Determining hole countersink dimensions?

[Anonymous]

I’m using a stock off-the-shelf screw (SPAX #10 2” multipurpose self-drilling) as an OEM part for my product I’m designing. I want the screw head to sit flush with the surface of my part. I’ve read there are essentially two basic head angle standards: 82 and 90 degrees. I called SPAX to ask the head angle on the screw I intend to use. The customer service rep checked with engineering and told me the head starts at 30 degrees and then tapers to 45 degrees. That...doesn’t sound right? I assume I need to use a head angle in my design that meets the countersink bits common to machine shops.

How do I determine this to design my holes specific to the screw I intend to use? And how much additional relief do I need to build into the hole design to allow for powder coating?

[aaronkcap]

If you have the screw in hand you can break out a pair of calipers and measure from the top of the head to the start of the fastener diameter. or you can use this chart http://www.carbidedepot.com/formulas-cb-inch.htm.  the extra allowance for powder coating depend on how thick the coat is applied. It could be anywhere between 0.5mil to 10mil 1mil=0.001in

[etfrench]

This link to the Spax site shows a cutaway view.  In order to manufacture the countersink hole, you may need to use two operations.  One at 30 degrees and one at 45 degrees.  Another method would be to create a custom countersink cutter.  It's actually fairly inexpensive to have custom cutters made. 

I'd ask Spax for a technical drawing with enough information to create the correct countersink for materials other than wood.

[lichtzeichenanlage]

If I remember right, you can download all the information from here but you have to register for this.

[Anonymous · Accepted solution]

It looks like the countersink angle is actually 90 degrees (so...45 degrees on each side x 2). Thanks for all the assistance.