3D printer progress – assembly and test

At this point the frame is largely assembled. The carriages are mounted, the heated bed is installed and things actually move (at least manually).

I used a MK2A 300x300mmaluminum heatbed and had to move the motor motor and leadscrew mounts. The motors need to move out from the back as well. This is a good thing as otherwise the motor move would interfere with the 3×3 triangles. Flipping them over fixes that issue. However the smaller top 3×1 brackets do need to get trimmed for clearance. This was a quick trip to the band saw. .

The first piece to get moving is the bed elevation. The critical part of the motor alignment is at the bottom end. Need to get the motors under the drive screws. Sight along the frame to see that the screws are parallel to the legs in both directions and then tighten them down. The safety stops in the firmware need to be over-ridden as normally you can’t move the  axes to a negative position. In this case, negative is UP . So in Configuration.h make the changes as shown below to get the over-ride for testing and the homing directions:

// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1 // left
#define Y_HOME_DIR 1 // rear
#define Z_HOME_DIR -1 //top

You need to comment out the block below. It prevents the use of the max direction endstops. It took a while to find as I was troubleshooting why X&Z would home nicely but Y would not do any homing movement at all.

// Disable max endstops for compatibility with endstop checking routine
//#if defined(COREXY) && !defined(DISABLE_MAX_ENDSTOPS)

#define min_software_endstops false // If true, axis won’t move to coordinates less than HOME_POS. — allow for testing
#define max_software_endstops false // If true, axis won’t move to coordinates greater than the defined lengths below.

This will allow moving the bed upwards under manual control.

I also made the initial settings for the stepper calibration. I am using 32 step microstepping (rather than the more typical 16), 8mm pitch threaded rod and a Micron EME cobra extruder. So the step calibration at this point looks like:

#define DEFAULT_AXIS_STEPS_PER_UNIT   {200,200,812,1168*2} // 32 microstep 16 tooth gears, 8mm acme rod & micron extruder

Belt installation was straightforward, but make sure to place a screwdriver blade behind the nuts for the clamp bars before inserting the screws. It is far to easy to push the nuts back and have them fall out as you attempt to clamp the belt to the carriage.

Currently all 3 axes are moving, and homing. Calibration still needs to be checked.

I was also configuring the temperature sensors to get the thermistor for the heated bed to work and get ready for print head testing. I am also running a thermocouple for the print head. I want to run thermocouples for the print head to use high temp plastics such as Nylon. The low output signal from a thermocouple requires an additional amplifier or special A to D convertor.  I had purchased the Max6675 thermocouple digital adapter. However, it turns out it is not compatible with having a 128×64 display!!! There are shared conflicting pins. NUTS!. Now I have to order some AD597 adapter analog boards (and wait for them to come form China, as I could not find any stocked in the US).

When I started the project I downloaded the Marlin software directly. I would have been better off starting with the package on the d-bot page (or at least using the configuration.h file). It was in a line by line comparison that I found the Y axis homing culprit. http://www.thingiverse.com/thing:1001065/#files   and select d_bot_marlin.zip

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