Is a draft needed for a side-action cam for a spring clip?

cinnamongirl · Feb 27, 2016

I am reverse engineering a plastic part that has a run-of-the-mill spring clip created by a side-action cam. There doesn't seem to be draft on any of the cam surfaces (bottom face of the "hook" and the parallel face right below it). Is this common practice or would it be preferable to have a draft on both surfaces?

Paulkuklych · Feb 29, 2016

A picture would help

Paul Kuklych

http://www.improve-your-injection-molding.com

cinnamongirl · Mar 31, 2016

Here's a picture to help explain my original question. I'd like to know if I need a draft on the bottom-facing surface of the spring clip using a side-action cam.

The tool will release top-to-bottom and the parting line is at the base of the part.

MikeHalloran · Mar 31, 2016

No, you don't need draft on the bottom of the hook, or on the inner face of the related beam, if you are pulling those surfaces with a side-action cam. However, said side-action cam is cut in half by the core for the top half of the central hole, so you can't disassemble the mold.

It would be better to forget the side-action crap, and form the bottom of the hook, and its inner face, with a tang extending straight up from the core that hollows out the bottom. Again, no draft should be necessary.

Mike Halloran
Pembroke Pines, FL, USA

cinnamongirl · Mar 31, 2016

Thanks for the reply. Excuse my ignorance, but what's a tang?

MikeHalloran · Mar 31, 2016

Take the area of the hook bottom, and project it downward until it meets the metal that forms the bottom relief core. That will leave a rectangular hole in the part, directly under the hook.
... and greatly simplify the mold.

From dictionary.com:
[tang]
noun
...
5.
a long and slender projecting strip, tongue, or prong forming part of an object, as a chisel, file, or knife, and serving as a means of attachment for another part, as a handle or stock.

In this case, it doesn't serve as an attachment means, it's just a long projection that's part of the mold, and it forms the underside of your hook, and one long face of the hook's projecting stem.

Mike Halloran
Pembroke Pines, FL, USA

cinnamongirl · Apr 1, 2016

Yes, I agree that with your suggestion, it would greatly simplify the tool and reduce cost. But I was trying to reverse-engineer a part that my current company already makes. The tooling already exists (some vendor in China has it), but our engineering file is missing the appropriate details, such as drafts.

MikeHalloran · Apr 1, 2016

Then there's something odd going on, e.g. that central counterbore is pretty much impossible to mold unless the tool has two delicate cam slides, which is unlikely. I'd guess that it's bored as a secondary, or maybe the spring clip is molded in a deflected position, and straightened as a secondary.

I'd be really curious to see some closeup photos of the actual part, if you can do that without giving away the store.

Mike Halloran
Pembroke Pines, FL, USA

cinnamongirl · Apr 6, 2016

Here's the best photo I was able to take. I noticed that the "hook" part on top has a parting line all around it. I'll try to take more photos after I figure out how to focus correctly.

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Is a draft needed for a side-action cam for a spring clip?

cinnamongirl

Mechanical

Paulkuklych

Mechanical

cinnamongirl

Mechanical

MikeHalloran

Mechanical

cinnamongirl

Mechanical

MikeHalloran

Mechanical

cinnamongirl

Mechanical

MikeHalloran

Mechanical

cinnamongirl

Mechanical

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