Bob’s designs rely heavily on nutplates, especially in the wing inspection panels. You can buy a special jig for drilling for anchor nuts, but we have found over the years that the following technique works just fine. Gather the following tools:
• Drill with a #40 drill bit
• A handful of silver 3/32″ and copper 1/8” clecos
• Microstop countersink attachment for your drill with a 3/32” piloted bit
• Rivet squeezer with flush sets
• 3/32 flush rivets (AN426AD3-x, most likely -3.5 or -4, but measure with your rivet gauges to be sure)

We start with the drill, anchor nut and clecos. Place the nutplate upside down on the outer surface of the skin. Reach under and run a silver cleco up through the #40 pilot hole from the bottom, through the nutplate threads. This is the hole where eventually the screw will be.

To save time, batch your tasks as in a production line. For example, you can cleco a whole row of anchor nuts at once, as shown below:

Next, drill just one lug of each nutplate. Having the clecos on the bottom allows for better drill chuck clearance, especially if you are using a shorter bit than the one pictured.

Put a cleco in that one side to prevent the anchor nut from moving while you drill the second side:

Now remove the anchor nuts, and use a Microstop countersink cage to countersink the rivet holes just enough that the rivet will sit in the hole and be flush with the surrounding skin. The picture to the below shows the tool setup, but careful observers may see that the photo does not follow the sequence correctly. The photo only serves to show what the tool looks like in this case. The outside frame of the countersink tool does not spin and is adjustable to control the depth of the countersink. Some cages have a protective plastic base, which helps prevent scratches on the skin, but may also limit access.


In the photo above, our young helper is demonstrating a good technique for countersinking a hole. Note that with one hand he is keeping the cage from spinning and marring up the wing skin.
The next photo shows the countersunk rivet holes for the anchor nut installation. The hole in the middle is the original hole drilled at the factory.

You may recall the dimple vs countersink considerations from the riveting section. When installing structural rivets, it is important to never countersink thin material that will compromise the rivet’s holding capability. Dimpling is always preferred to countersinking when the material thickness allows, and this is why the wing skins are dimpled where they join the wing ribs. In some cases, such as the fuel tank bay, you’ll have to countersink. The rivets are merely holding the nutplate during screw installation. Once the screw is installed, it provides the holding strength.
The next step is to enlarge the original center pilot hole so that it will accept a #6 screw. Drill each center hole out to #30 and swap your countersink cage bit for one with a #30 pilot. Countersink each hole just deep enough that a #6 flush screw will sit in it flush with the surrounding skin. After countersinking, drill the hole to final size with a #25 drill bit.

The photo above shows how the holes look after completing this step.
Now debur all holes and remove any debris between the skin and the spar or rib flange. Cleco the anchor nut in place through one side lug and one of the side rivet holes. Use your rivet squeezer to set one rivet on the other side lug. This is one job where a pneumatic hand squeezer will certainly earn its worth. If you’d rather not buy one, consider borrowing one from your local RV builder. Offer to carry his luggage to Oshkosh one year- he’ll likely be eager to accept your offer. Don’t be too smug about it, since he’ll have a shorter flight to get there. If this doesn’t work, consider child labor. It is important that we introduce the next generation to the hobby.

Note: make sure to position the squeezer so you are smashing the rivet and not the threaded portion of the anchor nut. We’ve all done it. If you mess up and squeeze the threaded section, especially with a pneumatic squeezer, remove the nutplate and discard it. As frustrating as it is to do so, it’s much easier to replace it now while you have your tools handy. Keep in mind that these locking nutplates get their locking function from a slight deformation of the threaded section. If you deform it further, you won’t be able to get the screw in place. Don’t run a tap through the hole to chase the threads, since that will eliminate the locking function.
With one side of the anchor nut riveted, you can remove the cleco and rivet the other side. It will look something like this:

You can dimple the nutplates with dimple dies in a squeezer. You’ll likely want to remove a bit of material from the female die to clear the threaded portion of the nutplate.