Important Warning: This is a historical archive text, not a current joint specification, standard, load rating or work instruction. Measurements, threads, materials, tools and described procedures must be checked according to valid standards, manufacturer’s documentation and actual application conditions. Drilling, cutting, riveting and working with metal requires appropriate expertise, stable fixation of objects and personal protective equipment.
This text is not an offer of rivets, screws or tools from Savo Kusić. The current offer is focused on windows, doors and custom carpentry production.
Riveting
Riveting is the connection of objects, by which relatively soft and easily machined rivets are fixed into a pre-drilled workpiece. We can say that this connection is similar to the connection between nails and wood. It is more complex as metal is harder than wood.
Rivets are cylindrical metal elements with a head that can be hemispherical, lenticular, countersunk or flat. They are produced from aluminum and copper.
When riveting, the following are used: a hammer, tensioner, punch, riveter, cutter, as well as a spiral drill for drilling holes, and for sheet metal, a cornerer. In the first stage of work, we mark the workpieces (plates or strips), then we drill them and place them on the work table for riveting. The riveting table can be larger, made of solid steel, with recesses made to fit the rivet head. We pull the rivets from below through the pre-drilled sheets that are connected and thus place the workpiece on the metal plate. The head of the rivet should rest on the bottom of the recess in the metal table top. After this, we put the tubular tensioner on the standing end of the rivet and with the blows of the hammer, we tighten the workpieces that are assembled in this way (picture 1).
Figure 1 — manual riveting
The next step is to shape the stem of the rivet, going around with a hammer in a circle, by breaking it into another hemispherical head. In this, we are helped by a shaper that, with its indentations, shapes the split ends in different ways and rivets them into almost the same forms.
A rivet with a countersunk conical head is used if the head of the rivet should not be above the surface of the workpieces to be joined together. It is not enough to just punch a hole. It is necessary to make funnel-shaped extensions on both sides of the opening, slightly larger than the diameter of the body of the rivet lining (with a cone reamer or a spiral drill with a smaller blade angle). The rivet head will now enter the funnel extension. By hitting the locksmith’s hammer, the standing body is simply pushed into the funnel-shaped expansion until it closes the metal surface well. A new rivet head, shaped by hammer blows, will be good if the visible body length is 1,2-1,5 times its diameter. If the rivet is short, it does not bind, while a longer rivet makes it difficult to rivet. The diameter of the hole drilled for the rivet body should exactly match its diameter. If possible, we use a drill bit of the same diameter, as it normally drills a larger hole.
“Dismantling” or removing the rivets gives us quite a bit of trouble. If the head of the rivet is bulging, we can remove it with a file and punch the rivet on the opposite side. When the head of the rivet is large, try to get the cutter from the side, between the head and the plate, and cut the head off the body of the rivet. Rivets with a lowered head cannot be removed in this way. In such a case, remove the recessed head of the rivet, in the funnel-shaped recess, with a suitable spiral drill, and knock out the rivet with hammer blows in the opposite direction (picture 2).
Figure 2 — removing a rivet
It happens that we need not a firm but a looser connection with a rivet (eg when attaching a hand on a dial). In this case, we use a rivet smaller in diameter than the hole and place a flat washer under the head. It is a well-known rule: A single rivet is not a rivet. In order to have a strong and not a loose connection, we will use at least two rivets. If, when hitting a rivet with a hammer, we hear a tinkling sound, we should know that its stem has broken. If the assembled workpieces move towards each other, this is a sign that we did not tighten the rivets enough or compress the ends well. You should also know that the rivets are standardized. Cold rivets have a diameter of 1 to 37 mm, with a length of 1,5 to 8 diameter. It is very important to use a rivet of the right size, because otherwise even a qualified worker will not be able to do the job easily.
Tubular rivets are also used (especially in telecommunications technology as well as in the handbag and decorative haberdashery industry). The stem and head of these rivets are hollow, so the heads will not be formed by hammering, but with a special tool.
Tightening rivets
A new way of riveting is the tightening of rivets, the essence of which is that the head of the tensioner’s stem does the fixing and tightening in order to form the rim of the tubular rivet. The tensioner stem breaks off beyond the tension limit. The rivet shank is tightened by the riveting pliers.
Rivets are standardized and can be open ended or closed ended as well as slotted. Open rivets are used to join thinner materials, primarily sheet metal, and rivets with closed ends are used for materials that cannot pass water and air. Grooved rivets are used for soft and crumbly materials (eg wood). The rivet head can be half-round or countersunk. Rivet stems that enter the rivet cavities can be short or long broken. The rivet head either fits into the hollow rivet seat or pops out. The rivet is made of aluminum, copper, mild steel, or a nickel-copper alloy (monel). The strength of the rivets depends on the quality of the material, thickness, type. Shear strength ranges from 60 to 150 kp. We drill the workpieces with a spiral drill with a diameter larger by 0,1-0,2 mm than the diameter of the rivet stem. Place the body of the fastening rivet into the opening of the riveting pliers, and the hollow rivet into the drilled hole. Applying pressure with these pliers on the workpiece, we clamp the handles towards each other. One tightening is not enough, but you should know that the body of the rivet usually breaks on the third tightening. After each tightening, we slide the pliers onto the rivet body. The advantage of blind riveting is that the riveting connections are the same, so poor performance is almost impossible. The coating from the painted surfaces does not splash during this work. In closed or hard-to-access parts of the workpiece (e.g. in pipes) only a space with a width of 4,8 mm is required to perform the sealing head. The tensioned material does not deform, even sheets with a thickness of 0,5 mm. We replace the rivet by drilling the rivet with a drill of the same diameter (picture 3).
Figure 3 — replacing a rivet
Screws
The most widely used connection elements that ensure the disassembly of the connected working elements are screws. According to the threads, screws can be: metric, fine, Whitworth and tubular. According to the shape of the head, we distinguish polygonal, grooved, countersunk, drilled, average screws, etc. This also applies to the nuts-nuts of the screws that we use when the screw is not accepted by the tapped threads of the hole, but by the thread of the nut at the other end of the smoothly drilled hole. Screws are usually made of steel, but copper, bronze and aluminum screws and nuts are also used. The support plates under the screw head prevent damage to the surface of the workpiece from the tightened head, do not allow uncontrolled unscrewing of the screw, as well as loosening, but transmit the clamping force to a larger surface.
Screws with metric threads are mostly used. The angle of the cut threads, the angle of their edges is up to 60°. The diameter of the screw thread is a whole or a tenth of a millimeter, and the pitch of the thread (by this we mean the movement of the screw in the direction of the longitudinal axis during one full turn) is also in whole millimeters. Standardized metric screws are given a thread pitch. For example, M 10 indicates a thread diameter of 10 mm with a thread pitch of 1,5 mm (this is also the distance between the threads). The finer thread, which is different from the previous one, is marked with M 10x1, which means that, unlike ordinary threads, it is more finely toothed, because the pitch of the thread is only 1 mm, i.e. smaller than the previous one.
Although less common, bolts with Whitworth threads are used (eg on English-made motor vehicles). They get their name from the name of the English factory that first standardized screw threads. Thread diameter is given in English inches, inches (1“=2,54mm), as well as an angle at the top of55°. The angle of inclination of the threads is determined by the number of threads in the length of one inch, ie. according to the number of “teeth” on the spindle, the length2,54mm. If the diameter of the thread is not a whole inch, we indicate it in the form of a fraction. When we encounter such a thread marking, such as7/8“, then it means that it is the diameter of the bolt22,2mm, and the number of teeth on one thumb is9, that is the pitch of the thread is2,8mm. A non-standard Whitworth thread is marked W 3/4x10. This means that the diameter of the screw is three-quarters of an inch (19 mm) with dense serrations, 10 serration teeth on one thumb length with a pitch of 2,5 mm.
The most common application is tubular threads in the execution of tubular installations. They are marked with the letter C, their values are given in inches and correspond to an angle of 55° at the top. The threads are relatively fine ie. with a greater number of “teeth”. We must be very careful that these thumb marks do not represent the diameter of the threads, but the inner diameter of the pipe on which the threads are threaded. Referring to the previous example, the designation C 7/8“ represents such a pipe thread, the outer diameter of which is 30,2 m, and one inch of pipe length is cut with 14 teeth with a pitch of 1,8 mm.
At the free end of the screw, the spindle gets threads, by which the nut is screwed with its own threads. The internal threads of the nut are formed in a pre-drilled hole, and the threads of the bolt are formed by tapping on the cylindrical body. The threads of the nut are slightly wider to accommodate the screw threads. That is why their diameters differ somewhat. By previously drilling a hole in the material and using a drill bit to cut the vine, we make threads in the nut. The diameter of this hole is equal to the screw core, and much smaller than the diameter of the thread. The core is the part of the screw after the thread has been removed. E.g., for metric threads of a nut with a diameter of 10 mm, we pre-drill a hole of 8,4 mm.
External and internal threading does not require any special expertise. It is important to give the spindle the appropriate dimensions of the thread, that is, the thread of the nut to cut to the prescribed dimensions of the core (picture 4). If the screw turns clockwise, it is a right hand screw. If, on the other hand, a screw with the same direction of rotation comes out of the hole, then it is a screw with a left-hand thread, which is marked by a small notch in the corners on the side of the head, while two more notches are marked on the head with a notch. Such a thread is marked on the drawing with M-10. If it is necessary to fasten the screws, without rough threads, we will perform threads with beginnings in several places. This is denoted by 3 beg. M 10x1, which represents a slot spacing of 1mm, although one turn lowers the screw by 3 mm. Screw threads are controlled by a thread gauge comb. A simpler solution than this is to compare a known bolt by placing it next to a bolt with unknown characteristics. Screws are the same if their threads touch the entire length of the spindle. The diameter is determined using a template.
Figure 4 — cutting a thread
Screws are turned with a screwdriver, a key and by hand. For working with a screwdriver, screws with a notch, with a cylindrical, half-round and countersunk head are used. Screws with a butterfly and slotted head are tightened by hand, and screws with a hexagonal and square head are tightened with wrenches. Special screws are supplied with hexagonal recesses. They are turned by means of a key with a hexagonal cross-section, which is inserted into the head of the screw formed in this way (such is used in MULTIMAKS machines for making tools). More and more in use are screws with a cross-shaped notch, which. require the use of a four-blade screwdriver. Nuts of various shapes are also produced (picture 5).
Figure 5 — types of screws
We have already said about screw keys that they must be exactly adapted to the screw head. This also applies to nuts used when using countersunk head screws. The screwdriver must not be sharp or blunt. The width of the blade should be adjusted to the length, and the thickness of the blade to the width of the notch. With a screwdriver, it is possible to turn a screw without a head, the so-called track bolts.
When applying nuts with heads that have a notch (we also call them knurled heads), a special fork-shaped screwdriver is used.
Several ways of working with the screw
Install small steel screws using a screwdriver with a magnetized end or a key. For our screw driving needs we can use soft metal wire with a loop end. If the head of the screw is broken off, we cut a notch on the screw into which we insert a screwdriver and remove the screw.
In the work, we pay special attention not to damage the screw threads. If it does happen, let’s try to trim the damaged part of the thread with a small hacksaw. Pre-testing the screw in order to shorten its height is performed only after we have already placed it between the soft jaws of the mangel, so as not to damage the threads. We first oil the steel screws, which are exposed to the weather, and screw them into place. If the screws are rusty, grease the threads with petroleum and after some time hit the screw head with a hammer.
On the screws, which we screw into soft materials, we must place a washer with a large diameter. It should be remembered that the screw threads do not catch close to the screw head unless we cut the thread on the stem to below the screw head.
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