The Day the Tool Meets Reality

T1 is the first trial shot from a new injection mold. Weeks of steel cutting and fitting end with a box of parts on your desk, and every assumption in the design gets tested at once. Handled well it is a controlled discovery event costing a couple of weeks; handled badly it becomes an argument about who pays for the next round.

T1 parts are not supposed to be perfect. Two to three trials is normal, and a molder who promises otherwise is padding the schedule or hiding problems. The goal is to learn everything that needs changing while the steel is still easy to modify.

What a T1 Run Is and Is Not

A T1 is a short run, usually 20 to 100 shots, on a production-intent tool in a production-intent press with production-intent resin. It is not a validation run, a capability study, or sellable inventory.

The distinction matters commercially. Tell the factory you need trade show parts out of T1 and you get parts optimized to look good rather than parts that reveal problems. Ask instead for shots at nominal and at both ends of the process window, and for short shots: deliberately underfilled parts show how the cavity fills and where air traps.

What to Inspect on T1 Parts

Work through this in a fixed order, because dimensional and cosmetic problems have different owners and different fixes.

  • Full dimensional layout. Every drawing dimension, on at least five parts across the run, and on each cavity separately. Cavity-to-cavity variation averaged away is the most common inspection failure.
  • Fit and function. Assemble the real product: snap fits that engage, threads that run, gaskets that seal, boards that drop in. A part can be in tolerance and still not assemble, a signal to revisit tolerance stack-up analysis rather than blame the tool.
  • Molding defects. Sink marks, warpage measured on a surface plate rather than by eye, short shots, flash, burn marks, and knit lines, each mapping to a cause and fix in injection molding defects.
  • Ejection marks and drag. Pin witness marks, scuffed side walls, and stress whitening point to insufficient draft or badly placed pins; check against draft angles and parting lines.
  • Gate and parting line location. Confirm they landed where the drawing said and that the vestige does not foul assembly or sit on a cosmetic face.
  • Texture and finish. T1 tools are usually untextured, so verify polish on cosmetic surfaces and settle the texture spec and its draft implications before etching, per mold texture selection.
  • Color, material, and weight. Confirm the exact resin grade and masterbatch, since a natural-resin shot says nothing about color match or pigment-driven shrinkage. Record part weight: the cheapest ongoing process control signal in production.

What to Demand Along With the Parts

Parts alone are half the deliverable and factories rarely volunteer the rest, so specify it in the purchase order: the process sheet with barrel and mold temperatures, injection pressure and speed, hold pressure and time, and cycle time; the molder's own dimensional report on the features you will check, so discrepancies surface as measurement disputes rather than surprises; short-shot samples; parts bagged and labeled by cavity; photographs of the tool open with parts on the core; and a written change list for T2 with an owner per item.

Running the T1 to T2 Loop

Sort every finding into one of three buckets before sending anything back.

Process issues are fixed by machine settings and cost nothing. Sink marks, short shots, and some flash fall here, and a good molder resolves them with hold pressure and temperature before touching steel.

Tool issues require steel work. Adding material to a part is easy, since it means cutting steel out of the cavity; removing material is hard, since it means welding steel back in, which is why molds are cut steel-safe. Expect one to three weeks per revision.

Design issues are yours. If the part is molded exactly as drawn and still does not work, the drawing was wrong. Change the CAD, issue the revision through a controlled engineering change order, and pay for the tool change without argument; that is faster than a month of email.

Bundle every change into one revision. Three separate requests over two weeks turn a two-week correction into a two-month one, since each triggers its own scheduling, machining, and trial cycle. That is the largest schedule risk in tooling, compounding an already long injection mold lead time.

When Samples Become the Standard

At some trial, usually T2 or T3, parts are good enough to approve. Make it formal: a signed golden sample retained by both parties, an approved dimensional report, and a locked process sheet. The golden sample then settles every dispute about color, texture, and fit, and the process sheet is what a new operator sets the press to.

Approval has contractual weight. Confirm tooling ownership before signing, particularly offshore, where the questions in who owns your injection mold in China are best settled before the tool proves valuable. Then run a real pilot production run to expose what only appears over hundreds of consecutive cycles: cooling drift, cavity imbalance, tool wear.

How to Get a Better T1

Most T1 problems were designed in months earlier. Run mold flow analysis before cutting steel, hold wall sections uniform, agree gate and ejector locations in writing at the design review, and give the molder a fully dimensioned drawing with datums, not only a STEP file. Assemble the whole product with printed parts first: a fit problem found in prototyping costs a day, the same problem at T1 costs three weeks.

Get an Independent Read on Your First Shots

Projects House runs T1 reviews for clients tooling their first product: inspection plan, defect diagnosis, separating process from tool from design, and one consolidated change list the factory can execute in a single revision. Send your part drawing and trial date through our contact form.