add dwell after retraction

I am experimenting with a novel nozzle design, and am having trouble with the extrusion bead being pulled with the nozzle at the end of a pass. Retract alone doesn't help, and would like the extruderhead to pause (dwell) for 2 or 3 seconds after retracting to allow the bead to cool enough to detatch from the nozzle when it pulls away. I know nothing about postprocessing scripts or perl or any of that, but I am hoping it would be pretty simple to add to the g-code. I think it would make a big difference in my print quality with only a minor cost in added print time. I did a quick search on the subject and found no answers, forgive me if I overlooked an obvious solution.

A related but more complicated problem, is I would really like to add a dwell anytime there is a radical change in direction in the print path, say anything over a 90 degree sharp turn. I have a similar problem when the bead backtracks along side itself, it pulls itself back along the path. I know I can slow the print down overall, but I don't want to sacrifice the overall speed for an occasional turn.

Any suggestions would be greatly appreciated.

I don't think there'd be any way to do that without a post-processing script. You'd have to look for everyplace the e axis moves in a negative direction.

But thinking this through, I'm not sure it would solve your issue. When you retract, you are not stopping the ooze necessarily - you are just buying some time to get to the other end of the move before it starts oozing. Also, by leaving the head in place, I think you'd be subjecting the area to increased heat which would mean, to me, that it wouldn't solidify like you want.

Also, I think you are underestimating the negative effect it would have on your printing time. I never tried to quantify it, but it seems to me that there's a lot of retraction going on in my prints, and 2 to 3 seconds on each would end up being a lot of additional time.

And then stopping on corners would just exacerbate this increase in time. Rather than stopping in corners, it would probably be better to tune your acceleration settings. If you slow acceleration, it would turn corners more smoothly without actually stopping. Also, stopping will still have issues if you do it at high acceleration.

Hi jbernardis,
I'm not worried about ooze so much-- these prints are being resurfaced in wax for investment casting. My problem is that the bead is being pulled out of place because they don't have enough time to cool. I've got extra fans cooling the extrusion, but they don't have time to have an effect with the immediate movement of the printhead.

With regards to the effect on print time, I design my models to minimize sharp changes in gemoetries. For these models, I figure it'll add a total of 10 sec per layer, on average, 17 minutes per 100 layers-- I can live with that. The issues are arising in places where the slope of the model is requiring more than one perimeter to have sufficient support for the next layers, which will create realtively short loops in the print path. To better explain my problem, I am printing thin walled models with fat layers. I can't rely on adhesion to the previos layer to prevent the bead from being pulled by the printhead, and when I lose that part of a layer, it takes many layers for the wall to be recovered. Essentially, I am trying to push the geometry produced by the nozzle to its maximum.

I suppose what I'm asking for is a quick primer in how to write that kind of postproccessing script, or point me in a direction to figure that out for myself as effiently as possible, if such a thing is possible.

According to the wiki, the G4 gcode is supported. A simple search and replace for retracts and add a newline after it with "G4 P3.2" (for example) will cause a dwell of 3.2 seconds. Modify the P value to suit your needs.

The hot nozzle will keep the bead of plastic it is in contact with molten no matter how long you pause.

Dave