Die Cast Zinc part and screws

[surplusjohn]

I am in the final design stages of a die cast zinc part for good volume production, commercial product. I originally specified a cored, drilled and tapped 10-32 hole, 2 places. I was able to increase the height of the screw boss, to about .250 [room for more if needed] and anticipate the call for cost reductions. I am paranoid about self tapping screws and field installers stripping them out. How do you guys feel about this, especially considering the extra depth of the boss? Also, I changed to 10-24 thread. If I do go to a self tapping screw into a die cast hole, what is the ideal hole geometry and the ideal thread?
Thanks

 

[Heckler]

Their are really a number of variables that need to be answered before you can go to a self tapping screw. Here are a few but you as the designer should know all.

Die Cast Quality:
The Function of this threaded hole:
Assembly Process:
The Mechanical Loads this fastener is expected to see:


We use Plastite Trilobular screws with our plastic products. But even so we have experienced some broken bosses due to improper assembly or manufacturing.

http://www.taptite.net/taptite/product.asp

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
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_`\(,_
(_)/ (_)

This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.

 

[CoryPad]

Are you concerned that stripping is more likely when using a thread cutting (or thread rolling) screw? As long as the screw isn't used by the installer as an alignment pin and driven off angle, stripping is not more common for thread forming screws compared with pre-tapped holes.

I would advise you to review the products available from REMINC (same people that Heckler mentioned above). They have several products, as well as preferred cored hole dimensions.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[surplusjohn]

I am reviewing the Reminc info, I have used Plastite screws many times in past, Good point about likelyhood of striping of self threading vs prethreaded holes, a clumsy monkey can do either. Thanks