Overhang and bridges - what are the limits?

Hello,

for a LED lamp I'm developing, I printed a test object, to try out, what are the design limitations regarding overhang and bridges (attached pictures).

The object is printed with ABS at 230° extruder and 120° bed temperature over PET tape. It has a large 45° overhang. At the beginning of printing the fan was switched off, resulting in some problems (circle 1 in the pictures). I switched on the fan and the overhang was stabilized.

Bridges up to 20mm came out with a only small (in this case acceptable) slack.

I'm not shure if these are the limits, which I can expect, or there are settings in Skeinforge for further improvements.

Another problem, I discovered, is a gap between layers (circle 2 in picture 2), probably by some thermal strain during printing. Is there a way to avoid this?

Generally I'm looking for a way to improve the layer adhesion, to avoid heavy structures at the arm of the LED lamp.

I haven't used a fan with ABS since using a heated bed. I expect that is causing the de-lamination. You could try extruding hotter to prevent that. I extrude ABS at 250C.

Alternatively you can improve the bridging by stretching the filament more. I.e. making the extruded cross section smaller than the cross section you get extruding into mid air. Also keeping the width / height ratio close to 1.5 will bridge better than bigger values in my experience.

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