Bucking flush rivets

[Gary Wallace]

I am not too happy with the way my flush riveting is going. I started with the ailerons last night...it seems to me the dimpling makes the holes too sloppy which make it very difficult for consistent shop heads. Before dimpling i left the holes slightly undersized at #42 so the dimple die would just fit into the hole, as i was afraid of this happening. i do ok with the easy access rivets...ok, and each rivet here seems to me to be a chore, but as soon as i have a bit of and obstruction or what have you i am not getting the result i am happy with. i have driven a lot of dome head rivets on my last 140 project with very good results...but not so now. i am very careful for proper rivet length selection, and have been cutting rivets to half lengths for exact rivet length with my gauge before setting....help.....very frustrated...so much i have it for sale on barnstormers...im ready to give up. I know i have a lot ahead as im ready to start to skin the wings but dont think i can deal with the frustration.

[S Lathrop]

Just thinking about your problem. You might make a bucking bar with a hole the size of the rivet and countersunk just enough to close the dimple down on the rivet. Then use a regular bucking bar to form the shop head. I have never seen this done nor have I ever seen it recommended. But I think I would give it a try. I think the trick will be to get the countersink in the bucking bar just deep enough to close the dimple up a bit but not leave an indentation in the aluminum. The edger of the countersink will have to be polished.

[Steve W]

Hi Gary. Saw your add on Barnstormers and now your post here. Flush riveting can be difficult. My two cents worth: always use fresh stock rivets. They harden with age. Anyone tells you otherwise call bullshit on it. Hardest rivet to buck is one that is cut. Half sizes can be found with a little research. Do not use one that is on the longer end of OK. Use the widest set you can fit especially for thin skins, minimum 1 1/4" face diameter. Use the heaviest bar you can fit in the work area. Do not use too much air pressure at your gun. If the rivet is straight after an attempt bucking and needs a little more, then OK. Hit it again. Use a 2x gun for any 3/32/#40 rivet. Again, call bullshit on anything larger. From what I have learned, control is everything with the smaller rivets. If it starts to roll to the side then stop. Drill it out (undersized drill bit) and do it again. Keep everything as square and as flush as you can. Practice is the best tool.

[Gary Wallace]

I haven't sold my project yet...so I have another question. I was using the 3/4 flush set with the slightly convex head. There is a 1 1/4 inch at Aircraft spruce. AT-107A-3 with no rubber around it or I have seen the one with the rubber vision around the perimeter. Any recommendations here Steve or others?

[Mark Goldberg]

Practice on scrap before attempting to rivet real parts. Mark

[S Lathrop]

Just thinking about your problem. You might make a bucking bar with a hole the size of the rivet and countersunk just enough to close the dimple down on the rivet. Then use a regular bucking bar to form the shop head. I have never seen this done nor have I ever seen it recommended. But I think I would give it a try. I think the trick will be to get the countersink in the bucking bar just deep enough to close the dimple up a bit but not leave an indentation in the aluminum. The edger of the countersink will have to be polished.

[rv8bldr]

I use one of these. I built my RV-8 with it and am using it on the Bearhawk. I can't imagine building a metal airplane without one. Everyone I know who has built an RV used one of these.

http://www.aircraftspruce.com/catalog/topages/flushswivel.php

[Gary Wallace]

Thanks Mark. I ordered one of them. I was contemplating that but a lot of people have a lot of opinions. Now, the sloppy to me dimples holes must be normal and dealt with by everyone as there is no way to start with a smaller hole as simple die male end just fits in the 3/32 hole. Is this correct I'm assuming?

[Gary Wallace]

If I was designing a dimple die after what I see, I would think the male die and female should be more undersized for a smaller drilled hole to come up with a proper sized dimpled hole for proper rivet fit. Is there such a thing?

[Steve W]

I tell a couple of guys I am helping with their projects when they come up with ideas like this; "your re-inventing the wheel". There are billions of rivets flying around that were drilled with a 40 bit, dimpled, and bucked with obvious approval from Q&A. As long as the final diameters and distances are met after they have been worked, then move on. Perfection is a good thing in moderation but a stopper when it becomes anything more. Personally, I drill everything with a 3/32 bit. Yes the dimple die does open up the hole a bit. If the numbers of the rivet are there after it has been worked, then away you go to the next one. The only other set than I've seen that I wished I had to to the skins on my wings was from YardStore. 2" face. I bet the results would be close to the appearance of back riveting.

[Gary Wallace]

Thanks all. As I mentioned I have ordered the flush swivel rivet set, two different Tungsten bucking bars as well as a few other bars I don't have. I'll have a week to relax till these come in, then remortgage the house for the two bucking bars, and have another go. I'm sure I'm over reacting and it's not as bad as I make it out to be but I was extremely frustrated. Thanks for all the input. Appreciated

[N3UW]

You will never regret those tungsten bucking bars. They are amazing. I have not used any of my other bars once i got them.

[Gary Wallace]

I believe it will be money well spent. I expect some new tools and a bit of time, and I'll be ready to look at it again next week.

[fairchild]

Gary---
I was restoring a cessna years back and needed to do a little flush riveting. Didnt have a tool to make the dimples---- so I made one. It worked fine. AND it solved
your problem.
I started with some 3/8 bronze rod. Put it in the lathe and drilled an 1/8 inch hole in one end. I made two of these - one about 1 inch long and another about 5 inches long.
In the ends with the 1/8 hole --- I cut an "outy" cone on the longer one and an "inny" cone in the short one. In one of then I drove a piece of 1/8 steel rod and cut it to
portrude about 1/4 inch out. Then I drilled the other bronze rod very slightly bigger (1 numbered drill...) This allowed the 2 bronze rods to fit together with the steel rod
as a guide. Allow the rod to go into the other rod enough to keep the rods parallel with each other. The longer one went into the rivet hammer and the other fit into a socket of a steel block (aka- bucking bar)
Drill an 1/8 pilot hole through your sheets...... insert tool....... about a 1/2 sec. of light blows (with pressure reduced) and the dimple was about 80% made. Ream drill with 3/32
to accept rivet. Install rivet. Cover with paper tape. Set as usual. I found it worked best if the dimple was only made 80-90 % and you let the flat set finish the job- the last 10-15%.
After doing about 10 test ones--- (figuring out not to make the dimple 100%) I could reliably make heads which all most couldn't bee seen. The edge of the head just disolves into the sheet
and you cant see it or feel it.
This solved the problem of the holes wallowing out too big from the stock dimpling tool. Seemed to work fine. My IA liked the results--- he wanted to hire me !

If you know someone with a lathe---- its easy to do. The dimpleing is so gentle the tool doesnt wear any !
I still have it somewhere...... DONT sell your baby just because something seemed hard....... My daddy ALWAYS SAID .... "when you see something that looks too hard to do-
you just remember that SOMEBODY did it..... and that somebody wasnt any smarter than you ! " And he was right-

Tim