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Pulled rivet grip length

A

apatti

Well Known Member
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,
 
Riveting the LE

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
 
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.
 
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.
 
The actual specifications

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.com/PDFs/aerospace/catalog/CA-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.... :eek:

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
 
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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.
 
Holes...

Jconard said:
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.
Click to expand...

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
 
Thanks

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,
 
Gil is correct

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.
 
I was speaking generally about cherry max rivets, and they are available in countersunk and universal heads. You will use the countersunk version on other parts of the plane, and as I said, they will seat into the dimples beter, if you dress the dimples slightly with the deburring countersink.
 
CherryMax rivets need a drilled hole...

Jconard said:
I was speaking generally about cherry max rivets, and they are available in countersunk and universal heads. You will use the countersunk version on other parts of the plane, and as I said, they will seat into the dimples beter, if you dress the dimples slightly with the deburring countersink.
Click to expand...

Jconard,

My previous post still stands, I don't think the CherryMax rivets are suitable for dimpled sheets in the usual configuration we have in our RVs. That is, multiple dimpled thin sheets, dimpled after drilling.

They need holes with straight sides. A 100 degree countersink should not have an effect on a good 100 dimple anyway... Are you talking about regular driven rivets? ....and using the 100 degree countersink to compensate for a poor dimple?
Or is your comment really for CherryMax rivets? If so, I don't think it's an appropriate use of these high quality rivets. They need a cleanly drilled hole (post dimpling, if any dimpling is to be done....)

CherryMax are an acceptable substitute for driven rivets, with no strength loss, if applied correctly per the data sheet (link in previous post). If you don't follow the manufacturer's data, then you don't know what strength or properties you are getting.... :(

gil in Tucson
 
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As an example, they are suitable for the canopy deck to the longeron joint.

They are also suitable for the bottom wing skin to rear spar. What normally happens is that the cherry max is used after a driven rivet fails to be drivable...cannot get in to buck it. In that case there is a 3/32 dimple, you drill the hole to 1/8", and lightly dressing the dimple seats the rivet better.

By the way, the shank does expand slightly and the large bulbed end also provides grip.

Vans has approved the countersunk cherrymax in several situations. In fact, according to Vans, the CS-4 or LP-4 can be substituted for ANY 3/32 rivet on the plane.
 
The correct rivet...


Quote - Jconard:
They are also suitable for the bottom wing skin to rear spar. What normally happens is that the cherry max is used after a driven rivet fails to be drivable...cannot get in to buck it. In that case there is a 3/32 dimple, you drill the hole to 1/8", and lightly dressing the dimple seats the rivet better.

Now that makes sense..... it's a cleanly drilled 1/8 hole.....
However, I would be careful using the countersink to "lightly dress" - a very subjective term.... :) - the existing 3/32 dimple. A 3/32 dimple is about 0.176 inches diameter, and the dimple needed for a "standard" CherryMax (CR3212) rivet is 0.225 inches diameter (very close to the 0.222 in the rivet MIL-Spec).
If you "lightly dress" too much to get a really nice seat for the rivet, then you have enlarged the countersink diameter by about 0.050 inch. This doesn't sound like much, but it has probably removed over half of the thickness of the 0.032 skin that you dimpled for the original 3/32 rivet! Not good for the strength of the joint.
The correct answer is to use the NAS1097 (aka "oops rivet") equivalent CherryMax rivet for the dimpled repair you mentioned above. In this case no "lightly dressing" of the hole should be required for a flush repair.

This would be a CR3214 CherryMax... but I wonder how many builders would know to ask for one?

Which CherryMax rivet are you using in the cases you quote?


By the way, the shank does expand slightly and the large bulbed end also provides grip.

Agreed .. but it doesn't expand sideways as much as when a solid rivet gets pounded on by a rivet gun, or with 2000 pounds of squeezer pressure.... :)

Vans has approved the countersunk cherrymax in several situations. In fact, according to Vans, the CS-4 or LP-4 can be substituted for ANY 3/32 rivet on the plane.

Yes... but does he approve of removing half or more of the skin thickness under a rivet??

Use the correct rivet for the job.... and don't get carried away with a countersink tool..... :D

Above discussion only relevant to 100 degree countersunk rivets...

gil in Tucson
 
Riveting the LE

This may be the solution to my current problem. Cherrymax rivets could work but how did you pull the rivets? The head of that G-47 Hand Gun appears to be to large to get close enough to the rib. I would think twice before taking a grinder to a new $100 hand riveter. Will my old modified cheapie pull the Cherrymax?

Bob
RV7A, Wings
 
Try a test case

Bob... I think a cheapie it will do it for a 1/8 diameter rivet.

Make a quick test case and try one out.

The critical part is the hole diameter of the pulling tool. It must bear on the little driving ring of the CherryMax. As a one-off fix, I guess you could make up a little drive washer with a minimum size hole to fit over the stem of the rivet before pulling....

The CherryMax specs. of a previous post tell you what a well set rivet looks like....

gil in Tucson
 
Harbor Freight Cheapie

Slingshot said:
This may be the solution to my current problem. Cherrymax rivets could work but how did you pull the rivets? The head of that G-47 Hand Gun appears to be to large to get close enough to the rib. I would think twice before taking a grinder to a new $100 hand riveter. Will my old modified cheapie pull the Cherrymax?

Bob
RV7A, Wings
Click to expand...


Bob,
I ground off an el-cheapo HF hand riveter. I think I paid less than $6 for it. It is the same one I used to pull the rivets in the Z brackets on the tanks. I ground the thing down so far that you could see the pulling mechanism inside the head. :)
Also, keep in mind that Van's has said LP4-3's and LP4-4's can be used. There was a thread back in Nov 2005 where someone posted a response from Van's to a question on this. The rivets don't have to be CherryMax. I only used CherryMax's because I didn't have any LP4-3's on hand.
 
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