3D Printing Instructions: Things to Know for Best Results

Most failed prints are not machine faults. They come from a handful of settings and one geometry decision, and the print file usually shows the problem before the machine starts. Layer height controls the vertical step and the surface you will feel with your thumb. Wall count controls how much solid material sits behind that surface. Orientation decides which faces need support and where the layer lines run.

No set of 3D printing instructions will turn a printed part into a machined one. FDM parts carry visible layer lines and slightly weaker bonds between layers. Resin parts hold fine detail but stay brittle under impact. When the part carries a bearing load, seals against a fluid, or threads into metal, print it to check fit, then plan a machining pass for the production version.

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  Print for form and fitGeometry, clearance and assembly checks are fast and cheap in plastic.
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  Machine for functionLoad paths, sealing faces and threads belong on a machined part.
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  Do not mix the twoA print that passes a fit check still tells you nothing about fatigue.

Every FDM part is anisotropic. The bond between two layers is weaker than the filament inside a layer, often by a wide margin, so the direction of the layer lines decides where the part will split. Lay a flat bracket on the plate so the layers stack along its thin axis and it will snap at the first load. Stand the same bracket on edge and the load runs along the filament instead.

Supports are the cost of that decision. A face that touches the build plate comes out clean and dimensionally tight. A face that hangs over open air needs support, and the surface under it will be rough enough to need sanding. Count the supported faces before you commit. Two is usually acceptable. Six is a warning sign that the part should be split or reoriented.

Round features behave differently again. A horizontal hole prints as a teardrop at the top because the plastic sags before it cools. Vertical holes stay round but carry staircase steps on the wall. For a bearing bore or a dowel pin, print the hole undersized and ream it to size, or leave stock and machine the bore afterward.

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  Keep layers off tensile pathsRun layer lines perpendicular to the pull direction, not along it.
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  Minimize supported facesEach supported face adds cleanup time and dimensional scatter.
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  Print critical bores undersizedLeave 0.2–0.3 mm of stock and ream or bore to final size.

Layer height is a trade, not a quality dial. A 0.2 mm layer prints roughly twice as fast as a 0.1 mm layer and shows visible steps on shallow curves. Dropping to 0.1 mm helps a cosmetic shell but does not fix a weak part. Strength comes from wall count and print temperature, not from finer layers.

Three perimeters is a reasonable floor for a functional prototype. Four or five if the part will be clamped, dropped, or handled daily. Below two perimeters the shell is mostly air, and any screw boss will crush. Infill above 30 percent adds time and material for very little stiffness gain. Most of the bending resistance sits in the walls.

Print speed and cooling matter more on tall thin sections. Slow the outer wall to about half the infill speed, and keep part cooling on for PLA. ABS and polycarbonate prefer a heated chamber and minimal cooling, or the layers will delaminate along the corners.

Slicer preview is your inspection tool. Step through the layers around every hole, boss, and snap fit. If the toolpath jumps or the wall thins to a single strand, fix the model before you print.

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  0.2 mm layersGeneral prototypes, brackets, and housings where speed matters.
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  0.1–0.15 mm layersVisible cosmetic surfaces and small text or fine detail.
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  3–4 perimetersFunctional parts that see handling or light structural load.

Printed holes come out smaller than drawn. The nozzle drags material inward, and the slicer's arc approximation rounds the profile. On FDM, add 0.2 mm to a hole diameter if you need a close slip fit, and test one hole before you commit the whole plate. Resin shrinks during cure, so the compensation runs the other way, and the amount depends on wall thickness.

For a press fit or a bearing seat, do not rely on the printer. Print the pocket undersized by 0.3 mm and finish it with a reamer or a boring bar. That single step moves the feature from an approximation to a real tolerance. Our machining cells hold ±0.005 mm on bores and faces when the printed prototype graduates to a production part.

Threads are the same story. Printed internal threads work for a light hand-tight assembly, but they strip under torque. Print a plain hole and cut the thread with a tap, or design a heat-set insert boss. Leave the boss wall at least 2 mm thick or it will split when the insert goes in.

Clearances between mating printed parts should start at 0.3 mm per side. Below that, elephant-foot bulge at the bottom layers will fuse the two parts together. Above 0.5 mm the assembly feels loose and rattles in a handheld product.

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  Hole compensationAdd 0.2 mm on FDM, subtract for resin shrinkage after cure.
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  Bearing seatsPrint undersized, then ream or bore to the final fit.
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  Mating partsStart at 0.3 mm per side and adjust from the first print.

A printed prototype earns its keep when it answers a question: does the assembly go together, does the cable route clear, does the user's hand reach the switch. Once those answers are locked, the same geometry usually moves to CNC machining for the parts that carry load or seal. The model does not need to be rebuilt, but the tolerances, fillets, and surface finish do need a second pass.

Two changes come up on almost every handoff. First, printed parts hide generous radii and thick walls that a machined part cannot keep without extra tool time. Second, a printed boss that worked fine in nylon becomes a stress riser in aluminum with a sharp internal corner. Add a fillet at the base and open the corner radius to at least one third of the wall thickness.

We run both processes under one roof, so the print and the machined version can be compared side by side before the design freezes. A printability review comes back with the quotation, usually within 12 hours, and flags any feature that will not survive the transition.

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  Keep the modelThe print and the machined part share the same nominal geometry.
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  Revisit radiiSharp internal corners become crack starters in metal.
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  Compare bothPrint for fit, machine for function, then verify the assembly.