Rudder is giving me trouble

RVG8tor · #1 01-15-2008, 08:52 PM

OK I think I know what is wrong but I will ask the gallery. I started to rivet the stiffeners on to the rudder today and it has been giving me fits. I can't seem to consistently get them set straight. My back rivet set was too wide so I flattened one side, this allows me to get straight over top of the rivet. My back rivet plate is recessed in a 3/4" piece of MDF that is plenty big.

I tried to be careful and not deburr too much, but I think between drilling and deburring the holes have enlarged to the point that it is difficult to set a rivet straight. I have done one side of the rudder and quit. I am giving thought to ordering a new skin and set of stiffeners and try again. I am not sure I could get all the bad rivets out without trashing the skin. I did not have this trouble with the VS or HS so I am not sure what else to do. I was taught a trick at a building class that I guess is not an approved technique which is why I did not do this on my rudder. But this person would dimple the holes without drilling size, (just for the stiffener holes). I must say it made for nice rivets. I feel like I should have gone that route. My other thought if I get new parts is to drill to #41 in hopes the holes don't end up too large.

The first photo is to show how much room there is around the rivet, the other photo show some of the bad rivet. I think I would have to drill out at least 20% of the rivets on the side I have done. BTW, the practice project back rivets came out great, I don't know what is up with this!

What does it look like to you builders out there, are the holes too big and that is why my rivets are falling off? I am making a good effort at holding he rivet gun plumb and holding the rivet set with my fingers so that it does not move. Also, I ease into the set and tap a few time before going more heavy on the trigger, I have the gun set at 40 psi.

Thanks for any help or suggestions!

G-force · #2 01-15-2008, 10:56 PM

The top of the tipped rivet does not appear parallel with the rib, the set had to be tipped for that to happen. I assume your using the set that has the spring loaded plastic collar? Try placing the set over the rivet, but dont compress the collar yet. Tip it front to back and side to side untill the collar is sitting square then push it down without moving the rivet gun. The holes always enlarge when dimpled, I measured it once and found it to be several drill sizes over. Perhaps try pre squeezing the rivets in a squeezer untill they just fit through the skin/stiffener?

wfinnell · #3 01-15-2008, 11:40 PM

I am not a back rivet expert by any stretch of the imagination but I felt compelled to respond because I have had so many problems with this myself.

I have found (the hard way) that you not only have to be careful about having the back rivet set square but it has to be pretty much centered to get good results. It looks to me like the center of the rivet head in your photo has a little bit of a scuff. Usually when this happens to me it is because I am off to one side a bit. I actually look through the little hole in the side of the white collar on by back rivet set.

Be patient and persistent and it will come.

Bill Finnell
Tucson AZ
RV-8 Tail

mike109g6 · #4 01-16-2008, 12:33 AM

Mike,
your top photo looks pretty normal. Instead of drilling each hole #40, I now ream every hole with a #40 reamer, less deburring, and very consistent with the hole sizing. Avery and others sell both #40 and #30 reamers-now I can't live without them.
Second photo looks very familiar. I took that stupid nylon bushing off my back riveter-it pushes the riveter off center due to the stiffener flange. With my left hand I place index and middle finger either side of dimple capturing exposed back shooter less nylon bushing between my fingers, and pushing down on metal surface. Carefully tap the rivet, teasing the trigger till it snugs up dimpled metal. Then finish it off to a good shop head. It will pinch your fingers if not carefull, but I found that I could consistently get perfect shop heads with this technique. You can also see the rivet being formed, and if properly centered and square on the rivet shank, this way. That nylon bushing causes it to be BLIND riveting.
Hope that this helps,
Mike H 9A/8A

N916K · #5 01-16-2008, 01:23 AM

Mike
How long are you driving the rivet? It looks over shot to me. Also try to set your gun so you squeeze the trigger all the way for a second or so to set the rivet. Don't try to feather it in.

One thing that makes a big difference in getting consistent rivets is to regulate the air flow at the gun and run max pressure in the air line. That way you don't get an air pressure drop when you start riveting. Keeps you from accidentally smashing up your plane when you go between your drill and rivet gun also.

When it comes to riveting the rudder stiffeners ( I remade a cracked rudder this weekend) tape all your rivets in first then when you are riveting press down on each side of the rivet with your figures to hold the stiffener tight to the skin and back plate. that will also hold the rivet centered in the hole.

Cam

skyfrog · #6 01-16-2008, 06:15 AM

I just finished my rudder stiffeners and they came out really well. (Except for the part where the plate was not under the rivet and I dented the skin, and then made it worse by trying to fix it, which caused another dent...doh!).

Anyway, it does look like the holes are somewhat big. Something to check, that hasn't been mentioned is the dimple die set. Perhaps you had a -4 set and it stretched the hole? Also, I dropped the pressure of my 3X gun down to 37-38psi, because I thought 40 was too much.

yakdriver · #7 01-16-2008, 06:23 AM

Get the back rivet set from Cleveland Tool. It is smaller in diameter and the outside plastic piece has a much thinner wall thickness. It will allow you to center the set and your problem will go away. Buy one now as you have a lot of back riveting to do and the Avery set is just too bulky. Don

DaX · #8 01-16-2008, 06:42 AM

Mike,

I did the exact same thing on my RV-7 rudder a few months back, see here:

http://www.vansairforce.com/communit...ad.php?t=20229

I ended up re-ordering skins and stiffeners (now I have a lot of scrap metal to play with!) and deburring VERY lightly, still drilling with a #40 (though #41 may work better), and gently dimpling with my C-Frame (no DRDT-2). The rivets still had a little bit of slop in the hole, but this is kind of the nature of the beast when you drill and dimple thin skins. I just forged ahead and back riveted and they came out great the second time around.

I thought about just dimpling the un-drilled holes too, but when talking to other builders, began to fear this would cause cracking. I just chocked the whole thing up to a $150 mistake and a lesson learned.

David-aviator · #9 01-16-2008, 07:12 AM

I would drill out the bad rivets and try it again. I had good luck doing #40 rivets at 35 psi. The image of the crooked rivet looks to me like the gun was not straight over it.

Make sure the back rivet plate is flush with and not below the MDF surface.

RVG8tor · #10 01-16-2008, 08:30 AM

Thanks for all of the input. Just to answer a few of the questions and add some thoughts I have come too. After more thought and looking on line I do not think my holes are too large, just the way they came out, I am careful and up to now no problems. I also used a #40 ream for these holes.

The rivet set I think is my problem, due to the size it is not easy to make sure it is square over the rivet, I hold the set secure with my fingers but perhaps it is not sitting straight. For those buying tools I would avoid the back rivet set sold at Planetools, however other than this tool I have been happy with my tools and service from Planetools, I would still buy tools from them. This set is just too large to rivet the stiffeners.

I am using the tap and drive technique, I tease the trigger and let it tap a few times to hopefully expand the rivet some and get the parts to tighten up I then give the trigger a good squeeze for what is less than a second, you can hear the sound as the rivet sets. I think I will take the collar off and try it that way and or find another rivet set. I may see if I can borrow one from a -7 builder here, I think he bought all of his tools from Cleveland. I bought my tools from all of the big tool suppliers. I basically chose what I thought was good from each, what I did not know was the size of the back rivet sets, Cleveland seems to have the narrowest set, you don't know what you don't know when you a initially buying tools. Thanks for the help gang, it is a new day and I will try again. Time to get more practice drilling out rivets.

I still have not decided to get the new skins, I want to see how drilling out the bad rivets go. I think I will have to re-dimple some since the clenched rivets have fallen off and crimped half of the dimple. I just don't want any weakness since in an aerobatic aircraft the rudder a control surface that gets a lot of stress. I want that sucker at design strength or better, which is why I may go the new parts route, only $95 for new parts that and a new rivet set i might be better off. I know from experience how drilling out rivets can make things worse but most of these rivets are just too bad to leave in. Up to this point I have only trashed one part (a stiffener), I guess every builder at some point has to spend some money on new parts to make up for errors.

Cheers