallel port connector and the breakout board is designed to correspond to these same pin numbers. As the computer parallel port is an internationally standardised connection certain pins are designated for output from the computer and some are designated as inputs. Within the software configuration for "ports and pins" the motor axis output pins are defined, one for step (pulse) and one for direction. The port definition is standard as port "1" although a second parallel port could be added if the computer has one. The tutorials give good guidance on how such a second port might be set up, but for most like me there will be the one port only.

Having assigned pins to an axis it is of course then important that the breakout board's pins are actually wired to that axis motor driver and not a different one.

With the assignment completed and wiring checked it should be possible to switch everything on and drive the motors using the "jog" control in the software. The jog control can be operated either by the mouse on a screen button or by assigned keyboard keys which is by far the easier of the two to use.

At this time it becomes important to appreciate the way the signals to and from the computer work as it is possible nothing will happen when first switched on. The signals are termed either "active high" or "active low". What this means is that when something is happening i.e. "active", the signal when that something is "active" will be 0 volts or "low" or 5v and "high" depending on how the hardware is wired. By way of further explanation, when a signal goes open circuit e.g. a switch opens (like a limit switch operating and therefore being 'active') the computer pulls the signal voltage up to 5 V which would make it "active high". When the switch is closed (in its normal state) the 5V signal is "earthed" and therefore become 0 v or "low". Within the software the pins can be configured to be in either state so as to match the hardware conditions.

The Emergency Stop is the very first thing that has to be configured as that determines the ability to "reset" the software or machine. Without any input signal coming from the hardware the signal has to be set at "active low", i.e. a tick in the box not a cross. My E Stop switch was configured as normally closed and went open circuit when pushed which meant the signal was "active high" when operated and thus needed a cross in the assignment box when the computer was connected to the hardware. If I were running the computer unconnected then the pin setting had to be changed to active"low" so the software would reset and run. (There is a big reset graphic switch on the display). Again the first video tutorial covers this in some detail.

The motor drivers may require either state "low" or "high" depending on manufacturer. The Arc Euro Trade drivers require the signals to be set active "low", i.e. a tick in the box (however when the breakout board was changed they had to be set to "active high"). With these settings the motors should operate under jog control. (As far as pulses are concerned there is little difference between active 'high' and active 'low', however the difference may be significant as the pulse width will be seen as either a narrow pulse or a wide pulse by the driver).

At this stage the motors may be turning but not sound to good or be smooth running. However they may not be running at all ...... well some of them might not. In my case I found that I had a problem with the breakout board as some pins would not configure as step (pulse) pins but configure as direction pins. Which confused me quite a bit until I realised what was happening. I managed to get three of the four drives working but ran out of pins that would give the step signal so the fourth drive initially was not commissioned until help was sought from CNC4PC which was readily given. (See page 2).

To get my three drives running smoothly the motors had to be "tuned" using step, velocity and acceleration configurations in Mach3. The step figure is calculated as a result of the micro step setting on the motor driver and the TPI of the leadscrew to give the total number of steps per inch of travel (or millimeter of travel if you are working in metric units). The velocity and acceleration is set by "graphical sliders" to give the maximum velocity (rpm) and start/stop profile or acceleration to max velocity and deceleration from maximum velocity to stop. This is a suck it and see exercise and the sliders are tweaked until the motor sounds right without missing steps and runs smoothly from start to stop.

With the changed breakout board (see page 2)all four drives were successfully commissioned.