Layer height in reation to z-axis micrsep

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cbensch
Posts: 54
Joined: Fri Jan 24, 2014 9:52 pm
Location: Simsbury, Connecticut US

Layer height in reation to z-axis micrsep

Post by cbensch »

I'm having issues with my filament bulging every 4 or 5 layers. So I did some reading and found an interesting article that talked about how it is critical that the layer thickness is a multiple of the z-axis lift per microstep. It involves knowing how many microsteps the motor has and the diameter and pitch of the Z screw. Has anyone done the math out?

Also, I see there is a Firmware Configuration in Repetier Host for steps per mm. This seems like a very crucial setting.

My printer is a 2.0 with the 3.0 upgrades - single extruder.

Here is the article: https://www.reddit.com/r/3Dprinting/com ... ltiple_of/

Dreide
Posts: 176
Joined: Sun Sep 29, 2013 12:32 am
Location: Lausanne, Switzerland

Post by Dreide »

cbensch wrote: Here is the article: https://www.reddit.com/r/3Dprinting/com ... ltiple_of/
Interesting. Thanks for the link.
I don't think that this is relevant with the Felix though, because we have 0.01mm/step, so the usual layer heights (0.1, 0.15, 0.2, 0.25) are all multiples thereof, provided that the µsteps/mm firmware setting is left at 1600µsteps/mm; but why would one ever want to change this? Does anybody know the tolerances of the Z spindle used in the Felix?
Irrespective of this, I don't think that the reason given in the post of why the layer height should be a multiple of full steps is quite right. It is not because the motor will then always "stop" at full steps but it rather is because the motor will always stop at the same µstep position relative to the next full step. This can be at full steps but does not necessarily have to be so. Why? Because of Z homing! The homing position might be at any µstep position and not just at full step positions (at least that is how I interpret the Repetier firmware code). So there will be a µstep offset which we cannot control (unless the firmware provided an option for it).
One other potential source of irregularities in layer height is the heated bed. The height of the bed slightly depends on the bed temperature, which is why it is important to get the control parameters for the heating right.

cbensch
Posts: 54
Joined: Fri Jan 24, 2014 9:52 pm
Location: Simsbury, Connecticut US

Post by cbensch »

Good info. I have read about the heated bed being an issue as well. The odd thing is that the cyclical expansion and contraction of these layers lasts through the entire print. I printed a small tube that was just about the full height of the printer's capabilities and the layer oddities continued to the top. I can't see the bed temperature being an issue at that height. Agree?

This z-ribbing or z-banding (as some have called it) is very frustrating. I've checked my belt tension and all screws to make sure they are tight. Nothing mechanically seems to make a difference. I'm going to try different parameters in slic3r and see if that changes anything.

Dreide
Posts: 176
Joined: Sun Sep 29, 2013 12:32 am
Location: Lausanne, Switzerland

Post by Dreide »

cbensch wrote:I can't see the bed temperature being an issue at that height. Agree?
Depending on which change in bed position (and tilt) is caused by bed temperature, the effects at high Z can be everything. In the simplest case, the bed moves up and down (relative, with respect to the gantry), which would cause the same effects at all heights. But the bed could also be tilted (e.g. with the 2 off-center holding screws being the tilt axis), in which case the effect would even be bigger at high Z due to a longer lever arm. And it can be a mixture of different position/tilt changes.
I think the most common reason for Z banding is a wobble in the Z lead screw, see here http://www.soliwiki.com/Banding. They also mention temperature swings in the hot end, bot these are usually rather high frequency and depend very much on what exactly is printed, so it would not cause very regular patterns which need several layers to repeat.
In order to rule out the bed heating as a cause, just print a test piece with and without bed heating and see if it makes a difference. You can also just shut off bed heating during the print, which should stop the repeating pattern then.
Patterns caused by imperfections of the Z lead screw would repeat after 2mm height for the Felix, because the lead screw has a pitch of 2mm/turn.
Felix 2.0->3.0dual * Repetier (host+firmware) * KISSlicer Pro, Simplify3D * Cubify Design

Karsten Beck
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Joined: Thu Jun 15, 2017 1:38 pm

Post by Karsten Beck »

I've exactly the same problem with my new Felix 3.1 printer: Every 2mm the layer expands in X- and Y-direction so that every object has "riffles". I found that the screw wobbles on the spindle and I'm pretty sure that this is the reason.
I've just ordered a new screw at my distributor Comprise and will try whether this solves the problem. I'm hoping that it's not the spindle...

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