countersink question 2

[aero101]

not sure if this is the correct forum to put this - is there a table referring to countersink dimensions? specifically I am after 90 deg countersink for 1/4. your tips will be greatly appreciated. thank you

 

[MadMango]

http://tinyurl.com/y9yshpz

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[BigJimbo]

I would think that would be determined by the spec of whats going in the hole (screw?) and thickness of material. Our company has a guide designers use to determine what the range of the countersunk hole should be and min. material thickness for screws & rivets.

 

[MadMango]

My point is that standard information is readily available, people have been doing it for years. BigJimbo, you bring up good points.

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[KENAT]

Check out Machineries, if nothing else they have the dimension for the fasteners from which you can extrapolate the correct countersink based on function.

However, are you sure you want 90° & 1/4?

Whey you say 1/4 do you mean a 1/4 inch screw? Inch fasteners don't have 90° heads, they have 8° or 100° unless a custom special.

Think long and hard about your function, bigjimbo makes a good point about material thickness. You also need to consider if the mating part has threaded holes or if you're using nuts. If threaded holes then you have a problem as both the head and the thread are fixed and cannot float. There are workarounds for this if your functional requirement is just to keep the heads flush or under flush, however they have stress and aesthetic implications.

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[PeterStock]

82° or 100° for inch flat head screws

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[aero101]

this is for 1/4 28 socket button head cap screw

 

[aero101]

thank you for your responses

 

[KENAT]

Why on earth are you using a countersink with a button head cap screw?

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[aero101]

KENAT thanks for going back to this,
just redrafting this drawing, got the screw information additionaly, is .285 hole acceptable?

 

[KENAT]

Sorry aero, your question doesn't make sense.

You don't usually use countersinks with a button head screw. A countersink is generally used to recess a flat head screw.

If you mean counterbore dia then .285 sounds far too small.

If you just mean what hole size you need, then you need to calculate this based on function. .285 isn't unreasonable so long as it meets your requirement and the tollerances of position on the holes and the mating parts are set appropriately. I think the suggested normal clearance holes for 1/4" in Machineries is .281 which I believe corresponds to a fairly standard counterbore tool.

So, with the information you present I have no way of telling you if .285 is acceptable.

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[MadMango]

1/4 clearance holes could be .257 (Close fit), .266 (Free fit), or .281 (Loose fit)... depending on what your application needs.

If you are talking counterbores instead of countersinks, then .285 is too small as maximum head diameter on a 1/4 buton head cap screw is .437

You should buy Machinery's Handbook or reference one.

"Art without engineering is dreaming; Engineering without art is calculating."

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[aero101]

meant 1/4 clearance hole, dont too much info about application at this point, but thanks for your input everybody