I use 3d printing pen to glu and fill with exact same filament you used to print the parts. It is very strong and bound is good. You may need some polish if your gluing technique is less than optimal, but it is easy to learn. xyzprinting 3d printing pen on sale at newegg for $15-20
Coating with Epoxy Resins and Paints also works, bound less as well as melted PLA, but good for coating and smooth.
for Chemical Treatments, use Ethyl Acetate (often called M.E.K. substitute) and THF (Tetrahydrofuran). Both chemicals can be applied as either a controlled vapor or by dipping. Ethyl Acetate is a lot safer than THF, it is basically purified alcohol and vinegar mixture, but you may want to google for best protocol.
(Da Vinci 1.0, Jr. 1.0 RAMPS, miniMaker) X4, (Creality CR-10S, CR-10 mini, Ender-3) X4, Anycubic MEGA X4, Anycubic Chrion X1, ADMILAB Gantry X2 (MonoPrice Maker Select V2, Plus, Ultimate)X4--Select mini X1, Anycubic photon X4, Wanhao duplicate D7 X1.
iNSTONE Inventor Pro X2, CTC Dual X2, ANET-A8, Hictop 3DP-11, Solidoodle Press, FLSUN I3 2017X1