Help with OLD MOST Delta Rep Rap. Print head lifts between columns.

[Jason Beatty]

Hi guys

I recently received an old MOST Delta Rep Rap printer from a retired teacher.  This is one of the pre-Beagle Bone models where we use Repetier host connected directly to the Melzi board via USB.  I'm a newbie to 3D printing, but I'm an engineer and tech geek, so I've learned a ton already.

It prints OK, but not great.  I can't get the calibration quite right.  I did the paper test at each tower and in the center and got all readings within 0.1 mm, but then it printed terribly.  

 

I went through and looked for loose hardware.  I actually found some loose bolts that I tightened, but it didn't make a difference in the performance.

Then, I just adjusted the vertical stop screws until it printed decent, based on visual inspection of the "dog toy" print.  It prints OK, but if I go back and verify the calibration at each column, they vary by +/- 2 mm!   There's also some print size innacuracy, but only in one direction (X vs Y - spot on in one direction, off by 3-4% in the other direction)

Then I created a test "star" with flat legs to see what's going on when printing in between columns (and in between the legs of the dog toy).  Now the print is pretty decent in front of the columns, but the head lifts when printing in between the columns.

Then I measured distances between the columns and found some pretty significant errors (at least it seemed significant).  Between my Y and X columns (as indicated by the dog toy print), the rods are 1.2 mm closer at the bottom than the top.  Also, the space between Z/Y is about 2 mm less than spacing between X/Z or X/Y.  

So, what do you guys recommend?  I've been all through the wiki and can't find any solutions there.  Any ideas?  

Thanks in advance for any insight!  It's much appreciated.  

Thanks,

Jason Beatty

Square One Education Network

[Dr. Bas Wijnen]

Hi,

First of all, you may want to consider getting a newer printer instead.

About your questions: the model of this machine is a Mendel, correct? Those
have a separate motor for each direction (x, y and z). Which means that there
should never be a problem with the scale, unless the machine is configured
incorrectly. I don't see how this can have happened unless someone changed it
though.

If it's using the EEPROM to store the settings, you should be able to change
the steps per mm for each motor so they correspond to reality. If not, you need
to get the firmware source, change the configuration file and flash it into the
Melzi. Did I mention you may not want to bother with this? ;-)

As for reality: the motors have 3200 (micro)steps per revolution. I think the
gear has 16 teeth and there is either 2 or 2.5 mm distance between the teeth on
the belt. This should give you the correct value for steps/mm. For z, the pitch
of the M8 rods is 1 mm, so it has 3200 steps/mm.

Thanks,
Bas

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