blobs in my holes

Hi all,..

RepRapPro Huxley.
0.5mm Nozzle
1.75mm PLA
190 Degrees Nozzle
Cooling Fans Fitted
Bowden tube extruder
Slic3r and pronterface.

printing nicely.. except... my holes !

The place where the head starts the shell around the hole, there's always a "blob". Its quite a big blob.
The holes in the pic go from 1mm to 5mm.
The blob is big enough to fill the 1mm hole and leave a sizeable artefact in the others.
I've upped my retraction to 2.1mm (from 1.6) I *think* that helped a little.

I'm going to next check my extruder calibration. (not done it for a while),
maybe up my retraction a bit more ? 2.4mm ?

Before I do more testing by printing these test pieces, I'm wondering if anyone has any suggestions.

for instance, I'm wondering how long my bowden tube should actually be on a Huxley, the tube that came with my Huxley looks awful long !

anyway..

any suggestions to test, gratefully received.

Dave.

Cant remember off hand ( im not at my printer now ) but some of the slicer software has " extra length on restart" after a retract. Maybe its that ..assuming that a retract was performed prior to the hole shell being printed. Worth a look i guess.

Hi all, an update.

Spent all day printing calibration pieces and messing with retraction etc in an very organised manner. (I do a logical day job, logical is my basket)

improved just about everything, but could not lose those artefacts. Then I measured the holes.. all 0.5mm under.

It's a 0.5mm nozzle, but it turns out it's actually extruding at about 0.65mm

So, I put 0.65 into slic3r, hey presto, they disappeared. I worked it out by looking at the laydown pattern and watching very closely.
You can see where the inner shell (inner to the object, furthest away from the hole) of the 2 shells has swelled a little and pushed out the end bit of the shell that lines the hole, into the hole. (if that makes any sense)

so, a bit of thinking later, and more test prints, and I thought "hang on" it's obvious that it's not 0.5 wide, it's some sort of die swell, and it was.

oh.. and slow,... I've just about slowed everything down from the RepRapPro recommendations.

Next step.. I was thinking a 0.3 nozzle for gears and things, but tbh, I'm now printing so well with my 0.5 I'm leaving it alone. I'm going to build another Huxley with a 0.3 Nozzle and have a 0.3 and a 0.5 one !

Hi!

It is a BUG in last slic3r beta version !
Try older version 0.9.8 with no any blobs!

MANY thanks for the info!
I believe I have greatly improved my prints trying to get rid of those blobs, so it wasn't wasted time either!