Resources
DFM Resources
A design problem caught on the screen costs an email. The same problem caught after steel is cut costs a tool modification and weeks of schedule. These are the checks we run on every quote — published so you can run them first.
Injection molding rules of thumb
Starting points, not absolutes — the right number depends on resin, flow length, and what the part has to do. Where a design has to break one of these, that is fine; we just need to know so the tradeoff is priced and understood up front rather than discovered at first article.
| Feature | Guideline | Why it matters |
|---|---|---|
| Nominal wall | 0.040–0.140 in, uniform | Thick sections cool slowly → sink, voids, warp, and longer cycle time (cycle scales roughly with the square of wall thickness) |
| Wall transitions | Taper over 3× the thickness change | Abrupt steps concentrate stress and create visible sink lines |
| Draft (smooth) | 1–2° per side | Below this the part drags on ejection — scuffing, stress marks, tool wear |
| Draft (textured) | Add ~1° per 0.001 in texture depth | Texture is an undercut; insufficient draft shears the texture off during ejection |
| Rib thickness | 50–60% of nominal wall | Thicker ribs sink on the opposite show surface |
| Rib height | ≤ 3× nominal wall | Tall thin ribs are hard to fill and hard to eject |
| Internal radius | ≥ 0.5× nominal wall (0.25× minimum) | Sharp internal corners are stress risers and restrict flow |
| Boss OD | 2–2.5× the screw diameter, cored | A solid boss is a thick section — it will sink |
| Hole-to-edge | ≥ 1× hole diameter of material | Thin walls around holes cause knit lines and weak sections |
Die casting rules of thumb
| Feature | Guideline | Why it matters |
|---|---|---|
| Nominal wall (aluminum) | 0.080–0.180 in typical | Thin enough to solidify soundly, thick enough to fill |
| Nominal wall (zinc) | 0.030–0.100 in typical | Zinc's fluidity allows meaningfully thinner walls than aluminum |
| Draft (aluminum) | 1.5–3° per side | Aluminum shrinks onto cores and grips harder than zinc |
| Draft (zinc) | 0.5–1.5° per side | Lower shrink and smoother surface allow less draft |
| Fillets | 0.030–0.060 in on internal corners | Sharp corners cause turbulence, gas entrapment, and hot-spot porosity |
| Machining stock | 0.010–0.030 in on features to be machined | Machining into as-cast skin exposes subsurface porosity; stock keeps the cut in sound metal |
| Ribs | 60–80% of nominal wall | Stiffens without creating a heavy section that shrinks late and pulls porosity |
| Uniformity | Avoid isolated heavy sections | Last-to-freeze regions are where shrink porosity forms — the #1 die casting defect driver |
Pre-RFQ checklist
Send these and you will typically get a quote without a round of clarifying questions. Missing something? Send it anyway and flag what is pending — we would rather start.
- 3D model (STEP preferred) — lets us assess moldability/castability directly
- 2D print with critical dimensions and tolerances actually called out (not a blanket tight tolerance)
- Material: specific grade, or the functional requirement if you want a recommendation
- Annual volume AND initial order quantity — these drive tool class and cavitation
- Existing tooling status: new part, or transferring an existing tool?
- Cosmetic requirements: which surfaces are show surfaces, texture/color standards
- Secondary operations: machining, finishing, printing, assembly, packaging
- Required documentation or certifications (FAI, material certs, regulated-industry paperwork)
- Target production date
Tolerances: the most expensive habit in engineering
A blanket ±0.005 in title-block tolerance on a molded or cast part is the single most common cost driver we see. Molded and cast dimensions vary with shrink, tool wear, and process; holding a tight tolerance means either tighter process control, secondary machining, or sorting — all of which you pay for on every part, forever.
The fix takes ten minutes: identify the handful of dimensions that are genuinely functional (fits, sealing surfaces, mating interfaces), tolerance those properly, and open everything else up. It routinely takes double-digit percentages out of a part price with zero effect on how the part works.
Deep dives
Injection Molding DFM
How we run DFM review on molded parts during quoting.
Learn more →Die Casting DFM
Casting-specific review: porosity risk, draft, machining stock.
Learn more →Design guidelines article
Wall thickness, draft, ribs, and radii explained in depth.
Learn more →Reduce secondary machining
Design choices that cut machining cost out of castings.
Learn more →Injection molding RFQ
What to send for a fast, accurate molding quote.
Learn more →Die casting RFQ
What to send for a fast, accurate casting quote.
Learn more →Have a part in hand and want a read on it? Send it through the RFQ form — DFM feedback is part of quoting, not a separate paid service.
Ready to talk about your project?
Send your drawings or describe your part — an engineer will follow up, not a sales queue.