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What is a T1 sample, and what happens at a mould trial?
A T1 sample is a part from an early trial run of a new mould, usually the first run intended to produce parts for measurement. The trials are numbered T0, T1, T2 and so on, each followed by corrections to the steel or the process, until parts meet the drawing and are approved. Numbering differs between toolmakers, so agree what each trial should deliver before the mould is built.
"T" stands for trial. A new mould almost never makes correct parts on its first shot. Dimensions are often left "steel safe", meaning slightly too much steel is left so the toolmaker can remove it after seeing real parts, because adding steel back is far harder than cutting it away.
What each trial is for
| Stage | Main purpose | Typical checks | What it does not prove |
|---|---|---|---|
| T0 (first shot) | Show the mould runs | Filling, ejection, venting, cooling, moving parts; short shots, sticking, flash | Final dimensions or cosmetics |
| T1 | First engineering samples | Critical dimensions, fit, function, shrinkage, warp, sink, cavity balance | That the mould is finished |
| T2 | Confirm corrections | Re-measure the features that were changed; look for side effects | Long-term stability |
| T3 and later | Production readiness | Repeatable output at agreed settings, cycle time, consistency between cavities | Approval is automatic |
The table follows the stage descriptions published by Pioneer Plastics and Mastars. Pioneer notes that T0 is often run before final texturing or polishing, and that naming conventions vary from shop to shop. As one example of scale, Axiom Molds' trial guide describes keeping 30 to 50 sample parts per cavity at T1 and running a 300-shot continuous run at its T2 stage; other toolmakers use different quantities.
What a T1 review should look at
- Every critical-to-quality dimension on the drawing, measured on parts from each cavity.
- Fit with mating parts, including assembly by hand.
- Appearance against agreed standards: gate and ejector marks, sink, flow lines, weld lines.
- Warp and flatness, measured the way they will be measured in production.
- Function: snaps, hinges, threads, seals.
- The process settings used, so later trials can be compared like for like.
First article inspection
A first article inspection (FAI) measures the dimensions on the drawing for parts from a defined trial and compares each with its tolerance. Several consecutive parts from each cavity are often measured so both the average and the spread are visible. Parts should be measured after they have stabilised; moulded plastic continues to shrink slightly for some time after ejection, and some resins also change with moisture.
How to avoid trial surprises
- Agree in writing what each trial will deliver: number of parts, measurements, photos and process sheet.
- Name the critical dimensions and appearance standards before T0, not after.
- Ask that trials use the production resin and colour; samples in a different grade or colour can behave differently.
- Expect steel-safe dimensions at early trials and plan time for at least one round of corrections.
- Keep labelled samples from each trial for comparison.
- Approve formally, with signed samples or reports, so production can be checked against them.
Trial naming and deliverables vary by toolmaker. Use this as a checklist to agree terms, not as any supplier's standard.
Questions buyers ask
How many trials does a mould need?
It depends on the part. Simple parts may pass after one or two rounds; parts with tight tolerances, cosmetic faces or textures usually need more.
Why are T1 parts out of tolerance?
Often because dimensions were left steel safe on purpose, or because real shrinkage differed from the estimate. The T1 measurements tell the toolmaker how much steel to remove.
Can I use T1 parts for testing?
For early fit and function checks, often yes. For certification or reliability testing, use parts from the approved mould and process.
When is texture applied?
Often after the dimensions are confirmed, because texture is hard to change once it is on the steel. Texture also needs extra draft, which should already be in the design.
Sources
- Pioneer Plastics, Injection mold sampling process
- Mastars, Injection mold trial stages T0, T1, T2 and T3
- Axiom Molds, T1 vs T2 mold trial: what gets checked