A Dimpling We WIll Go, A Dimpling We Will Go......

High Ho the Dario a dimpling we will go.....

Just  couldn't resist that. As promised, I made what - for me - was substantial progress tonight. I managed to do the following in a couple hours time. All dimpling was performed with the handheld pneumatic squeezer (or heavy SOB as I like to call it), using the -3 dimple dies and the flange yoke:

1. Cleaned the dust off of the rear baffle plate of my Left Wing Fuel Tank Baffle assembly.

2. Removed and dimpled all remaining LE ribs

3. Dimpled the inboard and outboard LE rib holes in the outer skin

4. Dimpled the patch plate and access panel holes in the bottom of the outer skin

5. Verified my temporary installation of Z brackets for the fuel tank were still installed correctly on the wing spar, just as they were back in 2014 when I last touched them.

6. Re-measured the location of the bolt holes in each flange of the Z-Brackets that mounts to the main wing spar web. I reviewed an old post of mine the other day from back in 2014 were I was trying to apply Checkoway's advice to drill the initial bolt holes slightly off center. This was supposed to serve 2 purposes - to allow clearance for the most inboard Z brackets bolt heads so that a wrench or socket could fit around the bolt without interfering with the Z bracket web, and simultaneously allow a little more space for the AN470-4 rivets and Pop rivets to be applied with a rivet set and a pop rivet puller tool, also without interfering as much with the Z bracket web.

These rivets attach the opposite flange of each Z bracket to the back of the fuel tank baffle plate to complete the fuel tank installation. From researching Checkoway's posts further, it looks like you still have to grind away part of a rivet set or pop rivet tool to set those rivets, even if you make the 1/16th of an inch adjustment from center when you measure the location of each hole.

The problem with this approach was trying to figure out how to measure the lengths and widths of each Z bracket flange properly, because of the odd way that these Z-shaped aluminum extrusions were formed. From looking at the bolt holes that I drilled previously, it looks like I was using a flange width of 20/32 of an inch, or 10/16ths, or 5/8ths of an inch, as measured from the flat outer side of each flange. This means that this measurement would include the thickness of about 1/16th of an inch for the web of each Z bracket.

So the middle measurement would then be 10/32nds of an inch, or 5/16ths.

Then a 1/16th of an inch adjustment from that center mark in either direction would be 8/32nds (4/16ths or .25 inches) or 12/32nds (6/16ths or 3/8ths) of an inch, depending on which direction from the web you need to adjust. I am rehashing all of this hear so I can refer back to it as necessary when I get to the point where I need to finish drilling all the remaining holes in each Z bracket.

If I don't include the thickness of the Z bracket web in these measurements, the numbers reduce to a total flange width of 9/16ths of an inch, or 18/32s, and the halfway point would then be 4.5/16ths , or 9/32nds of an inch. Then the 1/16th of an inch adjustment to either side would be 3.5/16ths (7/32nds) or 5.5/16ths (11/32nds). Seriously, trying to figure out precisely where to drill the Z bracket flange holes is a pain in the ass, because these measurements can just drive you crazy.

When you further consider that the width of the hole you must drill for the bolts is 3/16ths of an inch, it does not leave much room to work with if you go either closer to or farther away from the web of the Z bracket. Crazy stuff. When I evaluated this situation, I realized that the "close" measurement would only leave about 1/32 if an inch from the web, and I don't think that a nut plate will fit on the flange with only that much space. So I chose to stick with the measurements that include the thickness of the web.

Then, when you finally look at the numbers, and realize that the only difference that you seem to be working with is just 1/32nd of an inch between the two different measurement methods, you realize that it probably does not make much difference either way, and you will still end up grinding away a large portion of whichever tool you need to use just to make it fit up against the Z bracket web enough to set the rivets.

7. Verified that each of the bolt holes I drilled in the left wing Z brackets appeared to be in the correct place based on the outer measurement technique. I had ordered a set of additional Z brackets after I accidentally drilling a bad hole in one of them in 2014, and I still have those spares today, just in case I need to re-drill any of them.

8. Dimpled the holes along the bottom edge of the Le outer skin. Unfortunately, I found out while doing this that I had missed the match drilling of several holes on both the top and bottom side of the rear of the LE skin where it gets riveted onto each spar flange. What this means is that I cannot countersink all of the corresponding holes in the main wing spar flange, because some of them still have to be match drilled first. Since I know I have to remove the LE one last time  before it gets attached to the wing for good, this is fine.

I will match drill the missed holes through the LE skin and the wing spar flanges, and then after the LE comes back off for the last time I will debur and dimple the remaining holes in the skin, and countersink the remaining matching holes in the wing spar flanges. So this is not that big of a deal, but I am bit surprised that I missed so many holes. Sure hope I did better on the right wing.

9. As I expected, when I dimpled the inboard rivet holes with the 426-3 dimple die in the outer LE skin, where the first inboard rib is located, there was one hole that was wallowed out pretty badly - so badly in fact that I am not sure if a -4 rivet will set in this hole correctly, but it is too early to tell just yet. Surprisingly most of the other holes that I was worried about seemed to have made a pretty good dimple. The acid test will come when I get ready to try to drive a rivet in these holes.

10. The holes in the skin for the custom rib that fits next to the first inboard rib have not yet been dimpled, because I will need the dimpling table, C-Frame tool, and my close quarter dimpling tool to dimple those remaining holes in the outer skin. It was getting late, so that is where I stopped for the evening. So I won't know the status of the rivet holes in the tip of the LE skin for of this rib until I get to them tomorrow.

So the next steps are to finish dimpling the remaining rivet holes in the outer LE skin for each of the inboard LE ribs, and then get my micro-stop countersink tool out and run some test countersinks to properly set the depth, and then go to work on the main wing spar flange holes that need countersinking. I envision needing about 2-3 days to complete this work, because there are A LOT of holes to countersink. This will also leave a mess of metal, the likes of which I have not experienced since I drilled all the nut plate holes for the fuel tank.attach points in the main wing spar flanges a long time ago.

Starting to knock things out a little at a time..... Progress! Yeah!

KPR.