Bosses thickness and height

[mmorleydesign]

Hi guys,

Looking for some advice, I am getting a lot of conflicting information regarding bosses. For example, Plastic One recommends that:

'wall thickness around a boss design feature should be 60% of the nominal part thickness if that thickness is less than 1/8". If the nominal part thickness is greater than 1/8" the boss wall thickness should be 40% of the nominal wall.' and ' the height of the boss should be no more than 2 1/2 times the diameter of the hole in the boss.'

But Bayer Material Science recommends the 'outside diameter of bosses should remain within 2.0 to 2.4 times the outside diameter of the screw or insert.' No specifics on the height are mentioned only to avoid long cores and very thick bases when drafted. When I look at existing parts for comparison it appears some of these rules apply, and some don't, and it differs from part to part.

Can anyone recommend a better guide for reference, or give advice from experience?

thanks,

 

[patprimmer]

The reason for the various recommendations are that there is not a "one size fits all" recommendation possible.

For the best surface finish with minimal sinks, the thinner the rib or boss and the smaller the rad where it meets the wall, the better the appearance.

For mechanical strength, especially if assaulted by a self tapping screw, the thicker the boss the better.

As to depth, draft angle, section thickness where it starts and finishes, required hoop strength, required finish, acceptable core temperatures and cycle times and core cooling all come into play.

It also varies by material type and distance from the gate and resistance to flow from the gate to the point in question.

Everything is a compromise of multiple points.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[MikeHalloran]

The best example available for learning by example is high volume consumer goods, e.g. razors, toothpaste containers, stuff like that.

Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

Nearly every raw material manufacturer will have a free design guide download. You will find there are some material specific guidelines and you will find some conflicting info too. Sometimes you just have to try and see since every product will have different requirements and unique tooling.

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