Bad experiences with MK4  

RE:

Your first point is rather peculiar, given that the Mk4 uses almost the same bed assembly as the Mk3s+. The only real difference is the way the first layer calibration is done. How does your first layer look like?If it is a wonderful almost flawless first layer as I have seen on all images from Mk4s so far, I would guess that your print sheet is the culprit here. You shouldn't need to change a z-offset on an Mk4 either. If you have to without some speciality application in mind chances are that something isn't right. Why do you think that different plates need  different z-offset settings on an Mk4?

Posted by: @martind

I have 4 pieces of MK3s (2 of them are upgraded MK3), my experiences with MK4 are mostly bad.
To explain

I am printing solely PLA, and on the textured plate.
1) All my MK3s are able to print the large object without warping or any issues. The MK4 cannot. no matter how I do set the z offset, or set the temperature of the heatbed or use the sticky spray, no matter how deep I clean the textured plate - there is always an issue with warping. While the same plate on the MK3s has excellent print of 18x18x3cm  block - no warping, no issues - without the spray. No way I could print it on MK4

RE: Bad experiences with MK4

Posted by: @thejiral

Your first point is rather peculiar, given that the Mk4 uses almost the same bed assembly as the Mk3s+. The only real difference is the way the first layer calibration is done. How does your first layer look like?If it is a wonderful almost flawless first layer as I have seen on all images from Mk4s so far, I would guess that your print sheet is the culprit here. You shouldn't need to change a z-offset on an Mk4 either. If you have to without some speciality application in mind chances are that something isn't right. Why do you think that different plates need  different z-offset settings on an Mk4?

Posted by: @martind

I have 4 pieces of MK3s (2 of them are upgraded MK3), my experiences with MK4 are mostly bad.
To explain

I am printing solely PLA, and on the textured plate.
1) All my MK3s are able to print the large object without warping or any issues. The MK4 cannot. no matter how I do set the z offset, or set the temperature of the heatbed or use the sticky spray, no matter how deep I clean the textured plate - there is always an issue with warping. While the same plate on the MK3s has excellent print of 18x18x3cm  block - no warping, no issues - without the spray. No way I could print it on MK4

I use different textures plates, and result is almost the same (warping).
The first layer on MK4 - just after the printing and pausing it after first layer - it looks great - nice and even.
However after the print continues the warp is starting to form, when print goes at about 1cm, it is visible, at about 2cm - the warp at the corners is about 1.5-2mm.

On the textured plate it is recommended to push the PLA a bit deeper - to the texture - so I gave the -0.02 Z offset  - which eliminates warp a bit, but not completely, anything higher (meaning Z offset) is too much. 
It just annoys me, I expected to be MK4 better than MK3s, but seems it have its own issues. I like the display, like the speed, and the rest of it, but this issue is really crucial to my prints.

RE:

Textured plates aren't that great for PLA regarding adhesion in general, no matter if you print on an Mk3 or Mk4. That is why smooth plates are generally recommended. If you really need to push in the filament deeper, then z-offset is the way to do it indeed. I can't see any reason why the Mk4 should be any different at the equivalent z-offset compared to an Mk3. 

Have you tested the identical print sheet on Mk3 and Mk4 and adhesion is worse on the Mk4 with the optimized z-offset on both printers?

RE: Bad experiences with MK4

Yep exactly, the same sheet, provides excellent result on MK3s, but warping on the MK4, i tried several Zoffsets with the MK4 as well as temperatures of heatbed (from 50 to 70) but could not get flawless results as on MK3s, I will try to lower the speed.

Posted by: @thejiral

Textured plates aren't that great for PLA regarding adhesion in general, no matter if you print on an Mk3 or Mk4. That is why smooth plates are generally recommended. If you really need to push in the filament deeper, then z-offset is the way to do it indeed. I can't see any reason why the Mk4 should be any different at the equivalent z-offset compared to an Mk3. 

Have you tested the identical print sheet on Mk3 and Mk4 and adhesion is worse on the Mk4 with the optimized z-offset on both printers?

RE:

Yes, try an identical print profile (speed, lane width, cooling etc). It makes no sense why the Mk4 would perform any different from the Mk3 in this regard if the z-offset is equivalent as long as the bed levelling is fine, which it is (first layer looks good). 

RE: Bad experiences with MK4

MK4 also has different cooling to the MK3, another potential difference.

RE: Bad experiences with MK4

True, but given that you commonly have the part cooling completely turned off for the first 1-3 layers that shouldn't effect adhesion to the build plate. 

RE: Bad experiences with MK4

A good tip, will try this! (and of course reply if it helped or not)

Posted by: @thejiral

True, but given that you commonly have the part cooling completely turned off for the first 1-3 layers that shouldn't effect adhesion to the build plate. 

RE: Bad experiences with MK4

The OP described it warping up after the print gets to 1cm up, that's quite a lot further than a few layers.  Bed Adhesion force = X, warping force at any time from the start =Y.  If Y is less than X then it doesn't warp up.  If at ANY point during the print the warping force Y goes greater than X then it warps up.  So better cooling causing more contraction as it prints can make Y exceed X at any point.  

To fix you either increase X, which we normally do by cleaning properly and adjusting Z, which the OP sounds like he is doing and has a handle on, or we do everything we can to reduce Y.  We do that normally by reducing environmental factors like drafts, redesigning the part with stress relievers etc.  We can also attempt to reduce cooling when its actually too much.  Not usually a problem on a MK3 but has been on some other printers I've owned.  

I don't have a MK4 so can't comment on if the cooling is better and I haven't read anything to that effect really but all things should be considered, tested and ruled out.

RE: Bad experiences with MK4

This is getting into complicated territory in which I am really no expert but the question if speed of cooling is impacting the warping force is also dependent on the material being semi-crystaline or not isn't it? In general I would have assumed that warping tendency for most common materials should be similar no matter how fast you cool, the main factor is the end point temperature in the printing chamber, after cooling. Isn't it?

RE: Bad experiences with MK4

Not really no.  Contraction occurs as it cools, this can be the fan as its printing sometimes or later on due to the chamber ambient.  Its one of the contributing causes of parts being smaller in areas that we see people posting about on the forums.  As it goes from the fluid to a more rigid structure in that initial area.  Even after its gone 'rigid' those stresses are still there unless a part has been annealed to relieve the stress.  Larger flat surfaces can still get air from the fan even some time after the nozzle has left and the plastic is ostensibly 'set'. So as the layers build up each one adding a little bit , to increase force Y it eventually and gradually overcomes it.

Its why fan speeds are something you tune for the material and the printer.  I used to have a modified Cr10 printer with a petsfang duct and a big fan.  It could bridge 200mm fairly easily with pla but for normal prints the settings were tuned way down to 30-40% as if you ran it at 100% parts would warp, as well as be brittle as the layer adhesion sucked.  All I'm suggesting is that the OP do some practical experimentation and see if it has any relation to their issue.  Given the fan size on the MK4 I wouldn't expect it to be the cause but I wouldn't rule it out.  Maybe the cooling is super efficient.  

RE: Bad experiences with MK4

I am aware of the basic principle of cooling and thermal contraction. What I was asking is how much difference it really makes how fast it cools from nozzle temp to enclosure temp, in regards to build up contraction releated stresses. But I guess that depends a lot on the actual enclosure temperatures. Which is why in some Voron builds people can run the part cooling at 100% and still get good results with ABS.

What I still struggle to understand is in how far speed makes a difference for warping if you print at room Temp without enclosure where the end temp you reach is the same but in on case it is faster (with steeper temporary gradients between different areas) and in one it is slower. So overall shrinkage of each layer should be the same no matter the speed of cooling and the lower layers should be more or less cooled down already at that point (layers close to the heated bed will differ in this regard of course). So why does warping stresses build up more if the current layer is cooling faster to the same final temp?

RE: Bad experiences with MK4

I received my Mk4 factory-assembled yesterday.  So far have not been able to get through a print without a stop due to the filament sensor bugging out.

RE:

When I print PLA on the textured sheet (because I want that surface texture on my print) I’ll add glue stick. If it is a large part, I’ll add it at the corners that would tend to lift. This doesn’t solve the issue of why the lifting.. but it can add adhesion so you might be able to overcome the lifting on that model. I don’t use Gluestick when not needed.. but I use it surprisingly often.

RE: Bad experiences with MK4

Explored the outside ambient temperatures?

Any drafts etc?

RE: Bad experiences with MK4

I am having the issue and the printer is in a closet, so no drafts happening.

RE: Bad experiences with MK4

If you are printing PLA, have you tried opening the closet door for the duration of the print? 

Can we see pictures of the first layer of a print, and a picture later in hte process, showing the issue?

regards Joan

RE: Bad experiences with MK4

First printer Prusa MK3 the new MK3s, then upgraded to MK3S+. Now have had a MK4 for 20 hours and still unable to get one print off. So many issue's never experienced with the MK3 series. Broken parts and firmware issues, etc, etc. seems they rushed this one and that is being lenient as I waited 3 months after being promised 5 weeks for the delivery of the unit. May have to return the unit as just not working out..

RE: Bad experiences with MK4

I do not recognise this at all

I have the MK4 kit and everything goes and work well.

No failures  yet