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Watch Out ! Plastic Product Design Pitfalls !


You’ve had a design done, you’ve had models made, you’ve got the quotes in and you’re ready to press the fire button. That’s often the moment where someone realises that the design they’d had done was great, as a plastic product design, but it hasn’t been designed with a specific plastic part production process in mind. Cue re-designs, re-modelling, re-testing, re-costing and DELAYS.

So here are 3 often occurring, easily prevented design pitfalls.

Adding draft afterwards.

If your part has been designed without draft, it’s sometimes possible to add it afterwards, but it really depends on the kind of part it is. The draft really affects the way the mould tool is made. Draft angles may conflict and the dimensions of the part change. For example something as simple as a tray to hold square parts – the pockets won’t be square once draft has been added ! To get around this, the whole part will need redesigning so the draft can be added. (Why do you need draft on a plastic mould tool ?)

3d printed model design

If you’ve had your models 3d printed, that’s great to give you a quick idea of what the part could look like. BUT 3D print design follows a very different set of rules than injection moulding design. Just two examples:

  • In 3D printing, the part is laid down line for line from the bottom up, so you can easily have undercuts (what is a plastic moulding undercut ?) In injection moulding you can have undercuts too, but they need to be carefully thought about in terms of unmoulding and tool cost.
  • 3D models don’t have join lines, which need to be thought about carefully in plastic moulding design, for both aesthetic and functional reasons.

Screw inserts

Technical injection mouldings may well need to take screws. You can either screw straight into it with a self-tapper, but if the part needs to be service-able, inserting a metal screw insert first is a better way of working. The design needs to allow for this, but has someone actually measured the screw and the insert ? Brass inserts are most often an off-the-shelf product. The nasty surprise could be that the part isn’t thick enough to take the screw insert or screw. So easy to prevent !


One way of preventing these issues is to come straight to us for your product design ! We’ll take the most suitable manufacturing method and the most economic way of making the product into account right from the beginning.

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