Here's an idea, bonding passes.

I was looking around for ways to improve interlayer adhesion (specially with ABS) and I had a thought, how about after a layer is completed have the nozzle move down very slightly (for example 0.05mm) and do a dry run over the part being printer, that is to say, just move over the previous path without extruding material, just reheating and compacting the underlying layer so as to improve the bond between it and the one bellow.

Crazy? Would it work?

It would probably mess up external perimeters, but if it's done on the inside ones only it may increase the strength of the final part. What do you think?

a) dry run will take time. Oozing will be a problem
b) I don't think it is possible to heat through the printed layer of plastic in small enough time. Just using larger extrusion width and higher temperature IMO should give better results (wide extrusion is pushing the molten filament into the model quite hard).

For ABS, I have found that giving the completed part a brief dip or spray in acetone or rub-down with a kitchen towel generously soaked in acetone improves the layer bonds tremendously as well as providing a polished appearance. The acetone seems to partially soak between the layers and "melt" them together as well as relieving stresses caused by shrinkage. Thin walls will get quite soft until the acetone dries off, so handle the part carefully while it is wet. Don't allow pools of acetone to sit in or on the part. Acetone can also be dribbled between any layer splits caused by warping, then clamped to squeeze the split closed while the acetone dries off, after which the split will be repaired. Acetone is cheap and readily available online or from shops dealing in fibreglass supplies.

You could also experiment with putting the part into an oven and heating to 170C or so. You need to find the temperature at which the plastic begins to get tacky without flowing and causing the part's shape to distort. I've not tried it, and I suspect that a normal domestic oven will not provide a stable or fine enough temperature control, though with the help of a temperature sensor inside a domestic oven you may be able to control the temperature adequately by hand.

Dave

What if you had the perimeters offset in the Z by 1/2 the layer height? That way the outer layer would be 'spooned' by the inner layer. Instead of having layers just touching at tangentially, they would fit into the 'groove' formed by the other perimeter, almost like tongue and groove. Lots more surface area, less gaps for cracks to propagate from.

Just google search 'stacked pipes' for images and see how pipes naturally want to do this versus stack up straight vertically like we do with layers now. I'd love to see this option in vase mode to help give better inter layer adhesion.

I suggested something similar to Alessandro a while back: "Once a part has a minimum of two vertical perimeters could the user choose for the number of perimeters to alternate between one and two (or any chosen combination of perimeters if than more two perimeters were specified) so that in-fill for alternating layers would extend over one (or more) of the vertical perimeters? The walls and the in-fill would knit together. This would give increased strength - I think - when strength was needed."

I'm not sure if I explained my idea clearly but every second row (or user defined) the infill would extend to the outermost perimeter (or other perimeter number depending on how many perimeters there were; again, it would be user defined) over top of some number of perimeter loops depending how many loops were specified.