Ejector pins are simple mold components, but very small pins can create serious problems.

For most injection molds, we recommend avoiding 0.8mm or 1mm ejector pins, especially when the pin is longer than 150mm.

A very short pin in a small product may still be acceptable. But a long and thin pin has a much higher risk of bending or breaking.

Why Are Long, Thin Ejector Pins Dangerous?

The main problem is not machining accuracy. It is ejection force.

After cooling, the plastic part can shrink around the core. This creates a strong holding force.

The ejector pin must overcome this force when pushing the part out.

A 1mm pin can handle only limited load. When the pin is also 150mm or longer, its ability to resist bending becomes very poor.

The result can be:

  • Pin bending
  • Pin breakage
  • Uneven ejection
  • Damage to the ejector hole
  • Product deformation

The problem may not appear during the first mold trial. The pin can slowly bend or become damaged after repeated production cycles.

Does a Support Pin Solve the Problem?

Not always.

A support pin can improve the strength of the larger section, but the small front section still carries the load.

If the front section is only 0.8mm or 1mm, it remains the weakest point.

When the local load is too high, it can still bend or break.

So, adding a support pin should not be treated as a complete solution.

The better approach is to reduce the load on the ejector pin or use a different ejection design.

Good Polishing Does Not Remove the Risk

A well-polished core can reduce friction, but it does not eliminate the holding force from the molded part.

During cooling, the plastic still shrinks around the core.

This is why even a high-precision mold with excellent polishing can have ejector pin problems.

The designer must consider both the pin size and the actual ejection load.

Check the Ejector Design During DFM

This problem should be identified before mold manufacturing.

When you see the following combination, the design needs careful review:

Small diameter + long pin + high ejection load

As a general rule, avoid 0.8mm or 1mm ejector pins when possible.

A small pin may be acceptable when:

  • The product is very small
  • The pin is very short
  • The load is low
  • The pin length-to-diameter ratio is reasonable

But a 0.8mm or 1mm pin over 150mm long should be treated as a high-risk design.

The Cost of a Bad Ejector Design

If the mold has already been built with an unsuitable ejector pin, the problem can continue throughout production.

You may need to:

  • Replace broken pins
  • Adjust the ejection system
  • Modify the mold structure
  • Repair the product surface
  • Eventually rebuild part or all of the mold

This creates extra repair costs and can delay the project.

More importantly, repeated mold problems can damage the customer’s trust in the mold supplier.

Conclusion

For injection mold design, 0.8mm and 1mm ejector pins should be avoided whenever possible, especially when their length exceeds 150mm.

A support pin can help, but it cannot remove the risk when the small front section carries a high load.

The best solution is to identify the risk during DFM and choose a stronger, more reliable ejection design from the beginning.

At Fentor Mold, we focus on practical mold design and manufacturing. Our injection mold manufacturing service helps identify high-risk structures before they become costly mold repair problems.