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| Flat Head Screw Strength |  | ||
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| Posted by: robertburrell ® 11/07/2006, 15:40:20 Author Profile eMail author Edit |
What is the affect on strength of a 1/4 flat head in a countersunk hole for a 3/8 flat head? So basically the conical surface is not properly seated, because it does not make complete contact as intended along the entire conical face. This situation has arisen due to unknown tolerancing. The seemingly best idea was to increase the through hole to allow more slop. I am concerned that the fastener will not perform as advertised. There is also possibility that the fastener will not be centered in its hole. What ill effects could this have? In this situation, the fastener only makes contact with a small crescent shape (not the entire circle). These situation do not seem all that bad just hearing about it. Please model it up or set up the situation to see how bad this looks. Any advice would be great. Requirements have kinda designed us into this situation; I know the obvious answer is not to do this. This is not what I am asking. I would like to know how likely this is to fail compared to a properly mounted fastener. If I can prove it is more likely to fail, then I have reason to stop this goofy design. If it won't fail, I guess my only argument is.. it looks bad? Thanks in advance Rob |
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| Re: Flat Head Screw Strength -- robertburrell | Post Reply | Top of thread | Forum |
| Posted by: Kelly Bramble ® 11/22/2006, 08:22:56 Author Profile eMail author Edit |
What exactly is the diameter and angle of the countersunk feature? What is the thru hole diameter? How thick is the material? Modified by Kelly Bramble at Wed, Nov 22, 2006, 08:23:19 |
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Posted by: gkemp ®  11/22/2006, 06:01:27 Author Profile eMail author Edit |
Hi Rob,
If the countersink angle is the same then the smaller screw will seat. The problem is that the smaller screw barely engages the material at the edges of the head. You are losing over half of your load bearing ability. If you add the combined loading created by misalignment it is even worse. If this is an application that could harm someone if it fails you need to do all you can to stop it. Gary |
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| Posted by: robertburrell ® 11/22/2006, 10:25:08 Author Profile eMail author Edit |
Gary, Sounds like you are the only one that understands what I am trying to ask. Yes the countersink angles are the same. Do we have any mathematical proof of what you are telling me? Or, at least an idea of what these calcs may be or involve? These will be used where nothing can come dislodged (as to cause harm to anyone) in a 9g load condition. I fear it may be too late, deadlines are nearing, and the part with countersinks has completed fabrication. (Aluminum honeycomb plate w/ skins, containing countersunk inserts for fastening) Thanks again Rob |
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| Posted by: Zip ® 11/22/2006, 00:51:19 Author Profile eMail author Edit |
Perhaps you can ream and countersink using a proper counter-sink tool bit. Proper socket head c sunk capscrews are easy to source. Many used on rear end of truck frames. However; a
son of a gun if material is thin. Maybe round head bolts? Good Luck! Zip Zip |
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