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rv10builder(at)verizon.ne
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 Posted: Thu Dec 14, 2006 10:35 am Post subject: #41 drill bit.. is it really better? |
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I know the difference between 40 and 41 in minor but anyone know if we want
a tighter hole? I would think as the rivet expands as it is being squeezed
to the correct length that it would put a slight more pressure on the
smaller hole and possibly create a stress crack? or is smaller really
better?
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owl40188(at)yahoo.com
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| Posted: Thu Dec 14, 2006 2:20 pm Post subject: #41 drill bit.. is it really better? |
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I don't have any specific data but slightly more pressure is probably good. It sets up a tensile residual stress field around the hole which helps with fatigue life. Now I don't know this for a fact as far as rivets go, however, with bolts, we normally use interference fit fasteners if we need to improve the fatigue life of a part just for that reason. Its based on the principle that if you take a piece of metal and overload it in tension then its fatigue life will improve assuming that the fatigue loading is lower. Don't try this on your airplane because if you really load it in compression it will have the opposite effect. Such a case would be a really hard landing with full fuel where the lower skin/ spar cap will be in compression. That would set up a compressive residual stress and reduce the fatigue life of the skin/ lower spar cap.
I don't know but I might have told you more than you were interested in knowing.
happy building
Niko
40188
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jeff(at)westcottpress.com
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| Posted: Thu Dec 14, 2006 2:50 pm Post subject: #41 drill bit.. is it really better? |
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For what it's worth, I've used a #40 ream where both holes were already pre-punched and a 41 bit followed by a 40 ream when they weren't. In the brief discussions I've had with Vans about this topic, I get the sense that they find it amusing that the builders get so wrapped up in this kind of detail. They really just want us to drill to #40, and dimple... just like they call out in the plans. If they wanted us to do something different, they would have said it.
I've been down this road, and it leads to "just build the plane."
Jeff Carpenter
40304
On Dec 14, 2006, at 2:20 PM, Niko wrote:
[quote]I don't have any specific data but slightly more pressure is probably good. It sets up a tensile residual stress field around the hole which helps with fatigue life. Now I don't know this for a fact as far as rivets go, however, with bolts, we normally use interference fit fasteners if we need to improve the fatigue life of a part just for that reason. Its based on the principle that if you take a piece of metal and overload it in tension then its fatigue life will improve assuming that the fatigue loading is lower. Don't try this on your airplane because if you really load it in compression it will have the opposite effect. Such a case would be a really hard landing with full fuel where the lower skin/ spar cap will be in compression. That would set up a compressive residual stress and reduce the fatigue life of the skin/ lower spar cap.
I don't know but I might have told you more than you were interested in knowing.
happy building
Niko
40188
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