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ManufacturingRev. Q3 2026

DFM review for machined parts

Walk a machined part design for manufacturability and cost: tool access, internal corner radii, deep pockets, thin walls, setup count, workholding, tolerance-driven operations, and the features that quietly multiply the price. Use whenever the user asks why a quote came back high, how to make a part cheaper to machine, whether a feature is machinable, or wants a DFM review before sending a part out for quotes.

Marcus Reed portraitMarcus ReedManufacturing EngineerProtolabs logoProtolabs

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DFM Review for Machined Parts

Reviews a part the way a good machinist quotes it: setups first, then tooling, then the features that force slow operations.

Required inputs

  1. Part description: overall envelope, material, and the features present (pockets, holes, bosses, threads, surfaces with callouts). A feature list with dimensions beats adjectives. If the user can export a screenshot or drawing, work from that and list what can't be seen.
  2. Quantity and cadence: 1 prototype, 50/year, 5000/year. DFM advice inverts with volume.
  3. Tolerances and finishes: the tightest ones, plus any GD&T that forces specific process steps.
  4. What is fixed: interfaces that cannot move vs. geometry that is negotiable.

Review checklist

Score each area, flag findings, and estimate relative cost impact (LOW / MEDIUM / HIGH).

  1. Setup count. Estimate the minimum number of setups a 3-axis shop needs. Every setup adds fixturing time and a tolerance boundary; features toleranced tightly across a setup boundary are a double penalty. Ask whether features on opposing or perpendicular faces can migrate to shared faces.
  2. Internal corners. Vertical internal corners need a radius at least equal to the cutter radius; specify radii of one-third to one-half of pocket depth where possible. Flag any sharp internal corner and propose a radius or a dog-bone relief if a mating part needs clearance.
  3. Depth-to-diameter and depth-to-width. Holes beyond 4x diameter start costing extra (peck cycles); beyond 8x, flag as a special operation. Pocket depth beyond 3 to 4x cutter diameter forces long-reach tooling, slow feeds, and chatter risk on the walls.
  4. Thin walls and floors. Walls under roughly 1 mm in metals (1.5 mm in aluminum for tall walls) deflect and chatter. Flag height-to-thickness ratios above roughly 10:1.
  5. Threads. Prefer standard coarse threads, thread depth max 2 to 3x diameter, and flag any custom or very fine threads. Tapped blind holes need drill point clearance below the last full thread; check the callouts allow it.
  6. Tolerance-driven operations. Anything tighter than about plus/minus 0.025 mm (0.001 in), true position under 0.05 mm, or finishes better than 0.8 um Ra typically adds grinding, reaming, boring, or inspection time. List each tolerance that forces a secondary operation and ask which are truly functional.
  7. Workholding. Does the part have parallel faces or a boss to grip? Parts that need soft jaws, custom fixtures, or double-sided machining of freeform surfaces should be flagged with the fixture cost called out for the stated volume.
  8. Material and stock. Is the part hogged from a block with poor buy-to-fly ratio? At volume, suggest near-net starting forms (extrusion, casting, pre-cut blanks). Flag hard materials (hardened steels, titanium, Inconel) and note the multiplier they carry.
  9. Edge breaks, deburr, and cosmetics. Blanket "break all edges" is fine; per-edge chamfer callouts and cosmetic surface requirements on machined faces add handling. Flag them.

Output format

  • Findings list ordered by estimated cost impact, each with: feature, problem, specific proposed change, and what the change trades away
  • Setup count estimate, before and after proposed changes
  • A short list of questions for the machine shop where the answer depends on their equipment (5-axis availability, max spindle reach)

Guardrails

  • Do not present cost impacts as dollar figures; use relative impact unless the user provides shop rates.
  • Preserve function: every proposed change must state its effect on the interfaces the user marked as fixed. If a change touches a fixed interface, present it as a question, not a recommendation.
  • If the part is clearly better suited to another process at the stated volume (casting, sheet metal, extrusion, additive), say so early rather than optimizing the wrong process.