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Warping PLA even with heatbed

Posted by Petehagoras 
Warping PLA even with heatbed
October 02, 2011 08:29AM
Hi all,

Another Problem occured.

To be able to print larger parts in PLA i desieded to install a heated bed, but there is still warping in some corners.
I print the PLA at 205C, Heatbed is at 60C. first layers are fine, after 10 or so, warping slowly rises. picture while printing attached.
My thoughts:

- When i print directly over the middle of the bed where the Thermistor is installed, The bed heats less than it should, because of some insulation process the above printed PLA gives. (Using PCB Heatbed MK2 with a hole in the middle where the Thermistor is installed)

- Maybe the type of thermistor doesnt match the choice in the Configuration.h (Using Sanguinololu 1.2 with newest Sprinter)

- The PLA i'm using needs more Temperature

I'm using no fans, and am printing on a glass plate over the heatbed.

Any Experiences or hints out there ?



Edited 1 time(s). Last edit at 10/02/2011 08:46AM by Petehagoras.
open | download - IMG_20111002_143908.jpg (286.1 KB)
Re: Warping PLA even with heatbed
October 02, 2011 12:22PM
205º is pretty hot for PLA; I print at 185º; any reason for the higher heat? Is the warping any better or worse with the heat turned off? What happens if you turn the heat off and cover the surface in blue tape?
Re: Warping PLA even with heatbed
October 02, 2011 12:34PM
Before i printed with heatbed i just had a tape over the thick sheet, the warping then made me install a heatbed. with 205C I get really nice surface and the PLA extrudes reliable. Had some Probs with lower Temps there, but till then I readjusted the Extruder. Guess i'll give it a try with 190C after the next piece is done.
Re: Warping PLA even with heatbed
October 02, 2011 02:10PM
The temperature setting needed to extrude PLA depends not only on the type of PLA but also on the type of hot end that you use. There are more than one type of PLA. There's a short section on the wiki on heater settings for different types of PLA.

In addition, the thermistor reading depends on the type of heater. The old nichrome wire around the nozzle with thermistor taped to it tend to read lower than the actual temperature. Thus it was common to set the temperature low to around 190-190 with those designs. With the aluminum or brass block with ceramic resistors, the reading is higher than the actual temperature. So, the settings for those tend to be higher. I think Adrian even noted that his heater setting went up to 205-210 when he switch to ceramic resistor on heater block.

Lastly, the table used to convert AD reading to temperature for the thermistor is not exact unless you calibrate you thermistor. They can very from part to part. Also, the reference resistor can also vary. Of course, if you have the wrong table, then your readings could be way off.
Re: Warping PLA even with heatbed
October 04, 2011 02:36AM
Wipe the glass with meths or some other spirit cleaner to remove finger grease, this makes a huge difference

Experimenting in 3D in New Zealand
Re: Warping PLA even with heatbed
October 05, 2011 12:02AM
I think the key is getting it to stick to the bed. I put Kapton on top of glass and I heat it to 85C, at least the ensor says 85C but It's porbably lower on the print surface.

Then I try to smash the 1st layer a bit and make sure it prints slow on that 1st layer.

these things all seemed to help.
Re: Warping PLA even with heatbed
October 05, 2011 01:03PM
Before I had a heated bed, the closer I mashed PLA down onto the blue tape surface the better it stuck. After I added heated glass, it actually stuck better if I had about a layer height between the nozzle and the bed.
Re: Warping PLA even with heatbed
October 05, 2011 05:56PM
thx 4 all those responses.

im using one of those brass block/ceramic resistor hotends, and it seemed as if 205 were even too low. made some tests with 220C (what my thermistor tells ;-) ) and it seemed much better. Shure, leveling of 1st layer and clean glass is very important.

In addition i get a better stability of the prints with the higher temp, but i'll go down to 215C, cause 220C are result in some promblems in bridges.

I raised Heatbed temp to 65C, also an improvement.

I use Car glass cleaning foam, and it does a very good job in degreasing, plus it a bit more handsome than meth or spirit winking smiley

Now there are bunches of other problems that bother me. some software, some hardware related, but im getting closer ^^

will make some test implementing your hints and report.
Re: Warping PLA even with heatbed
October 05, 2011 07:36PM
I run PLA at 170 without a headed bed. Prints fine on foam core board. When the configuration is small, where the head tracks over the same surface frequenty, I need to run a fan or the part gets distorted. To an early post you really don't know the actual temperature but I can't imaging running that high temperature without part distortion. Especially when heat is coming up from the bed.
Re: Warping PLA even with heatbed
June 08, 2013 02:16PM
i thought you didnt need a heat bed for pla it was for abs printing?
Re: Warping PLA even with heatbed
March 29, 2015 10:47AM

I use PLA 220 degree for the first layer and 210 degree for other layers. Heatbed temperature is 65 degree. And i have the problem of warping of the corner of the shape. what should i do to solve this problem? Another problem is after some time the printing material doesnt stick to the heatbed so the printing fails sad smiley
Re: Warping PLA even with heatbed
March 29, 2015 11:38PM
use a brim to help with bed adhesion, I typically use 3mm for all my abs parts and it just pulls off when the print releases after you are done.
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