ABS overhang printing issues

Thanks to the extremely helpful reprap community I was able to concur the evil curling overhangs with a 1.5 w/t and a printing temperature of 250C. However I now have another issue, while attempting to print the heart gear some of the teeth come out less than perfect specifically in , however some teeth come out nicely. I am slicing with Cura and I set my outer shell speed to 20mm/s. is this due to the layer always starting or ending there? Do I need more retraction? Any help would be awesome....I can almost taste completion.

Thanks!!!!!

250C is very hot if your thermistor is Ok. I have used max. 235C on ABS. Your part looks too melted. Use a fan or lower your hotend temp or draw a perfect support structure. My little parts got better with a fan and a duct (ABS). And I mean a fan blowing to the plastic, not a hotend cooler.

P.S. Slic3r has a random layer starting point option I think....

Edited 1 time(s). Last edit at 01/29/2015 05:35PM by Plasteroid.

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Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]

When I ran at 230C I had curling on my overhangs. I adjusted my xyjerk and I am printing now. If that does nothing I will try out the fan.

Xyjerk did not change anything. The fan prevented the print from sticking to the bed properly. I believe it's caused by the print starting and stopping in the same place. Will a z-lift help?

Thanks

How hot your bed is? I have 110C and I start the fan after the first layer and I use ABS juice. My ABS curling has gone better with a 40mm fan which has a tiny tip duct. Perhaps your blows too much?

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Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]

A fan blowing onto your print when using ABS!?
Such a fan is only needed when printing PLA, don't use a fan when printing ABS.

@Plasteroid; I print ABS at 250 C also, the manufacturer of the ABS advises between 220 and 260 C

Yea I tried a fan previously with negative results and I figure I would give it a shot again. Like I said before I have not had any success with one. But can a retraction help improve the blobs created when the extruder moves to the next layer?

You you have Z lift enabled? I had the same blobs when I had it on.
Since I turned it off I have no more blobs.

Hey! I thought that a fan is bad for ABS. But then there was this on the forum: [forums.reprap.org] . I think that a fan can "freeze" ABS before it starts curling up. It can also prevent ABS sticking so perhaps it is some kind of "correct balance" what it needs? On big parts I don't usually use the fan, but look what I achieved to print with a fan on: [youtu.be]

...and it was ABS plastic.

P.S. Is it good ABS if you need 250C? Perhaps your printer wobbles when doing some direction changes?

Edited 1 time(s). Last edit at 01/30/2015 04:14PM by Plasteroid.

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Prusa i3, Ramps 1.4. Catnozzle 0.4mm
SketchUp - Enveloping Globoid Worm Gear - Part One - 3D Printed: [youtu.be]
DesignSpark Mechanical & more precise screw thread: [youtu.be]
Nicer Screw Thread In SketchUp ( Bolts,Nuts): [youtu.be]
How To Model A Heart Shape In SketchUp: [youtu.be]
How To Draw 3D Printable Snap Fit Ball Joint In SketchUp: [youtu.be]

What tem is your bed? I am guessing 100c or more? Lower it to 90c

I lowered my hot end temp to about 240C....that is the lowest I can go without curling. I also set up retraction at 35mm/s and .5mm with some positive results. My bed is currently at 110C. Now I get small blobs on the parts only on 1 or 2 teeth of the gear (still trying to print the heart gear) and then along the tops when it is creating the rounded sides. Would this be a sign that I need more retraction distance or speed or is this something that just happens and cannot be fixed. I will post reference photos after I take them.

Thanks for all your help.

I meant to say Bed temperature in my post. Lower it to 85c or 90c.

Thanks for the response. What will lowering the bed temp achieve?

When the heat from the bed is high matches up with the heater block (same side) the part can get overly hot on that side and cause shrinkage and the same effect your photo shows.

[reprap.org]

Scroll down to "Part Temperature" that black block is mine and the problem went away with turning the bed temp down. It was highly prominant on the side where the heater block on the hotend was.

My tuppence worth.

My settings for ABS are:
Hotend temp of 230 or max 235 deg C for ABS. No fan.
Increase acceleration to get sharper corners. Set Slic3R on perimeters first, then infil.
No lift on layer change. Retract on layer change, 2.5mm retraction. Seam position aligned.
External perimeters first - leave this unticked, so most layer change blobs are on the inside.