GD&T -any draft angle specify method?

[samsangsam]

i have a plastic part, which have a screw hole for tapping screw, i am wondering why no draft angle specify in drawing? is it good to specify the draft angle as consder the pin to form the hole can be broken. and the draft affect screw tigthen torque. How to specify the draft angle in GD&T format?

 

[tbuelna]

With molded plastic parts or metal castings the drawing dimension are usually defined at the edge where the draft originates from. And there is usually a general note on the drawing stating that the draft applied to surfaces is additive. This means a hole feature with draft would be defined by its diameter at the upper edge. And a circular boss feature with draft would also be defined by its diameter at the upper edge.

 

[samsangsam]

any way to specify the angle in drawing? as the plastic part have many screw hole and different draft, if just in general note, it would be difficult if many hole and draft.

 

[tbuelna]

Use a general note to specify a max draft angle on molded part surfaces. Shorter surfaces normally require larger draft angle than longer surfaces do. If you require tighter control of the hole diameters you are installing screws into, you can always drill them to size after molding.

 

[Tunalover]

To do it right you should draw a section view for each type of hole indicating the starting diameter, the hole depth, and the ending diameter. The angle is not important and should not be dimensioned (that would be redundant anyway).

Tunalover

 

[KENAT]

If in the US/workin to ASME standards then take a look at Y14.8 Casting, Forgings, and Molded Parts.

You can even get an over view at:

http://www.youtube.com/watch?v=i8Y7l9RvwXs

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Tunalover]

I second KENAT's recommendation and I second my recommendation .


Tunalover