Lots of questions in your post!
There is a systematic process for getting correctly sized parts. I have not read the link but here is how it goes:
- Calibrate the extruder - this includes calibrating for the specific filament you are using. As you observed, filaments can vary a lot. Measure in 6 places over 12" and take an average for diameter. That should be good enough. It is a good idea to measure the diameter of the extruded plastic if you can. It is tricky since any stretch as it dangles down will affect the measurement. It is normal that it will be larger than your nozzle orifice, that’s called die swelling. Die swelling is affected by extrusion rate (back pressure) so extrude slow - say 10mm/s - for this test.
- Next you need to make sure that X, Y, Z steps/mm are calibrated accurately for your printer. The default values are in the ballpark but to take it to the next level of precision, calibrate your printer. You do this with a standard calibration cube. There are several (20mm cube) on the thing sites. This is where it gets a little tricky though - there is a relationship between final parts size, printer X/Y/Z calibration and slicer parameters. For instance, your X/Y/Z calibration could be perfect but parts may be larger or smaller depending on slicing parameters.
What I like to do is use a representative “no frills” slicer configuration (I use KISSlicer so I can’t help on that unless you use KISS too) and use it to calibrate the printer with a well behaved filament. I find ABS much better to use to calibrate than PLA because it has less die swell and the small amount of shrinkage after extrusion seems to compensate for that. Once I’ve calibrated the printer I never touch that. I then print a new part like your gear and measure it. If it is off, I compensate with the slicing parameters. I can usually get it spot on with 1 test print. I write all of this down (see my guide in my link) so the next time I use this filament I can usually get it right with the first print.
NOTE: you can actually calibrate your printer without printing by using a dial indicator mounted so you can measure distances along X movement, Y movement and Z movement. This is how we calibrate CNC milling machines. The same can be used with 3D printers, especially Cartesian printers like the TAZ.
3. Next, I calibrate the single wall thickness with a single wall calibration thing. This helps refine the slicer parameters for the specific filament I’m using.
4. Finally, I use my single layer test object to nail the single layer thickness for the first layer. I do this at least once at the start of every day/print session.
I designed and now manufacture 3D printed fly fishing reels. There are 9 printed parts and two assemblies that must rotate freely without slop. Here is a photo of the most critical:
These parts are “as printed” - no cleanup at all. The white part must have .05mm +/- .01mm clearance on the shaft for best operation. I print these in several dozen brands and colors of PLA and can get the perfect dimensions for all of them. But, some do require a slightly different slicer profile to get these results.
If you intend to produce precision parts with this level of 3D printer it can be done but you need to be systematic about it.
One thing I would like to stress, people always refer to “PLA” (or “ABS” or “Polycarbonate” - whatever the filament) as if it is a single material. It is not! Each filament within a chemical family (like PLA) has different pigments/dyes, plasticizers and even polylactic acid chain lengths and they ALL affect the properties of the filament. The good news is, you don’t have to know the details on what all of these attributes are, you can do a few simple profiling experiments to characterize a given filament so you get reproducible results in your printer.
Some other replies to your post:
Holes can be tricky - not only to print but to measure precisely too. There will almost always be a little “lip” on the first layer due to the smooshed filament on the bed. You need to trim that away with a hobby knife to measure. How you print affects this too. Most slicers allow you to print “inside to out” or “outside to in” and every slicer I’ve used defaults to outside to in. I printer my critical parts outside to in and I slow WAY DOWN on the perimeter print speed - something like 20mm/s for the final, outside perimeter. This is very reproducible (since print speed also affects part dimensions) and results in much better looking exteriors - no blobs from the start of the extrusion, better control over stringing, etc. For parts that have overhangs, it also provides a solid “base” for the perimeter paths to bond against.
Once you have been through this with your ABS filament you will be ready to tackle Nylon systematically.