100 degree vs 90 degree csk screws

Question

100 degree vs 90 degree csk screws

UTME83 (Mechanical)

(OP)

5 Oct 06 11:28

I'm using a Jonathan slide which has a 0.199 hole csk 100 degree x 0.395. I am attaching this slide to a unit with M4-10 screws that I can only find with 90 degree csk... is the difference in bearing angle enough to be concerned about? Is there a source for metric hardware with 100 degree csk? Thanks.

drawoh (Mechanical) · Answer 1 · 2006-10-05 13:14:45

UTME83,

   The .199" diameter is the exact sharp diamter of a #3 machine screw flat head 100 degrees.  I do not understand your .395" number, unless perhaps that is the diameter.  The sharp diameter of a #10 flat head screw is .385".  A .395" countersink would sit your screw below flush.  I am assuming you are using inches.

   A #3 screw has a major diameter of .099", and they are hard to find.  There are small solenoids on the market that use 3-48UNC tapped holes, and I am wondering what drugs the designers were on.

   A 100 degree countersink definitely is English.  Metric flat head screws are 90_degree.  Most English screws are 82_degrees.  Hopefully, a #10 screw will work for you.

   I do not know the consequences of putting a 90_degree countersink screw into a 100_degree hole.  It would look absolutely unprofessional.

                       JHG

drawoh (Mechanical) · Answer 2 · 2006-10-05 13:23:14

  Wait a minute!  The numbers do make sense.

  You have a .199" diameter hole with a .395 diameter x 100 degree countersink.  This is a hole for a #10 100 degree flat head screw.

  Be careful not to get the more common 82 degree screws.

                        JHG

UTME83 (Mechanical) · Answer 3 · 2006-10-05 14:23:53

The slide is designed for #10 hardware but in one case it is being attached to a unit that has metric threads so basically I need the 100 csk head on a metric size screw and haven't been able to locate it without going custom.

wes616 (Aerospace) · Answer 4 · 2006-10-05 18:26:20

Your 90deg screw head will not sit properly in the 100 DEG csk seat. The Forces introduced into the screw head will be at the base of the csk, reducing signifgantly the overall area designed for loading condition.

Force stays the same, area is reduced, thus tensil stress introduced into the screwhead increases inverley porportional to the decrease in area. If you sketch it out... eventually the head will **POP***.

Wes C.
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UTME83 (Mechanical) · Answer 5 · 2006-10-06 07:21:22

Sounds to me like I need to get Jonathan to provide a slide that accomodates the 90 degree heads on the metric hardware... thanks for the feedback

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100 degree vs 90 degree csk screws