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How deep to countersink the AEX wedge

JDA_BTR

Well Known Member
So today I got the rudder TE drilled - awesome. Used a wood block cut at an angle to drill on the chord line.

Now I'm using the jig I made to countersink the AEX normal to the wedge surface. I have the countersink adjusted so the rivet head is just flush (can run my fingernail over and it doesn't catch and it eyeballs not recessed).

But?.. do I advance the c/s another 5 stops (0.005"), or do I just let it ride?
 
I dimpled a scrap piece of alum. the same thickness as the skin and used it as a guide for the countersink depth.
 
In Section 5 (5.5) of the construction manual it says the following...

For a dimpled skin riveted onto a machine countersunk surface the countersink must be slightly deeper as mentioned earlier. Proper depth is .007
deeper than when the rivet head is flush. This depth correction corresponds to seven "clicks" on a microstop countersink tool indexed in .001 inch increments.


This is a general rule of thumb that doesn't take into account the difference for different skin thicknesses, but it is close enough to use for all of them (skin thickness has very small effect)
 
Sounds good?. that makes the wedge pretty well drilled out when you do that from both sides - but if it applies here like everywhere else, there you have it!
 
In Section 5 (5.5) of the construction manual it says the following...

For a dimpled skin riveted onto a machine countersunk surface the countersink must be slightly deeper as mentioned earlier. Proper depth is .007
deeper than when the rivet head is flush. This depth correction corresponds to seven "clicks" on a microstop countersink tool indexed in .001 inch increments.


This is a general rule of thumb that doesn't take into account the difference for different skin thicknesses, but it is close enough to use for all of them (skin thickness has very small effect)

I followed this guidance while CSing some .032 flanges for dimpled skin and had a hard time not enlarging the 3/32 holes at this depth.
 
I followed this guidance while CSing some .032 flanges for dimpled skin and had a hard time not enlarging the 3/32 holes at this depth.

This guidance only applies to situations where machine countersinking is necessary. You shouldn't be machine countersinking any .032 flanges to receive a skin dimple... it would surely enlarge the hole.

Holes in an .032 flange can be dimpled to receive a skin dimple. The common practice is to only machine countersink on material that is too thick to be dimpled.

May I suggest you read through 5.5 of Section 5. The most up to date rev. can be found HERE.
It explains the different circumstances where dimple countersinking and/or machine countersinking are/should be used.
 
This guidance only applies to situations where machine countersinking is necessary. You shouldn't be machine countersinking any .032 flanges to receive a skin dimple... it would surely enlarge the hole.

Holes in an .032 flange can be dimpled to receive a skin dimple. The common practice is to only machine countersink on material that is too thick to be dimpled.

May I suggest you read through 5.5 of Section 5. The most up to date rev. can be found HERE.
It explains the different circumstances where dimple countersinking and/or machine countersinking are/should be used.

Apologies if a thread drift, but does relate to the wedge CSing.

Thanks for the reply RVBuilder. I have read the updated section 5, talked with builder assistance, other builders, etc, etc:
Plans2.jpg


Plans1.jpg


In these two areas the spar must be machine CS because, similar to the wedge, the spar is sandwiched between the skin and another piece below. In speaking with support, the oversize holes (oversize about .004-.006 from the .093-.103 for a 3/32" rivet) are permitted (with the understanding that the holes above and below are proper size) due to the piece above and below and a recommendation was given to use a size longer rivet to fill the space. I really didn't like the idea of the oversized holes, so new pieces are on the way. However, while practice different CS depths, almost any CS begins to enlarge the hole. The issue becomes CS for hole size, skin not flush while riveting section vs. CS for dimple, hole becomes oversized. Somewhere there is a happy medium. As a new builder, I just have to figure it out;)
 
In these two areas the spar must be machine CS because, similar to the wedge, the spar is sandwiched between the skin and another piece below. In speaking with support, the oversize holes (oversize about .004-.006 from the .093-.103 for a 3/32" rivet) are permitted (with the understanding that the holes above and below are proper size) due to the piece above and below and a recommendation was given to use a size longer rivet to fill the space. I really didn't like the idea of the oversized holes, so new pieces are on the way. However, while practice different CS depths, almost any CS begins to enlarge the hole. The issue becomes CS for hole size, skin not flush while riveting section vs. CS for dimple, hole becomes oversized. Somewhere there is a happy medium. As a new builder, I just have to figure it out;)

I had the same struggle. I thought the hole was the perfect depth on one side. But they turned into canyons on the back. Ordered new wedge and made them shallower. The final rudder TE was good, but not great. Don't know what I could've done differently.
 
My plans noted that countersinking on both sides will wallow out the hole a bit, but that's acceptable. Once the two skins are riveted, the aex will be trapped between the opposing dimples and be quite secure.

Chris
 
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Apologies if a thread drift, but does relate to the wedge CSing.

Thanks for the reply RVBuilder. I have read the updated section 5, talked with builder assistance, other builders, etc, etc:
Plans2.jpg


Plans1.jpg


In these two areas the spar must be machine CS because, similar to the wedge, the spar is sandwiched between the skin and another piece below. In speaking with support, the oversize holes (oversize about .004-.006 from the .093-.103 for a 3/32" rivet) are permitted (with the understanding that the holes above and below are proper size) due to the piece above and below and a recommendation was given to use a size longer rivet to fill the space. I really didn't like the idea of the oversized holes, so new pieces are on the way. However, while practice different CS depths, almost any CS begins to enlarge the hole. The issue becomes CS for hole size, skin not flush while riveting section vs. CS for dimple, hole becomes oversized. Somewhere there is a happy medium. As a new builder, I just have to figure it out;)

My plans noted that countersinking on both sides will wallow out the hole a bit, but that's acceptable. Once the two skins are riveted, the aex will not be trapped between the opposing dimples and be quite secure.

Chris

There are a few instances where on RV's we purposely over countersink (two examples are above). Most of the time it is when the over countersunk material will be captured between layers as in the first example above. Service history and static test have shown this to work fine.
There is no place that over countersinking is specified, where a rivet head or other structural load fastener will be load in baring on its own, within the excessively deep countersink.
 
Yep, I meant to say the the wedge WILL be trapped between skin dimples, it definitely forms a VERY rigid trailing edge. I was amazed at how much it firmed up.
 
countersink depth

Hope this isn't too far off the subject, but as a first-time builder I'm trying to get the correct countersink depth on the RV-14 VS rear spar doubler. I'm practicing on scrap Aluminum. When I use the manual's value of 7 clicks beyond the flush rivet-head depth and test fit the dimple into the countersink, the dimple is a long way from being fully into the countersink. When I put the rivet in and set it, then hold up the pieces to the light, there's still a gap between the 2 sheets, the countersink is just too shallow to absorb the dimple. This doesn't seem right. What am I missing?

PS When I fit 2 dimpled surfaces together, the dimples still don't nest completely, but the riveting process seems to cinch things up nicely, not so in the countersink case.
 
This should probably be a new thread?. but?.

I don't think the idea is that the c/s piece fully accepts the dimple. I think the idea is that the rivet head is flush in the dimple on top of the c/s piece. If the rivet is flush, that is fine.

Now if the dimpled skin isn't tight against the c/s backing piece, then you have to look if they were held together well when riveting. It could be that there was insufficient pressure on the manufactured head during riveting so the rivet isn't set properly??
 
AEX

My plans noted that countersinking on both sides will wallow out the hole a bit, but that's acceptable. Once the two skins are riveted, the aex will be trapped between the opposing dimples and be quite secure.

Chris

If it's similar to the 7 rudder, there will also be proseal. It's a pretty strong sandwich.
 
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