Success with 1.75mm- But Quality Concerns

So I’ve had some great success with printing in 1.75mm (Inland from MicroCenter) on my Mini. By success I mean it hasn’t been jamming, it finishes prints, etc. etc.
For example, here’s a nice big print it did: http://www.thingiverse.com/make:266145
I was able to do this by printing this awesome little 2-minute part: http://www.thingiverse.com/thing:1673712

Here’s my issue though… it doesn’t seem to want to print very accurately, especially on smaller parts. As you can see here it has a fairly regular fluctuation in diameter of, what’s supposed to be, a solid shaft here:

The weird part though is the larger things get, the less of an issue this is. This is actually two pieces mated together. The large-diameter (1.6") lower part has a perfectly fine edge. The hexagonal mated sections had a .005" offset and mate perfectly (about as close as I’ve gotten tolerances in 3mm too). However, once we get down to the 1/2" diameter section below the hex-drive column it starts to get a little uneven, and then obviously really bad, as you can see, in the hex-drive section (9/32" widest part of hexagon).
Thoughts?
Chris

I hope you found a solution for that problem
Can you guide me how to use the 1.75 to work with my mini?

So you are using the 1.75 without any changes to the Mini Head? Or did you replace the head with another extruder?

The mini stock head is designed to work with 3.00mm. it has a 3.00mm spec hexagon bore, a 3.00mm extruder body, a 3.00mm wide extruder notch. You “can” print 1.75mm fillament with it. You “cannot” print 1.75mm fillament with great accuracy with it. That variance you are seeing is pooling in the extruder barrel, etc. To successfully print 1.75mm high accuracy parts, you will want to convert to a 1.75mm barrel hexagon hotend with a 1.75mm nozzle, and change the idler and the extruder body out for a 1.75mm variant such as this one: http://devel.lulzbot.com/TAZ/accessories/fangtooth_guppy/stl/ and possibly my idler from here: http://www.thingiverse.com/thing:1355106 which is a stock mini idler narrowed for 1.75mm fillament (well taz idler, they are interchangable though 100%) A source for the 1.75mm hotend is here: https://www.amazon.com/RepRapDiscount-Hexagon-Hotend-1-75mm-Cartridge/dp/B00W4AIAX8 There may certanly be other cheaper and better alternatives. Any 1.75mm e3Dv6 or hexagon nozzle will fit that barrel. You could implement any or all of those in stages and improve accuracy. The barrel and the nozzle will give you the most improvement, followed by the extruder body and the idler. You may also want to change your fillament guide tube to a smaller diameter as well, though that will just prevent strain on PLA.