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AD3 & #40 countersinks

Eztroller

Well Known Member
Howdy,

Page 8-04, Step 6: Machine countersink the middle nine holes (shown in Figure 1) in the top and bottom flanges of the HS-00902-1 Front Spar for AN426AD3 flush rivets.

Page 8-08, Step 4: Machine countersink, for dimples in .025 thick skin, the #40 holes in the flanges of the HS-00902-1 Front Spar and HS-00903-1 Rear Spar that correspond to the HS-00901-1 Skins

The bold underlined directions are confusing to me..... What is the difference between a countersink for an AD3, and a #40? Wouldn't these be the same?
 
AD3 hole size is #40. In the first instance the rivet will be flush so set up your countersink accordingly, in the second instance a dimpled skin will need to be accommodated so the countersink will need to be slightly deeper to allow for the skin thickness so it lays flat.
Info in section 5 on this.
 
Keep in mind, "so it lays flat" means no more than .002" between the countersunk member and the dimpled skin."

Not necessarily...... It depends on where you are measuring.

Section 5 gives a specific recommendation for countersink depth for a dimple regardless of the thickness of the skin that is dimpled.

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. It is also why the .007" deeper for a dimple rule is used. It will assure that in all situations, the dimple fits tightly in the countersink with no compromise in finished appearance.
 
I'm constantly impressed by the knowledge shared by Scott on this forum on a huge variety of topics.
 
Another one that got me, not remembering the section, it ask to drill 1/8" drill bit and later on asked to drill #30. I always took #30 as 1/8 size, only to learn that there is about a three thou difference. Now that is precision.
 
How does it looks when you countersink to deep?

This is the most building error that builders do, countersinking far to deep to nest a dimpeld sheet onto aluminum structure.

Look at this picture:
8QaUPkQyGwheq-rKaMUPWluvo8GJdAcFj5DypumGh06l4Cm4hkyH2BQZjg45cV2GNrcQoAZy9Lkvw1pQJRL3qdQWdBjpsi9cAkErbNIPhnmFTxGXMtaJavZqi_vsP81VDiP9bgcxDz7Qi-6ZS1n0_RT-jzAykKcHeMjkbZcnUDCFPjDN2VUDw0o5asBFr2-HPY7YngUuXG2oNgmgD5D4pOaaP1fKmEo0tCYQUqUXFWb7O3dkymDSi0h8C65STwK5PicImx7zSHh-dclOy7hTzRkSzSu-0e1GQFRU6m0HT_18s5SbN_IcfGZyudzbuiViJDr_J32xmLNHcknLZ8jOTnNCRXNdP-ZamOrTynKApo8xGcANGRenSrYZn9IhDPbCGwYPgn3gJeiliH9ns93mf8pjwWSUcyT4ZoUHL3fLEarX-HyjdbjNUgqucAwlMD7DMuJFV1jYL3KjeWLJQQhnqsEN7i6kvJcb9n_ocxBFGUmE4NJ1EQNs3ylQGIgzkU31-dNjAVEqY_go4MAXF6OC7EPV9vq777upreKhXwMy9e-TUCK7dOE4rg3IibHQYFJwBqBM8BLyFULZZa4OeTUxeOQA0oL6IBjJ9yusJWE=w1023-h203-no


This is a piece of aluminium angle, drilled and countersunk to accept a sheet aluminium which is dimpled. Then immersed in epoxy, cured, cut and grinded. So that the desaster gets visible ...

From left to right:
1. The aluminium angle is countersunk until a AN426AD-3-X rivet sits flush.
2. Countersunk until a AN426AD-3-X sits 0.01" deeper than flush.
3. 0.018" deeper than flush.
4. 0.02" deeper than flush.

The picture is not perfect, nor the samples are ... but it shows clearly what will happen. Where metal to metal is in contact and where are gaps. The gap between the angle and the sheet material, between the rivets doesent matter at all, but the gap of the two materials inside the countersunk hole and the dimple let me feel unconfortable!

For sure this got measured with a rivet ... which has also its tolerances.
The measurements are done by a caliper ...

Stay strong with Vans instructions, chapter 5 ! as Scott mentioned (he was working many years for Vans Aircraft btw ;)):
vcArH4PWza1eHlIwJt6LujngeC50NiDa8QpumSRFTrozxmr7DFKSLsVhvvJSj0xll429SBgVeA-85_gYQTwKeHLOv8LEcK9WvFkoD6A9Te4Nn8clyMJRl_2rwm2XtVb3x1JeWv07WkkckwDIBqo5071-h4lnPhCKm3aiagwTIpQl9KR1c9ME2T0WRwLJtLvdjdg8DAHrxA9UC8oM0ul2rqkzMbtA1zgrM-C3HhwgVyPGwfJeP0Svmm-PB5YhIH1AczdtK-D3F6SyU6rUSM5vy7iijxP0mo24jPQniFD2r2gqyLaHpV2jEzIc7QV8Zk9AvDI0_veT2P1CKheIX4V_Is18u7wfGco3nndRUpIOGObc1DK09rrW_UsKqEE9cUc0zeCEMYO4oJN_2T613vG0FedV5q_dnjH0T45WmB50yRh5b8W_o5niUqtqnKU0S6XoMv6sCBa3OF1yXTb6w3yk6z3hhat-ygNlplZIdrecCruoeSFUTrpjJzE95ZW-3ZkLpcTKEV2y17rswqTQMNH2J8EWJDXMHD0J8yc1pU618XC5YMthsHFfnxtsOfG72faFHPgGJ-ibULB0wLY-56EMV4M0VsVxmLWC4N9B0aA=w1132-h105-no


The clicks may be not the same on all brands of countersunk cages! Test on scrap first.
 
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.
 
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.
 
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 ;)
 
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.
 
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.
 
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
 
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.
 
Never to late to learn from the old times ...

I belive Marc is refering to this:
bujVpl4rOaRWU9owAVmadxlWTRuqTvCC0kUh8UCn0waWVAUFiEb3PXpcepGs9wSuk7TfQAkdILIYRGW60rfo5KWY8t-4340QSGJ-Wxc1GZBUgswAaFGdu2b-SZzVXzLWgl5_i3mZyKzgXg8uhiJuhbD_p9knk0YLhSnrQLJC4fRZN5Jz-hLzKzTdQMVcIPPDl5zI0tAjfRXc88Reps2-11NFfUjyHcL2gydJgXAuOI16hIdRbCx0kMow9fugOEVNTn_jvGtrYV0z5VOmmuWFN_CB8pNSXRGKrmAgPcmj1eRC6I19vNmLT7H-yl29gxUEqcPofMNSoGc9G7FdcOQXlPjfGVzFLONEC80iI7YZrz6WoAv3TMDaG-aDkpvhw3TJevVkc4weeSr7LqwPxLvPvVa7ItxDFgelUx99hawYBF9DFS9wQl0v-X0SCksFFIYs5YZ2gpJvNnB2cYPndBF0qL5dC6vUzsf1FrYn9F02cLStjlo37QhmeuRULthGsjzNL93UfMTAYOtPR471V1koLHohfqeEISSxKW9s2erqmwXDihYtLVea8XjKtraT2Mf8sNLkRBp4FYpOyh9hQfQT2X8QWX-tiWan9dGZoXM=w655-h445-no


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.
 
I belive Marc is refering to this:
bujVpl4rOaRWU9owAVmadxlWTRuqTvCC0kUh8UCn0waWVAUFiEb3PXpcepGs9wSuk7TfQAkdILIYRGW60rfo5KWY8t-4340QSGJ-Wxc1GZBUgswAaFGdu2b-SZzVXzLWgl5_i3mZyKzgXg8uhiJuhbD_p9knk0YLhSnrQLJC4fRZN5Jz-hLzKzTdQMVcIPPDl5zI0tAjfRXc88Reps2-11NFfUjyHcL2gydJgXAuOI16hIdRbCx0kMow9fugOEVNTn_jvGtrYV0z5VOmmuWFN_CB8pNSXRGKrmAgPcmj1eRC6I19vNmLT7H-yl29gxUEqcPofMNSoGc9G7FdcOQXlPjfGVzFLONEC80iI7YZrz6WoAv3TMDaG-aDkpvhw3TJevVkc4weeSr7LqwPxLvPvVa7ItxDFgelUx99hawYBF9DFS9wQl0v-X0SCksFFIYs5YZ2gpJvNnB2cYPndBF0qL5dC6vUzsf1FrYn9F02cLStjlo37QhmeuRULthGsjzNL93UfMTAYOtPR471V1koLHohfqeEISSxKW9s2erqmwXDihYtLVea8XjKtraT2Mf8sNLkRBp4FYpOyh9hQfQT2X8QWX-tiWan9dGZoXM=w655-h445-no


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.
 
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 :rolleyes:

I'm using only dimple dies from Avery and Cleveland. I like much more those from Avery, especially the spring back dimple dies.
 
Has anyone?s ever tried the double dimple method?

I suppose if you had two 20 thou sheets it may work?
 
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