Counter sinking rear spar Rv-10

[PrescottB787]

Step 8 on page 6-3 call for counter sinking flange hole. I am doing this but the countersink seems to be going very deep. I did five countersinks and attached a small strip of .025 aluminum to it. It doesn't seem to be a perfect fit and I feel the countersink is already to deep.



Above is a close up picture. How does it look to any of you experience builders. Any suggestions?
Thanks in advance!

[CharlieWaffles]

To gauge the depth of my countersinks, I made a test tool. Take a piece of scrap aluminum and dimple it to the correct size. Mark it appropriately and keep it long term. Before countersinking my material, set the countersink guide to an approximate setting (eye-ball it) and use a scrap piece of thick aluminum - old angle works great for this. Countersink and try your test dimple piece. If it moves around too much, you have too much countersink. If the piece sits proud of the hole, you need to countersink more. Adjust your guide, and countersink another hole and try again. Once you are dialed in, lock the guide and use that for your work at hand. Note the countersink depth will vary based on the hole size (screw size). So as you change bits in the countersink, the guide will need to be changed to reflect the amount of depth needed.

[Wyzepilot]

While I'm sure builders with far more experience than me will chime in on this one I'll offer you my opinion. If you're looking for the skin to sit flush on the spar it may be too deep of a countersink. The last thing that you want to do here is enlarge the hole. In my opinion you can never go wrong with what it says in section 5. Going .007 past flush or seven clicks on your countersink tool should serve you well and keep you out of trouble. Good luck and enjoy your build.

Dave

[N427EF]

From looking at your picture, the countersinks are definitely not deep enough.
You should not be able to see daylight between the adjoining pieces.
When joining any two or even three pieces of material, the overwhelming rule is to keep the fit tight without any gaps.

To gauge the depth of my countersinks, I made a test tool. Take a piece of scrap aluminum and dimple it to the correct size.

That is good advice!
Make your test tool for just one hole. By using a strip with several holes you might possibly introduce a poor line up of rivet holes to make it appear as though the countersink is not deep enough.
For me, a "very slightly" proud dimple would result in a perfect fit after a rivet was set. If you see light between the pieces after riveting, its not acceptable.

Although good general guidelines are provided in the building manual, precise
countersinking requires a bit of adjustment depending on the material and location of the material.
You may achieve a perfect countersink on a .063 piece of aluminum rested
on a bench and find that using the same setting on a flange produces a different result. The spar flange is unsupported and somewhat yields to the pressure you apply when machining the countersink. You'll need to support the flange with your fingers or a piece of backing and be consistent on how much down pressure you apply.

The good news is that your countersinks appear to be too shallow and taking off more is much easier than dealing with the reverse problem.

[rvbuilder2002]

Originally Posted by N427EF

From looking at your picture, the countersinks are definitely not deep enough.
You should not be able to see daylight between the adjoining pieces.

Use caution......

One of the more common critical mistakes that we have to help builders through is when they countersink too deep for dimpled skins.

If you go too deep, you will still have no gap between the skin and the sub structure but the strength is likely compromised, With countersinks that are slightly too shallow (as in the attached photo) the strength is no different, but there is assurance that it is not too deep. That is the reason for specific recommendations in Section 5 of the manual. The depth was derived from doing samples of different depths and then machining off 50% to allow magnified inspection of the rivet joints.
Countersinks only deep enough for a rivet head still produced totally acceptable riveted joints (though not quite as nice ascetically). Countersinks any deep than about .009 " beyond what would be needed for a flush rivet began to produce visible gaps in the riveted joint.

[HAL Pilot]

https://www.dropbox.com/s/or4ebmve0u14elc/GAP.jpg?dl=0

HS 902-1 spar and HS 901 skin


I am finding some gaps in the skin to spar area the widest is around .5 mm but on the other hand I can not get a .04mm feeler gauge to go all the way through. Is this an issue or build on? The gap is not due to too little countersinking but to the primer paint.

Pete

[MJarreau]

Scott,

Do I understand you to say that if a rivet will sit flush on the counter sunk part, it is good?

Thanks,
Mike