Posts: 1
Joined: Tue Apr 16, 2019 2:12 am

Coasting issue

Tue Apr 16, 2019 4:32 am

I’m trying to fix the blob that forms at the end of the loop. I calibrated the extruder steps and the multiplier.
The only parameter I could find to deal with this issue is coasting. After I printed several cubes, I noticed that it created another vertical blob which I couldn’t explain. Using the high-speed camera, I recorded the extrusion using three different coasting parameters (off, 2mm, 8mm) to get a better understanding of what it does.

Coasting feature: ... ch-plastic
Coasting will turn off your extruder a short distance before the end of the perimeter to relieve the pressure that is built up within the nozzle. Enable this option and increase the value until you no longer notice a defect appearing at the end of each perimeter when the extruder is coming to a stop. Typically, a coasting distance between 0.2-0.5mm is enough to have a noticeable impact.
The problem is, when the extruder stops at the defined coasting value, the movement doesn't continue at the same speed, but it stops for a brief moment before it continues the movement to the end of the perimeter. This was a surprise as I was expecting that the speed won't change until it closes the loop.

Is this how the coasting feature works or is the problem somewhere else? Some other parameter, firmware?

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Posts: 9
Joined: Tue Sep 02, 2014 4:53 pm

Re: Coasting issue

Tue Apr 16, 2019 12:08 pm

This is exactly what I have been trying to solve since V4 came out. I guess Cura is the only option now as this has been broken for a long time.

Also, awesome use of a high-speed camera!!

Posts: 852
Joined: Fri Oct 17, 2014 5:00 pm

Re: Coasting issue

Wed Apr 17, 2019 4:09 am

It seems to be a bug.

What coasting has to do is to stop the extrusion of material to relieve pressure in the nozzle and prevent blobs and not interrupting the print line.

Bug or not, it will be the question how the coasting-command does work and therefore it can also be a general firmware problem. Or both together.

I never use coasting, it makes more trouble than it is useful.

Beside, as you can see in your very excellent video (!!!) you are missing cooling. The printed material stays soft for 3 or 4 layers.
The mass of material (0.75 x 0.50 LH) is to big and the lines the print head has to go is to short to win enough time for cooling down by itself. This also will enforce the bad coasting effect, because the material runs out of the nozzle, more than unavoidable.

Only using the coasting without a retract makes no sense. My opinion.


Posts: 444
Joined: Thu Aug 30, 2018 1:23 pm

Re: Coasting issue

Thu Apr 18, 2019 10:23 am

I took a look at your gcode and everything appears in order. It is possible that the firmware of your printer takes a second to process this G1 command and so in turn pauses slightly but there is no way to my knowledge that the gcode could be written differently to avoid this side effect.

Posts: 208
Joined: Tue May 20, 2014 11:23 am

Re: Coasting issue

Thu Apr 18, 2019 1:29 pm

I think it is more a firmware issue since all G-Code commands are processed sequentially. This is why I switched to Linear-Advanced, so the E-Axis is handled independ and coasting is not needed anymore.

PS: Nice Video footage

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