A part that comes off the printer looks finished. It holds its shape, it has dimensions, you can pick it up off the platform. But bring it close to your eye and you will see the print layers running one over another like rings in a tree trunk.
Sometimes that does not matter. Other times those same layers are exactly where a fluid will leak, where paint will peel, or where the part will break under load.
Printing is only the first stage. What decides whether a part actually works in the field is what happens after it — post-processing. We run finishing and painting in house, so a project stays under one roof from file to finished part.
The short version
- Finishing changes physical properties, not only appearance. Surface roughness affects durability, sealing and behaviour under repeated load.
- A part that looks solid can leak. Porosity between FDM layers opens a path for fluids and moisture, and needs dedicated sealing before field use.
- The finishing method follows what the part is for, not an aesthetic preference. A display model and a functional clamp need completely different treatment.
- Working with solvents, paints and sealants is environmentally regulated. Having it done by the bureau takes that exposure off you.
What post-processing is, and why it costs money
Post-processing is everything done to a part after it leaves the build chamber to turn it from raw output into something usable: support removal, cleaning, sanding, sealing, coating and painting.
It is not cosmetics. It changes the physical properties of the part.
Take a concrete example. An FDM part in ABS comes off the machine at a roughness of 15–25 micron Ra. After chemical smoothing it drops to 1–2 micron — close to the look of an injection moulded part. That difference is not only beauty. A smooth surface collects less dirt, wears more slowly, and distributes load better.
Why two identical parts need completely different finishing
Two people send us the same STL. One wants a model for an exhibition. The other wants a clamp that will hold an engine in an off-road vehicle. Same file, two entirely different finishing jobs.
A display part — an architectural model, a marketing prototype — is judged by eye. The finishing is aesthetic: sanding, primer, even colour, perhaps a lacquer. The criterion is that your customer looks at it and reacts.
A functional part is judged differently. Here the roughness between layers is a stress concentration point. A small crack starts exactly there, in the valley between two layers, and propagates inward until the part fails. Correct finishing rounds those valleys and reduces the concentration, which extends the life of the part under repeated load. In medical, defence and aerospace work that consistency is a threshold requirement, not a bonus.
Sealing against fluids, moisture and vacuum
Here is what surprises people: a part that looks completely solid can leak like a sieve.
The cause is porosity — microscopic voids that form between layers in FDM printing, and to a lesser degree in other technologies. Those voids open a path for water to travel inward. For a tank, a pump housing, or an assembly that has to hold vacuum, that is a real problem.
Vacuum tightness in printed polymer assemblies is achievable, but only with the right secondary processing. Our sealing options include resin impregnation that penetrates the pores and cures inside them, dedicated coatings that close the surface, and in some cases a combination of the two.
A rule of thumb from the floor: if the part will contact a fluid or has to hold pressure, assume it needs sealing — rather than discovering it after it leaks at your customer’s site.
Mechanical finishing, coarse to fine
| Step | What it does | When you need it |
|---|---|---|
| Support removal | Takes off printed or soluble supports | Any FDM or resin part with overhangs |
| Bead blasting | Removes residual powder, evens the surface | Standard on MJF and SLS |
| Tumbling | Smooths edges and surfaces in bulk | Series work where every unit needs the same feel |
| Sanding | Targeted smoothing by hand | Specific faces, or before painting |
| Chemical smoothing | Takes ABS from 15–25 to 1–2 micron Ra | When the surface must approach moulded quality |
Colour and coating
- Dip dyeing — the most common finish for MJF and SLS parts, giving an even, professional appearance
- Single and two-component paint — where a specific colour is required
- Metal coating
- Lacquer and UV-protective coatings — worth considering on resin parts, which age under sunlight
Assembly hardware
Heat-set metal inserts give a printed part a real metal thread that survives hundreds of assembly and disassembly cycles, where a thread cut directly into plastic wears out after a few.
One thing to settle before printing: the hole diameter for an insert is the customer’s responsibility, and it is not the same as the insert diameter. Too tight splits the part; too loose and the insert spins. Ask us for the recommended dimensions before you close the model — it saves a whole print cycle.
The regulatory side nobody photographs
Solvents, paints and sealants are subject to environmental regulation — handling, ventilation, storage and waste disposal. Doing finishing in house means we carry that, along with the equipment and the permits, rather than you setting up for it.
How to specify finishing without over-paying
Tell us what the part has to do, and let the finish follow from it:
- Internal or invisible part? Often no finishing at all. The mechanical strength is already there when it comes off the machine.
- Held or seen by a customer? Dyeing or paint.
- Contacts fluid, or holds pressure? Sealing, decided up front.
- Assembled and disassembled repeatedly? Threaded inserts.
- Lives outdoors? UV protection, or a different material choice altogether.
Not sure which finish your part needs?
Send the file and the performance requirements. An engineer from our team will review it and come back with a clear recommendation and a matched quote — including where the honest answer is that no finishing is needed.
Indus3D is an additive manufacturing bureau in Israel, an approved supplier to the Israeli Ministry of Defense, AS9100D and ISO 9001 certified. We run a range of printing technologies under one roof and support projects from file to finished part.