397.5 hours on the hobbs - trim tab reinforcement bracket platenuts installed

So today I tackled the dreaded nut plates on the trim tab support bracket that I had previously back riveted to the elevator skin. Several notes again about this - MAKE SURE TO INSTALL THEM IN THE BRACKET BEFORE MOUNTING THE BRACKET TO THE ELEVATOR. Next, BE SURE TO GRIND DOWN ANY EDGES OF THE NUT PLATE THAT STICK OUT BEYOND THE EDGE OF THE MOUNTING FLANGES OF THE MOUNTING BRACKET BEFORE YOU INSTALL THEM ON THE PART.

If any of you future builders stumble across this part of my blog, be sure to use the tips above to avoid the hastle that I went through. The good news is that the nut plates are successfully installed. I was able to reach all of the rivets with my hand squeezer and a combination of the flange yoke and the standard 3 inch yoke, and had to use my C frame tool to set the rivets on the last nut plate on the side where my yokes would not reach from inside the access hole in the bracket.

Here are the yokes I used in the hand squeezer to rivet the nut plates to the bracket.

Note that I used a 1/2 inch wide x 1/8 inch flat set over the manufactured flush rivet head and the smaller diameter 3/8 inch x 1/8 inch flat set for setting the shop head of the rivet. I did this to ensure that the flat set would not interfere with with dimpled for the screw in the center of the nut plate. turned out to be a non-issue but I wasn't sure in the beginning so I opted to be sure. Using the smalled rivet set definitely adds more challenge, especially when you using it to set shop head. You have to ensure that the rivet shank is pretty much dead center on the rivet set to avoid setting a bad rivet.

Next shows the process I used to set each rivet. You use once cleco to hold the nut plate in place while you insert the rivet into the other hole. then you slide the yoke onto place, ensuring that each flat set is where you need i to be, and squeeze the rivet. Definitely chose the hand squeezer over the pneumatic one for control reasons. I had to heep the larger diameter rivet set away from the edge of the elevator skin to avoid damaging the skin, while ensuring that the smaller rivet set on the other side was adequately centered over the rivet shank. Had I used the the pneumatic squeezer for this I most certainly would have damaged something.

You can see the completed rivets on acouple of the nut plates at the bottom of the previous pic. Once you set the the first rivet, you remove the cleco, insert the final rivet on the other side, and set it exactly the same way you set the first one. Wash, rinse, repeat. Also note the flanges of the rounded nut plate slightly sticking out beyond the edge of the flange. These will absolutely interfere with the clearance of the trim tab servo that will be mounted to the access plate, so you have to file these down to match the edges of the opening.

Next is my setup to hold the skins out of the way while I set the rivets for the nut plates:

Next is another concern about the clearance of the trim tab servo case from the lowest edge of the mounting brackets as shown. Not a lot of clearance for a rivet head, much less a dimple. Thanks to Steve's builders log post, I found out that he simply countersunk the metal for the flsuh head rivet so that no dimple was needed, and he then used a 1097 rivet that has a smaller head on it to avoid interference with the output shaft of the servo. I will do the same.

Note the angle of the mounting brackets in the next pic. The wires are also routed through the access hole that is precut into the bracket.

Next, all the nut plates rivets were set with the hand squeezer except for the last one. The yoke with the shortest span that I possess is the flange yoke. Unfortunately, even that one cannot fit inside the access hole at a point where it allows the last set of nut plate rivets to be squeezed. So I needed another solution. Enter the C Frame....

So I need to take some time to explain how I set this up. One nice thing about the C frame is that you can use it to set rivets as well as make dimples. I used 2 1/2 inch x 1/8 inch flat rivet sets. I decided not to use the smaller 3/8 inch diamter flat set because to set the rivets you ahve to bang on the ram with a hammer, similar to setting the dimples. The parts will inevitably move a bit while you are banging on the rivet, so I wanted a little more leeway on the rivet set to allow for this movement.

The setup was C frame perpendicular to the long edge of the table, set on top of a 3/4 inch piece of plywood. On the opposite side, I stacked two 2x4s on top of each other, long side down, and placed a blanket over the top to prevent sratching the outer surface of the skin.  Then I placed the skin on top of the 2x4s. Again, the idea is to get the skin at approximately the same height as the bottom set in the C frame.I could ahve used the C frame table for this, but because the dimple dies and flat rivet sets are different dimensions, I would ahve had to adjust all the legs on the C frame table for the flat rivet set, which is much lower than the dimple die. This jury rigged setup took much less time and trouble and worked out well enough.

Next, I took another 2x4, short side down, and slide it uder the skin next to the C frame took for additional support. I used rivet tape to hold the manufactured head of the rivet in place, with the cleco in the other hole, just as I had done with the hand squeezer setup. I may have reversed the cleco so that it was as out of the way as possible from the rivet while positioned in the C Frame. The last step was to borrow another set of hands from my son to hold the top skin out of the way while I bang on the rivet to set it. I used a ball peen hammer for maximum affect and energy transfer to the rivet with each blow. I took 1-2 blows, and then checked the clearance of each rivet set on the top and the bottom as well as the depth of the shop head of the rivet, and re-positioned the skin as needed. Then I followed up with another 1-2 solid blows to finish setting the rivet. Worked out fine.

So here are all nut plates installed on the flange of the trom tab mounting bracket:

Now the only problem was the excess portion of each nut plate that is hanging over the edge of the flanges. I took a square file and proceeded to file down all of the nut plate edges until they were almost flush with the edges of the flanges of the bracket. I stopped just a bit short to prevent myself from accidentally filing away part of the flange itself. I may need to fnish up the last but of filing with sand paper, a scotch brite wheel, or a dremel tool of some sort. The trim tab and its mounting brackets just barely fit into this access hole, so every edge dimension has to be spot on.

Lastly are top and bottom shots of the nut plates after being filed down flush with the flanges: