Sunday, November 11, 2018

Tank Attach Nutplates Riveted, LE Skin Cut Preparation

I was able to finish riveting the remaining tank attach nut plates on the subskin. T do so for the forward-most holes I had to change my approach as well as my tool setup from what is was previously. My support blocks were too big to clamp on the inside of the subskin near the bend, so I had to basically reverse the approach.  I moved the support blocks to the outside of the skin, re-clamped the skin to the support blocks from the opposite side from before, switched my flat sets in the squeezer so that the wider set was on the ram and the smaller set was in the stationary part of the yoke, and I had to feed the skin in a slightly different way to maintain tool clearance from the clamps and ensure proper operation of the squeezer.

Here is the pic after I had finished setting all the remaining rivets. Call it being lazy or whatever, but once I had changed the setup to allow me to squeeze the most forward rivets - 2 nutplates on the bottom side and two more on the top, I decided that instead of switching everything back to the previous clamping and setting method, I would just keep going with the new setup. Why is this significant? Well, the change in the setup also meant that instead of pulling the stationary part of the yoke against the manufactured head of the rivet and the skin, and allowing the ram of the squeezer - the moving part - to smash the rivet tail, the process is reversed. So I had to place the moving ram over the manufactured head of each rivet, and try to keep it centered on the rivet head as it moved upward to close the gap with the stationary part of the yoke on the other side.

SO the difference is that when configured one way, you are holding the squeezer stationary against the rivet while the ram moves and sets the rivet. For the other configuration, the ram is moving upward and you have to try to keep the rivet set over the center of the rivet as it moves. THis is how I have messed up so many rivets in the past that I cannot even begin to count. Trying to keep a flat rivet set stationary over a small rivet head while the ram is moving is counter-intuitive, but the problems is that, as is the case here, sometimes you do not have much of choice as to how things need to be configured in order to get the job done. So you have to learn how to rivet using a lot of different techniques and setups - that's just the way that it is. In the above pic you can see how the ram will push on the skin and the rivet head as it moves up, so you end up developing this sense of allowing the ram to move up while the squeezer moves backward a bit, and, if everything stays in alignment, i.e.the rivet set on the ram does not slip off the center of the rivet head, the other flat set will eventually make contact with rivet stem and smash it to the proper size.

Fortunately I was able to set all the remaining rivets that way, and they all turned out fantastic! So I did not even have to drill out or reset any rivets. All 14 nutplates for the tank attach edge of the subskin were set successfully and correctly, and I was very pleased with that. it is not often that I engage in a rivet setting session and I do not have drilled our any rivets or fix a problem of some sort. I was glad to get that behind. me. Here are the finished nut plates - all riveted on.
With that done I decided that the next major task was to drill the corner holes in the LE skin to establish each corner radius as closely as possible and provide the relief holes for the straight cuts that I need to make to remove that portion of the LE skin that will now be "removable."

The steps were:
1. Clear off my work bench to allow the LE skin to sit on the top surface
2. DEtermine how high above the work bench I would have to stack other drill boards to account for the depth of the unibit to create a 1 inch wide hole with the necessary 1/2 inch radius that I designed each corner to have.
3. Charge my batteries for my electric cordless drill, which is once again the tool that ALWAYS use when drilling holes in metal with a unibit. NEVER use a high speed air drill with a unibit. I learned this lesson a very long time ago and have heeded it ever since. Air drills turn way to fast, and unibits cut much too quickly and efficiently, and the drills lack sufficient torque, to ensure that the hole will be drilled properly without distortion or without accidentally over-sizing the hole.
4. Install the correct unibit with a 1 inch diameter step in the drill
5. Stack the required number of drill boards on the work bench uner the Le skin to ensure that the unibit will not drill into the work bench top. IN my case I had to ensure that I had at least 2 inches of drill board under the LE skin.
6. Clamp the LE skin over the drill boards. Again, the idea here is that the unibit needs to drill into the thin flimsy metal of the LE skin and then into the wood underneath to keep from marring the hole in the metal and causing substantial burs. This is why you need a high torque drill - because you have to drill through so many layers or thickness of wood, in addition to drilling the hole in the metal.
7. Measure 1/2 inch x 1/2 inch from the cutlines on the rear and sides of the LE skin, mark that location and use the punch to mark that location. This is to be the center point of where the unibit must start drilling in order to achieve the 1/2 inch radius that matches the curvature of the skin that I had already drawn on the surface. I started out  by drilling a #40 pilot hole, so the 1/4 inch wide center point of the unibit would be able to locate a good center without wandering. Then I just inserted the unibit tip in that hole and started drilling slowly to ensure that it was entered correctly. I did NOT drill the hole up to 1/4 inch before using the unibit, as I did not consider that necessary. 
7. Drill the two corner holes on one side of the skin, unclamp, flip the skin over, reclamp, and repeat the steps to locate the drill hole and drill the two holes on the other side of the skin.

Here I am beginning to stack the required drill boards on the bench after determining that I will ned at least 2 inches of wood to prevent drilling into my work bench top.
I decided to use my Dremel tool and an EZ lock reinforced cutoff wheel to make the necessary straight cuts, and for this job I wanted a fresh wheel on the tool, so I changed out the old one which was about down to the shaft, with ab rand new disk:
Another blurry pic, but this is my harbor freight unibit that has a 1 inch wide step in it that is about 2/3 up from the tip. You can just see on the right side where I marked the step just above the 1 inch step with a sharpee so that I could tell which step I was on as the tool advanced through each step in the drill bit. I frequently stopped to clear debris from the drill hole and to check the progress of each step against the lines I had drawn on the LE skin, just as I had one before when I cut out the hole for the new access panel so long ago.
Next are the two holes on the bottom skin after I had drilled as close to the pre-marked lines on the skin as I dared. In fact I got a little too close on the first one.
And here is my clamping setup. I ended up using a 3/4 inch particle board, 2 2 x4s, and a 2x6 board on top of my work bench to provide the depth that I needed to keep from drilling into my work bench. Used a very haeavy can of clecoes and my clamps to secure the skin on the workbench. The top of the skin draped over the front of the work bench just fine while the bottom skin layed relatively flat. This setup worked great.

And here is the top of the LE skin after flipping it over. Of course when you do this the side of the skin that you are drilling on is reversed, so you have to reposition drill boards and clamps accordingly.

And finally a pic of all four corner holes drilled in the LE skin. I had hoped to also perform the big cut on the remove the section of the Le skin, but I was exhausted and needed to get some sleep first. Unfortunately the weather is going to change and get cold and snowy for the next two days, and I will NOT perform the cuts of the LE skin unless EVERYTHING is optimal. I have come too far to screw this up now, so I am not taking any chances. SO the best I could do for now was setup the LE sin for the next step, which is to FINALLY cut out the section that will ultimately be removable.

Here is the sequence of pics showing how I did that:

Thursday, November 8, 2018

Subskin Nutplates Part 3

Here is a pic after dimpling the #40 rivet holes for each nut plate with my pneumatic squeezer, using the reduced radius female die and the standard sized #40 male die. Setting dimples was pretty easy.
The next pic is blurry but shows the process and positioning of the nut plate on the dies for setting the dimples on each nut plate flange. This also went quickly. There are 14 nut plates for the fuel tank attach portion of the subskin.

The nut plates sat a little proud on the dimples in the subskin, but they actually riveted on quite nicely I think.
With the required dimples completed, everything was clecoed in place:
And here was the creative clamping structure for this round:

I used the pneumatic squeezer to set these rivets. I switched out the dimples dies on the same flange yoke for flat sets, one if which was the same reduced radius die as the female dimple die. I always get nervous when I have to use such a small radius die for setting rivets, especially when the smaller one is the one that must be used to smash the rivet tail down. Everything has to be centered pretty well, ad there is not a lot of room for error. it is very easy to slip off target and cause the rivet to become deformed. Fortunately all the rivets I set were completed successfully, with out the need to drill any of them out, so I was quite pleased with that.
The clamping structure was set up to allow me to pull on the wider top flat set to apply pressure to force the manufactured head of the rivet against the dimple in the skin, and close any gaps between the skin and the nut plate flange on the other side as shown below:
The trick for alignment is to place the 1/3 inch wide set just below the rivet head and slide it up over the head making sure that it is centered as much as possible. Then you make certain that the flat set is truly flat against the rivet head and the skin. One of the biggest problems with this set on an air squeezer is trying to ensure that the set is truly flat. I found that you have to take into account any angle to the skin that might exist ir is created when you apply pressure to the skin and the rivet head. once you know that the rivet set is flat and centered over the rivet, then you are ready to engage the trigger and set the rivet. I always try to position everything so that I am pulling on the rivet head as the plunger goes up from the other side to set the rivet stem.
One other trick that use religiously is to set the air pressure going the squeezer to 75-80 psi max. The instructions with the tool always say to use 90 psi, but I figured a long time ago that this causes the ram to actuate much too quickly and can cause the rivet sets to move out of position just enough to ruin the rivet or the parts. I found that when I reduced the air pressure it was much smoother and less jerky, and the sets tend to stay in position better and you can watch the ram as it comes up to smash the rivet and make sure that it s positioned correctly before you commit to the full smash. The ram still has plenty of force to set the rivet, even though it moves a little slower.

First the rivet goes in the hole:
One down and one to go.....
And one nut plate riveted, 13 more to go:

This also turned into a creative clamping exercise because after each rivet was set the clamps had to be repositions and the part moved into position to allow enough clearance for the squeezer to set the next rivet. I was able to do 5 of the rivets and had to stop when  I got to the two most forward ones:

It was too cold tonight to set the remaining rivets, but I'll get this done as soon as possible. Unfortunately it looks like when I get the tank attach nut plates riveted I am going to need to cut the skin on the LE and then reassemble everything one last time before final riveting of the entire LE so that I can make the file folder template to mark the hole locations for the removable LE skin, and THEN I can drill the remaining nut plate holes to final size, debur the holes, dimple them, and rivet them to the subskin. So the to-do list is getting shorter, but it will still take a lot of time to get to the finish point. 

Subskin Nutplate Rive Holes Part 2

I continued to clamp and drill the nutplate rivet holes for all 14 fuel tank attach nutplates using the methods shown in the previous post. Once those were done I decided to mark and drill the #40 nutplate rivet holes along both edges in the subskin that will be used to attach the removable outer skin to the subskin. I used a different method for these holes by taking a nutplate and inserting a #30 cleco in the center screw hole to secure it to the skin. I had to use this method instead of the nut plate jig because I am not ready to increase the size of the screw holes with the #19 drill just yet. So this was the only option for locating and drilling the rivet holes for each of these nut plates.

The problem with it is that you end up using the nutplate rivet holes to match drill the $40 holes in the skin, and that cleco does not exactly tightly secure the nutplate to the skin, so it is possible for the nutplate to shift a bit when drilling the rivet holes. How do I know that? You will see in a bit...….

Step 1 was to use a sharpee and a straight edge to draw lines next to each #30 hole that I had already drilled so that I had a reference line to align each nutplate. At the end of the day it does not matter too much if the rivet holes are all nicely aligned with each other, as long as the center screw hole is aligned properly. However, it does look better if the rivet holes are aligned with each other.

IN this pic I had already drilled the holes after adding the lines, but you can see how it looked.
Each nut plate was mounted on the outside of the skin, and the #30 clecoes were inserted from the other side as shown here:
I thought  had snapped some pics when I started match drilling the #40 rivet holes through each nut plate, but apparently I did not. How I did that was to align each nut plate with the lines that I drew so that the rivet holes would align  properly, and I simply held each nut plate with my fingers on my left hand while I drilled the holes through each nut plate with my right. As you will notice, this lack of securing the work properly ended up causing the drill to slip when I got to the most forward nut plates along each edge.
You can see how "off" the rivet holes are from the line that was drawn. At the end of the day this will not affect anything, but it really pissed me off when the drill slipped.After drilling the first hole I put a #40 cleco in from the top side, and then drilled the second hole.

When all the rivet holes were drilled it looked like this:
After these holes were drilled I removed all the clecoes and the nut plates and deburred all the new holes. Then it was time to mark and drill the holes along the rear area of the removable section of the subskin. I basically used the same process for these holes that I did along bot sides:

I had to get creative once again about how to clamp everything down so that each of the holes was being drilled into a piece of wood underneath the metal:

Here is a series of pics showing the clamping arrangement of the other side of the fuel tank attach nut plate holes. The wood and clamps had to be repositioned each time to drill each hole, and yes, it was just as much of a pain in the ass as it was for the other side:

After that was done it was time to dimple the #8 screw holes in the center of each nut plate position o the skin for all the fuel tank attach nut plates along one edge of the subskin. This time I made sure that the male AND female dimple die were installed on the C-Frame. The C-frame was used instead of a squeezer because the dimple are much crisper. I have seen many airplanes where the builder obviously used a squeezer instead of a C-frame to dimple these holes, and there is a very noticeable difference. ALL the screw holes had been deburred long ago, but I went over then one more time to be sure, because this is a step where cracks can form in the dimple. I read one post from a builder's kit log where he was using a squeezer and he ended up ordering new skins and parts because his dimples kept cracking. Had he used a C-frame he might have had those problems.

Here is the photo sequence:

The most forward holes closest to the bend in the skin were tricky to dimple. I basically used my head, hands, and whatever else I could to try to straighten the skinor at least orient it with the bend as it sat on the male dimple die so that the dimple would be properly oriented with the bend. I think this came out OK.
Next I needed to dimple the #40 rivet holes for each of the fuel tank attach nutplates. I did these with my pneumatic rivet squeezer. Once the skin dimples were done I now needed to dimple the #40 rivet holes in each nut plate so that it will sit flush with the dimpled skin. I should also back up a bit to note that prior to dimpling the fule tank attach rivet holes I did quite a bit of research on other build sites and on VAF, and ultimately called Vans, to find out if I should dimple those holes and use normal sized rivets for each nut plate, or if it was acceptable to use the NAS 1097 "oops" rivets with a smaller head so I could countersink the subskin holes instead of dimpling. The reason for using the NAS method s to avoid having to dimple the nut plate flanges by countersinking the skin.

I had seen builders do it both ways, but I wanted to be sure, since this is a potentially structural area of the aircraft where several parts of the wing are under stress. The general rule is that in that case you should dimple the holes and nut plates, because a dimpled hole is stronger than a countersunk one. Vans ended up telling me to dimple the holes and also dimple the nut plate holes using a squeezer.The problem with that is that the plans do show to use an AN426 rivet, but they do not show the dimple, which implies that the joiner plate is countersunk. They also state to use an AN426AD3-3.5 rivet, which is probably correct for a countersunk hole, but according to my rivet gauge the correct size rivet to use for a dimpled hole is an AN426AD3-4 rivet, so that is what I used.

Now, the problem with having to dimple the K1100-8 nut plate rivet holes, is that the center screw hole is already countersunk, so the area of the nut plate around he center expands outward quite a bit toward the rivet holes. If you use a standard sized #40 dimple die the female die is too wide for the nut plate center hole, and you will damage or deform the nut plate or mis-align the dimple in the #40 rivet holes. SO the solution for this is to use a reduced radius female die, or you can take a standard sized die and grind down one side so that it clears the countersunk center hole of the nut plate and cleanly dimples the #40 rivet holes on either side.Here it is installed in my squeezer:
Notice how the female die on the right has a smaller radius than the male die on the left.This allows you to dimple the flanges of the nut plates without damaging or deforming the center hole. I'll continue with more pics and info about this process tomorrow. Tonight I actually got tote point where I started setting rivets for the nutplates, and I had not set any rivets for quite a while, so that was refreshing. Eventually I will get the blog caught up with my actual progress, but my focus right now is to stay on track to finish all the remaining steps necessary to complete this mod. The closer I get to that point the more I want to finish it. Anyway, more later.