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  #11  
Old 02-12-2018, 03:32 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Every microstop countersink cage I have ever used was indexed in single thousandths of an inch per each tooth rotation.

They usually have a .001" marked on it somewhere.....

So if you start from a setting that results in a flush fit for a rivet head, and then adjust 7 clicks deeper, you should be at the recommended .007" extra depth.

BTW, the .007 value was developed using a cut-away test sample similar to what was posted by Dominik.

The dimples in his posted photo look like they may have been just a bit under formed which makes the gap between the angle and skin bigger than they typically have to be, but it still gives the general idea.
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  #12  
Old 02-12-2018, 03:56 PM
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swisseagle swisseagle is offline
 
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Location: 20km outside of Zurich, Switzerland
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Default How to measure ...

Take a AN426AD-3-X, put it into the countersunk hole, take the narrow end of a caliper (depth gauge end) and measure how much deeper the rivet sits below the surface.
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Dominik

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  #13  
Old 02-12-2018, 04:00 PM
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swisseagle swisseagle is offline
 
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Default The sample maybe not perfect ...

Yes, Scot is right, the sample is not absolutley perfect ... this was done by a builder that I assist. So he could see what would happen if he countersunk to deep.

You start hopefully at a toolbox and flap segment, read alot, maybe take a course ... then start at the empennage of an RV. Your skill will grow with every rivet, dimple and countersink
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  #14  
Old 02-12-2018, 05:27 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
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Quote:
Originally Posted by rvbuilder2002 View Post
Every microstop countersink cage I have ever used was indexed in single thousandths of an inch per each tooth rotation.

They usually have a .001" marked on it somewhere.....

So if you start from a setting that results in a flush fit for a rivet head, and then adjust 7 clicks deeper, you should be at the recommended .007" extra depth.

BTW, the .007 value was developed using a cut-away test sample similar to what was posted by Dominik.

The dimples in his posted photo look like they may have been just a bit under formed which makes the gap between the angle and skin bigger than they typically have to be, but it still gives the general idea.
I wish my microstop countersink cage were as accurate. Both of my cages cut a bit deeper or shallower based on how much force is applied to them. Drill press will result a set of depth and hand drill will result a different depth. I have just learn to apply uniform set of pressure when using these cages.
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  #15  
Old 02-12-2018, 10:33 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Bavafa View Post
I wish my microstop countersink cage were as accurate. Both of my cages cut a bit deeper or shallower based on how much force is applied to them. Drill press will result a set of depth and hand drill will result a different depth. I have just learn to apply uniform set of pressure when using these cages.
Technique used can vary the depth very slightly but only by about .001 or so one way or the other.

Not a factor when countersinking for a dimple, but just one more of the reasons that .007 is the recommended additional depth.
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  #16  
Old 02-13-2018, 08:05 AM
Marc Bourget Marc Bourget is offline
 
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Location: Stockton, California
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Quote:
Originally Posted by rvbuilder2002 View Post

Different skin thicknesses can result in differing amounts of gap between the sub structure and dimpled skin, in the areas between the rivets. From a strength consideration a small gap here is not of concern.

The strength comes in tight joints at the rivet locations. This is where no more than .002" is acceptable.
IMHO, the differing amount of gap is a result of incomplete execution of the "dimpling process." Technically, between the upper and lower skins when joining sheets and a special angle (110 deg) countersink.

I believe "mismatched" (male vs female) dimples contribute to "smoking rivets." If not matched, accurately, it's similar to stacking "teacups" and permits relative motion contributing to the "smoke"

FWIW
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  #17  
Old 02-13-2018, 08:14 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Marc Bourget View Post
IMHO, the differing amount of gap is a result of incomplete execution of the "dimpling process." Technically, between the upper and lower skins when joining sheets and a special angle (110 deg) countersink.

I believe "mismatched" (male vs female) dimples contribute to "smoking rivets." If not matched, accurately, it's similar to stacking "teacups" and permits relative motion contributing to the "smoke"

FWIW
If you computer model dimples and assume that they are formed perfectly by dimple dies, you can see that there is a difference in how they will nest, depending on what the skin thickness is.

But it doesn't matter.

As long as the dimples are fully formed for each layer, a tight fit is still achieved (I have tested it with machined cross section samples).

I am not sure what a special angle (110 deg) countersink is that you are referring to. I have never seen such a tool.
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  #18  
Old 02-13-2018, 11:56 AM
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swisseagle swisseagle is offline
 
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Default Never to late to learn from the old times ...

I belive Marc is refering to this:


The video with all the information you can find here: https://www.youtube.com/watch?v=IDbTUt3OG9s
4: and 6:10

It is quite an old video ... how they build planes in the past.

I was always wondering myself, how they do it now? Do they get build like all the Vans plane are built?

If you look at the cross-section of a dimple these angles make sense. A few vendors are offering "understructure dimple dies". But they just set deeper with the same angle.

To go very accurate, you should use special dimpel dies that fit to the sheet thickness. But I think, in the end it doesend matter, the force of the rivet during riveting will correct the angles, so that they nest onto each other.
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  #19  
Old 02-13-2018, 12:46 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by swisseagle View Post
I belive Marc is refering to this:


The video with all the information you can find here: https://www.youtube.com/watch?v=IDbTUt3OG9s
4: and 6:10

It is quite an old video ... how they build planes in the past.

I was always wondering myself, how they do it now? Do they get build like all the Vans plane are built?

If you look at the cross-section of a dimple these angles make sense. A few vendors are offering "understructure dimple dies". But they just set deeper with the same angle.

To go very accurate, you should use special dimpel dies that fit to the sheet thickness. But I think, in the end it doesend matter, the force of the rivet during riveting will correct the angles, so that they nest onto each other.
Interesting

I have never seen that video.

I have also never seen any standard practices document that specified using different angles of dies for male and female halves or top vs bottom sheet.

I wonder if this is assuming the use of heated dimple dies which was common at that time.

Test samples I have done show that the fit of two dimples to each other is quite good if quality dies and proper technique is used.
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  #20  
Old 02-13-2018, 02:01 PM
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swisseagle swisseagle is offline
 
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Default Different material thickness

When you are dimpling, the sound is different ...

If you dimple thick material, then the cone on both sides of the material gets in contact with the dies and take over the form of them.

By thin materials, like the rudder skin on a RV, the sound is much different, the dimples only pushes the material into the cone, but not forming it completely. Have a look at the side where the material is pushed out, there you do not see contact marks of the female dimple on the cone.

So, for very thin materials, a special set may be would help ... but on the other hands, more than 10'000 RV's are flying ... and never where in contact with special dimple dies for thin skins

I'm using only dimple dies from Avery and Cleveland. I like much more those from Avery, especially the spring back dimple dies.
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