Very excited to report that we got our first rivets done today!
Riveting is probably the scariest part of the build, as it’s used for joining all the pieces together. We don’t plan to count, but one RV builder has done, and he reckoned there were 22,500 rivets on his finished aeroplane in total.
There are several different techniques you can use to rivet – each has its advantages and drawbacks and will result in a different level of consistency in the finish. Sometimes you get to choose your technique, and sometimes the bit of the plane you’re working on dictates it due to accessibility or the material of the part.
As we’ll be getting to know them pretty well over the course of our build, it’s worth a little intro to rivets here.
Rivets are small bits of metal, which look a little like screws with a smooth shaft on first inspection, at least to those who (like me) haven’t had much to do with them before.
Rivets have what’s called a ‘manufactured head’ (or ‘factory head’, the part of the rivet that is in its final form when it comes to the builder). The manufactured head sits on one surface of the metal, and on the other side is the ‘shop head’ (the one that the builder forms whilst riveting the metal together).
Rivets used in the Van’s aircraft kits can be ‘universal’ rivets or ‘flush’ rivets. These descriptions refer to the manufactured head of the rivet – ‘universal’ rivets are domed and stick out from the surface, whilst ‘flush’ rivets sit (perhaps unsurprisingly) completely flush with the surface.
When preparing for riveting, any holes which will receive a flush rivet have to be dimpled or countersunk, so that the head of the rivet can be sunk down into the metal and sit flush with the surface. For universal head rivets, this isn’t necessary as they stick out above the surface.
Rivets are designed so that the shaft can be manipulated once (via a variety of techniques, see below), and it then holds its form with a head on either side.
Once set, depending on the type of rivet, there are minimum specifications that the ‘shop’ head has to meet, both in terms of diameter and height. To check the rivet is within the acceptable range, we use a rivet gauge to measure the shop head after it’s been set.
Techniques for setting rivets
There are even more ways of setting rivets than I’m going to mention here – for the sake of space I will focus on the ones we’ll be using for our build.
The shaft of the rivet can be manipulated and a ‘shop’ head created by squeezing the head of the rivet and the bottom of the shaft between two ‘dies’. The dies used depend on the rivet type – for universal head rivets, the die has a domed shape in it to accommodate the head, and for flush rivets the dies are flat.
There are various hand squeezer tools that can be used for this purpose, but as we’re going to be doing so many rivets on this build, we have got a pneumatic squeezer, which will save our hands!
Using the squeezer is a very controlled way of setting the rivets – you can press the trigger slowly and take up the slack, making sure it’s in absolutely the right place. Once you’ve got the hang of it, it gives a very neat and consistent finish.
Gun and bucking bar
Because the pneumatic squeezer has jaws (called a ‘yoke’) that have to be able to get around an area in order to rivet, there is a limit to the areas it can reach. For less accessible rivets, we’ll mostly be using a rivet gun and ‘bucking bar’, which is a large flat lump of steel that is used to drive the rivet against. The gun has a head on it which matches the manufactured head (so domed for a universal rivet and flat for a flush rivet), and the bucking bar is flat and is used to create the shop head.
This technique is more versatile as you can reach into corners and under skins where the squeezer wouldn’t be suitable, but it is less consistent because it relies much more on human input. The resulting rivets will still be strong as long as they meet the specifications (and if they don’t, we’ll be doing them again!), but they will probably look less neat.
In many situations it’s better to have two people when using this technique – one with the bucking bar and one with the gun. In some cases this will be pretty much essential – for example when riveting either side of the fuselage skin when no single person can see both sides. We’ll have to develop a good method for communication when we work together on this, to avoid riveting each other’s hands (I’ve already done this to myself once, not recommended!) or bits of the skin without rivets on. We’ve already realised that “STOP” is more effective than “NO”, as the latter could be mistaken for “GO” over the noise of the gun and compressor!
My experience so far is that the force of the rivet gun causes it to skip across the skin and it’s very easy to mark or damage the surrounding metal, so practising on scrap metal and getting the hang of control is really important before moving on to the aircraft itself.
When setting flush rivets on a skin, the technique of ‘back riveting’ can be used to produce a neater finish on the outer side (the one which will be visible once the aircraft is fully finished). This is especially desirable for areas like the fuselage and wings, where there are large areas of skin with flush rivets.
The standard way of using a rivet gun is to have the gun on the manufactured head, and the bucking bar used to create the shop head. When back-riveting, you have a large, flat bucking bar that goes against the manufactured head, keeping it smooth and straight, and the gun is then used to form the shop head instead.
A very useful invention that comes into its own when back-riveting is rivet tape – when the rivets are in place, you tape over them. The tape is sticky at the edges but does not stick to (and pull out!) the rivet heads themselves. I discovered how helpful this is when I accidentally flipped over two bits of metal from the practise kit and dropped all of my carefully prepared rivets onto the floor. These need to be discarded if that happens, as they can be contaminated by dust or bits of other metals on the floor of the workshop. Rivet tape is (hopefully) idiot-proof and stops this from happening!
Our first rivets (and our first broken rivet!)
So how did we get on? Well, not too bad actually! The first riveting task on the vertical stabilizer is to attach the spar doubler (a thick piece of metal used to strengthen) to the long spar, and then connect up various small attachment pieces that help with later assembly.
Luckily for us, this first task can be completed using just the pneumatic squeezer, which at the moment is our favourite technique as it gives such a neat and consistent finish. We experimented with the different dies and settings, and got going once we were happy.
There is a mix of universal and flush rivets on this piece, and a range of sizes and lengths too, so it’s a good opportunity to get a sense of what an acceptably-finished rivet looks like. We are using the gauge to double check every single one, but you quickly get an eye for when the shop head is right.
We managed to get a good, consistent finish and the rivets well within spec, save for one (my fault!). The pneumatic squeezer is a relatively quiet and unassuming tool, but it’s important to remember that it’s exerting an enormous amount of pressure (about 1,000 psi) on the rivet. If you’re even slightly off-centre, it is immediately a problem.
On some of the attachments, the rivets are relatively hard to reach due to bends in the metal. I was acutely conscious of the need to avoid accidentally squashing the metal out of shape, whilst also remaining centrally aligned on the rivet. In one case I protected the metal part at the expense of the rivet, which I hit off-centre and it cracked in two with a loud bang!
Our first drill-out of many, I expect. As long as the surrounding hole hasn’t been damaged or enlarged, the broken rivet can simply be drilled out, and a new one set in its place.
Only another 22,400-ish to go…