Strange top layer on large flat prints  

RE: Strange top layer on large flat prints

Flip the part over and examine that bottom corner. The likelihood is that the corner warped up during printing which means the layers above it have less space and so get compressed as you have pictured. You should be able to tell from looking at the bottom. This is why we stress so much getting the plate scrupulously clean and grease free and getting your live z perfect.
However large rectangular prints are the most prone to the stresses that cause warping.  

RE: Strange top layer on large flat prints

I've looked closely at the bottom layer and as near as I can tell it's fine. Generally whenever I've had warping I can see the line where it's lifted off the bed, I see nothing in this case. I do give the plate a good scrubbing with IPA between every print, for this next one I'll do a full soap-and-water cleaning and see if that makes any difference.

Also it's extremely odd to me I don't see any artifacts until the very top layer. The next layer from the top looks perfect, then the top layer comes out looking like the picture. It's mystifying to me.

RE: Strange top layer on large flat prints

I'm seeing the same problem with large flat items.  Did you ever get anywhere with theis problem?

RE: Strange top layer on large flat prints

165mm circle, no lifting from plate.  I tried different infill and densities.  Made it different, but not gone.  Everything up to the very last layer looks perfect.

RE: Strange top layer on large flat prints

I just had this happen to me for the first time and it was definitely a warping issue as Neophyl mentioned. Next time I'll try adding a mouse ear to the corner and see if that helps.

RE: Strange top layer on large flat prints

I am no stranger to lifting prints, but these prints are definitely not lifting off the plate.  to test this, i created a 100x100x8mm cube and printed with various speeds/options.  I added a brim to the object to be sure it stuck to the plate.  so far i have found that:

1. the print is perfect up to the last layer, no imperfections/waves no matter what i do to the settings.

2. the addition of the last layer is when things go nuts.

speeding up the top layer speed to 80mm causes the waves to increase in size, and increases the distance between wave peaks.  lowering the speed to 20mm causes the waves to decrease in overall size, and shrinks the distance between wave peaks.

I am starting to think that the print bed itself is actually distorting.  I am going to test this tonight by moving the 100x100 square around the print bed, and see if the area with the waves moves with the print object, or stays on the same area on the print bed.  I did look at the bed to Y carriage, and it looks correct and solid. 

I will post pictures of the results tonight

RE: Strange top layer on large flat prints

Before removing the plate check it with a steel rule to make sure the plate itself isn’t lifting. I have had at least one occasion where the part to bed adhesion was so good it lifted the platter away from the magnets. I had to use good old binder clamps positioned to not hit anything to keep the bed down. 

RE: Strange top layer on large flat prints

lots of tests last night, with more to come tonight.   bottom line is that when i print my 100x100x8 rectangle on the left side of the build plate, there are no artifacts whatsoever (surprise to me)!  and as i move to the right side of the plate, i start to get the artifacts shown in the pic.  the worst artifact is achieved in the lower right of the build plate.

I am running the input shaper, and cant help but wonder if that in conjunction with the fact that the right side of the Y carriage has the single bearing, where the left has the dual bearing, isnt somehow causing this.  i will print tonight with the input shaper off just to see.

it also looks like over extrusion to me as its printing, so i will try to drop the extrusion multiplier tonight as well, to see what happens,

also checked my plate with a straight edge, and its flat.  

stay tuned for more....

RE: Strange top layer on large flat prints

I too have see the build plate get pulled up by the model.  For me this occurs with large footprint objects that are near the edge of the build plate.

RE: Strange top layer on large flat prints

oh, and the reason i was suspecting some over extrusion was that i printed the top layer in octagram spiral (just to see if it made a difference) and the corners looked like this:  they should all be nice and flat, but where you see the ridges are where it printed a line between two completed areas.  looks like too much material.  

where it printed the fill as a contiguous feature, it all looks nice and uniform:

RE:

@lynn yes, i definitely see that now, and i was having that problem as well as others.  i have created a smaller object to print in the hopes that i can isolate down to each problem!  its not easy!

RE: Strange top layer on large flat prints

Alright!  Success has been achieved!!!

First, the problem wasn't the input shaper (i had to test it). And, the problem wasn't the print lifting from the print plate. The problem was the print plate lifting from the heat bed!

I added clips as suggested above and immediately achieved a perfect print with all defaults.

Now, this was an early make mk3 upgraded to a mk4.  I wonder if that has anything to do with it.  My friend has a new mk4, and I had him run these tests, and he has no issues right out of the gate.

RE: Strange top layer on large flat prints

@drllama, was the affected corner of your print near the edge of the build plate?  If so, try the clip method above.  

Also, is your printer an upgrade, or new?  I am wondering if this is a mk3 to mk4 upgrade issue