3D Printing Materials Comparison: FDM, SLA, SLS and MJF

Most bad 3D printing quotes are caused by bad requests. A service bureau can only price what you tell it: the process, the material, the tolerances that matter and the finish you expect. Send an STL with no notes and you will get the cheapest interpretation of your part - which is rarely the one you wanted.

Once you need real resin properties, tight repeatability or hundreds of units, compare against CNC machining and bridge tooling. Around 250-500 parts, an aluminum bridge tool usually beats printing on unit cost and always beats it on material fidelity. Related: rapid prototyping with 3D printing and CNC machining services.

Material choice only matters once the process is right. Fused deposition modeling is cheap, fast and anisotropic, so parts are meaningfully weaker across layer lines and should be oriented with load direction in mind. Stereolithography and DLP resins give fine detail and smooth surfaces at the cost of brittleness and UV sensitivity, which makes them excellent for appearance models and poor for functional parts left in sunlight. Selective laser sintering produces isotropic nylon parts with no support structures, which is why it dominates functional prototyping of clips, housings and living hinges.

Orientation is a design decision, not a print setting. A snap fit printed with the beam parallel to the layers will hold; the same feature printed across layers will snap on first assembly. Deciding orientation early lets you place features so the strong axis aligns with load, and it determines where support marks land on cosmetic surfaces.

Tolerances differ by an order of magnitude across these processes. Plan on roughly plus or minus 0.5 percent with a floor near 0.2 mm on FDM, considerably tighter on resin, and design clearance features rather than press fits until you have measured your specific machine.

Printing scales linearly: the thousandth part costs what the first one did. Molding scales the other way, with a large fixed tooling cost and a small piece price. The cross-over for a typical small enclosure sits somewhere between five hundred and two thousand units, moving with part size, tool complexity and how many cavities you can justify. Below that band, printing wins outright. Above it, continuing to print is usually a cash-flow decision rather than a cost decision, and it is a legitimate one when tooling capital is scarce.

There is a middle path many teams miss. Bridge tooling in aluminum costs a fraction of a hardened steel tool, delivers in two to three weeks, and produces a few thousand real molded parts in the production resin. It lets you launch, learn and validate demand before committing to a tool that has to last a million shots.

Whichever route you take, design for the end process from the start. A printed part with uniform wall thickness, draft and no undercuts converts to molding cleanly; one designed with printing's freedom has to be redrawn.

We run this transition regularly through rapid prototyping, low volume manufacturing and 3D printing services, keeping one CAD model that stays valid from first print to first shot.

Print time is rarely the expensive part; finishing is. Support removal, sanding, vapor smoothing, priming and painting can easily exceed machine cost for a cosmetic part, and the labor does not drop with quantity. If you need twenty painted appearance models, price the finishing separately before assuming printing is the cheap option.

Functional parts have their own post-processing needs. Resin parts must be washed and properly UV cured or they will remain soft and keep changing dimension for days. Nylon SLS parts are porous and absorb moisture, which shifts both dimensions and electrical behavior, so seal them if they matter. Threaded features are more reliable as heat-set inserts than as printed threads, and designing the insert boss correctly at the start avoids drilling every part by hand later.

An in-house desktop machine earns its cost quickly if you iterate daily, because the value is turnaround rather than price per part. Printing a fixture at 5pm and testing it at 8am the next morning changes how a team works. The hidden costs are real though: someone has to maintain the machine, dial in profiles, manage failed prints and keep material dry, and that person is usually your best engineer spending an afternoon a week on it.

Service bureaus make sense when you need process breadth or production-grade quality. No small team justifies owning SLS, resin and FDM machines plus finishing equipment, and a bureau gives you all of them with calibrated output and no maintenance burden. The practical setup for most hardware teams is both: a desktop FDM machine for fixtures, checks and rough form studies, and a bureau for anything a customer, an investor or a test protocol will see.

Small FDM parts start around $15-$50, SLA parts $40-$200, and SLS or MJF nylon parts $60-$400 depending on size and finish. Most bureaus apply a $75-$150 minimum order.

STL or 3MF for printing, plus a STEP file and a dimensioned drawing when tolerances, threads or press fits matter. Include units and scale explicitly.

SLS or MJF in nylon. Both give isotropic-enough strength, no support marks and tolerances near ±0.1-0.2 mm, which is why they dominate functional prototyping and low-volume production.