engineering fundamentals Draft & Texture
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The reason for draft
  • Drafts (or taper) in a mold, facilitates part removal from the mold. The amount of draft angle depends on the depth of the part in the mold, and its required end use function.

  • The draft is in the offset angle in a direction parallel to the mold opening and closing.
  • It is best to allow for as much draft as possible for easy release from the mold. As a nominal recommendation, it is best to allow 1 to 2 degrees of draft, with an additional 1.5° min. per 0.025 mm (0.001 inch) depth of texture. See below.
  • The mold parting line can be relocated to split the draft in order to minimize it. If no draft is acceptable due to design considerations, then a side-action mold (cam-actuated) may be required at a greater expense in tooling.
The reason for texture

  • Textures and Lettering
  • can be molded on the surfaces, as an aesthetic aid or for incorporating identifying information, either for end users or factory. Texturing also helps hide surface defects such as knit lines, and other surface imperfections. The depth of texture or letters is somewhat limited, and extra draft needs to be provided to allow for mold withdrawal without marring the surface.

  • Draft for texturing is somewhat dependant on the mold design and the specific mold texture. Guidelines are readily available from the mold texture suppliers or mold builders.
  • As a general guideline, 1.5° min. per 0.025mm (0.001 inch) depth of texture needs to be allowed for in addition to the normal draft. Usually for general office equipment such as lap-top computers a texture depth of 0.025 mm (0.001 inch) is used and the min. draft recommended is 1.5 °. More may be needed for heavier textures surfaces such as leather texture (with a depth of 0.125 mm/0.005 inch) that requires a min. draft of 7.5°.
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