1 Topic by spapadim (edited by spapadim 2013-06-17 15:34:51)

  • spapadim
  • Member
  • Offline
  • From: Jersey City, NJ, USA
  • Registered: 2013-05-16
  • Posts: 185

Topic: ZWobble guidelines

I've been playing with the zwobble software fix, and trying to tune it, but I'm not getting far, so I'm beginning to wonder if I'm looking at the right place (or should instead be looking at x/y axes).

I tried to find examples of what to expect for z-error, but couldn't find any, so I thought I'd ask. This is the movement error curve I get (thick blue line):
http://imageshack.us/a/img543/941/80d3.png
Measured with a depth gauge (and Ian Johnson's excellent mount), with .1mm moves.  For the life of me I cannot see a clear, strong periodicity, sinusoindal or otherwise.

Sure, there are two modes, but doesn't look like these are sufficient?
http://imageshack.us/a/img526/7061/ux2.png

I should note that these are with the new aluminium platform + this: http://www.thingiverse.com/thing:100053 .  My walls are decent:
http://imageshack.us/a/img703/764/i635.jpg
but still not perfect (a bit blurry, but see corner edges):
http://imageshack.us/a/img829/8628/9wsb.jpg

Any feedback/suggestions on diagnosis and how to proceed (or not) would be appreciated!

2 Reply by mconsidine

  • mconsidine
  • Member
  • Offline
  • From: Randolph, VT
  • Registered: 2013-03-07
  • Posts: 122

Re: ZWobble guidelines

Just so I'm clear on the y-axis : is that a movement of +/-10 microns you are seeing?  That seems pretty good to me, though I haven't yet tried to measure my z-axis wobble.  I'll probably wait until after the M5 upgrade for that ...

3 Reply by elmoret

  • elmoret
  • Filastruder
  • Offline
  • Registered: 2012-10-11
  • Posts: 6,048

Re: ZWobble guidelines

Yeah, 10 microns is probably within the error bounds of your measurement device.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

4 Reply by tealvince

  • tealvince
  • Member
  • Offline
  • Registered: 2013-01-16
  • Posts: 319

Re: ZWobble guidelines

Even with the poor precision of the depth gauge, it looks like you need compensation at a phase of either 0 or 180 degrees, and can experiment with various amplitudes at both of those phases.  To get better precision, you can use the laser pointer mount I made if you have a laser pointer handy and the associated directions:

http://www.thingiverse.com/spapadim/col … ing-231747

5 Reply by spapadim

  • spapadim
  • Member
  • Offline
  • From: Jersey City, NJ, USA
  • Registered: 2013-05-16
  • Posts: 185

Re: ZWobble guidelines

Thanks, good to know!  Yes, I've been meaning to try that too, but I've lost my laser pointer.  Might go ahead and buy another -- in which case, which pointer are you using (might as well go with one that's guaranteed to fit your design)?

tealvince wrote:

Even with the poor precision of the depth gauge, it looks like you need compensation at a phase of either 0 or 180 degrees, and can experiment with various amplitudes at both of those phases.  To get better precision, you can use the laser pointer mount I made if you have a laser pointer handy and the associated directions:

http://www.thingiverse.com/spapadim/col … ing-231747

6 Reply by tealvince

  • tealvince
  • Member
  • Offline
  • Registered: 2013-01-16
  • Posts: 319

Re: ZWobble guidelines

spapadim wrote:

Thanks, good to know!  Yes, I've been meaning to try that too, but I've lost my laser pointer.  Might go ahead and buy another -- in which case, which pointer are you using (might as well go with one that's guaranteed to fit your design)?

It was just a cheapie no-brand combo pen/laser I got off ebay.  It's slim, but you can use almost anything and just tape it to the outside if it doesn't happen to fit.

7 Reply by spapadim (edited by spapadim 2013-11-10 04:14:17)

  • spapadim
  • Member
  • Offline
  • From: Jersey City, NJ, USA
  • Registered: 2013-05-16
  • Posts: 185

Re: ZWobble guidelines

Just for the record, I *did* finally(!!!) get around to measuring with the laser pointer jig (while re-installing the well nut) and, yes, there is a periodic pattern.  Here are the new measurements:

https://docs.google.com/spreadsheet/oimg?key=0Ajh3Mupk84uIdHhmbUU2M0JMTHc1cVQ0alBvNGhTa0E&oid=1&zx=na54925tbjc6

The y-axis numbers in the plot are actual wall measurements (about 10-12ft away).  I advanced the axis in 0.1mm steps, for three periods, and then used my calipers to measure each period twice (the legend Dn/m stands for delta-step on n-th period, m-th measurement, and last two curves are mean and median). 

As you can see, with a freshly installed well-nut, the error is on the order of a few (~5) microns, so it's indeed below the accuracy of the dial gauge + mount (perhaps the wiki instructions should point out that dial gauge may not be accurate enough?).  Also, it's not perfectly repeating, but taking avg/median of a few periods and measurements gives a clear pattern.

Still, even though it's a few microns, the z-wobble fix helps very noticeably.  Here is the proof (full size):
http://img18.imageshack.us/img18/1459/snhz.jpg
Right is w/o fix, left is with fix, back-to-back prints, 0.2mm layers. FWIW, I used the cumulative sum of the above median values in my start gcode.

I hope this info is useful to others, and thanks for the great work on the firmware fix!