Blob when printer restarts after manual color change.  

RE: Blob when printer restarts after manual color change.

try searching Beauty Spot.  there should be a number of posts on this subject. 
 
regards Joan

RE:

Will check, thanks for the quick replyl!

For now the issue seems resolved by enabling the wipe tower with No sparse layers selected, making it only 1 layer,

still have to catch some filament deposits when the extruder returns to the last position before the M600 [using ultra fine tweezers seems better then trying to use pliers] but the blob is deposited into the wipe tower
thinking about editing out the return to last position in the gcode, but for now should be enough to finish this batch of prints

RE: Blob when printer restarts after manual color change.

update, adding a loop around the object of 2 layers solved the 'touch last position' with the M600 command.

combined with 2 layers wipe tower - no more unexpected blobs and extrusion on the models

RE: Blob when printer restarts after manual color change.

I'm also suffering from this issue now having print aafter print fail du to it. And I don't think it's slicer related but firmware how the M600 works.
My prints are flawless, the filament change goes fine, when I say I'm ready the nozzle starts to move to where it needs to. So far so good, but here comes the fail.
Once at the print start spot the nozzle pauses and sits there, then extrudes a HUGE blob, enough is extruded that the printer complaints about a stuck filament and starts grinding. It then return to the change spot and ask me to reload which it does fine, then continue printing. But more often than not the print is ruined because the nozzle hit that big blob hard and gets knocked out of position causing layer shifts, it it didn't the first time it will do it the next round. 
If it wasn't for this weird pause and mass extrusion after a change I would have absolutely flawless two-tone prints.
I've tried deleting the after filament change gcode or changing the value of it, none of that makes any difference, I've tried with and without wipe tower, no difference. Not even using PrusaSlicer.

RE: Blob when printer restarts after manual color change.

For those still interested, I believe I have found a solution:

Set the "Extra length on restart:"  setting equal to the negative value of the "Length:" setting  (4 default) under the bottom extruder setup "Retraction when tool is disabled (advanced settings for multi-extruder setups).

When I set this to -4 I do not get the G1 E4 commands

If you set the "Length:" to zero to disable it it will actually place a G1 E-.8 retraction and G1 E.8 at each tool change...  This is my default retraction length and then behaves as the other M600 commands.

RE: Blob when printer restarts after manual color change.

I had similar issues at one point with Manual MMU (using M600 in the tool change gcode). I was seeing "G1 E4" in my print gcodes after tool changes. I tracked this down to my printer profile in the Extruder# settings all the way at the bottom there was an expert setting "Retraction when tool is disabled (advanced settings for multi-extruder setups)/Length:" that was defaulting to 4. I don't recall noticing, but there was probably a "G1 E-4" right before the tool changes, but since it was soon followed by an M600 its effect would have been hidden.

Looking at the Prusa supplied profiles for MK3 and MK3S this value is 4 but grayed out because they are single extruder profiles. If you are modifying a MK3 printer profile for Manual MMU, change the value to zero or get big blobs at every color change. The current Prusa supplied profiles for MK4 (single extruder) the grayed out value is 0 so modifying a MK4 printer profile now for Manual MMU shouldn't have this issue.

I haven't experimented, but I doubt this would happen in regular layer-based M600 injection in the gcode preview, so YMMV.