Blind rivets, sometimes called hollow rivets, are invaluable when you have access to one side of the work only. With solid rivets you need access to both sides. Blind rivets may be set with a special plierlike tool which is easy to use and inexpensive; because the rivets require no hammering, they have become increasingly popular with the amateur — even when there is access to both sides of the work.
The rivets, which are available in aluminium alloy, copper, stainless steel and nickel/copper alloy (for extra heavy duty work), are particularly suitable for fastening all types of sheet metalwork.
Material preparation is exactly the same as for solid rivets, although selection of the twist drill bit is easier since the manufacturers specify a particular diameter drill bit for each rivet size. Remember to remove any burr from the pieces of work before setting the rivets to ensure a tight fit.
The blind rivet is expanded by the head of a pin, or mandrel, which you pull into the end of the rivet with the setting tool. When the pin meets the extra resistance of the work, the head breaks off and remains in the rivet. You can then pull out the shaft of the pin.
Types of rivet
There are many sizes, in terms of length and diameter, of blind rivets for precision work. For domestic use there are basically two diameters — 3mm and 4mm; a 5mm rivet is also available, mainly for repair work on boats. The rivets, which are available in short, medium and long lengths, come in countersunk and surface versions.
Each blind rivet has a mandrel — a length of steel pin with a knob at one end and a point at the other. The mandrel is available in a variety of forms, although you will have difficulty in obtaining a supply of the unusual ones in small quantities. The most common are break-head and break-stem; as the rivet is set, at a predetermined pressure, the stem of the mandrel breaks just beneath the head in the case of break-head mandrels and just slightly further down the stem in the case of the break-stem form.
The head of a blind rivet left inside the work will not form a seal. A waterproof version is available where the mandrel is completely sealed in the rivet; when it breaks the seal remains.
When riveting very soft materials with blind rivets, sometimes the rivet will not grip the work adequately because it deforms the shape of the hole; in this case you can use a backing washer to protect the hole. A backing washer can also be used to enable a rivet to be fitted into a hole that is too large, and it can be used to adjust the effective thickness of the workpiece. This is useful when the rivet chosen is just too long and the next size to it is just too short. The washer has a central hole equal to the diameter of the rivet and is placed over the rivet behind the work.
There are a number of makes and sizes of blind rivet; the heavier ones need a hydraulic gun to drive them properly; but some rivets can be set with an inexpensive hand gun. They are used especially for repairs in metal structures.
The simplest setting tool is a pressed steel plier-action device with a pair of hardened jaws set in a tapered seat so that the harder you pull the tighter the jaws grip. More robust and versatile versions are available, with different nozzles to accept different diameter rivets and, for example, extended noses for use in restricted spaces.
This is extremely powerful and fairly expensive. The arrangement of zig-zag levers is designed so you can set the larger diameter rivets, which require considerable pushing force. You can hire the tool for the odd job. Otherwise you will have to apply great force with the standard setting tool.
Setting hollow rivets
Insert the mandrel into the setting tool until the head touches the nozzle; the pointed end aids entry while the jaws are opened, by pulling the operating handles apart. Without
squeezing the handles, insert the rivet into the drilled hole in the work and hold the rivet head firmly in place. As the rear half of the rivet becomes deformed apply increasing pressure — at a predetermined breaking point the mandrel will snap and the job is complete.
If the rivet is slightly too long for its job, it may be possible to squeeze the handles of the tool without breaking the mandrel; in this case you will need another bite at the work. Pull the handles apart to release the mandrel; it will slide forward out of the tool. With the handles still apart, slide the nose of the tool along the mandrel until it reaches the head of the rivet; squeeze the handles again and this time the mandrel should break. If you find you cannot exert enough pressure on the handles to break the mandrel, you should advance the tool for a second bite. Do not take it up to the rivet head; just bring it a little closer than before.