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Countersunk holes

henry_methorsthenry_methorst Member Posts: 4

When I go to add a preconfigured countersunk drill hole, the drill size changes when I select, say, #48 (0.076) vs any other, but the countersink diameter doesn't change at all no matter what size drill hole I select.   Is this normal?   


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    eric_pestyeric_pesty Member Posts: 1,500 PRO
    Yes, that's normal: there is no "correct" size countersink for a given drill size, so in that case you have to set the value yourself. What would you expect to change to?
    It you change the hole type from "Drilled" to "Clearance" then the countersink will adjust to the selected fasteners size.
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    henry_methorsthenry_methorst Member Posts: 4
    Thanks for the info.  Just looking into my bag of random screws, I can see what appears to be different head sizes.  Probably because I have metric and imperial style
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    PeteYodisPeteYodis Moderator, Onshape Employees Posts: 519
    edited March 28
    @henry_methorst Its more than just different head sizes, there are different head types.  As part of those head types the countersink angle could be different and the height of the fastener head could be different (oval heads verses flat heads for example).  There is no "correct" countersink size without a given fastener to consider it for.  The same could be said for counterbores.  
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    S1monS1mon Member Posts: 2,359 PRO

    In my experience using the countersink option, it puts the nominal flat head of the screw co-planar with the outside world. With tolerances this could mean the real screw might protrude from the outer face. This is not good practice for many use cases (either it interferes with another part which covers the screw head, or it would provide a sharp edge to catch on fingers or other parts). We really need some amount of clearance added.
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    PeteYodisPeteYodis Moderator, Onshape Employees Posts: 519
    @S1mon Yes the countersink right now always assumes a countersunk head fastener and at "perfect" head to mating surface alignment, which we all know is a unicorn in the real world.  There is a separate improvement to recess a countersink/counterbore by a user defined amount, and this could also eventually be improved by a connection to a specific fastener, because the recess amount may be specific to fastener geometry.  
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