ABS Curling Overhang

Hi,

I'm trying to print the calibration object called 'precision-block' with ABS. I don't have a problem getting the ABS to stick to the Kapton, but the overhangs curl up. I tried using cooling fans, but that made it worse by warping the object off the bed.

Anyone?

Thanks.

Try printing a little hotter.

Are you running any cooling fans during the print?

Fl0yd

Edited 1 time(s). Last edit at 03/30/2013 12:16AM by Fl0yd.

Looks like radiated heat from the hot-end may be causing it to curl - print is very thin at the tip of that object.

I've had this same issue as long as I've been printing ABS (on a cupcake and prusa).
The possible fixes we come up with always seem contradictory (print hotter/print cooler, thinner layers/thicker layers).

From just watching the printer it looks to me like you want to minimize the fraction of the thread width that is overhanging. This sounds like it means thinner layers (eg if you had 50% width overhanging from one layer to the next at 0.3mm layers then that would go to 25% per layer with 0.15mm layers).

Besides printing ABS the other constant in my case has been a makergear nozzle (which is pretty flat). I wonder there is more heat going back into the print than there would be with a pointier nozzle).

This is caused by the extra heat coming from the platform. The same feature 15mm from the bed wouldn't be nearly as distorted. The layer can't cool fast enough with so much heat from below. A fan should help, but I've not yet bothered. So far, I avoid having more than about 30° overhang within about 10 mm of the bed. Of course, layers that don't have time to cool would have the same problem. Maybe I should get around to mounting up a fan.

Actually problem is caused because layers cool too fast before next hot layer is extruded on top of it.While ABS is cooling it shrinks and then new hot layer which sticks to previous layer and cools down (shrinking)...eventually you see warping upwards.

On small objects kapton can fight against warping, but on overhangs and larger objects you can see the problem.

I added heat lamps to slowdown cooling of top layers on my miniFactory printer.

On my first picture you can see example with my printer without using heat lamps. Nozzle 0,35mm, temp 240C (535F), bed with kapton tape and temp 70C(158F). Room temperature 18C (64F).

On my second picture only difference was using heat lamps.

I would actually think of using IR lamps instead of those bulky things. Or something that radiates heat on a surface, instead of just heating air.

Has it been done? Anyway, nice you found a solution, but I think building an enclosing for your printer might also work a bit? Thats what I did and it solved most of my issues.

Marco, what you dealt with is a general warping problem, not a problem of distorted overhangs on early layers. The overhangs Axis posted pics of would probably be fine if they were a couple cm above the bed.

Ohmarinus Wrote:
-------------------------------------------------------
> I would actually think of using IR lamps instead
> of those bulky things. Or something that radiates
> heat on a surface, instead of just heating air.
>
Maybe I used wrong word, but these are IR lamps (Philips Infrared lamp PAR38 IR 175W 240V E27 ES).

Yes, they are too bulky.

tsb4k Wrote:
>
> Besides printing ABS the other constant in my case
> has been a makergear nozzle (which is pretty
> flat). I wonder there is more heat going back into
> the print than there would be with a pointier
> nozzle).

I've also had problems with overhangs curling up on me, and the nozzle I made for my custom extruder was also pretty flat - flatter than the makergear ones. Your comment about the flatness got me thinking so I re-machined my nozzle to make it pointier, and generally expose less surface area to the ABS underneath. The attached photo shows a 60 degree overhang I printed with the new nozzle. When I printed this same part with the old, flatter version (same print settings - 235 hot end, 115 bed, 50 mm/s), the edge had a really wicked curl to it. I suspect the nozzle profile is actually a pretty important parameter which I haven't seen discussed much.
-Jeff

Interesting..

How pointy did you make it?

I have problems with the bottom ~3mm of my prints shrinking, the more infill, the more shrinkage.



Also pointy features like gear teeths tend to curl up, not to mention overhangs..

I have been suspecting that my hotend was too blunt, so I was actually about to write a post about it..

I also have a rather flat hotend, with ~2.5mm from the heater block to the tip, and the tip itself is rather blunt. I made it this way to get as much material as possible around the oriffice, in the belief that temterature would be more even.
But this might be a mistake.. I mean if you print slow, the heat has plenty of time to reach the tip, and if you print fast, the molten filament, will to some degree heat up the tip..

I notice this curling on small features too, particularly the balls in ball bearings just can't be printed because the ball edges curl upwords while being made, as a result, once there is enough curl, the ball is ripped off the base as the nozzle moves around.

I did a remake of my nozzle tonight, and from preliminary testing, it seems as it has fixed my problem with shrinking first layers.

The tip is now protuding ~6mm from the heater block, and as an added feature I made a PTFE heat shield, to keep the heat inside the nozzle, and away from the print.



The edge of the PTFE is ~120 degrees when printing at 230 degrees.

I did the same, only with ceramic wool, packed my whole heated block with the material and taped it up with Kapton. Works like a charm!

Here are before and after photos of my nozzle. I, also, added a little insulation on the underside of the heater block using a few layers of kapton tape. The pointier version solved my curling.

-Jeff