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  #21  
Old 12-20-2014, 09:45 PM
DaAV8R DaAV8R is offline
 
Join Date: Jul 2009
Location: Lee's Summit, MO
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Default Countersinking

I'm surprised at the comments to countersink at high RPM. A lower RPM seems to prevent chatter, although that doesn't seem to be the problem being discussed here.

Are your countersinks deep enough to be knife edged? They appear to be knife edge and if so are way too deep in .063. I wonder if going to a number 4 rivet will be an option. Something to discuss with the mother ship.

When you countersink deep enough to create a knife edge condition you loose the pilot as it extends beyond back side of the base material. The countersink cutting edge will remove material either in depth or laterally if the pilot is too deep to function properly.

On a side note, I have seen cutters where the pilot was not centered. They still work but the cage wobbles a bit when the cutter is used. Still have a few of those in my arsenal.
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  #22  
Old 12-20-2014, 10:49 PM
ijustwannafly's Avatar
ijustwannafly ijustwannafly is offline
 
Join Date: Oct 2014
Location: Colorado
Posts: 243
Default

Quote:
Originally Posted by R. Daniels View Post
A dimpled piece of aluminum is a different dimension than a rivet.
Im working on some counter sinking myself at moment. A different part of the plane but none the less countersinking that must accept a dimpled piece

I would normally agree with what you saying above but section 5 does specifically state .007 deeper then flush for a dimple into a countersink. This is easily found using the end of a dial micrometer or now a days more likely a digital one.

What says the group on discretion here? I have been going with nearly exactly .007 but you do notice the CS does not always allow the parts to sit flush.
So the question is do you go further to get them flush or stick with what vans says?

Also more to the topic, i have an additional question on this. If you are CS past the pilot obviously the cutter is producing a larger hole then the original pilot. Is the problem here the fact that the hole is larger or simply the fact that it is not perfectly round? The hole being larger i would expect. The center hole in the OP picture that is not perfectly round is where the center of the nut plate goes on this part correct? So is the primary concern with the hole being elongated, you loose the ability to locate the nut plate or is it a strength concern?
Please excuse my ignorance as I'm not at this stage in my build but very interested in learning about this for the future.

Last edited by ijustwannafly : 12-20-2014 at 10:59 PM.
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  #23  
Old 12-20-2014, 11:18 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by ijustwannafly View Post
I

I would normally agree with what you saying above but section 5 does specifically state .007 deeper then flush for a dimple into a countersink. This is easily found using the end of a dial micrometer or now a days more likely a digital one.
There is an even easier way to do it than using a dial caliper.

It is pretty much standard that each tooth click on a microstop countersink tool is .001"
So, if you adjust a tool 7 clicks deeper than when it was adjusted for an exactly flush rivet, you will be .007 deep.

.007 deep was chosen as a compromise rule of thumb. I reality, it would be slightly different depending on the rivet size and the thickness of the skin that is dimpled.
It is far better to be slightly short on depth, than too much.
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