Upgraded to metric rods

Hi guys,
one more thing I tried based on some other thread here in the forum about the nozzle bumping into the object once a certain height is reached.

Yesterday, after a relaxing (close to boring) xmas, I bought a 8mm threaded rod and replaced the z-axis rods. Done within an hour, so, not a big deal.

Before the change I printed Mr. Jaws and re-printed it after the change with the same gcode file. What's interesting: I finally got rid of those little waves on edges as you can see on the pics. I think this happens because the M8 nuts simply for much better in their housing of the extruder z-axis assembly.




What's more or less expected is that the object isn't as high as before. I'll need to do some calibration now....
It was 10.8 mm before, now it's 9.85 mm. Assuming, that it's supposed to be 10mm,I'm getting pretty close for the first shot.



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what is the type of rod in their currently?

 

No idea, it's some imperial/inch thread, close to 8mm. I'm printing thing 53688 right now to really see how it's supposed to be.

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For the records: http://www.thingiverse.com/thing:53668 printed in 0.3mm layer height, so pretty rough object, don't take the measures too serious, it may vary by +-0.1, depending on where you measure :

X : 49.1mm (should be 50mm)
Y : 49.2mm (should be 50mm)
Z : 4.9mm (should be 5mm)

I didn't print this with the ootb rods, so I can't tell what the differnce would be, but from Mr. Jaws, it's 1mm per 10mm, so I'd assume it would be around, 5.4-5.5mm.
To me it seems like RoBo _should_ have metric rods, but may be too hard to get in the states.

One serious issue I'm having is that the -z direction sometimes hangs and the steppers make a bad noise. It's caused by the rods being poor quality and the nuts sometimes jam up. I 'll get better (stainless) M8 rods tomorrow morning.

 

I just finished calibration as per http://www.thingiverse.com/thing:53668.
Here's the values that you need for measure preserving prints:

M92 X80.1058 ; calibrate X
M92 Y80.1786 ; calibrate Y
M92 Z2526.2145 ; calibrate Z

You should be using those as starting points instead of the ones on thingiverse. You can save some iterations with it.
I'm now within 0.05mm in all directions. As perfect as it can be for now...

 

The waves are z-ripping, it's caused by imperial rods, and rounding errors in the number of steps, Metric rods round of to even numbers of steps and imperial don't, So some lays are squished more and some are not.
Print a calibration cube.

 

Yes, that's what I figured, quite a difference in quality as you can see.

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I had no idea the threaded rods weren't metric. McMaster-Carr, here I come...

 

I'm looking now. Sadly, the precision rods don't start until 10mm so we have to use non-precision.

I'm going to order this:
http://www.mcmaster.com/#94185a160/=q0rpz9
http://www.mcmaster.com/#94150a355/=q0rqpq

 

Hmm, NM. The 1.2mm pitch results in a repeating number for steps/mm. Looking again.

 

It's not stainless but, at least it has a proper even division steps/mm:

http://www.mcmaster.com/#98861a320/=q0rt92
http://www.mcmaster.com/#93850a320/=q0ru70

Steps per mm should be: ((360/1.8)*16)/1 = 3200 steps/mm

 

Added to the FAQ

 

I tried non-precision, but at least mine have a good probability to hang and jam.

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Will the software settings have to be changed to allow for the finer thread pitch ?

 

No, it seems to be ok as it is. But I'd recommend to run the calibration process described on thingiverse

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It may be ok on yours as I imagine the standard imperial pitch is pretty close to the standard metric pitch but the ones Leon is going for are 0.2 mm per thread difference so surely that will require adjustments somewhere or are the differences negligible

 

Hm, the stainless rods jam as well... need to get some precision rods from somewhere. Any more ideas what could have gone wrong when exchanging the rods? Seems to be pretty straight forward, though...