Out-of-the-box, 3D printers often produce "fuzzy" prints, especially at higher resolutions, and particularly when printing with ABS. In the picture above, the two green standoffs were printed in ABS from the same .STL file (shown in the lower picture.) The upper green part was printed with the default settings, while the lower one was printed using an adjustment that this Instructable shows you how to do.
Step 1: Fuzzy 3D Prints
"Fuzzy" 3D prints, as shown in the first picture above, have random extra blobs of plastic sticking out from the sides. In the second picture you can see that the part--created using different settings--follows the original design more closely and provides a smoother, more uniform surface.
Step 2: Understanding the Problem
So why is this happening? There's a widely ignored setting your printer uses to figure out how much plastic is squirting out when it pushes a given length of filament through the nozzle: the filament diameter setting. I had always assumed that all filament was manufactured with the correct diameter, but it turns out this is not the case. My printer uses filament advertised as having a diameter of 1.75 mm, the default value in the software is 1.77 mm, and my filament (purchased from MakerBot) is actually 1.95 mm in diameter.
The picture above shows the modified setting in the MakerBot desktop application, but there is a similar setting in ReplicatorG and other print preparation/slicing applications used on other printers.
Note: While an incorrect diameter is usually the problem, this can also be caused by the extrusion multiplier setting, the nozzle diameter setting, the extruder steps per mm setting or manual extrusion settings being set incorrectly. Getting these set up correctly is beyond the scope of this Instructable.
Step 3: Measure Your Filament and Change the Setting
To find the diameter of your filament, use a micrometer caliper to measure it at several points--on the filament that has not gone into the printer--and average them. (Filament that has gone into the hot end has often been melted and narrowed to fit into the nozzle.) Then put this value into your print preparation/slicing software, generate a new print (G code) file, and try printing. The new part should be less fuzzy. Remember to measure and change the setting again when you switch spools of filament.
No caliper? If you are doing 3D printing, you really should have a micrometer caliper. Harbor Freight regularly puts an inexpensive 6-inch digital one on sale for $11 with a coupon, so do yourself a favor and pick one up if you don't have one. While the $11 one is better than nothing, if you are doing any serious work, you will probably want a better one. Mine is a dial caliper that I got at a clearance sale years ago when the digital ones first came out. It works well, and if you like old-school equipment, you can still find dial calipers on eBay.
Step 4: Experiment
Once you have your printer producing reasonably good prints, you may still want to experiment with increasing/decreasing the filament diameter to get the best possible prints. You may want to do the same with the hot end temperature. Have fun making good prints!