August 2008 Design Tip

You've Got to Check This!

"Flaps 10 degrees………check, cabin air intake………check, landing light………check."

Ever dream about being a pilot running through your preflight checklist with your co-pilot? Well, now as a designer, you can have almost as much fun when you design plastic parts using the Protomold Plastic Part Design Checklist. You too can be confident you won't miss a single aspect of parts design when you use this handy resource tool.

Like a pilot's preflight routine, our checklist below is a handy reminder of some of the considerations to keep in mind when you're designing injection moulded plastic parts.

And, in addition to our checklist, we've catalogued dozens of tips that can aid in making your parts easier to manufacture, lighter, stronger and offer improved performance. Each tip is chock full of great manufacturability pointers, including coring out, preventing sink, drafting for easy ejection, adding text, and more. Some of these useful design tips are referenced in the designer checklist; or you can download our complete Design Tip compilation volumes here.

Also, you can access ProtoQuote® automated design analysis, which can help to identify potential design problems once a 3D CAD model has been submitted. These free services allow you to quickly see issues that are easy to overlook. Our suggestions and recommended design modifications are returned to you just one day after your part is submitted.

Try our Checklist! It's a practical tool that allows you, the designer, to spot potential issues and correct them beforehand.


Designing with Protomold in mind

Fig. 1

Design Considerations

Are the cores and holes drafted towards the ejector pin side (low cosmetic side) of my part?

Check YES

Does my part design include sufficient draft for part removal from mould?

Check YES — We strongly advise using at least 0.5 degrees on all "vertical" faces. Learn more.

Do I need to add draft to my design?

Check MAYBE — For aluminum moulds, increments of 0.5 degrees (shallow features) to 3 degrees (deep features) should be added. A good rule of thumb is 1 degree per 25mm depth including cam/side pull cores.

Fig. 2

Does my part have a wall thickness that is greater than 1mm and under 4.5mm?

Check YES

Check NO — Parts under 1mm may produce a part that has shorts, voids, weak knit lines; parts over 4.5mm may have excessive sink, internal voids, warp, poor texture pick-up.

Learn more — recommended uniform all thickness for Protomold


What do I need to consider when selecting a material that is best for my design?

  • Selection of the proper material is crucial to part production. Designers should consider the mechanical characteristics, moulding properties, and cost of the resin used.
    Learn more about material selection.


Does my part have two dimensions that are larger than 6.35mm and less than one of the following? (Dimensions (in mould) = X x Y x Z (depth of part))

  • 770mm X 340mm X 6mm
  • 720mm X 290mm X 25mm
  • 670mm X 240mm X 50mm
  • 620mm X 190mm X 76mm

Check YES — proceed to Volume

Check NO — My part is over 76mm.

My part is over 76mm deep, is my parting line in the middle of the part?

Check YESLearn more.

Check NO — Protomold may not be able to mould your part


Does my part have a volume greater than 82mm3?

Check YES — proceed

Check NO — Protomold may not be able to mould your part

Does my part have a volume less than 966,837mm3?

Check YES — proceed

Check NO — Protomold may not be able to mould your part

Surface Area

Does my part have a surface area of less than 112,413 square mm?

Check YES — proceed

Check NO — Protomold may not be able to mould your part


Is it a straight pull mould?

Check YES — proceed

Check NO — Off angle geometry may need to be modified or cams/side actions need to be applied

Check I DON’T KNOWlearn more.


Are the undercuts located towards the outside of my part?

Check YES — Proceed to next question, Protomold may be able to use cams/side actions to mould the undercut

Check NO — Pass through cores or filling in the undercut geometry will be required. Protomold can certainly mould your prototype parts, however may not be able to mould your production parts. You could cut the undercut geometry with a secondary operation for testing or low volume production.

Is the undercut on my part less than one 213.84mm X 60.38mm X 73.66mm? (Dimensions (in mould) = Horizontal x Vertical x Depth of cam pull)

Check YES — Protomold will use cam/side action to mould the feature
Learn more.

Check NO — Can you use sliding shut offs?

Read past Protomold Design Tips on Sliding Shut Offs:
October 2006
September 2007