MPCNC part 5

By telleropnul, June 7, 2019

GCODE maiden flight

Some important Gcode instructions:

G20 = everything is in inches
G21 = everything is in mm

G90 = everything is in absolute coordinates (go to coordinate position)
G0 X30 = move to absolute X coordinate position ’30’ on the X axis.

G91 = relative coordinates (move relative from current position)
G0 Z30 = move 30mm vertically up relative to current position (= positive Z axis value)

G0 F600  = set feedrate to 600mm/min for all subsequent move commands = 10mm/sec = 1cm/sec = slow
G0 F6000  = set feedrate to 10cm/sec = fast

I have connected both Y axis stepper motors to logic board outputs ‘X’ and ‘Y’.  As I have not yet flashed the firmware for the GT2560 v3 logic board, so ‘X’ and ‘Y’ need to be driven in pairs in my Gcode.  Also, as I haven’t yet set the steps per mm in the firmware, movements may not be true to scale.

The following commands allowed me to carefully test my MPCNC successfully:

G0 F600
G0 Z10
G0 Z-10
G0 X10 Y10
G0 X-10 Y-10
G0 X300 Y 300
G0 X-300 Y-300
G0 F6000
Repeat instructions and experiment with values.

All I had to do was flip one of the stepper motor connectors to make it turn in the opposite direction.

Now it is time to start wiring the stepper motors to the logic board more permanently using crimp connectors and extension leads.

Wiring harness

I would have liked to purchase parts from the webshop, but shipping from the US to remote Australia is expensive.  So I had to invest in some crimping pliers and various crimp connectors.

I recommend purchasing a Dupont header connector kit.

I successfully used long nose pliers to crimp some of my Dupont connectors in combination with a magnifying glass and a sheet of white A4 paper as backdrop for better visibility, but a “SN-28B” model ratchet crimper tool is recommended.  I purchased an IWISS “SN-2549” model ratchet crimper tool that has a better quality die set and can crimp AWG18-28 wire connectors.

Higher AWG value = smaller diameter wire:  American Wire Gauge (AWG) chart.

NEMA stepper motor wire is about AWG22-24.

Here is a brief instruction video how these type of connectors are crimped (poor quality, mute sound)

Crimping Electronics Connectors (Dupont, PH, XH, VH, KF2510)

X, Y, Z

The GT2560 v3.0 logic board uses JST XH 2.5mm pitch 4-pin connectors for the X, Y, and Z axis stepper motor outputs.  I ordered some JST XH ‘pigtails’ and crimped Dupont 2.54mm pitch male connectors to the open ends.  This allowed me to connect them to the stepper motor leads easily.

(E0), E1, E2

I prefer to connect each stepper to its own output rather than creating a series cabling wiring harness.  In my case this means I will have to use the extruder stepper motor connectors, which are connected to Molex Micro Fit 2×6 connectors:

<insert picture>

Stepper motor extension leads

You can use 22AWG 5 wire trailer cable, 4 wire security alarm system cable or IPC rainbow flat ribbon cable.  I found some 1 meter long 4 pin Dupont extension leads (male to female) on the internet.


Steps per mm

A4988 = 1/16th microstepping
DRV8825 = 1/23 microstepping
NEMA17 = 1.8 degrees per step = 360 degrees / 1.8 degrees = 200 steps per revolution

X, Y axis

GT2 Belt pitch = 2mm
Pulley 16T = 16 Teeth

Steps per mm = (Motor Steps per Revolution * Driver Microstep) / (Belt Pitch * Pully Number of Teeth)

Steps per mm (A4988) = (200 * 16) / (2 * 16) = 100
Steps per mm (DRV8825) = (200 * 32) / (2 * 16) = 200

Z axis

A lot of the leadscrews state they are 2mm pitch, but dont say how many (start) leads they have, most are 4 lead, meaning 4 seperate threads.

T8 leadscrew (8mm diameter, 4 start leads, 2mm pitch)

Steps per mm = (Motor Steps per Revolution * Driver Microstep) / ( Leadscrew Pitch * Start Leads )

Steps per mm (A4988) = (200 * 16) / (2 * 4) = 400
Steps per mm (DRV8825) = (200 * 32) / (2 * 4) = 800





















Cable drag chain solution

DIY Cable Chain Looks Great, Stays Cheap

<to be continued>

Totem corner rethink

You will require 4 X m5 bolts @ 95mm in length,or 100mm will be fine.

To do list:
“Note that if EEPROM is enabled, saved values will override these. steps/mm”
Emergency stop
Drag chain / tape solution
Install 5x DRV8825 + Vref (measure pot to ground)
Logic board fan JST PH 2 pin
Extension cables: longest length to corner of table is 5 * 30cm = 150cm = far less than 1 meter = wait for 1 meter 4pin dupont cables I ordered
Marlin firmware to drive current X + Y motors and E1 + E2 as a single axis + step/mm
MKS Gen L + Pi enclosure (+LCD touch color + SD Card) + T slot rail mount ?
Convert to ER11 using “ER11 6.35mm collet” or “C6 ER11A 60L”