For the sections that are sagging, you can try a couple of methods:
1) Print at lower layers. If you are printing that at .3mm, printing it at .1 (for example) would take 3 times longer, but you would have as drastic of an overhang.
2) Under speed settings in Slic3r, check your "Bridges" speed. Stock runs at 60 mm/s. Increasing the speed for bridging would allow the overhanging filament to cool faster. I don't know if the top sag is a bridge or a perimeter, but you can try this and see if it helps. If it doesn't, just scale the speed back to whatever setting you prefer.
3) Mount a fan to your hotend. This is pretty much mandatory for printing PLA if you want good results, but it can also come in handy for some ABS prints

Things I done after last post (2014-11-01);

1) I printed a anti-blackslash;
2) Ajust E VREF and Z VREF;

The improvement was huge, but still have some minor problems to fix. I need more advices.
Thanks in advance.

I recommend starting a calibration cube print with relatively long walls (try 50mmx20mm and let the 50mm side face the side where you will be when you adjust VREF). Turn VREF down (Moire indicates too high in my experience) on E in *small* increments. Give yourself time to look for differences. By the looks of it it's not too far off, so go slow. You may want to run a few calibration prints and look carefully. As AZERATE mentions, you are using 1/16 steppers so you will never eliminate it 100%, but you will come close.

Also, it looks like you are having some backlash from the Z rod. There are many printable designs on Thingiverse to combat this. If you go this route, bare in mind that the stock Z rod is 5/16".

1. balance bed
2. Tighten and/or align belts
3. Calibrate extruder steps per mm
4. Calibrate extrusion multiplier.

Is slightly better , but still having strings and therefore to compress the object (see photo compared with a printed before start of the problem ) .

The nozzle is .35 mm and i bought the SD3 in May of 2013.
I kept the nozzle diameter at .42

What should I do now ?

Thanks in advance .

In that case OP you should double check that!

Your filament settings look fine since the SD3 has a 0.35mm nozzle.

FYI not all SD3's came with a .35 nozzle. Sometime between August and October of 2013 they started to ship with the .40. I think that's the correct timeframe.

thanks for the tips. i will try and give you feedback.

Nelson

AZERATE,

what should be .42? The layer_height?

Thanks.

Nozzle diameter. You want to allow 20% for expansion.
For exapmle, if you have a .4 nozzle, the setting should read .48

There are a couple things off, but nothing simple calibrations can't fix
jagowilson's previous post is a great way to start and diagnose.

If you google or use the search function on this forum you will learn how to do all of this. Do *all* of this (you can't skip steps in 3d printing), and report back. If you get stuck along the way, we're happy to help.

I know you said you did all of these things, but do them again. I've done it so many times on my machine it makes me sick, but it's the only way you're going to improve your prints, which is the goal, right?

The reason I say this is blobs are the least of your worries based on that print. You have a lot of calibration to re-do first. A lot of the things I mentioned above can in fact *cause* blobs, so fix these things first.