Have any of you hotend makers tried electroplating after milling to increase smoothness?
Deezmaker does gold-plated barrels. We experimented with plating several different metals, and gold seemed to work best. The idea was to find something that the plastic wouldn’t stick to, though my personal hypothesis is that this worked by increasing the thermal conductivity between the barrel and the cooling block because the soft gold layer (besides being very thermally conductive) deformed to conform to the shape of the cooling block’s threads, thus increasing the contact area.
It may also be more lubricious than the stainless surface, but the plating on the inner surface probably wears away pretty quickly. I hadn’t considered that this wear would leave the surface smoother than it was before it was plated.
My general idea is that the electroplating would fill tiny scratches and crevaces so that plastic could not get in there for other plastic to stick to. It may increase quality while decreasing the necessary quality of the actual milling.
Electro-polishing may be better than plating.
Polish instead of or before plating. In general surfaces don’t get better without effort. A hard chrome or electroless nickel might be a good choice because they will have excellent wear resistance.
@Thomas_Cox electropolishing?
But the chemicals 
Electropolishing is basically the reverse of electroplating. The work piece is the anode instead of the cathode, so the surface of the work piece dissolves into the electrolyte instead of having something in the electrolyte deposit onto the surface.
Through the wizardry of electrolyte selection and current manipulation you can get the peaks on the work piece to dissolve before the valley or main body to get closer to a smooth surface.
We electroplate the brass tips w nickel. The cold end is anodized but Teflon is in the inside. Carl says it’s not for smoothness of looks, it spreads heat better. I nod and agree… Whatever he says! I asked how much better are the thermal properties… He says around 2%. I love his passion… It he can improve it 1%, he does.
We electroplate the brass tips w nickel. The cold end is anodized but Teflon is in the inside. Carl says it’s not for smoothness of looks, it spreads heat better. I nod and agree… Whatever he says! I asked how much better are the thermal properties… He says around 2%. I love his passion… It he can improve it 1%, he does.
I come from electroplating industrie 
Joe is right polishing or electropolishing would be a better idea.
But it will really result in larger production cost.
Because you can’t make the nozzle canal.
You would need to make the body first.
Then carefully clean them, polishing it.
Clean it again.
And add the canal for the nozzle.
But I don’t think that will really help.
Electropolish and then electroplate?
@Sebastian_Schmidt what do you mean by the canal?
@NathanielStenzel , the hole in the nozzle.
The Prometheus hotend is electro polished. I have had really good results with it and found it to be extremely reliable.
I do not understand why you could not make the nozzle hole before electropolishing or electroplating. I guess you might need to use a wire going through it as the anode/cathode with a porous liner around it, but I thought it would be doable.
@NathanielStenzel Probably because by drilling the nozzle hole you have precise control over its dimensions. Plating or polishing would modify the hole dimension.
I guess that the nozzle hole does not need this treatment just the interior of the hotend. Once the plastic leaves the nozzle it will undergo dimensional changes which would negate the effort put into smoothing the nozzle channel.
@Neil_Darlow The nozzle hole and heat break hole must be smooth so that it takes less effort to push the plastic out.
I’ve wondered if it would be worth coating steel nozzles with titanium nitride for improved performance (ie extreme hardness and slip) with abrasive filaments like metal and carbon fill
For smoothing, ther’s always abrasive flow machining/polishing
https://www.google.com/search?num=30&q=Abrasive+flow+machining&oq=Abrasive+flow+machining&gs_l=serp.3..0l10.9305.9305.0.9448.1.1.0.0.0.0.106.106.0j1.1.0…0…1c.1.64.serp…0.1.106.gqDPGOBVjfU
Think of it as silly-putty with abrasives and oils mixed and pushed through the part to be polished.