Issues with combing

[Bad_Mechanic 0]

My Ender 3 was making a very strange "thump" sound while printing. Unfortunately, the sound is quite loud and disturbs my wife. I finally figured out what it is. Right before Z moves up one layer, the table executes a very rapid and very short back back and forth movement, and it's that movement which is causing the sound. It turns out that movement is caused by combing. However, when I turn combing off, I get blobs on the surface at the Z axis transition points.

 

I'd appreciate any help in figuring out a solution to eliminate or minimize the thumps, while also preventing surface blobs. 

[burtoogle 516]

Hi @Bad_Mechanic, please attach a sample of the gcode that exhibits this problem so it can be investigated. Thanks.

[Bad_Mechanic 0]

There are two gcode samples attached. They are from the same STL file, with the only different being the print temperature and combing being turned on/off.

 

200.gcode has combing turned off, it does not make the thumping sound when printing, but has surface blobs.

 

195.gcode has combing turned on, it does make the thumping sound, but does not have surface blobs.

200.gcode

195.gcode

[burtoogle 516]

Hello @Bad_Mechanic, thanks for the files. Actually, both of those gcodes are using combing. The only differences they have are in the print temperature. I think the project file could be more useful as that will show me the settings so could you please attach that. Thanks.

[Bad_Mechanic 0]

There's a very good chance I mixed up the files as I was doing this at midnight this morning. When I get home I'll redo my test files with combing being the only difference, run both of them to verify them, and then update this thread.

[burtoogle 516]

Thanks. Meanwhile, I think I know what's happening. You can reduce the size of that little wiggle by using the "no skin" combing option. It will still wiggle a little but not as much. I am looking into how it can be removed completely.

[burtoogle 516]

FYI, this little wiggle is not caused by a problem with the combing per se. What's happening is that the slicer is moving the nozzle away from the perimeter wall so as to avoid doing a retraction on the wall. This may have made sense in the past, I am not convinced it is beneficial. There is currently no way to disable it.

[Bad_Mechanic 0]

Sorry for the slow reply. The new files are attached. They should be identically aside from combing. I printed both an verified that no combing left blobs and with combing made the thumping sound.

 

I also tried the no skin combing option, but it didn't seem to be any different from the combing option.

 

 

200_combing.gcode

200_no_combing.gcode

[burtoogle 516]

3 minutes ago, Bad_Mechanic said:

I also tried the no skin combing option, but it didn't seem to be any different from the combing option.

 

Using the no skin combing only reduces the size of the wiggle, it doesn't remove it altogether.