Old Subject..Just Not to Me

[Bayou Bert]

Hi ya'll, my progress is frozen in fear.
I am to the point of counter sinking the HS spars on the 9A emp.
I have looked at old threads. I have played with test pieces of
dimpled skin and counter sunk holes.
Van's says:
If there is going to be a dimpled skin riveted onto the machine countersunk surface, adjust the machine countersink tool a few
?clicks? deeper than flush. This will make the rivet/screw sit about .005? below flush when dropped into the hole.

I have flushed the rivets and then couple of clicked and measured with
vernier calibers and .005 is almost nothing.
It might just be my not knowing, but when I put the test dimpled piece
in the hole....it just seems like it will spin in the hole a lot easier than
in a hole a few, .008-.009, thou deeper. The deeper CS just feels like
a better fit.
I assume when together the bottom of the dimple and the bottom of the
CS should almost touch?
If there is something else someone can direct me to go read or see,
it would be mightily appreciated.

[Mike S]

Test on scrap until you are happy with the results.

[Gonzo24]

Bert,

A great help during your build for all C/Sing that you will do is to have small test dimple cards made up to keep with your tools. I have several approx 1"X2" pieces of .020, .025, .032 pieces of flat stock with various sized holes dilled in them on the different sides. (example #40 on side 1, #30 on side 2, #19 side 3, etc).

Then dimple these holes like you would for the various applications called for throughout your plans (rivet and screw locations). This way you can drill a hole in a test piece and dial in your countersink cage to fit up your dimpled cards. I do this in the vise on the bench with scrap before moving to the plane.

I forget who I stole this idea from but it works well.

[Bayou Bert]

Mike...I have been using scrap but I am not sure I know what
a good fit should look and feel like..that's my problem.
Jeff...I am getting a good dimple using Cleveland dies.
How do I dial in the microstop based on the dimpled piece?
Ya'll see how rookie I am now.

[Lemmingman]

Bert,

I know what you're talking about and here's how I arrive at the solution. Take a small scrap of aluminum. Drill a #40 hole into it and dimple it. Then take a piece of thick scrap aluminum (angle from Lowes/Home Depot is good) and drill and counter sink it.

I place the dimple in the countersink and then try to wiggle it around. If the hole is too deep the dimple will move around in the hole. If the hole is to shallow the dimple will bottom out and the dimpled piece will teeter-totter in the hole. After a minute or so of fiddling with the countersink depth I am good to go.

Don't get paralyzed with fear here. Remember, tractor not space shuttle. You'll have plenty of opportunities to enjoy that pucker factor when you're you're working on the wing spars.

[rv9av8tr]

What Gil says!

[Bayou Bert]

Thanks Mike and Gil, I have been looking at that.
I put the dimpled part in the CS hole and try to move it
around without feeling a high point at the dimple.
I have it to the point there is no lateral movement in the
dimple piece in the CS hole and the area around the dimple
appears to be laying flat. In other words, it won't swivel in the
hole very easy, where some I made, would swivel very easy.
I can feel when the metal around the dimple feels like it making
good contact with the flat area and no lateral movement in
the CS hole.
That is what I am supposed to feel? Thinking so now.
How would I know too deep on CS just looking?

I don't mind messing up something fairly small, like the Emp
attach brackets, first pair I just didn't like, second pair
with new angle was a go in my book.

Thanks to everyone for the help and suggestions.

[rv9av8tr]

The main thing is you must have the bottom of the skin laying flush with the adjoining part, if the CS is too shallow the poor fit will be obvious. Too deep... not as easy to know, other than a calibrated eye. Once you get the depth gauge set on your scrap, you can move along with confidence. The depth will have to be adjusted slightly for different thickness of skins.

Just do it! 8-)

(I'll tell you the mid-span nose ribs in the HS are a PITA to fit and rivet!!! The forward most portion of the rib doesn't conform well to the skin and a bear to suck up with a cleco and buck!!)

[Lemmingman]

One last step, Bert. The most obvious one, and the one I didn't do for a long time either.

Take your scrap that you are testing with and then rivet it.

Can you see light between the pieces of metal around the rivet? If so it may not deep enough.

Does the sheet aluminum appear deformed around the dimple? If so it may be too deep.

The rivet should sit nice and flush with no deformation in the sheet and no light, or bulge, around where the rivet is.

Try this and I'll bet you'll find your countersinks are spot on.

[Bayou Bert]

That I can do Gil. I will do that this afternoon and see.
Based on what ya'll have told me so far, think I am real close.
Sure appreciate the help and tips.