Help - Problems with new 0.3 mm hot end setup - Prusa i3 RAMPS 1.4

[iras]

I just changed from an older J-Head 0.5mm hot-end to a new Mk 8 0.3 mm hot-end.

My old prints using the 0.5 mm nozzle were OK (none of the problems described below), but detail for small parts was not what I was looking for, so I purchased the 0.3 mm hot end. Very nice. Simple Install.

Now I’m having a few problems, which I believe are settings and not the head itself. I’m using the same filament – PLA.

I’m now seeing Three problems, probably related - pictures below: (1) I’m now getting some very fine hairs as the print is being printed. (2) The first part of my initial layer (actually a skirt to get material flowing) tends to “skip”, putting down material/gap/material/gap, etc. (3) When the print is finished, the nozzle continues to extrude material. I’ve even manually retracted 2-3 mm and it still extrudes material for a while (a couple of inches worth of extrusion of regular diameter - 0.3mm approx. – not just a wisp).

I’m using Slicer with Repetier-Host. I have the filament size correct (same as before, 1.75), nozzle size at 0.3mm, first layer height at 0.25mm, subsequent layers at 0.2mm, printing at 205C (what I used with my 0.5mm nozzle), bed temp at 45C. I think I’ve correctly readjusted the bed level for the new head (piece of paper between the head and glass will slide in with a little resistance. I have retraction set at 3mm.

Any ideas what setting(s) I might change to get this to print well? Thanks. Pictures:

This shows the hairs (this happens to be a better print). The strand going off to the top-right is what happens after the print is finished and I manually have the extruder move to the right limit, raise up 10 mm or so and retract about 3 mm. Then it keeps extruding off to the side for a bit.

[3dkarma]

1. Ooze. Do you have retraction set on the slicer? You'll need to fine tune this to get ride of the ooze and hence the strings.
2. Head is too far away from the bed and the first layer isn't being smooshed down into the bed enough.
3. Same as 1.

[iras]

I have the retraction set to 3mm. Should it be more? What's strange is that I can use manual control to retract a few mm and it still keeps oozing.

I will try with the bed closer to the head. Simple to try.

I was wondering if my temp might be too high? Maybe the PLA is liquifying in the barrel - although once I retract I'd think that there wouldn't be pressure to cause the liquid PLA to keep coming out. But if I leave the hot-end heater running after printing and after retracting a few mm, it will continue to ooze for a couple of minutes! Not quickly as if under pressure, but a strand (nozzle diameter) that will get a few inches long.

Thanks.

[3dkarma]

What temperature are you printing at? The higher the temp the more ooze you will get, but lower temperatures will affect printing speed with a 0.3mm nozzle; you also need to be careful of inter-layer adhesion at lower temps.

[iras]

I'm printing at 205C with the heated bed at 45C