Alternating layer height

Hi me again,

I am having an issue with height and have discovered that when printing there is a issue with power to the z motor every other z adjustment, I have tried various firmwares and they all seem to have the same issue. I have swapped around drivers changed pmeter untill my power supply shuts down with under current protection but nothing resolves it. My x y and e drivers are all at about 25% so i don't think upping the pmeter is what is needed. Seems if I slow down the print it is not so bad but the 20mm cube does'nt seem to move at all where as the 40mm tower has the alternating issue at 16mm/sec. I can't find anything on a search so figured this is a ramps issue?

attached my two gcode filesfiles.zip

Is this from Skeinforge? You maybe going too fast on the z-axis. Did you turn on the Limit option? A limit of z of around 1 mm/s would be a good start.

The layer heights look fine in your Gcode, and I'd expect solid state electronics to be pretty consistent (barring marginal connections). Perhaps dirty or bent Z axis screws causing lost steps, or some other mechanical sub-optimality.

Solved,

brnrd, your a gem thank you. Didn't spot that setting on the z for limit and it was turned off. Once again thanks. Thanks Dale, the machine is quite free on the z-axis.

cheers
rob

I know you say this is solved but I just thought I would add that your Z must be some what tight. Mine was tight and I had to limit the speed to 75mm/s until it was loose and now it moves at 150mm/s. The transition between layers is so fast that I get almost no ooze. It may only be possible because I am using teacup and it has acceleration.

brnd pointed out these are actually mm/m (mm per minute) not mm/s

Edited 1 time(s). Last edit at 04/16/2011 03:53PM by Sublime.

Seriously? Your z stage moves at 150mm /sec! my god that must mean that your stepper is running at 120 RPS or 7200 RPM! You sure about that?

Your math looks to be correct and that does seem impossible but like I said it has acceleration, so it starts at 0 and ramps to 150mm/s but for only .4mm per z stage move so its just a burst of movement. I would imagine it does not reach the full speed in that short of distance. Any movement over 10mm will overheat the pololu driver running at 75%. I know how hard this is on the driver but I slowly increased the speed until it would move as fast as possible to make the ooze as little as possible. Also the gearing on my z stage is 1:1 on nc20 rod and I only run it at 1/2 stepping.

This is a line from the gcode I generate:
G1 X11.14 Y4.36 Z3.8 F30000.0 E0.0245

And these are my config settings:
/// used for G0 rapid moves and as a cap for all other feedrates
#define MAXIMUM_FEEDRATE_X 2000
#define MAXIMUM_FEEDRATE_Y 2000
#define MAXIMUM_FEEDRATE_Z 150
#define MAXIMUM_FEEDRATE_E 250

/// used when searching endstops and as default feedrate
#define SEARCH_FEEDRATE_X 100
#define SEARCH_FEEDRATE_Y 100
#define SEARCH_FEEDRATE_Z 75
#define SEARCH_FEEDRATE_E 30

I guess this means we can no longer talk about feed rates the same with acceleration.

@hexitex - you're welcome.
@sublime - The units in the firmware code is in mm/min, not mm/s. So your firmware limit is 2.5 mm/s which is still pushing it but more reasonable. But did you actually check to make sure it can move this fast throughout the whole range of z-axis movement? Your x and y max is on the slow side. It can easily go at 3000 mm/min and higher.

Edited 1 time(s). Last edit at 04/16/2011 03:55PM by brnrd.

@brnd
Thank you for straightening that out for me (and likely others). It really make me wonder why the default settings in teacups ramps config is set as follows:

/// used for G0 rapid moves and as a cap for all other feedrates
#define MAXIMUM_FEEDRATE_X 200
#define MAXIMUM_FEEDRATE_Y 200
#define MAXIMUM_FEEDRATE_Z 100
#define MAXIMUM_FEEDRATE_E 600

/// used when searching endstops and as default feedrate
#define SEARCH_FEEDRATE_X 50
#define SEARCH_FEEDRATE_Y 50
#define SEARCH_FEEDRATE_Z 1
// no SEARCH_FEEDRATE_E, as E can't be searched

I feel kind of stupid, I just assumed they were mm/s because that's what the gcode produces and the default sizes being 200mm/s made more sense than 200mm/m that's just stupid slow. After increasing them 1000% I thought there was something weird going on. And yes my z/stage can move at the 2.5mm/s second except the driver overheats and goes into protection mode after about 10mm so I just don't auto home the Z and its no problem. As for the other speeds being slow, they are not moving nearly as fast as possible. I have only been printing for one week and I'm still tweaking settings. Once I get it printing accurate sizes I plan on printing a new extruder, my current extruder is bodged together from old printer gears and only has 2.35:1 gearing so I don't have enough torque to extrude any faster which then limits my other axis speeds.

Any idea why we use mm/s in one place and mm/m in others, it seems really.........ummmm....

[geometricobjectdepositiontool.blogspot.com]

Edited 1 time(s). Last edit at 04/16/2011 03:55PM by Sublime.

I think g-code, which came from the CNC world, specifies rates are specified in mm/min. But Skeinforge uses mm/s. I don't know why that is.