Did I find another bug in 1.4.1.4 ? (video)

[Lothar Merl]

Dear all,

yesterday I printed some gear wheels for my hobby lathe, when I noticed a strange print speed on the first layer.

Since the gear should be as accurate as possible, I set the print speed all the way to 'precise' in KISSlicer.
That worked fine for the 2nd and all following layers, but the first layer is printed far too fast. Especially on the perimeter
of every half tooth, the printer 'jumps' leaving a very thin trace of poor quality.
See the video I took: http://youtu.be/YaHKGsXLBk8
You can see the print of the 1st layer teeth perimeter, than the cool down for the 2nd layer and then the slower print speed of the following layers for comparison.
I attached the KISSlicer configuration files (I used the "Kossel" settings) and the zipped up gcode of the gear.

Is this a bug?
Or did I do something wrong?

Thank's!

  Lothar

[Lothar Merl]

I did some research now and learned a lot about gcode on the fly.

I found: The gcode generated by KISSlicer is correct.
Ripped fragments of the gcode containing the strange behaviour run perfect when printed on their own.

There seems to be a problem in the Marlin firmware when it comes to slow print speeds.
I tweeked a little with the firmware settings and reduced the number of calculated DELTA_SEGMENTS_PER_SECOND
which makes the controller much more responding and reduces the speed error.

So: I'm sorry I posted this request here in the KISSlicer group. KISSlicer is fine - the problem is in the firmware.

Thank you!

  Lothar

[lonesock (Jonathan)]

Heh, this is my favorite kind of bug!  The "Somebody Else's Problem" bug.  [8^)

Jonathan