Corner lifting problem - ABS and heated bed

Hi:

I am seeking advice about a problem I am having when trying to print objects taller than about 1cm. The problem is that the corners tend to lift off the heated bed about half way through the print, getting worse as more layers are added. I have a heated bed at 110C, covered with Kapton tape. I extrude ABS at 255C, layer height is 0.4mm. The print sticks to the bed so well, I can hardly get it off. It usually requires a chisel to pry it up. Yet on thick things the corners lift. Please see the attached picture. Note that i am not printing solid objects, the one in the picture has a wall as a perimeter, and others are at 0.2 fill ratio. Is this just a fundamental limitation of not having a heated build chamber?

Any guidance would be greatly appreciated.

thanks

john

I had that problem when I was first using my Mendel printing on masking tape switched to glass got the temp right and now they never lift. That's printing with PLA though.

I mean the bed temp has to be right about 60C and I extrude PLA at a relatively low 175C

Edited 1 time(s). Last edit at 08/09/2011 10:51PM by NelsonRap.

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Experimenting in 3D in New Zealand

For thin walled parts I run elmers wood glue after a few layers. I drop a generous blob and run a swab along the perimeter and it dries fairly quickly. Afterwards the part is pretty easy to remove and cleanup is simple: scrapes really well off of the kaptone and peels right off the part. I will say that I have only done this on PLA but should work just the same with ABS. Also I'm using a heated bed.

Not sure how it would work on your photographed part but its simple enough to try....

for ABS, you need to turn up the heat on the bed, and lower the heat on the hot end.

Bed temperature should be 120'C-125'C, Extruder Temperature should be 230'C-240'C (this is more dependent on the ABS though).

To get the bead good and hot, and here I'm assuming you are using the red PCB, you will need to insulate the bottom properly.

Mounting the Heated Bed On Prusa

Are you using a bed, where the y table moves?

I have been experimenting with an air flow disruptor for an also experimental abp for Mendel, and one issue that I'm trying to resolve is the air flow that skims across the bed, when it moves back and forth as an object is being built, that basically changes the air flow direction.

The easiest method to resolve this is place an object about 1cm high around the front and back and is the width of the table that moves in the y direction.




Another option is to build a separate wall in front of the object you want to print. Typically I will create a sacrificial wall and make it also have corners to stick better.

Heeks cad [code.google.com] has the ability to combibe several stl files together.
Make a 10mm high 1mm wide object in openscad [www.openscad.org] , then in heekscad open up your stl and then import the wall shape. Correctly position wall shape and then save. Your object now will have a barrier that prevents the base part from cooling to quickly.


This wall only needs to be .5cm to 1cm tall, and its sole purpose is to stop the cooler air from going to the base of your part, causing it too cool down and become hardened, where it will peel up and off the bed. Skein 40 has skirt feature, although there are some other issues with that such as it is only 1 width thick..


Heating the bed higher will improve adhesion control, but you will still see some minor warping.

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Bed temperature should be 120'C-125'C

The Prusa bed I have will not get that hot with 12V, glass on top, corrugated cardboard underneath.

PCB copper thickness tolerances are only about 10% so there will be some spread from one to another. I normally use 140C for the first layer and 110C after that for ABS on PET. To get 140C in a reasonable time I find I need 17V. That means instead of 10A falling to 7A I have 14A falling to10A. Even then the warm up time is a lot longer than my mains beds, mainly due to fact the resistance increases so much as it heats up.

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[www.hydraraptor.blogspot.com]

@Nophead: I'm really stumped by your HBP temperature limits at 12VDC. Admittedly, 125'C is the maximum I've been able to get mine up to, but 120'C is no problem at all.

If you're interested, I have a FLIR thermal camera available this weekend, so I'm going to see what the "real temperature" difference is. I'll be broadcasting video and on IRC.

The max temp probably will vary depending on airflow in the room, humidity and air temp


then again a silicone thermistor at best is +/- 1%

then there is the voltage supply +/- 10% or the copper trace thickness variation. These effect the power level as to heat produced. All this is a natural part of the world of analog electronics

It is easy to see why your max temps are slightly different.