D

DJR

Active Member
Here is what I have NOW...
1qpc1g.jpg


I thought I was being smart when I removed the wind tank screws before painting. Well, when i put the screws back in after paint, the paint (primer, sealer, color & clear coat) blistered up at every screw as I tightened it down.
I was able to remedy the problem with #8 SS countersunk washers, but they look a bit bulky and I wonder about aerodynamic flow and drag caused by the slightly raised profile. Because I have silver paint, I think it looks ok.

Here is what I'm looking for....
35mk00w.jpg


I took a pic of an RV a couple of years ago at Arlington when I found these washers with a "very small" radius and profile.
Does anyone know where I can get these. Perhaps they were custom fabricated or it is a non-aviation washer modified with a #8 dimple die or something.
Anyone have thoughts about the aerodynamic drag issue with the larger washer?

DJR

Thanks in advance.
 
I could use a dozen of those, too. I was told that they are the washers in your first photo that someone turned down on a lathe. I don't have access to a lathe, so have looked for them, but found nothing.

Perhaps some ambitious VAF'er might think about spending a few hours in their shop and making and selling them...
 
They are called flush countersunk washers. I ordered some #6 and #8 from aircraft spruce, but I can not find them in their catalog - tommorow I will be at the hanger and can look up the aircraft spruce #
 
What if you took a stack of them and put them on a screw and put a nut on to hold them all tight together and then put the end of the screw into a drill. Then you could hold them up against some sandpaper and "grind" them down to whatever diameter you wanted. I have never done this so I don't know if it will work, just thinking out loud......
 
Here's part number from Aircraft Spruce:

#6: 39006F
#8: 39008F

The picture is not correct, but I have them in my hand with the A/C Spruce number on the plastic bag.

Hope that helps - a lot easier than trying to make them

-Bob
 
The washers are not the answer

Hey Fellas:

Bennair, Dunnatt with the paint problem. But, fear no more!

Take out your handy de-burring tool and remove the paint from the countersink area. Piece o cake. Might put a bit of ACF50, or similar, in the area to prevent corrosion, but that's about it.

Mr Bennair, and Mr Dunnatt, can teach us quite a bit!

Carry on!
Mark
 
These are called Tinnermann washers and are pretty easy to obtain at any aircraft supply outfit. They come in both galvanized and SS.
 
The Tinnerman's are the washers in the OP's first photo. What he was asking about is the much smaller washers in the second photo.

I am looking for those, too, but not for paint issues. The person that build my plane countersunk a few holes on the tanks too much, and if I am not careful the screw pulls through the tank skin. The small radius washers will prevent the head from pulling through, but not be as visually undesirable as the Tinnerman's.

Thanks to those that provided links.
 
Hey Bob,
I was wondering about that pic they have. It didn't look like a flush cs washer. Thank you for the part number. I will give them a call and ask about them.
As you look at the washer, is it much smaller in diameter than the regular washer?

Thanks again Bob

Regards,
Dana

RKURRLE said:
Here's part number from Aircraft Spruce:

#6: 39006F
#8: 39008F

The picture is not correct, but I have them in my hand with the A/C Spruce number on the plastic bag.

Hope that helps - a lot easier than trying to make them

-Bob
Click to expand...
 
nas390

The ACS webpage lists the 39006F as NAS390BXP. The NAS390 standard shows these as 82 degree washers. I think the structural screws that hold the tanks skins on are 100 degree. You need to check this out carefully.
 
Dana
The ones I have from A/C Spruce are not tinnermans, which is what is shown on there picture. They are what you showed in your second photo. When installed, only a small rim shows around the screw head that is basically flush. I used them on my inspection panels and they look great. If I remember correctly, I used the #6 washer with #8 screws to get the best fit. They are inexpensive. If you need photos I can take some.
 
Here's another tip. Use ones size smaller Tinnerman than the screw that is being inserted. You kind of have to run them up the screw prior to insertion but they look really nice this way,
 
39006F is the correct part number from Spruce. They are listed with the interior washers. Buy the number 6 washer and use a number 8 screw with it to get the look in OP's second picture. I just picked up 500 of these.


Oh...Spruce sells these in bags of 50.
 
Washer washer

Here are some pics I took when I was fooling around with different washers, trying to decide what to do. They are not great pics but were for my reference in the future. I finally decided against the finishing washers because of the size of hole that was needed in the fiberglass.
The 100 degree stainless countersinks to me actually look a little classier but each to his own, and I may still change my mind, since all my old fiberglass is not done.

The first picture is different washers in sizes 6 and 8 and the center screw below the open hole is an 8 screw in a 6 finishing washer NAS39068P.

The second picture was some quick drilling in fiberglass to get an idea of what it took to make the screw actually flush. YMMV

washer2.jpg

washer1.jpg


Dave A.
6A build
 
GAHco said:
Go to this link for information about Countersunk Large Area Washers.

http://www.gen-aircraft-hardware.com/amelia/details.asp?store=&id=532&TName_HID=subcat Read the intro and then click on the pdf Icon.

We were the one that produced the #4 Countersunk Shiny Washers per many requests from this forum.

We still stock them.
Click to expand...

Using GAHco's link...

http://www.gen-aircraft-hardware.com/images/pdf/specialwash.pdf

The possible trouble with the NAS390 washers becomes apparent.

They are not structural. The little downward lip at the edge and the 82 degree "dimple" would both make it hard to fully torque a 100 degree screw against a 100 degree countersunk hole. The role of a washer (except bellville and lock washers) is to conform to the screw/bolt head.

I wouldn't use them on a tank where they are structural. On a wing tip it might be OK because the fibreglas would distort/cut to fit the little lip aound NAS390 washer.

Carefully check out the cross sections in the link above...
 
az_gila said:
Using GAHco's link...

http://www.gen-aircraft-hardware.com/images/pdf/specialwash.pdf

The possible trouble with the NAS390 washers becomes apparent.

They are not structural. The little downward lip at the edge and the 82 degree "dimple" would both make it hard to fully torque a 100 degree screw against a 100 degree countersunk hole. The role of a washer (except bellville and lock washers) is to conform to the screw/bolt head.

I wouldn't use them on a tank where they are structural. On a wing tip it might be OK because the fibreglas would distort/cut to fit the little lip aound NAS390 washer.

Carefully check out the cross sections in the link above...
Click to expand...

Yes, I definitely don't want a downward lip and I must have 100 deg's for proper seating. This link shows a washer with a smaller radius, but its hard to tell if there is a"downward lip" on them.
If not, then I believe these would work after running them thru a #8 dimple die.
Thanks for the info Gil.

This link has the pic.http://www.wicksaircraft.com/catalog/product_cat.php/subid=12026/index.html
 
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DJR said:
Yes, I definitely don't want a downward lip and I must have 100 deg's for proper seating. This link shows a washer with a smaller radius, but its hard to tell if there is a"downward lip" on them.
If not, then I believe these would work after running them thru a #8 dimple die.
Thanks for the info Gil.

This link has the pic.http://www.wicksaircraft.com/catalog/product_cat.php/subid=12026/index.html
Click to expand...

Checking the 603-8 part number from Wicks links to this...

603-8 NAS390B8P FINISH WASHER FLUSH #8

http://www.aerohardstore.com/anmsnaswashcot.htm

It looks like an alternate part number for a NAS930.

The #8 dimple die should fix it though...:)
 
DJR said:
I thought I was being smart when I removed the wind tank screws before painting. Well, when i put the screws back in after paint, the paint (primer, sealer, color & clear coat) blistered up at every screw as I tightened it down.
Click to expand...

I have several friends who have painted the tanks seperately and none have had problems with the screws affecting the paint.

It is highly probable that your problem is symptomatic of an unsatisfactory adhesion of the prime coat to the aluminium. Who did your paint job and what was the preparation and paint spec.
 
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