MPCNC Testing

The MP CNC (Mostly Printed CNC) is now working and being tested as a pen plotter before attaching a rotary tool. There have been some interesting problems. To find out more about those and my recommendations read on.P1010718   One of the first problems I ran into when testing the electronics was trying to find a parallel port cable. The first one was made using ribbon cable and a crimp style connector. At first it appeared to operate correctly. The red fault light went out when the cable was plugged in, showing that the G540 controller was receiving a charge pump from the computer, the motors had a holding current and the Mach-3 software detected that the controller was connected but when the G-code commands were sent the motors didn’t move. Mach-3 showed the changing position on it’s display that it believed had occured but nothing happened. After re-installing the software and drivers, trying to use a USB to parallel port replicator (drivers no longer supported), re-checking the power supply, motor connections and computer the problem was eventually found. A test of the cable revealed that only a few wires were connected, the charge pump, fault (output to PC) and grounds.

An old parallel cable was eventually located and things started moving.

Then a new problem emerged. One axis had trouble operating intermittently. A close inspection of the wires revealed damage that had occurred in transport or during manufacture.P1010627   After the wires were cut and spliced the axis moved just as well as the others.P1010628   Finding a good CAM software to create the G-code is still in progress but EstlCAM works quite well.P1010718   The curvy software is a good test of the machine and has also found the 500-line limit of the Mach-3 trial software. The Mach-3 software is a bit over $200 to buy. Not too expensive and works well with a lot of support and plenty of users however it does look like it was designed in the 90s with little changed since and it is still targeted at using the parallel port to output the control signals. This can be affected by other software running on the computer and does not work well with port replicators or converters. There are a number of good controller options starting to emerge like Smoothieboard, that can use either a USB or an Ethernet connection, though there isn’t a real stand out yet that has been adopted in large numbers like Mach-3 and the parallel port was.

The EstlCAM has the option of also work as a control software using an Arduino as a USB controller, which may work out as a good short term option.

P1010631    This image shows another problem that showed up. My recommendations – Don’t make the IE (International Edition) MP CNC – the 25mm outside diameter tube was harder to locate than the 3/4″ OD tubing would have been, it also caused galling on the vertical z-axis tubing where the horizontal spinning bearings dragged. This had to be fixed by filing a few flats on both z-axis tubes to clear.

P1010620   Care was taken to make the flats where the x & y-axis bearings were and keep the OD untouched where the z-axis bearings rolled.

P1010622   The lead-screw and nut for the z-axis was also swapped back to an M8 threaded rod & nut to improve it’s operation. The speed of the lead screw pitch was more suited to a 3D-printer but since this machine will be milling the M8 threaded rod, with a 1.25mm pitch, is slower but transmits a higher force.

P1010719   This custom adapter for a Dremel style tool will go on next. I have a few blocks of extruded foam to start on before trying harder material.

If you are interested in building a MP CNC there have been a few updates to the design so download the latest files. I think ABS, PET or PC would be tougher than PLA material. I also recommend finding your tubing first to check that you can get the correct OD before starting. If you do print the IE, I hope the bearing clearance has been fixed or print out some small shims to add clearance.


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