What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

A Question for the Rivet Experts

L

lr172

Well Known Member
I posted a few weeks ago about my incidence challenges. I have since pulled both lower rear wing spars and am ready to put the new ones in. I used a poor method to remove the rivets and bent the inner flange on the interior ribs, making it difficult or impossible to get a solid rivet back in there. My plan was to use cherrymax rivets there and use pressure from behind to hold the flange in in place while my son pulls on the cherrymax. Vans did not seem to have a problem with this approach as it is only a few rivets. I could also just drive the new rivet skipping the web flange and only hitting the rear support, as for all the other rivets, but preferred to have contact there. Vans didn't have any real issue with this either.

I got to thinking how will I know if I am getting shop heads close to correct on all of the other spar rivets. I certainly cannot feel them and I am not sure I can get both a mirror and a flashlight in there. I will be using a long steel rod as a bucking bar. The question is, which is the better risk, cherrymax rivets for all of these or possible risk of poor shop heads? I did a bunch of research before feeling that a few Cherrymax would be ok and it seems they are pretty close in strength, without the vibration problems associate with pop rivets. However, it is a critical part.

Thanks for your guidance.
 
Last edited:
Since this is a structural question and you have asked the experts that designed your aircraft, what is your hesitation about following their recommendation? There is no loss of manhood by using cherry max in general.

I had rather have a good Cherry Max than a bad, then boggered, rivet in an impossible to reach to drill location. YMMV

That's just me, again going back to mothership approval already.
 
If CMax are approved for the application, then I would use these rather than risk bucking in very difficult location (the hole is probably a tad OS already making it even more difficult). Just make sure the hole diameters are correct as CM will not expand in a hole like a solid rivet will.
 
Thanks for the opinions here. I only asked Vans about using the CherryMax rivets in a few holes, not all of them. Their opinion was that they are not as strong as solid. Their initial response was "your the builder." After pressing a bit, they said a few wouldn't hurt. I didn't really get the comfort that I was getting an "Engineering" based answer.

I was thinking the same as you guys, that a well executed Cherrymax would be better than a poorly bucked solid rivet. I can drill them out if bad, my problem is finding a way to see if they are good or bad. Because I can't see or feel how level the bucking bar is, I don't feel that I can trust my "feel."

I think I will work on the outer rivets first, as I can see those with a mirror and flashlight. If I can reliably hold the bucking bar, I will proceed as far in as comfortable and then switch to Cherrymax.

Thanks,

Larry
 
In the spam world we've always been told that the nominal oversize c-max was a direct strength replacement for an MS20xxx rivet. Like a CR3243 for a dash 4. This would require a 27 drill. Pretty good for making ovular #30's round again. I would do everything in in my power to get that flange pushed up tight before pulling or bucking. Vise grips, wedge, clamp, pry rod, whatever. Good luck.
 
Another option

An old trick (if there is not too much pressure) is to stick a piece of thick foam tape on your bucking bar so when you push it down to meet the rivet and compress the foam, it will push the flange against the skin in most cases, and it will buck it enough to clinch the joint, then re-strike with non-foam bar to finish. I use this set-up often when working with thin materials.
 
Thanks for the ideas guys. My holes are pretty exact. I did not really understand rivet removal when I did this. I used a small drill to relieve the outward stress and used a punch to get the rivet out. Good news, hole is clean. Bad news, I bent the flanges, not realizing they were there. Given the close proximity to the skin overhang on half of the rivets, I am not sure I could have drilled them out the proper way without boring the hole larger.

I did some playing and I can get the flanges pushed up, but it is a lot of pressure. I don't believe I could buck them as well, without a special built tool. I think that I will fab a small socket to a bar, center it over the CM rivet, apply pressure and have someone squeeze it. I think the CM's should be good enough for 5 of the 30+ rivets on that spar.

I also today found at mirror with led lights attached. I think I will be able to use this to examine the shop heads and will do as many solid rivets as I can.

Larry
 
fixnflyguy said:
An old trick (if there is not too much pressure) is to stick a piece of thick foam tape on your bucking bar so when you push it down to meet the rivet and compress the foam, it will push the flange against the skin in most cases, and it will buck it enough to clinch the joint, then re-strike with non-foam bar to finish. I use this set-up often when working with thin materials.
Click to expand...

A great idea. I fear this won't work, as the pressure to bend the flange back is pretty significant. They seem to be .031. I will give it a try though.

Larry
 
Rears spars DONE!!

I only had a to use 3 or 4 cherrymax on each side. I ended up using a cleco to hold the flange in tight, added a second rivet to hold it then went back to the original. Not a fun project, but glad I did it. Will have lines around my arms for a few days from trying to fit a fat arm in small lightening holes.

Larry
 
You must log in or register to reply here.
Back
Top