Slic3r adding extra move before retract causing blobs

Hey all,
I have been doing calibration print after calibration print trying to get things perfect. I've never gotten holes to be the right size, so that is what I was working on when I found this problem. I made a simple calibration piece with four holes and four pegs. I'm getting a consistent row of blobs in the holes.

It's not wipe, retraction, z-lift, extra length on restart, avoid crossing perimeters, or anything else I could think to turn off; the offending move is still present when I turn all of that off.

Here's a good example of what happens in the gcode

G1 X87.448 Y83.330 E1.59741  ; the last move of the arc that makes up a hole I'm printing - head is at the 270º point in the circle
G1 X87.662 Y83.634 F12000.000  ; THIS IS THE PROBLEM LINE
G1 F2700.000 E1.09741  ; retract
G1 Z0.400 F12000.000  ; lift Z
G92 E0  ; zero extrusion
G1 X87.583 Y83.007  ; non-extruding move to the next area to print

This example has the retract (but not wipe) enabled to show why this is a big problem. On the problem line, the extruder moves part of the way out into the hole and allows plastic to ooze out forming a blob before it has a chance to do the retraction. The feedrate matches what I have set for non-print travel, but I don't know why it chooses to move there into hole before it does the rest of the things. It could be that Slic3r is trying to move the print head into the part before doing retraction but is mistaking the outside for the inside.

I can attach files and pictures if that would help. I'm thinking this is worthy of a bug report. Hopefully someone here will have an answer instead.

EDIT: Commands very similar to the problem line seem to exist after most (all?) connected paths before non-extruding moves. Most of the time they move the print head into the part (good) but in these holes, the moves should be in the opposite direction.

Edited 1 time(s). Last edit at 07/09/2013 04:28AM by duckythescientist.

I've noticed the same thing on MY prints Duckey. I'd like to see any replies to your question. Also, I've noticed on this forum that if you type the name nophead in a post, a knowledgeable guy (named nophead) magically appears and may help you!

Nophead Nophead Nophead. Like Bloody Mary, right?

But anyway, I submitted a bug report to the Slic3r Github. I'll post back if I find out anything.

And Nophead, if you do show up, I'd like to let you know that your auto retracting z-probe idea is absolutely amazing. I borrowed the concept for my printer, and it made a world of difference.

Ha, that used to be true as I used Google Reader to search for nophead or Mendel90 at lease once a day. Since Google pulled it I have no way of keeping up with these forums because Feedly doesn't have a search and only updates about every three hours.

Having said that I can't help you with slic3r problems. It is riddled with bugs and doesn't do anything the way I would do it. For example it combines retracts with moves. With my own software I retract at the end of a run before moving and if it is an outline or a hole I wipe by moving a little further round the loop before moving off to the next filament run. Retracting while moving might be a bit faster but I prefer quality over speed.

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[www.hydraraptor.blogspot.com]

I took a quick look but couldn't find your slicing software to download. I may go ahead and try Skeinforge again even though I really like Slic3r most of the time. It'll be a hassle to get Skeinforge working because of all the config options, but I'm getting tired of blobs in my holes, strings, and holes too small.

I don't have any slicing software. I use Skeinforge and process the gcode with a Python host before sending binary UDP packets to my older machines. I haven't published it and now use Marlin and Pronterface for my new machines.

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[www.hydraraptor.blogspot.com]

The problem has been fixed in the current but unreleased version of Slic3r. I got it built and working in Ubuntu.

I still can't get holes the right size, though.

Was that the 9.10b version?