Help printing large flat square
I need to print a large flat square object, about 170mm on each side and 5mm thick. It has 10mm tall flanges on the side. The piece is going to be used to hold PCBs during a pick and place operation. I created my design in FreeCad and printed it with the 0.20 FAST profile. The problem is that the object is not exactly square, which is something I require.
I'm printing with PLA.
What can I do to ensure the piece is a square as possible?
Is it possible that the flanges on the two sides is causing uneven shrinking? 
Best Answer by infinitemachinery:
I was able to get it aligned properly! I followed this squaring procedure, Prusa Knowledge Base | Squaring your MINI (prusa3d.com) and found that the X axis was misaligned at the end of its travel. It's looking much better now.
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RE: Help printing large flat square
Hi,
firstly, I don´t much like PLA as I believe it is a crappy material, usable for throw-away toys but not for functional stuff. So I would print this sort of thing in ASA such as Spectrum ASA 275, which requires a bed temp of 60 degrees C only and thus in my experience does not suffer much from warping; additionally I typically reduce the fan-cooling of the part to not artifically cool the part down; it´s large enough to cool down anyways before the extruder comes around the next time.
Secondly, I´d certainly increase the number of vertical contours from 2 to at least 4, to make the outer walls much more stable and thus shrink-resistant. 20% infill should work, but I´d switch the infill from grid to honeycomb or gyroid to improve lateral stability.
Thirdly, I´d print it in .15mm layers, to limit the volume of hot filament further.
Finally, I would print this part in a closed environment to ensure that the heating and cooling is consistent.
Cheers
Chris
I try to give answers to the best of my ability, but I am not a 3D printing pro by any means, and anything you do you do at your own risk. BTW: I have no food for…
There is nothing wrong with your basic settings, I would use cubic infill to resist some twisting.
You are probably seeing warping due to the plastic cooling slightly unevenly. The flanges will have a slightly greater influence as they pull from a little further from the base.
You have two main strategy choices.
Annealing: place the part between two flat plates and reheat the whole thing in an oven at just over glass transition temperature, 60C for PLA, for a few minutes. There may be some other distortion, especially if you overdo it.
Or: If the design can accept it, place some slots in the upper surface. Most warping is caused by contraction in the upper layer so anything that breaks up the longer dimensions splits the tension into local zones and greatly reduces the effect.
Your upper skin is 1.2mm thick so I suggest a grid of slots 2mm deep would be enough, 50mm spacing should be OK but you might choose something that relates to the end use, marking standard sizes or similar...
There is no need to add perimeters. PLA is perfectly acceptable for this task; there is a strange aversion to PLA in some quarters but unless you are working hot it will be fine here. 0.2mm layers are sensible for this part there is no advantage in going smaller. There is no need for an enclosure but do protect the printer from drafts.
Cheerio,
RE: Help printing large flat square
Thank Diem,
I've implemented your changes and I'll know in 6 hours what the outcome is 🙂
RE: Help printing large flat square
Well, it finished printing and the piece is out of square just like the first one. Over the inside length of the base, 150 mm it is out of square by a little over 1 mm. Is it possible there is an issue with my Mini? This is a new printer with only a dozen or so hours on it. I bought it pre-assembled, not a kit.
So about 0.7% that's a little high, you would normally expect no more than half that with a 0.4mm nozzle ...
Can you show us the error against a straight edge and please indicate the axis of the picture?
Cheerio,
RE: Help printing large flat square
Here's it is lined up with a sheet of acrylic, which is exactly square (I tested it with an engineer's square).
OK. I had assumed you were getting warping in the Z direction, a common problem with large area prints.
The principle is the same though, try to break up the long fibres that pull the shape as it cools, in this case notches in the outer perimeters of the long, thicker wall. I would also try rotating the print on the bed so the offending area is facing away from the print cooling fan.
Is it possible there is an issue with my Mini?
Very unlikely. To test try printing a single layer, 0.2mm thick, large square and check it's true.
Cheerio,
RE: Help printing large flat square
I printed a single layer. It's still not square.
Very Odd.
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Cheerio,
RE: Help printing large flat square
I was able to get it aligned properly! I followed this squaring procedure, Prusa Knowledge Base | Squaring your MINI (prusa3d.com) and found that the X axis was misaligned at the end of its travel. It's looking much better now.
RE: Help printing large flat square
Thanks for sharing the solution.