Working notes from the plant
Technical notes
Short notes on the decisions that get made before steel is cut: shrinkage, wall thickness, drying, draft, gate position, and tolerance. Written for the engineer who has a model and a date.
- Notes filed
- 6
- Latest
- July 14, 2026
The file
Every note, newest first
None of this is proprietary. It is the same guidance we give on a phone call, written down so it can be read before the call.
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Why the part comes out smaller than the steel
Every moulded part shrinks as it cools. The mould is cut oversize to compensate, which is why the resin has to be chosen before the tool is cut, not after.
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Wall thickness decides your cycle, and your unit cost
Cooling is most of the cycle, and cooling time rises with the square of the wall. Taking a wall from 4 mm to 3 mm can take a quarter off the price of the part.
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Drying is not a precaution for some resins. It is a requirement.
Nylon, polycarbonate, PBT, and PET absorb water from the air. Moulded wet, they do not just cosmetically splay — the polymer chain is cut, and the strength does not come back.
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What one degree of draft buys you
Draft is the taper that lets a part leave the mould. Leave it off to hold a dimension and you trade it for drag marks, longer cycles, and a tool that wears.
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The gate decides where the weld lines land
Wherever two flow fronts meet, the part has a seam that is weaker than the material around it. Gate position is what decides where those seams fall.
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Which tolerances are worth paying for
A tight tolerance on a moulded feature is not free — it buys tool work, slower cycles, and more inspection. Spend it where the part actually has to fit.