Hello

Background:
I am new to 3D printing. I need to create a prototype for a product that will ultimately be made from PE (Polyethylene/Polythene). I have just received my first 3D prints back from a 3D Printing Service (in London, UK). They use SLS to print in PA2200 Nylon. Fwiw, the are using an EOS Formiga P100 (or P110) 3D printing machine. I think the layer height is 0.1mm.


A) GAP SIZE
My model I have designed involves a 'Male' part that goes into a 'Female' part so as to form a sort of 'piston'. The diameter of the male part is 7mm.
In my first 3D print, I made the diameter of the Male part of my piston 0.2mm smaller than that of the 'Female' part that it goes into. However with a bit of sanding the Male part is now seems too loose in the slide.

For next time, how much gap (if any!) would you recommend, given that I will need to sand down the surfaces to create a smoothly sliding mate?


B) FINISH
As a result looseness as described above, I now need to add bulk to the male part! What would you recommend I use for this?
I have seen people dip a 3D print made from ABS in ABS dissolved in a solvent such as Acetone or a solvent cement (e.g. Tamiya Extra Thin/EMA Plastic Weld).

I suppose that I could apply a thin layer of some sort of robust paint (or lacquer?), over the whole of the exterior of both parts including the area of the male part where the sliding surfaces of the 'piston' mate. This might help create a nice shiny looking model and thereby mimic the plastic finish of the ultimate product I am designing. A smooth paint or lacquer finish would also help stop my parts from attracting fingerprints & dirt.

However in order to create a nice smooth slide, I will need to be able to sand the mating surface down without ruining the finish. And moreover I would like to have a prototype with a mating surface with a smooth sliding action that will not get damaged too quickly through use of the slide.

Any thoughts?

Many thanks

J