Z axis remains lifted when using homing for x and y axes after each layer

Hi all,

I have had this issue of layer shifting even after slowing down my print speeds and accelerations to near zero speeds. The solution I found after weeks of searching on the net is to home x and y axes after each layer. This is done by entering G28 X0; and G28 Y0 in the "after each layer" tab in Sli3r. Seemed pretty good to me. The only problem, my printer started printing in mid air. When I viewed the code in Pronterface, it showed that the z positioned before homing of x and y axes. I think that this is the root of the problem. At the start of each layer, the x and y axes should home first as their homing causes the extruder to lift up. This should be followed by the positioning of z axis.

The solution, I think, is to home x and y axes "before" each layer. This can be done by entering G28 X0; and G28 Y0 in the "before each layer" tab in Sli3r.. Will be doing as soon as I get time. I will post the results thereafter. Any comments are welcome.

You could use G92 Zxxx to relevel Z-axis "after layer", but I'd rather try to sort out the layer shifting.

Yeah, o_lampe is right, makes much more sense to fix the layer shift issue than to apply a (sort of) fix as a bandaid. You'll still have issues with layer shifts since the shift is unlikely to happen right at the end of your layer, right before you home.

1. Any advice on how to counter the layer shift then? I've slowed down my prusa as follows: max accl: 500; max jerk:7.5 for x and y axes. Max speed is 60mm/s. On top of this, I put the print speed to 40% while printing with pronterface. Do you propose slowing it down further? Or are there any other methods to combat layer shift?

2. I printed with homing "before" layer change and it did work. Now my printer is not printing in mid air. Still, if someone has a better idea then this band-aid solution, I would be grateful. Thanks.

OK guxys, my layer has shifted despite homing after each layer. I'm at my wit's end in here.

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Vatsal J Tanna
OK guxys, my layer has shifted despite homing after each layer. I'm at my wit's end in here.

If you are having a layer shift during a print it is typically one of a few things:

Your stepper is not strong enough to move and/or it has a "strike" on a printed section of your part.
* Your stepper current is not high enough
(but increasing it may just make your print head bash the part over and dislodge it!) Make sure you aren't striking the part during the print.

Your stepper rate is too fast and you are skipping. You have already slowed your rate down, so this doesn't seem likely.
You would hear a "buzz" somewhere if this was happening.

You have a mechanical issue that is causing one of your axis to skip or jam at some point. I have had bearings cause this on a printer.
Listen for a "gronch" sound that tells you a mechanical condition may exist.

You have too much current set and your stepper driver is overheating and skipping steps.
A fan of any size blowing air over the driver chips will solve this.

I wish you all the luck on your troubleshooting. I recommend that you watch what is happening very carefully and see if you can better characterize what is going wrong.

DLC

Like I said, re-homing after each layer is only going to help if you layershift right at the end of your layer. Turn your printer off and move each axis by hand. Does it run smoothly and move easily? If not, there's your issue. Also, check belt tension. Too loose and the pulley could be skipping teeth (does it always layer shift a specific distance?), too tight and it would be putting too much load on the motor and stalling it. Lastly is, depending on how drastic your layer shift is, your drivers could be overheating and temporarily shutting down during the print, try adding extra cooling.

What axis is the layer shift occurring on? One? Both? Does it shift by regular or random amounts? Is it a shift of the layer or does one axis seem to shut down entirely for a brief period of time?

Layer shift is happening on both axes. I've posted the picture along with this message. Things I'll do in my next print:
1. Oil both the axes
2. Put an extra fan to cool the motor drivers.

One thing that boggles me though is that as you can see in the picture, the shift is progressive i.e. the distortion increases after each layer despite the fact that x and y axes are homed before each layer. This just doesn't make any sense.

Friction in the axis could be due to more than just a need to be oiled. You bearings could be busted, the rails could be misaligned (so could the bearings), etc. Check how the movement is first. If it's grating in a specific spot, or just everywhere, these sorts of things will help you narrow down the issue.

Overextrusion is another cause for shifting. Does the nozzle scratch over the survace when the print builds up? Then you have to calibrate e-steps ( again )

As I said I would, I did the following 2 things
1. Oil the axes
2. Keep another cooling fan to cool the ramps 1.4

I printed the Nautilus gear and the print has come out fine. Thanks guys. I think I'll experiment further with bigger prints but the problem seems to be solved.

It's wierd, looking at the print it looks like it twisted. Usually a layer shift is in one direction. Makes me think it's something like the bed surface rotating. Do you happen to be using some type of removable bed, like glass? Is it properly fastened down so it can't move?

Upon aluminium bed (which I never heat) I place a sweet box's cut out. On top of this, I stick a label paper (not sure what it is properly called) with a glue stick such that the label paper's sticky side is facing up. This setup is fastened with the use of paper clips. It might be that the setup was not fastened properly during that time. But I seriously doubt it. Since I've oiled the axes and added an extra cooling fan for the arduino, the same bed setup is giving me fine prints. I'm not an expert, so I really don't know what happened.

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Vatsal J Tanna
Upon aluminium bed (which I never heat) I place a sweet box's cut out. On top of this, I stick a label paper (not sure what it is properly called) with a glue stick such that the label paper's sticky side is facing up. This setup is fastened with the use of paper clips. It might be that the setup was not fastened properly during that time. But I seriously doubt it. Since I've oiled the axes and added an extra cooling fan for the arduino, the same bed setup is giving me fine prints. I'm not an expert, so I really don't know what happened.

I recommend a borosilicate glass plate affixed with spring-clamps. This will give you a very flat and smooth surface. If you are doing just PLA you can use blue painters tape (which you don't need to heat) and your PLA will stick great. That plate will probably cost you about US$15, cheaper at Banggood or AliExpress.

DLC