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Standards Regarding Counterbore Clearance Holes for Various Screw Types

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Harry Houdini

Aerospace
Jan 22, 2021
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Hello everyone, hoping someone could point me in the right direction. I am currently aggregating all possible information regarding clearance hole sizing for a fixed fastener calculator. See image below.

image_ogsdhv.png


All of the values in the tables are based off ASME B18.2.8-1999 which can also be found in the Machinery's Handbook. See images below.

image_uvglsl.png


This is what my calculator looks like, but I am missing information regarding minimum counterbore diameter for pan heads, button heads. I can get the MAX head diameter of the different screw types either from NAS or Machinery's Handbook. I could also calculate what the minimum CB diameter could be for a specified position tolerance, but that seems kind of arbitrary. Also I use Soliwroks as a CAD program but the clearance hole values seem to not correlate to any standard.

My question is, is there a standard out there that talks about counterbore depth and width for different fastener types?

Also for anyone who is curious, this is what the calculator looks like.

image_qzdcgi.png
 
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