Mold Shrinkage — Acrylic (PMMA)
Cavity dimension to cut for a target Acrylic (PMMA) part size (nominal shrink 0.45%).
PMMA's 0.45% shrink is optics-friendly, but packing-induced birefringence — visible through crossed polarizers — is the real spec on lenses and light guides. Steel-safe practice: cut the cavity to the LOW end of the shrink range — adding steel later is welding; removing it is machining.
Formula
Note: Starting-point process values — the resin grade's datasheet and an in-mold study govern. Verify with a gate-seal study and a cooling-time ladder on the actual tool.
Cavity dimension to cut for a target Acrylic (PMMA) part size (nominal shrink 0.45%). A free injection molding cycle & process tool — no sign-up, no upload, instant results in your browser.
About Mold Shrinkage — Acrylic (PMMA)
Mold Shrinkage — Acrylic (PMMA) computes the governing relationship L_cavity = L_part / (1 − s) live as you type. PMMA's 0.45% shrink is optics-friendly, but packing-induced birefringence — visible through crossed polarizers — is the real spec on lenses and light guides. Steel-safe practice: cut the cavity to the LOW end of the shrink range — adding steel later is welding; removing it is machining. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Mold Shrinkage — Acrylic (PMMA)
- 1Enter your values — Target part dimension, Shrinkage (sensible defaults are pre-filled).
- 2Read the live results: Cavity dimension, Steel oversize.
- 3Check the "with your numbers" line to see L_cavity = L_part / (1 − s) substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Mold Shrinkage — Acrylic (PMMA)?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula L_cavity = L_part / (1 − s) with authoritative sources cited on the page (Resin supplier processing data sheets (per-grade values govern); Rosato, Injection Molding Handbook, 3rd ed.)
- ✓PMMA's 0.45% shrink is optics-friendly, but packing-induced birefringence — visible through crossed polarizers — is the real spec on lenses and light guides.
- ✓SI ⇄ Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the mold shrinkage — acrylic (pmma) use?+
It evaluates L_cavity = L_part / (1 − s), exactly as published. Sources: Resin supplier processing data sheets (per-grade values govern); Rosato, Injection Molding Handbook, 3rd ed.. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
PMMA's 0.45% shrink is optics-friendly, but packing-induced birefringence — visible through crossed polarizers — is the real spec on lenses and light guides. Starting-point process values — the resin grade's datasheet and an in-mold study govern. Verify with a gate-seal study and a cooling-time ladder on the actual tool.
When is this calculator the right tool for the job?+
Cavity dimension to cut for a target Acrylic (PMMA) part size (nominal shrink 0.45%). A free injection molding cycle & process tool. Steel-safe practice: cut the cavity to the LOW end of the shrink range — adding steel later is welding; removing it is machining. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes — the SI ⇄ Imperial toggle converts the values already in the fields, preserving the physical quantity, so you can flip mid-calculation without re-entering anything.
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