Old Subject..Just Not to Me

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.

Test on scrap until you are happy with the results.

make test dimple check plates - quick & easy

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.

Been working on Scrap

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.

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.

What Gil says!

OHHH...That I Understand

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.

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!

(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!!)

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.

Good Deal

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.

I start with the countersink intentionally set a little shallower than I need. After countersinking I try the dimpled piece and see if I can see any light between the two pieces. If so, I'll give it one more click (or more, depending on how far off it is). When the dimpled piece sits perfectly flush with no gap, I know it's dialed in right.

Sometimes I can use the real pieces, sometimes I have to make a test bit of sheet aluminum. I really need to make up some test cards and label them so I remember what's what. I have a bunch laying around, but none are labeled.

One last piece of advice. Get several countersink cages and cutters (I have 3). You get it setup one time and after that you just chuck it up. Test it and start countersinking. Very little fiddling required.

Testing as mentioned above is the best method, and I also have three countersink cages, on set for #40, #30 and #19. Once I found the correct setting for flush I marked the cage with a vertical line across both halves so I can find it again (although I still check on a piece of scrap). My testing for depth for dimples came out to be pretty close to the skin thickness deeper than flush. Each click is supposed to be 1/1000 th of an inch, so my starting position to test is the number of clicks equal to the skin thickness deeper than flush. Never got good results with 'just a couple of clicks...'

==dave==

Much Thanks

I sure do appreciate the tips. I do have two cages at this time.
I did rivet my test piece yesterday and no gap, deflection or anything
that does not look right.
One thing I was worried about is the rivet sitting flush in the dimple.
I talked to Mike at Cleveland and he was right. The rivet feels a little
low in a fresh dimple but after riveting it swells a little and is flush.
Worked just like he said. After riveting the test piece I could feel
almost no diff when I ran my finger over the rivet and not looking
at it so I would know.
I really, really appreciate all the help. I am off today and will CS the
emp spars and get on with this section.
I retire the end of June and plan on devoting most of my time to getting with
the program to get the plane in the air. Wife is going to work another year
so no distractions
Heck, when you are on the back side of the bell curve....things look different.
Thanks to all again!!

Excellent thread. Thanks for all the great, plain language, usable advice.

One thing I'll add from my experience-- Avoid using your high speed air drill for cutting countersinks. I did that at first and it made it very hard to get a consistent depth due to chattering. Using a slow speed rechargeable or corded drill works much better for me.

Just thought I'd throw that in for any readers just starting out.

Iluke said:

Excellent thread. Thanks for all the great, plain language, usable advice.

One thing I'll add from my experience-- Avoid using your high speed air drill for cutting countersinks. I did that at first and it made it very hard to get a consistent depth due to chattering. Using a slow speed rechargeable or corded drill works much better for me.

Just thought I'd throw that in for any readers just starting out.

Click to expand...

We use this:



For countersinking at work, including 130* c-sinks in uniaxial carbon fiber using indexable carbide or diamond tipped inserts. If I were building an RV from the start, I'd buy one REALLY nice (Sioux, dotco, etc) palm drill with a keyless chuck, a pan american yellow (2300rpm) drill with a keyless chuck, and a panamerican green (700 rpm) drill with a 3/8 keyless chuck, and maybe 3 countersink cages. The pan american pancake drills are nice too.

http://www.panamericantool.com/novar-700-rpm-high-torque-pistol-grip-drill.html

Rumor has it that a 100deg c-sink with the right pilot, screwed into a pancake drill makes it really easy to deburr on the inside of C-channels, or anything else with bad access. The 700 rpm drill is nice for deburring everything else.

The 700 rpm drill also has plenty of torque and will turn 1/2" reamers in hardened steel and other things that would overheat most home-size electric drills.

Finally, you need one of these on EVERY AIR TOOL YOU OWN!



http://www.panamericantool.com/swivel-air-regulator.html

We buy most of our clecos, drill bits, reamers, threaded bits and especially piloted bits and piloted reamers from panamerican and are almost always really happy with them. Their wingnut style clecos, in the right size hole will pull just about anything together (hint, use a 15/16" 6pt socket on the wingnut to really pull 'em tight).