tool called a caulking tool is used. This tool is about 3/16 in. thick at the end and 11⁄2 in. wide, with the edge ground to an angle of 80°. In case of boiler plates these are usually planed on edge to a bevel of about 75° to 80° to facilitate the forcing down of the edge. As shown in the diagram the effect of caulking is to burr down the plate at the joint, forming a metal to metal joint, care being taken not to damage the plate below the tool, or spring the joint open. Usually both

D

R

Fig. 9-Caulking.

edges C and D are caulked, and the rivet heads also, if they leak as at R. Caulking has no legitimate use in structural work. It is used to make loose rivets appear tight, instead of cutting out and replacing such rivets. It is also used when the edges of the rivet head are not quite close to the plates, or when an opening exists between the plates themselves. The edge of the rivet head is usually hammered down until it indents and slightly penetrates the surface of the plate. This makes a loose rivet appear tight when tested with a hammer. Close inspection should detect and condemn such rivets.

CHAPTER. V.

Riveting.

A Rivet is a pin of metal consisting of a “head” and a "shank" or cylindrical body which is driven through two or more pieces of metal, and then the point is bent or spread and beat down fast, to prevent its being drawn out.

Material. Rivets are usually made of soft steel or wrought iron. Copper rivets are sometimes used where iron. would corrode too quickly. The steel used for rivets will generally have an ultimate tensile strength between 52,000 and 60,000 lbs. per sq. in. In such steel the carbon may run down to .06 per cent. with the sulphur between .02 and .03 per cent. and phosphorus even lower. Rivet steel must be ductile and tough and must stand well the effects of variations in temperature. Wrought iron rivets are less affected by temperature than steel rivets. In driving field rivets or in riveting done after the parts to be riveted are in place, the usual method is to heat the rivets in a portable forge resting upon a temporary platform made of planks, and then each rivet is thrown through the air to the riveters at the various points where riveting is being done. While the rivet is thrown through the air it partly cools off. Steel rivets may thus cool down to a point where good riveting can no longer be obtained, while if the steel rivet is heated in the forge to a slightly higher temperature and then thrown through the air, the rivet is often injured and the steel composing it is red short or liable to crack at a red heat. Wrought iron is less liable to injury from overheating and is less affected by the drop in temperature immediately after leaving the forge. For these reasons wrought iron rivets are preferable to steel rivets for field riveting.

Manufacture. Rivets are made either by hand or by machinery. They are indicated by means of their length and diameter. The length of a rivet is the length of its shank when cold, and does not include the head. The size most commonly used is 3/4 in. diam. rivet. In order to allow the hot rivet to enter holes easily the holes are punched 13/16 in. diam. for a 3/4 in. rivet and in general 1/16 in. larger than the diameter of the cold rivet.

The hot rivet should not drop into the hole. It should require slight pressure to put it in. The diameter of the rivet holes must not be less than the thickness of the plate, other

wise the punch in the shop is liable to crush. For plates less than 5% in. 34 in. rivets are commonly used; for plates 5% in. and over, either 3/4 in. or 8 in. rivets are used.

The length of the rivet depends on the grip or total thickness of the parts joined by the rivet, and on the number of pieces to be joined by the same rivets. A hot rivet has a tendency to fill up any slight openings between the plates. through which it passes. Hence to find the length of the cold rivet add to the grip about 1/32 in. for each opening between plates; then add about 15% times the diameter of the rivet for the new head and about 8% for filling up the hole which is slightly larger than the rivet. For instance, to join two 3/4 in. plates with 34 in. rivets we need for:

to this add about 8% or 7/32 in. and this gives in all about 3 in. as the required length of shank for the cold rivet. The same value could be obtained from a table at the end of the volume which gives the length of rivet shanks to the nearest % of an inch. For countersunk rivets add only one half the diameter of the rivet for the new head. No rivets should be used which are too short; such rivets do not leave sufficient material for the new head and the usual result is loose rivets. Rivets that are too long require additional hammering and are hard to make tight.

Form of Rivets. There are in use several forms of rivets. These forms are generally indicated on drawings by the conventional signs shown in Fig. 10.

The diameter of a head of a rivet, when such head is finished with a tool called a "snap," should be about one and a half to twice the diameter of the shank.

The height of the head of a snap finished rivet should be about three-fifths the diameter of the shank.

Fitting Connections. Before riveting the two or more parts which are joined by this process have to be brought close together and in such a relative position that the corresponding rivet holes should match as nearly perfect as possible. In connections taking in a large number of rivets, like column splices or large gusset plates, the various pieces are made to match by hammering the buckled or bent parts with a sledge hammer and then by placing temporary bolts through about thirty per cent. of the rivet holes. When

these bolts are made tight, all the holes in the connection will match, if the shop punching was carefully done. With careless punching some of the holes may not fall fair anywhere from 1/32 in. to 4 in. and more. In such cases the holes are made fair by reaming, using either hand reaming or machine reaming. Where the rivet grip is to be two or more inches machine reaming is essential.

It is a common practice in building work where holes do not match by 1/16 in. or a little more, to drive a drift pin through the holes and make them match.

A drift pin is a round piece of steel made slightly tapering, and should be used only for easily bringing pieces together preparatory to riveting. The drift pin may also be used in correcting burrs and in smoothing out holes. It should not be used, however, to enlarge a hole. Forcing a drift pin through a hole injures the metal, causing a hardening of the material around the hole, with a corresponding increase in the elastic limit and a decrease in ductility. This is considered injurious, and good specifications prohibit the use of drift pins for enlarging holes. Instead of this, reaming should be used whenever possible. For this purpose compressed air reamers are employed on many good structures. The action of these reamers is similar to that of a drill of large diameter, and the holes are made perfectly smooth. In some cases it will be found that one or more holes have been omitted by mistake in some of the parts to be riveted. This can be remedied only by drilling through the blind hole. It also may happen that the men in the shop have punched more holes than required. In good work any hole which is not to be filled in by a rivet or bolt is plugged up with lead. This prevents corrosion to a certain extent; it also fills up the cross section, which is desirable in compression members.

Riveters. The work of fitting up connections is partly done by "fitters" and partly by the riveting gang. A riveting gang consists usually of four men, i. e., heater, passer, holder up, and riveter. Such a gang will drive about 250 rivets in a day of eight hours. Each man gets about five dollars a day, and adding to this the cost of supervision and of the materials, together with the depreciation of tools, etc., the cost of field rivets will not be far from ten cents apiece. Where two or more riveting gangs are employed there is usually a boss riveter and fitter, at about six dollars a day, who is responsible to his superintendent for the work done by the riveting gangs and fitters.

Tools and Instruments Used in Riveting. Following are the essential parts of a riveting outfit: