Unnecessary retraction on first layer

Using Slic3r0.9.9.

I have slic3r pretty well tuned with my printer, but I still have a bit of a mess at the start of prints. For the first 25-50mm of skirt, nothing is extruded. Then it finally starts flowing fine. It can cause a problem because on the second go around, it will start dragging the bad skirt around and it eventually dislodges somewhere in the print. It's more of a nuisance than anything else.

Anyway, I never had that issue with skeinforge, so I sliced the same file with both slicers, and compared the gcode. Taking into consideration the prefix gcode I add, the first G1 command that slic3r generates is to retract 1.5mm of filament (G1 E-1.500). I DO have retraction between layers turned on, and the value I specify is 1.5mm, but I wouldn't think it would apply to the first layer. Besides, at the beginning of a layer, it should be doing a reverse retraction - putting filament back into the hot end.

If I edit the gcode before printing and change the 1.5mm to 0.5mm, then the print starts fine. I don't understand why this is being done or what setting might turn it off.

Edited 1 time(s). Last edit at 06/11/2013 11:08PM by jbernardis.

I guess it retracts initially to stop any plastic being deposited while moving from home position to the start of the skirt.

SInce I don't want to edit the gcode all the time, and since I don't want to write a post-processor for such a trivial change, I'm going to try adding 1mm of extrusion as the last line in my preamble.

I used to have a similar problem but I changed things somewhat. Firstly, I removed all the temperature presets in Slicr3 (Filament settings). I slice the model independent of Pronterface and save the gcode.
In Pronterface, I load the gcode file then set the bed temp followed by the hotend temp. When both are at working temp I purge the hotend 5-10mm to get a good head of plastic (which I nip off) then hit "Print". The printer immediately starts the job with a good head of extrusion instead of that long wait I used to get in Pronterface when it was buggering about with temps.

My startup procedure is as follows:

1.) turn on the heat for the hot end and bed.
2.) while they are heating, I slice/load file file as necessary from within my host program. Within the slicer I place a preamble on the front of the code.
3.) once the hot end and bed are ready I extrude until I get a good flow, and I nip off the end.
4.) THEN I hit the print button

Once I hit the print button, it verifies temps, homes, lifts 1.5cm, extrudes 1.5mm of filament, pauses for 5 seconds for me to clean the head, then drops 1.5cm (all of the preceding takes place in my preamble gcode). Then is starts executing the slicer generated code, but of course for slic3r it starts by retracting an additional 1.5mm.