Printed Cubes bowed in.

So I've recently noticed that when I print things with flat sides like a cube they curve in slightly making the corners of the cube not 90 degrees.


Any idea what causes things like this?

Could you explain clearer, maybe with an image?

Not straight corners can mean many things, loose belts, too fast printing because the mass of the x-carriage has to slow down and not make a sharp corner, but it can also be that it's extruding more than it should be. That will make the corners also less sharp and detailed.

Sorry my camera isn't very good at taking pictures..

As it is moving in from one corner to the next it appears to bow inwards making a parabola between the two corners.

I see what you mean, this is a strange one, I can't come up with a reasonable explanation, it looks as if the middle part has more shrinkage than the corners, and maybe it's overextruding and moving too fast so it adds more material near corners?

Could that be something? Maybe someone else can contribute some valuable insight?

On first sight I might think shrinkage from cooling. What infill percentage are you printing at? Have you tried other cubes, or is it just that file? Are you running a fan? PLA or ABS? What size is the cube?

I'm printing 1.75mm pla with a fan. The infill on this particular file was 25%. I've done other cubes at different infills but most have this same issue. This particular one is rather flat but the others are actual cubes.

I'm still messing around with this. I've tightened the belts further but so far haven't had much luck.


EDIT:

Would a XY Jerk setting of 10 cause this?

Edited 1 time(s). Last edit at 02/17/2014 08:30PM by jaeg.

Quote
jaeg
I'm still messing around with this. I've tightened the belts further but so far haven't had much luck.


EDIT:

Would a XY Jerk setting of 10 cause this?

I'm wild guessing that there is more material deposited at the corners that caused the sides to look bowed in. Have you tried measuring the corners or the sides? You can try other slicer too and see if the problem goes away.

For a 30mm cube corner to corner is 30.40mm and side to side is 29.73mm.

I'm currently using Cura but I'll switch back to Slic3r to see if it's doing it now as well. (I don't remember Slic3r doing it but I'm just now noticing it happening)

It's the slicer. Cura for some reason does this to my prints but Slic3r does not.

Correction. It doesn't do it as bad with Slic3r it's still happening but more so on the top than the bottom.

Edited 1 time(s). Last edit at 02/22/2014 02:04PM by jaeg.

I've tried recalibrating my extruder (It's a Greg's Hinged Accessible Extruder) and I just want to confirm my math here: I have RAMPS 1.4 set to the default 1/16 steps driving steppers that require 200 steps to go completely around. The gear set is 47:9 Fishbone gears and the effect diameter of the hobbed bolt is 6.54. So... (200 * 16) * (47/ 9) / (6.54 * pi) = 813.76298

I am however still getting fat corners.

It was suggested on my reddit thread about this issue that it could be my machine warping. I replaced the bed since its alignment was off and remeasured the spacing of the Y axis. I'm still getting warped parts.

[www.reddit.com]

If you slow it way down, can you see it printing with the corners bowed out? If not then i would guess it is shrinking. But that is a very odd problem.

Just ran at 10%. It does appear to be printing straight (no two axi are moving at once unless it's doing infill so I'm assuming it's not doing it). My fan kicks on right after the first layer. Could that be the cause?


EDIT: Actually on second thought I'm not ruling the frame out just yet. Since it's at a slower speed it's possible that it's just printing straighter due to less force behind all that moving mass.


Edit again:
Just did a full print at 70% the speed. The edges are no longer bowed in but the corners are still a little exaggerated.

Edited 2 time(s). Last edit at 03/04/2014 09:43PM by jaeg.

If it printed correctly at a slow speed then i would expect it to be a machine issue. Is your bed heavy or leveled on springs?

This is the bed: [www.makerfarm.com]

The top portion of the bed is a piece of thin plywood with back support of balsa to make it sturdier suspended on springs. The glass is held to the top of this by binder clips.

I can only think of 4 things
1. The springs are weak enough to cause the bed to shift
2. Maybe your acceleration is too slow, or too fast.
3. Hotend is loose enough to shift.
4.firmware problem, reload the firmware, i would build a new configuration.h file (assuming it's marlin)
All of those are long shots, but it's my guess.

Edited 1 time(s). Last edit at 03/05/2014 12:20AM by cat.farmer.

Well I'm getting closer. It seems it might be a combination of issues. But little by little I'm getting it to look better.

I figured I'd give an update. I've fixed the issue! Turns out my acceleration was too slow. I sped up the acceleration and the extra deposits on the corners ceased to exist. I'm rationalizing it like this: Since it would take it a relatively long time to speed up just to slow back down to get from one side to another it would spend more time at the corners than it would on the sides of the print. Thus leaving extra material on the corners.


Thanks for everyone's help! My printer hit a milestone the other day by successfully printing out a 40 tooth Lego Technic gear (without supports which was an even better feat for the printer) that not only worked with the Lego Technic plus shaped rods but actually meshes well with a worm gear. It is currently acting as a replacement part for my Throwbot Jungle.