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  #1  
Old 01-23-2019, 03:50 AM
TASEsq TASEsq is offline
 
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Default HS rear spar countersinking

Back in October, I countersunk the rear spars of the HS. I went to flush then 0.007” deeper as per section 5. I tested with a coupon in the same thickness as the skins and it seemed ok. The skins were dimples with the DRDT2 (and the dimples have for well on the front spar and ribs etc).

Since then I have primed the spars and skins and the HS is completed except for the rear spar.

Today I clecod in the spar but I’m not sure about the gap between the skin and the rear spar - i understand I shouldn’t expect the dimples to nest completely in the countersinks and Van’s doesn’t want you to do this (they want the dimples to lock into the countersinks for structural reasons).

But I am feeling something is not right here and the countersinks need to be a bit deeper? Perhaps the paint thickness made the difference. I have emailed Van’s and asked but haven’t heard back as yet.

Next step is I might remove the spar and drop a rivet in the countersink and see what it looks like.

Thoughts from the brains trust?

Here is a photo of the rear spar after it was countersunk - unfortunately no photos of a rivet in the hole.


Here is a photo of the skins against the spar - I have clamped it so it would be like it had been riveted. You can see quite a gap with a torch behind it. https://photos.app.goo.gl/KZ5gyGDY8jDA8Ycs7


And a second one, not clamped.
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Last edited by TASEsq : 01-23-2019 at 07:10 AM.
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  #2  
Old 01-23-2019, 06:34 AM
Eztroller Eztroller is offline
 
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did you add a 0 in there? Page 5-08 says...


"Use the appropriate rivet or screw as a gauge when you machine countersink. Stop when the rivet or screw is flush. 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."

I practiced this on scrap until I got it correct.
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  #3  
Old 01-23-2019, 07:09 AM
TASEsq TASEsq is offline
 
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Yes, sorry too many zeros. I went 7 clicks in any case, and I had previously checked the cage and it is 0.001 per click.
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  #4  
Old 01-23-2019, 09:53 AM
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kiljoy kiljoy is offline
 
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We've all done it before.

When I have to countersink for dimpled metal I use a test dimpled piece on a test piece of countersunk aluminum to get the cage depth right. I'll keep going three clicks of the cage at a time until I feel the dimpled test piece slide around in the countersunk hole then I'll dial it back 1 or 2 clicks and test it on another hole before drilling on the actual piece.
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  #5  
Old 01-23-2019, 10:11 AM
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djborko11 djborko11 is offline
 
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There are quite a few excellent homebuiling videos on youtube on this topic. Type this "Setting Up the Countersink Cutter" in the search window.
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  #6  
Old 01-24-2019, 04:34 PM
TASEsq TASEsq is offline
 
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Thanks all,

I had set up the cutter correctly, and as it turns out the paint has made little difference; i removed the spar and dropped in a rivet, and measured a sampling of the countersinks. They were all within 0.007" and 0.01" deep. None were under 0.007". This was what they measured before i painted them, so the paint has added almost no thickness (which is good to know).





I placed the spar back in, and squeezed a rivet to see how it looked. As you can see there is still a gap.



I emailed the photos to Van's - and this is their response. So, build on!

Quote:
That is OK and expected. It may be a little worse because of the paint, but the two will never have no gap unless you over csk. Because the csk and the dimple are slightly different. This way, the dimple will the reformed and packed into the csk spar when it is set, which results in a stronger joint.

What you have shown in your pictures is exactly what we expect to find and produces the highest strength joint between a dimpled and countersunk component. In assemblies like this you should not exceed a depth of .007 past flush.

Sterling
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