Not wanting to hijack Walts thread, but since it seems he was opening discussions on processes to use, I thought I would add a detailed explanation on how I do it. I hope some of you find it useful....
Regardless of how experienced a person is, it is nearly impossible for them to remove rivets by drilling down the length of the shank with a net size drill bit. Even a slightly smaller bit (3/32 instead of #40) will do little to help with the level of success.
The following is a process I have used for many years. Though I have very little experience with anything larger than 3/16, with slight variation it should work for everything from 3/32 rivets on up to what ever size you are dealing with.
1. Center punch the rivet head. If it is an AD rivet , use the identifier dimple in the head center otherwise eyeball where the center is.
2. Use a drill bit sized the same as the hole you are removing the rivet from, to drill into the rivet head just deep enough that the full diam. of the drill bit is at a depth approx. the same as the thickness of the manufactured head of the rivet (the point of the drill will be just slightly below the material surface of the underlying part/skin). I use a cordless drill running at slow speed. This gives me time to drift the hole back to center before the full diam of the drill point penetrates the rivet head. Some people prefer to start with a smaller diam. drill. This does help it stay centered in the previously made center punch, but for me it is far easier to tell by eye if the bit is staying centered, if the drill bit is closer to the actual diam. of the manufactured head of the rivet. Experiment and see what works best for you.
When in a situation where an angle drill must be used, I make a little wood spacer for the throttle lever and tape it to the handle so that it prevents the lever from being depressed all the way. You can then set the drill speed using the pressure reg. for the air line, and have it run at a consistent speed every time (this seems to work more consistently than turning the pressure way down low and opening the throttle all the way)
3. Use a drift punch or the blunt end of a drill bit that closely matches the hole diam., and pop the rivet head off… insert the punch and tilt it over to the side to snap the head off. If it doesn't immediately pop off, try prying in multiple directions… you may have been (hopefully) just a little bit off center with your drilling.
The reason for this next step is to relieve the expansion of longer rivets within holes, and give the rivet a space to collapse in on it self as it is being pulled or driven out.
If you were to look at a cross section view of most rivet holes, it is far from being a smooth bore. There are minute little relief areas because of the small chamfers that occur on the hole edges while deburring. If one or more dimples are involved, then there is even more void areas. When the rivet was originally set, the rivet shank swelled into all of these areas to some degree. That makes it grab and resist being pushed/pulled out of the hole.
4. Once the rivet manufactured heads are removed, change to using a drill bit one rivet hole size smaller than the hole you are working with (1/16” for #40 hole, #40 for #30 hole, etc.). The goal in this step is to drill down the center of the rivet shank, but stop short of drilling through the shop head on the other end. The ideal stopping point is about ˝ the rivet diameter before entering the shop head. On longer rivets, you can wrap some tape around the drill bit to use as a depth stop.
In cases where a short rivet (usually 3/32) is used to attach a skin to a rib, etc., you can usually skip this step, as the rivet is small enough it will still shrink and pull out easily without drilling a relief hole (using the rotating removal process described in the next step)..
The goal of the next step is to utilize the relief hole we drilled previously, to cause the rivet to stretch in length. If it will stretch in length, it will slightly shrink in diam. This will help get the rivet to let go of all of the small void areas within the rivet bore, and reduce the friction inside the smooth part of the bore allowing it to slide out much more easily.
5. This can be done two different ways.
The first is what works best with rivets 1/8 “ and larger, but particularly larger than 1/8”.
Insert a pin punch in the relief hole and drive with a hammer. Depending on the structure you are working on, you may need to also back up the material around the shop head to avoid distortion, but since you are driving at the bottom of the relief hole, the rivet should begin to shrink in diam. with the very first hit, and drive out relatively easily.
The second way to shrink the rivet diam is by rotating it. I have a rivet removal tool made of a long handle side cutters similar to THESE
. They have the smooth face (facing you in the photo) ground down slightly, and polished smooth so that the sharp portion of the cutter can get very close to the surface of a flange or skin to grab a rivet shop head. Note, they must be a long handle variety to provide enough leverage to grab the rivets tightly enough.
I grab a rivet shop head with the tool, squeeze hard, and wiggle the tool back and forth quickly, trying to rotate the rivet. Once you can get it to move about 10 deg., you can usually tilt the tool (while still squeezing hard) and pry the rivet out of the hole. This has low risk of causing any distortion to the parts (if you were able to get the rivet to break free and rotate) and it can be done with one hand… you don’t have to hold a hammer and punch, and then somehow also hold something to back up the material for the force of the hammering.
The added benefit is that you can use the process in areas where it is not possible get a punch and hammer onto the rivet. A perfect example being the rivets within the two skin bays of the horizontal stab., that attach the top and bottom angles to the spar webs, that need to be removed to install the spar doubler for the S.B. If the relief hole is drilled deep enough, even though the material stackup thickness is .157” the rivet will easily collapse and pull out using the side cutter tool.
When working in difficult areas, particularly where you might be using an angle drill where determining drill alignment is difficult, start with a hole that you can install a cleco in after rivet removal and still have access to the rivet(s) adjacent to it. The cleco can then be used as a visual guide to determine if the drill bit is square to the surface.
Try and avoid drilling through the shop head when drilling the relief hole. It removes the ability to drive with a punch in the bottom of the hole (obvious) and it increase the possibility that the shop head will break off the end of the rivet before you can get it rotated or pulled/pried out.
Short 3/32 rivets (ones that attach skins, etc.) remove very easily using the rotate / pry out method. I use this process exclusively when removing skins, etc. When the only drilling done, is just what is required to get the manufactured heads removed, there is very low risk of damaging the holes.