Slic3r print quality drops on certain parts of the print from 50% to 100% layers

I have a particular object that I can not get to slice/print correctly with slic3r.

The object is essentially a rectangular box which suspends letters within the box, if you pick the object up you can see right through the cut out letters the letters are held in place with 3 very small bridges between the letter parts and the main box, the bridges are made from layer 1 up to 50% the height of the object so you don't see them on the front face and makes it look more like the letters are floating in the box.

So essentially every layer between the first and halfway up the object is exactly the same, then from 50% to 100% in layers the object looses 3 little bridges but for 50% to 100% each layer is the same.

Now when I slice and print the object with 0.9.8 the first 50% of layers print perfectly (well apart from a few blobs which I seem to get in all slic3r prints) but from 50% layers to 100% layers something goes wrong the outer box area seems to continue to print with good quality however the floating letter parts seem to go down hill, there is a marked change at exactly 50% of layers, the perimeters of the floating letters seem to get very messy where they were perfect earlier in the print and extrusion rate on the infill of the letters seems to be too high as by the time the print is finished the letter parts are about 2mm higher than the last layer of the rest of the print so it seems to much plastic is being extruded on the infill of the letter parts causing the layers over time to build up higher than they should and causing the head to drag over this area by the time the print gets close to completing, again the box part of the print completes perimeters and infill almost perfectly.

The letter parts are not warping or peeling up during the print the fact that I can look down the inner line of the model and see an instant reduction in quality in part of the model at exactly 50% of layers onwards tells me it is something within the slice is the problem also that the other part of the model is completed correctly tells me that is is not my printer that has gone wrong.

I did read somewhere that slic3r does not properly take into account the widths of extruded material (although I may have misunderstood) and wondered if this was a possible cause in this case?

Are there any known bugs that may cause this behaviour?

Understand it maybe difficult to understand what I am explaining here so I will try and upload some pictures, the .stl and .gcode tonight, will also look for another slicer to try slicing it with for comparison.



**** Files now attached ******

Edited 2 time(s). Last edit at 02/08/2013 01:22PM by markab.

Now with the correct gcode file mb_fixed.gcode