Coast At End not working for support material nozzle

[andre]

Use to work on 2.1.x, noticed 2.2.1/2.2.2 does not work for support material nozzle (but works for main nozzle).

[JoeJ]

I disagree. I just created a sample file and checked both the preview and the gcode itself. Both show the coasting properly being applied to support material.

[andre]

You're right, the more I look at it, it is working, but not the way I expected it to. It says "stops extruding prior to end of loop", and while laying down a linear pattern of support material ,back and forth, it must be considering an entire layer as a loop. Thus, it is only coasting at the very last segment, where I was expecting it to coast at every long segment before it turns around and lays the next segment in the reverse direction.

They should probably allow us to define coasting after a specific length of segment, where oozing would be of most issue, rather than an entire loop.

Try placing a 40mm or so part, raise it a mm above the floor to force support material (in a linear pattern) to be placed. You should see coasting is not done until the last segment.

[jimc]

the coast happens before every retraction. the idea is to lower the nozzle pressure before jumping and starting the beginning of the next extrusion. be sure in the advanced tab you have "only retract when crossing open spaces" turned OFF.

[andre]

Right, but if I'm creating support, zig-zagging along, would coasting at the end of every segment serve a better purpose? If the coast only works before the end of a retraction, what is the point since I have retraction settings available to handle that situation?

[jimc]

no not at all. coasting is there to control blobbing and ooze. retraction isnt always enough. if you coasted in the middle of an extruded line your print would be terrible. the extrusion would look like morse code. its only for when the nozzle stops printing and lifts off the print to relocate only. keep in mind that your zig zagging or end of a segment is not the end of a line or extrusion. its a direction change only. even though the direction changes there is no reason to stop extruding.

[andre]

No, there is a reason to reduce extrusion during a coordinate change. When my bot (and other bots) decel to make a 90 degree turn, there may be an over pressurization of plastic built up, causing overextrusion right at the moment it turns.

The zigzag IS the end of a line extrusion. Look at the code, it will decelerate to a stop before making a direction change and starting a new short line. I need the ability to stop extrusion before every zig zag, which will help control over-extrusion from built up pressure.

This is what I thought this feature was for. Apparently it is simply just another step done before retraction? And if so, doesn't do me any good.

[jimc]

what your speaking of is something that is handled by the firmware of your printer not the slicer. the problem with doing all those calculations is that current controller boards arent fast enough. currently we are really completely maxed out processing power in these machines. yes the coast is for the end of the extrusion line then the retract takes place the the restart is for the beginning of the extrusion line.