Markforged Evaluation: 5 Key Additive Manufacturing Factors

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  Key takeaways
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  Material properties and anisotropy in a Markforged evaluation
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  Dimensional accuracy and repeatability
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  Production volume and unit cost
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  Surface finish and post-processing requirements
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  Software, qualification, and regulatory compliance
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  Five factors side by side

A continuous-fiber Markforged part is a composite with a direction. The matrix is usually Onyx, a chopped-carbon nylon, and a second nozzle lays continuous carbon fiber, fiberglass, or Kevlar inside the same toolpath. Because the fiber head deposits in the XY plane, stiffness follows the fiber direction and drops sharply through the part thickness.

That is the whole point of the process, and it is also the main engineering risk. Flexural strength along the fiber can exceed cast nylon by a wide margin. Interlaminar shear strength, impact resistance, and Z-axis tensile strength are much lower. A bracket that looks overbuilt can split along a layer line under a peel or shear load.

So the first question in a Markforged evaluation is not "how strong is Onyx?" It is "which load path does this part carry, and in which axis?" If the dominant load is bending along the fiber, the part can be very light. If the load pulls the layers apart, the same geometry may fail early.

Design around this by orienting the part on the bed so the primary tension runs in the XY plane, and by adding a machined or bonded insert at joints that see peel. Where behavior must be identical in every axis, a wrought billet is the safer answer. Aluminum 6061-T6, 7075, and 17-4PH stainless are isotropic, and their allowables are published rather than tested per orientation.

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  Good fitFlat brackets, jigs, end-effector arms loaded in bending along the fiber.
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  Poor fitParts loaded in peel, through-thickness shear, or repeated impact.
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  WatchNylon absorbs moisture, so stiffness shifts with humidity and temperature.

Closed-loop extrusion control has made desktop composite printing far more repeatable than it was five years ago. It has not made it a machining center. For a Markforged evaluation, ask for the tolerance on the specific feature you care about, not a single headline number for the whole part.

Large flat panels bow as they cool. Long holes come out slightly oval. Thin walls can drift by a few tenths of a millimeter depending on layer height and bed position. Locating holes, bearing bores, and mating faces are where this shows up first, because they need a fit that repeats across every unit in a batch.

The usual fix is a hybrid route: print near net shape, then machine the critical features. Ream a Ø6 H7 bore, face a sealing surface, or drill dowel holes after printing. This is normal practice and it works. It also adds a second operation, a second setup, and a second vendor if the printer sits in a different building.

GreatLight runs 127 CNC machines, including 16 simultaneous 5-axis centers, and holds ±0.005 mm on complex contours. If your part needs interchangeable fits across thousands of units, machining the functional surfaces after printing is usually cheaper than chasing print tolerance.

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  Print to fitNon-critical covers, cable guides, low-load housings.
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  Print then machineBearing bores, dowel holes, gasket faces, threaded inserts.
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  Machine onlyInterchangeable parts with published allowables and full traceability.

Printing has almost no tooling cost. That is why it wins on one-off fixtures and low-volume brackets, and why it stops winning once volume climbs. Each part still consumes machine time, fiber, and operator attention.

CNC machining flips the curve. Setup is front-loaded: programming, fixturing, and first-article inspection. Once the process is stable, cycle time per part drops and the amortized cost falls with volume. Above a few hundred units per year per part number, machining is normally the lower unit cost, especially when the geometry is simple and the material is a standard aluminum or stainless grade.

The crossover point depends on part size, feature count, and how much post-processing the printed part needs. A small printed bracket that ships as-built may stay competitive longer. A large printed housing that needs sanding, sealing, and reamed bores crosses over much earlier.

There is also a floor to consider. GreatLight has no minimum order quantity, so a single prototype and a 10,000-part run go through the same quoting path. That makes it practical to machine the prototype, test it, and keep the same process for production instead of re-qualifying a new route later.

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  Low volumePrototypes, fixtures, bridge tooling, replacement parts.
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  High volumeInterchangeable components, safety-related brackets, sealed enclosures.
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  HybridPrint the shell, machine the interfaces, assemble with inserts.

Fused filament printing leaves layer lines. On a vertical wall they read as visible texture; on a top surface they read as a slightly rough skin. The as-built finish is functional for many jigs and covers, and unacceptable for anything that slides, seals, or gets painted to a class A standard.

Post-processing is where printed parts quietly lose their cost advantage. Sanding is labor. Vapor smoothing changes dimensions and needs a fixture to stop warping. Sealing a nylon part against fluid means a coating, and the coating has to survive the same temperature and chemical exposure as the substrate. Each step adds a day or more.

Machined surfaces are defined up front. As-machined aluminum sits around Ra 1.6–3.2 μm, and a finishing pass gets to Ra 0.8–1.6 μm. Fine work reaches Ra 0.2–0.8 μm on sealing faces and bearing bores. Anodizing, bead blasting, electroless nickel, and powder coating are standard follow-on steps, so the drawing, the finish, and the inspection report all describe the same part.

If the printed part needs a cosmetic surface, plan the finishing route before you commit. Bead blasting hides light layer lines on a flat panel. It will not fix a stepped curved surface, and it rounds sharp edges that may be functional.

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  As-built is fineInternal brackets, jigs, cable routing, non-visible housings.
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  Light finishingBead blast or tumble to soften layer lines and edges.
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  Functional finishAnodize, hardcoat, electroless nickel, or fine machining of seal faces.

Print parameters live in software. Fiber fill pattern, wall count, layer height, and orientation all change the mechanical result, which means the qualified part is the process plus the file plus the machine, not the CAD model alone. Change any of those and the qualification evidence no longer applies.

That is workable for internal tooling. It gets harder for aerospace, medical devices, and automotive production parts. Those buyers usually need material certificates, process coupons tested in the build orientation, dimensional reports, and a documented change-control path. Some also need the build record tied to the serial number on the part.

Machining carries a simpler chain. The material certificate names the heat and the standard, the process is defined by the drawing and the program, and inspection data covers the finished dimensions. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022, with 100% inspection before shipment and reports on request.

For a Markforged evaluation, list what the program actually requires before comparing hardware. If the answer is "process coupons and full traceability," a printed part may still qualify with enough testing. If it needs isotropic allowables and a material cert per lot, the decision is already made.

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  Internal usePrint parameters under your own control, no external audit.
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  Regulated productCoupons, certificates, change control, serialized build records.
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  Machined routeMaterial cert, drawing-defined process, dimensional report per lot.