From 3D file to signed sample: T1, T2 and what can still change after the first trial
The cheapest moment to change a product is before the steel is cut. Every step after that has a price, and most disputes about tooling come from not knowing which price applies.
The steps, in order
We start once we have the complete 3D file, a 2D drawing, the material, and the appearance, assembly and inspection requirements.
- Drawing review (DFM). We check draft angles, wall thickness, undercuts, moulding risks and likely cosmetic problems, and send the findings back. Tooling starts only when you confirm the final drawing.
- Mould making: machining, EDM, fitting and polishing. How long depends on the size and complexity of the part.
- T1 — the first trial shot, normally within a day of the mould being finished.
- Full inspection of the T1 pieces: dimensions, appearance, assembly, sink marks, weld lines. You get a trial report with photos and measurements.
- Your review of the T1 samples. For each comment we decide whether a setting change will fix it or the mould itself has to change.
- Mould correction, if needed, then T2 — the second trial — inspected and sent the same way.
- Sign-off: you approve the sample, sign the approval sheet, and each side keeps a set.
For how these steps add up to our 50 working days, see our article on the tooling timeline.
T1, T2 — and how many trials to expect
T1 is the first shot from a new mould. Its job is to prove the tool and show what needs correcting; a T1 sample is rarely signed as it is.
T2 is the shot after the T1 corrections. A simple small part is usually approved at T2. A part with several snap fits or strict cosmetic requirements usually needs T3, and a few complex parts go to T4.
After T1: what is free, what costs a correction, what needs a new mould
| Kind of change | Examples | Cost |
|---|---|---|
| Process settings only | Injection speed, holding pressure, melt and mould temperature, cooling time — to reduce slight sinks, flow marks, gas marks, silver streaks, light flash | Free, but settings have limits |
| Mould correction | Small dimension changes (removing steel is easier than adding it), polish, venting, small wall adjustments, draft and radius changes, moving ejectors, cooling lines or the gate | A correction charge; the tool is kept |
| New mould | Major redesign, large undercuts added or removed, a big wall-thickness change (say 2.0 mm to 1.0 mm), a large change in overall size, a new parting line or opening direction, a switch to a resin with very different shrinkage such as PP to PC | The cavity no longer fits the part; it is effectively a new tool |
Wall thickness is the one to be careful with. A small adjustment can be made in the existing steel; a large one changes how the part shrinks, and that usually means starting again.
Who pays for a mould correction
The line is drawn at the frozen drawing.
- Your change: if, after the drawing is frozen, you ask for a different structure, look, size or function — adding a rib at T1, changing a radius, a snap fit or the shape — the correction and trial material are charged to you.
- Our mistake: if the part does not match the frozen drawing because of our review, machining, reading of the drawing or mould design — wrong dimensions, an undercut that will not release, a gate that stops the part ejecting — we pay for the correction and the extra trial.
One grey area is worth settling early. If our DFM report warned that a feature would produce, for example, a slight weld line, and you later ask for a design change because of that weld line, it counts as your change.
Samples, couriers and freight
Our standard is five pieces per model: one set for you to keep, one for us, and the rest for your own testing. If you plan reliability testing, tell us the quantity up front.
Samples go by DHL, FedEx or UPS, or the courier you name. The T1 and T2 pieces themselves are normally free and the freight is paid by you on collection; we can prepay it and add it to the order if you prefer. If samples have to be sent again because we made a mistake, we pay the freight.
What you sign — and what both sides keep
- An approval sheet listing the part number, material, colour, version, trial stage (T1 or T2), inspection standard and AQL, signed by you.
- At least two sets of approved samples, one for each side, labelled with part number, version and date, sealed in bags. These are the reference for every production inspection and every complaint that follows.
- The trial report, the dimensional report and, where cosmetic limits were agreed, photographs and a physical limit sample.
- For coloured parts, a signed colour plaque. For clear parts, a signed cosmetic limit sample.
It feels like paperwork at the time. Six months later, when a batch is questioned, the sealed sample is the only thing both sides will accept.