bucker
A holder-up; one who bucks rivets, typically holding a heavy bucking bar against the bucktail of a rivet which is heated if necessary till it is soft, while the riveter (or gunner or, before mechanisation, basher) uses a rivet gun (an adjustable pneumatic hammer) fitted with a rivet set, against the factory head to provide impulses which upset the bucktail into a field head.
bucker: the anvil end of riveting
A bucker is the worker who holds a bucking bar against the tail end of a rivet while a riveter drives the factory head from the opposite side. The bucking bar is a heavy steel tool, often weighing 3 to 10 pounds, shaped to match the profile of the rivet head being formed. The bucker must press this bar firmly against the soft, heated rivet tail while the riveter strikes the factory head with a pneumatic gun, creating the impulses that compress and upset the tail into a permanent field head.
Bucking is fundamental to structural riveting in shipbuilding, bridge construction, and aircraft assembly. The rivet must be heated to around 1000 to 1100 degrees Fahrenheit to remain plastic during upsetting; a cold rivet will shatter under hammer blows. The bucker controls this heating process in traditional work, often using a torch or furnace nearby, and must judge when the metal has cooled enough to handle but remains soft enough to form. This judgement directly affects joint quality: an undertreated rivet stays brittle; an overtreated one loses strength.
The physical reality of the role
Bucking is physically demanding and hazardous. The worker must position themselves on the opposite side of the joint from the riveter, holding steady pressure on a heavy bar while enduring vibration, noise, and radiant heat from the rivet. Poor bucking results in incomplete upsetting, leaving voids in the field head and weak joints. The work requires coordination with the riveter: the bar must be withdrawn immediately after upsetting to avoid the rivet welding to it as it cools. Timing is tighter in hot riveting than cold, and mistakes are expensive.
Modern bucking has largely been displaced by pneumatic rivet guns with self-contained bucking anvils, and by welding or bolting in many applications. However, the term persists in metalworking vocabulary and the role remains essential in restoration work and in shops that maintain riveted structures. The bucker's skill set, once a core trade apprenticeship, is now uncommon but still valued where structural integrity depends on sound riveting.