Pulled rivet grip length

apatti · #1 05-26-2006, 01:34 PM

Hi all,

I emailed the following question to Van's:

I am working on the wings for my RV8A. I decided to use CherryMax rivets to attach some of the more difficult to reach Leading Edge Ribs to the Main Spar. Before thinking (I guess you hear that a lot) I used -4?s on the third rib in from the wing tip. I thought that is what I used on the other wing. However, now I realize that I used an LP4-3 on the other wing and a -4 CherryMax where the .125 doubler is on the main spar.

So, my question is? Do I need to drill out the -4?s from the third rib in from the wing tip (no doubler)? The minimum grip length specified for a CherryMax -4 is .188?.

Here was the reply I got:

I wasn't aware the blind rivets had a minimum grip length, only a
maximum. I would say that if the rivets are not tight, then drill
them out. You might try turning them with pliers to check.
We have both LP4-3 and LP4-4 rivets available and they are a lot
less expensive than Cherry Max rivets.

Does anyone out there have any more to add? I can't reach the "shop" side of the rivets to try and wiggle them. I know I am below the minimum grip length. But I am not sure if I would do more harm than good if I try to drill them out.

Thanks,

mlwynn · #2 05-26-2006, 07:25 PM

Hi Tony

I am at that same stage. I bought a small pile of cherrymax rivets because I thought they would be a better structural substitute than the LP's.

I have a cherrymax guage and plan to use it to double check the rivet lengths at each station. Thanks for the heads up on a potential error.

I suspect that the answer really is, if it is tight, it is okay. If not, drill it out. If unsure, I would err on the side of drilling and getting it right.

Keep me posted on what you find.

Regards,

Michael Wynn
RV 8 Wings

rv9builder · #3 05-26-2006, 08:38 PM

Tony,

Get some pieces of scrap approximately the same thickness as the parts you riveted together with the CherryMax rivet. Drill a hole in the scrap and rivet the pieces together with a CherryMax Rivet. If the rivet is holding firmly in the scrap, it's probably doing the same thing in the actual pieces.

Jconard · #4 05-26-2006, 09:37 PM

For not much money, you can buy the cherrymax grip guage from Spruce. It will fit in the #30 hole that you must drill anyway, and will give you the correct reading. Cherrymax depend on the bulbed end for lastig tension, and you should follow their grip recomendations.

By the way, if you started by dimpling for -3 AN rivets and then drill for cherrymax, you can lightly dres the dimples with the countersink deburring tools, and it will help the rivets seat better into the hole.

az_gila · #5 05-26-2006, 11:00 PM

CherryMax rivets are way different from the commercial LP series pop-rivets.

Textron has a grip range of about 1/16 total for each rivet length.

The full specifications are here....

http://www.textronfasteningsystems.c...42-5M-1003.pdf

Page 8 is a good example of grip lengths, and there is a definite maximum and minimum grip length.

Vans reply was wrong in this case. I would calculate the thickness that you riveted, and check what rivet you used. If you have really good eyesight up close....

...you can read the grip length that is stamped on the head.

If you put in the wrong length, I personally would not rely on the "pull it with pliers" test, but would replace them.

This is a case of using good parts without looking at the manufacturers data sheets....

Let us know what you found out.....

UPDATE -- factoid

The Textron data sheet specifies (rather clearly) that the holes should be deburred, but have a sharp edge.
No use of a countersinking tool to bevel the hole edges.
The appropriate deburring tool probably would be a scotchbrite pad.

gil in Tucson

Jconard · #6 05-27-2006, 09:36 AM

You need a sharp edge on the blind side, but lightly dressing the dimple side allows the rivet to sit down just a little better in the dimple.

az_gila · #7 05-27-2006, 11:04 AM

Quote:

Originally Posted by Jconard

You need a sharp edge on the blind side, but lightly dressing the dimple side allows the rivet to sit down just a little better in the dimple.

Actually, for full strength, I don't think the sheets can be dimpled. These rivets need straight sides since they don't expand outwards in the same manner as driven rivets. You might dimple for 3/32 and then drill out to 1/8 and use the NAS-1097 equivalent (small head) CherryMax. This would probably give you a drilled hole with parallel sides.

You don't want a hole similar to that shown as a rivet height measurement in the middle of my home page.....

http://home.earthlink.net/~gilalex/

They are really good rivets, but must be used correctly....

gil in Tucson

apatti · #8 05-27-2006, 02:22 PM

All,

Thanks for the input. BTW, these rivets are not countersunk. They are the ones that attach the LE ribs to the main spar.

I am leaning towards drilling them out. I have not had to drill out a pulled rivet yet. Any advice on doing this? Are they pretty much the same as any universal head?

Thanks,

az_gila · #9 05-27-2006, 06:02 PM

You need to borrow one of these tools...

http://stylespilotshop.stores.yahoo.net/1341s.html

I think any attempt at removal without a good drill guide will screw up more than it fixes.
This is because the stem of the rivet is harder than the body, and your drill will want to wander off center...

good luck

gil in Tucson

apatti · #10 05-27-2006, 09:01 PM

Gil,

That is exactly what started happening when I tried to drill out the first rivet. So here is what I did. There are five rivets that attach the LE rib to the spar. I added an LP4-3 rivet in between those five rivets. Thus, there are now five CherryMax rivets that are a little too long and four LP4-3's holding the rib to the spar. I think this was the best solution.

Thanks to all who replied.