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Mastering Manufacturing: Design Guidelines

Efficient manufacturing is not just about the machinery or processes; it begins at the design phase. Every successful manufacturing project relies heavily on meticulous design guidelines that ensure seamless production, minimal wastage, and optimal product quality. In this comprehensive guide, we delve into the cornerstone of efficient manufacturing: Design Guidelines.


From determining the ideal size and projected area of your components to navigating the nuances of wall thickness and surface finishes, each aspect of design plays a pivotal role in the manufacturing process. We'll explore key considerations such as draft angles, undercuts, gate selection, tolerances, and material choices, providing insights that empower designers and engineers to make informed decisions at every stage of product development.


Whether you're a seasoned industry professional looking to refine your design strategies or a newcomer seeking to grasp the fundamentals of manufacturing design, this guide is tailored to meet your needs. Join us on a journey through the intricacies of design guidelines, where precision meets innovation and efficiency is paramount.


Our maximum moulding size is approximately 500mm x 500mm x 200mm but should not exceed the maximum projected area shown in the example materials table. (Figure 1)


Maximum material volume approximately 70cc.

Figure 1

Approximate Projected Area Guidelines


Nylon 6

510 square centimeters




1032 square centimeters

Project Area

A projected area is a two-dimensional area measurement of a three-dimensional object, by projecting its shape onto an arbitrary plane. You can think of the green projection as a shadow case from the part with a light source directly over it.

Illustration showing how a projected area is measured on a three-dimensional object by projecting its shape onto a plane, akin to a shadow cast by a light directly overhead.

Diagram depicting the concept of a projected area as a two-dimensional measurement of a three-dimensional object, akin to a shadow cast by overhead light onto a surface.

Red surfaces = surface area

Green surfaces = projected area of this part


A taper applied to the faces of the part that prevents them from being parallel to the motion of the mould tool opening is described as draft. This keeps the part from being damaged due to scratching or scuffing as the part is ejected from the mould.

Recommended draft:

  • 0.5 degrees as a minimum on all faces at 90 degrees to the moulds split line is strongly  advised.

  • 2 degrees works very well in most situations.

  • 3 degrees is average for a shutoff (metal sliding on metal) and will depend on the depth of the shut. 

  • 2 degrees is required for light texture.

  • 5 or more degrees is required for heavy texture.

Undrafted Part

Image showing an undrafted part adjacent to a mould tool split line, highlighting the absence of draft angles.

Drafted Part

 Image illustrating a drafted part next to a mould tool split line, showcasing the presence of draft angles for smooth ejection from the mould.



Undercuts can be created using mechanical, hydraulic or air side actions or in some cases by piercing through the moulding faces.


Mechanical side action – moving at 90 degrees the mould split line.

 Description of undercuts creation methods, including mechanical side action moving at 90 degrees to the mould split line.

Pierced through clip example to Part


Explanation of undercut creation methods, including piercing through moulding faces, illustrated by a clip example attached to the part.

Ejector Pins

Please be advised that with most parts there will be a witness of the ejection process. Parts with ejector pin marks are usually acceptable, however, if necessary, they can be designed out of the part in some cases.

Information regarding ejection process witnesses, emphasising that ejector pin marks on parts are typically acceptable but can be eliminated if needed during design.

Pin Marks

Slight Pin Witnesses

Noting the presence of slight pin witnesses from the ejection process on most parts, acknowledging their acceptability while also highlighting the possibility of design adjustments to minimise their appearance.

Wall Thickness

With injection moulded parts, trying to maintain uniform wall thickness will help to prevent potential issues such as sink marks and warping.


As a general rule, ribs should be kept to a maximum thickness not exceeding two thirds of the adjoining walls.

Advice on maintaining uniform wall thickness in injection molded parts to mitigate sink marks and warping, with a general rule suggesting ribs not exceed two-thirds of adjoining wall thickness.

Sink Marks

Keeping wall thickness and ribs within the limits above should prevent or at least keep sink marks to a minimum.

Bad Practice

Example of Sink Mark Bad Practice

Best Practice

Example of Sink Mark Best Practice

Sharp Corners

The best practice with moulded parts is to avoid sharp corners. Sharp corners can be points of weakness and in some instances can increase tooling costs.

Sharp Corner

Example of Sharp Corner Bad Practice

Radius Corner

Example depicting radius corner best practice

Surface Finishes

A variety of surface finishes are available from a heavy spark to a polished surface. Specialty finishes can be applied as a secondary process if required.


  • Non-Cosmetic – Machining marks remain visible – usually for part internals (unseen) or functional engineering mouldings.

  • Semi cosmetic – Most machining mark removed – functional engineering mouldings.

  • Cosmetic – Various sparked finish options

  • Cosmetic – Polished.

  • Cosmetic – Various specialty finishes – textures.

Sparked Finish Examples

Sparked Finish Example

Sparked Finish Examples


Gates are the method used to fill cavities.

Here is a list of the most common selection:

Sub / Tunnel Gate

Directly onto the part – leaves a small discreet witness particularly on small parts. Generally speaking, the larger the component, the larger the witness will be.

Description of gate placement directly onto the part, noting the resulting discreet witness, which tends to increase in size with larger components.

Gate shears on part ejection leaving small witness mark.

Tab Gate

Directly onto the part – leaves a witness where it is trimmed from the part. Tab gates can help to prevent sinking on larger sectioned parts, or to hold parts together such as a left-hand and right-hand side for assembly later.

Explanation of tab gate placement directly onto the part, indicating the resulting witness where it's trimmed, often used to prevent sinking on large sections or facilitate assembly of component parts.

Direct Sprue Gate

Directly onto the part leaving a snipped or machined witness. Can be in a hidden place (internal) or can be covered with a label.

Description of a direct sprue gate onto the part, indicating the resulting snipped or machined witness, which can be hidden internally or covered with a label.

Hot Tip

Usually directly onto the part – saves material.

 Illustration of a hot tip application directly onto the part, leaving a discernible witness mark, highlighting the technique's efficiency and potential impact on product aesthetics.


The tolerance table below is a guide only tolerances will vary from material to material. Critical dimensions should be advised before mould making. Moulds can be left metal safe during the manufacturing process to adjust the critical dimensions.



1 to 20 (+/-mm)

21 to 100 (+/-mm)

101 to 160 (+/-mm)


0.075 – 0.125

0.100 to 0.170

0.200 – 0.375



Please find below a selection of our stock materials, there are many more available should none of these suits your requirements. Including flame retardant and filled versions of most materials.




Acrylonitrile / Butadiene / Styrene



Acrylonitrile / Butadiene / Styrene / Polycarbonate



Liquid Crystal Polymer



Polyamide / Acrylonitrile / Butadiene /




(Acetal) Polyoxymethylene



(Acrylic) Polymethylmethacrylate



High Impact Polystyrene



Low Density Polyethylene



(Nylon) Polyamide 6



(Nylon) Polyamide 66



(Nylon) Polyamide 12












Thermoplastic Elastomer


Medium – High

We hope you found these design guidelines for plastic injection moulding insightful and valuable for your projects. By applying these principles, you can enhance the efficiency, quality, and cost-effectiveness of your moulding processes. If you're considering plastic injection moulding for your component parts, why not schedule a free consultation with us? Our team of experts is here to help you navigate the complexities of injection moulding design and ensure the success of your next project.

To arrange your consultation, call us at 01453 833 388 or email us at



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