Resin printing cures liquid photopolymer with light, layer by layer, and it produces the smoothest surfaces and finest features of any accessible additive process. That is why appearance models, dental and jewellery work and fine detailed prototypes go this way. The trade is in the material: photopolymers behave differently from thermoplastics and age differently too.
How the detail is achieved
Light cures a very thin layer at a time, and the resolution of the light source rather than a nozzle sets the feature size. Layer heights are far smaller than in filament printing, so stepping on curved surfaces is much less visible. The result is parts that look moulded straight off the machine, which is exactly what an appearance model needs.
Post cure is part of the process
A part off the machine is green: cured enough to hold shape and not fully polymerised. Washing removes uncured resin and a post cure under controlled light and temperature completes the reaction. Skipping or shortening it leaves a part that is weaker, tackier and dimensionally less stable. Different resins want different post cure schedules, and the supplier should be able to state theirs.
Where the material limits you
Standard photopolymers are more brittle than injection moulded thermoplastics and notch sensitive. Many yellow and embrittle under ultraviolet light over months. Engineering and tough resins narrow the gap considerably and do not close it. For a part that must survive load and time, sintered nylon or a machined thermoplastic is the safer answer.
Getting the best from it
Orient to keep supports off the visible surfaces and accept that the supported side needs finishing. Hollow large solid volumes and add drain holes so uncured resin escapes. Ask for the resin by name rather than by adjective, because tough, clear and castable behave nothing alike. And say if the part will live in daylight, because that changes the resin choice.
Questions people ask about resin 3d printing service
Why is resin printing so smooth?
Because layers are very thin and feature size is set by the light source rather than a nozzle, so stepping on curved surfaces is far less visible than in filament printing.
Are resin parts strong?
Less tough than moulded thermoplastics and often notch sensitive. Engineering resins narrow the gap. For durable functional parts, sintered nylon or machining is safer.
Do resin parts degrade over time?
Many photopolymers yellow and embrittle under ultraviolet light. If the part lives in daylight, say so and choose a resin rated for it.
What is post curing?
Completing the polymerisation under controlled light and heat after washing. It is part of the process, not an optional extra, and it changes strength and stability.