Prints with ABS have a corner curling, same corner every time

Hi,

It appears that when I print I always get a bad corner, and it is the same corner on each print no matter how many times I print it. It tends to curl up and cause the usual curling problems.

3 corners will look great, and that other one just curls up! ?

Prusa i1
Gen 7
Marlin
Slic3r
Pronterface

Does it with all 4 ABS's I've tried so far, some worse than others.

If it always makes a layer change in the same place, ooze will cause an overextrusion problem there. Retract will help, as well as other anti-ooze strategies.

One of the delicate areas in the physical alignment of print bed to nozzle is clearance. If my starting clearance is slightly off on one side, I'll have poorer adhesion there. If clearance is too tight, the nozzle will be too close to the glass on the first layer (I'm using glass with a hairspray coating) and the extruder will jam. If clearance is too loose, the first layer does not get pressed against the bed and really won't stick that well.

I would check your Z axis calibration for starters. You can print quite a bit without great adhesion, but more slab-like pieces will tend to curl up more. If you have good adhesion, it should be almost impossible to lift a piece off when you're done printing without cooling the bed. Nozzle clearance has a LOT to do with how well things adhere!

Generally the heated bed seems to produce somewhat uneven heating, so larger pieces will have more of a tendency to curl as you move away from the center (I'm assuming you're using a heated bed). Enclosing the print area (to avoid drafts) should help. When I started out I was using cardboard and duct tape; now I've moved to an acrylic enclosure.

I'll test out the anti ooze stuff, thanks.

It's not bed levelling or bed adhesion related as it can happen higher up an object with no sign of corners lifting off the bed. It also happens on small parts sticking out the top of larger parts.

Yeah, I've seen plenty of corners lifting off the glass but I've never seen curling only from the top. At one point I had slippage on my Z-axis rods and ended up tightening heatshrink tubing around the vinyl tubing that's used for coupling the Z-axis stepper motors with the threaded rod. That could cause irregular lifting. I also had used the wrong lubricant (grey silicone grease) on my Z-axis rods and stripped the nuts (which may have been inferior). That was also causing irregular Z-axis movement sometimes. I replaced the nuts and moved to an occasional coat of light sewing machine oil and all has been good.

When I've had severe lifting it has sometimes caused upper layers to get bollixed because the surface where deposition is supposed to be occurring is not where it's assumed to be.

I get a little messiness from oozing because I have lower retraction values (all-metal Magma nozzle which has issues with retraction) but that's usually only a problem when moving between separate "tower" type structures. Printing this [www.thingiverse.com] for example I get very messy results toward the top of the arches.

The other thing that happens to me is if I use M600 to do a filament change I sometimes end up with a small glob of ABS on the nozzle and it tends to "ripple" up through the layers, but that's fairly obvious.

I think the problem is always the corners where even from a slight overhang come back around to straight on top of the previous layer. As I rotated a print 180 degrees on the bed and the dodgy corner is the same one on the print, not on the printer.

If that didn't make sense, I don';t blame you. I haven't eaten in over 38 hours due to having gastro and am pretty wiped out / tired.

So the corner leading into the over hang is fine, but the corner coming out if it lifts.

It did make sense and you have my sympathies (on the gastro). Do you by any chance have an STL that reproduces this?

Here is a test I made up which always does the same corner issue. I included a photo of it. At the bottom of the photo is the bottom of the print. The tower is a 45 degree overhang. Near the top of the tower it looks good, this is because of the fan (I turned it on at that point in the tower. The bottom doesn't look as good as mid way up because it was lower temp, I started at 210, went to 230 and found 220 worked the best for this blue. The broken piece is a test I did with the fan all the way. As you can see it broke, quite easily in my hands. I cannot break the one without the fan running.

Both were 0.33 infill. 0.25 layer height and extrusion width of 0.4. Using a 0.35 Jhead

The print ran around it anti-clockwise, so that dodgy corner is where it came off of being an overhang to being straight on top of previous layer.


The other model that I have printed a lot of which does the same thing except not straight off the bed (small feature with overhang on top of a flat printed surface) is a design I sell so I cannot post it here.

Edited 2 time(s). Last edit at 11/13/2013 11:13PM by Phizinza.

I have a couple of thoughts on this...

The deposition process depends on adhering to the underlying layer. Stepped overhang is not a problem provided the angle is not too steep, but if the LAST point of deposition has nothing under it (i.e. it is precisely on the overhang) the print head moving away from the part on completion is going to leave something behind.

The slicer could probably take this into consideration and avoid ending on an overhang (or perhaps there's some option that controls this).

I've also found that smaller layer heights (e.g. 0.2mm or 0.15mm instead of 0.3mm which I use for most general purpose stuff) work better with overhangs.

My other thought is that this discussion prompted me to investigate some of my own ABS lifting problems.

Specifically I was working on this: [www.thingiverse.com]
which generates dozens of small square rods, which clearly exhibit lifting always in one area of my print bed.

Originally I had assumed this was due to uneven heating of the surface (which is in fact a problem - there's a good 15-20C difference between the middle and corners of the heated bed). I believe that Z clearance is more important to adhesion than bed temperature, however. I then saw that my Prusa i3's heated bed (which has 3 points of attachment to the smooth rods underneath, 2 on the right side and 1 on the left) has a very slight (~0.1mm) slant toward the left front corner, which is where I see lifting. It's a very interesting coincidence that the left side is the side with only one point of attachment to the smooth rod.

I can compensate for this in firmware but since it's a relatively fixed unevenness I can also adjust the bed itself to ensure levelling.

I don't think this has anything to do with your problem but very interesting nonetheless...