Welcome to the SeeMeCNC Community

Well, I had this issue forever, and I wouldn't mind to live with until my boss freak out. He basically wants me to fix it asap.

So here we go the picture is a gif animation, 3 sec for every pic.
You can see the small spot circled in red.

I know it could be a lot of things, whether the stepper is doing uneven work, the carriage is loose, cheapskate,etc. I have done few check already, and I couldn't figure out for a while. You guys got any idea? Or you can click the following link.
http://www.mediafire.com/convkey/452e/t ... u241fg.jpg

I have been having the same problem and I think it is mostly a slicer problem. I think what is happening is that the extruder nozzle doesn't go all the way to the perimeter because the slicer assumes that the plastic will flow forward a little bit and fill in the gap, but if the filament doesn't flow enough then it will not fill that gap.

Hey, I've been using both slic3r and cura. I still have the same problem over and over again.
On the ultimaker, I used to have this issue, until I have done a complete upgrade.

It can be a few of things, there is a setting in at least both Cura and KissSlicer that will change the edge infill overlap % increasing it can reduce the issue.
Printing the first layer slower can often help, sometimes if you watch what happens you can see as the head changes direction it pulls the plastic away from the edge leaving a small gap.
Any sort of backlash can cause it (loose belts, loose arms etc etc etc)
Using a wider first layer extrusion thickness can help, Cura won't let you do this, but increasing the overall extrusion width can help.
If you are under extruding you will get this, it's hard to tell from your images if this is the case.
You really have to watch the print closely and figure out what's actually happening.

One thing I have found that helps to eliminate those gaps is to set the infill width to be slightly less wide than the extruder nozzle width. My extruder nozzle (E3D V4) is .4 mm and I have the infill set to .39. If you leave that entry blank, Slic3r will set it to 1mm or more, which helps to create those blank edges because the software assumes the extruded plastic automatically covers a certain radius around the nozzle as it is being extruded. It doesn't account for the directional effect the nozzle can have on infill, which leaves edges around certain sections kinda blank. That sort of thing tends to go away when the infill width is smaller than the actual nozzle width.

Currently the infill overlap in cura is set at 15%, I may set it 18 or 20 on tuesday and give it a check.

How do you set the infill in matter control?

Is it the overlap setting?

.49/.50 = 2%