Software setup
Ripper is entirely controlled by Artsoft MACH 3.
This piece of software is already quite out if date, and has some strange bugs in it. However MACH 3 can be easily configured to fit almost any machines needs.
If you don’t know what MACH 3 is you can look it up on their website. Basically it’s the control software which generates the step and direction pulses out of pre-calculated NC-code (from a CAM software) and send them over the parallel port of the computer to (in my case) the Gecko G540 stepper driver.
When setting up MACH 3, the very first thing which has to be done is the setup of the parallel port and on which signals are which axis and limit switches.
After that the A-axis (or 4th axis) must be slaved to the X-axis, so the a-axis does exactly the same as the x-axis because of the dual screw system.
Next, the limit switches must be setup very carefully, because they help to avoid any damage on the machine if you accidentally press the wrong direction when moving the machine, or your code exceeds the machine bed during progress.
The G540 allows limits for all axis + one emergency stop.
The limit switches for each axis are just connected in series, so the upper or lower limit can’t be logically differentiated. Actually it would be enough to connect all limit switches of all axis in series, but I won’t recommend that as MACH 3 can’t differentiate which axis caused to limit then.
To verify the proper operation of the limit switches I triggered them manually by hand first.
Afterwards I set up the spindle top speeds and acceleration values. I did not test how far I could go up with the top speeds, but I honestly prefer a little bit slower jogging machine, because I am afraid to collide with something if it jogs fast.
The final step is to let MACH 3 know how many pulses are required to move the axis a certain distance. This step must be done very careful, because every mistake here makes every milled part out of size.
To do this I told the calibration utility to move 1 mm first. ( then the axis moved about 200 mm in my case – after it moved, I had to report how many millimeters that actually were. So I repeated this step, till I reached 160mm calibration length, which is the maximum measuring range of my caliper.
To check my calibration I placed my dial gauge in front and verified 5mm movement.
Software and Hardware limits, and what they are good for
When I was researching around the Internet for ripper, I was really disappointed that I couldn’t find any information about this question.
Basically all what the Hardware and Software limits are good for, are to protect the machine from serious damage in case of malfunction or wrong user input. It is however somehow possible to abuse the limit switches as a reference source for the axis, but as the hardware limit switches are still physical ordinary tactile switches they are no reliable source for reference.
When powering up the machine, MACH3 can’t know where the axis are positioned, and thus it requires some kind of calibration to know again at which position then axis are.
The process I am describing is call “homing” – this function is already programmed into MACH3. When homing the machine, one axis after the other moves slowly till it reaches a hardware limit switch. Using this technique MACH3 knows the approximate position of the axis again (depending on the used limit switches).
However this method is by far accurate enough to let the machine move automatically to the Z-length depth probe, to receive a reliable z (up and down axis) calibration, which is the most important when milling out a workpiece.
MACH3 is also capable to handle so called software limits, which have exactly the same job as the hardware limits. The software limits are typically a couple of millimeters tighter them the hardware limits, and should help to avoid collisions with a longer tool as normal into the machine bed for example.
When reaching a software limit MACH3 performs exactly the same reaction as when reaching a hardware limit switch: the spindle is stalled with the highest deceleration as possible, which is not very healthy for the bearings and ball-screws.
However the software limits can only be used, after the homing was performed properly using the hardware limit switches.