Die-Setting Fasteners—What Every Press Technician Should Know
January 23, 2025Comments
Die-setting fasteners are subject to cyclical loading due to vibrations from the stamping process and the retorquing required with reuse. Thus, die-clamping systems should incorporate redundant fasteners in the event that one setup should fail.
Two methods of die-setting fasteners find widespread use. T-bolts (typically 1-in. dia.) and nuts are the preferred method. The other frequently used system: a bolt and T-nut combination. Because T-nuts must fit inside of the bolster T-slots, the threaded hole in the nut typically measures ¾-in. dia., which offers about 60% of the tensile strength of a 1-in.-dia. bolt of the same grade. For equivalent clamping force, nearly twice as many clamps are required with the bolt and T-nut arrangement.
When using the bolt and T-nut arrangement, select a bolt that enters the T-nut threads equivalent to the bolt diameter, at minimum. That is, if the bolt diameter measures ¾ in., then the bolt threads must enter into the T-nut threads at least ¾ in. The preferred engagement is 1.5 times the bolt diameter. The proper-length bolt will require no more than two washers, with the bolt threads not extending beyond the bottom of the T-nut. Ensure that the selected bolts or studs are straight and that the threads are not damaged. To avoid wrench slippage, ensure that the hex head does not have rounded corners.
At minimum, stampers should use SAE Grade 5 fasteners for die-setting purposes. These fasteners are alloy steel, heat treated and tempered to industry standards. All U.S.-made specification fasteners feature a manufacturer’s mark or logo on the head in addition to the grade marking. A bolt without a manufacturer’s designation may be imported and fail to meet established specifications.
Avoid the use of plain-carbon or soft bolts, which provide half the strength of Grade 5 bolts. Never use commercial threaded rod, as there is no way to know its mechanical strength.
Die-Setting Washers
When selecting washers, the ID of the washer should fit freely over the bolt with little play, and the OD should extend beyond the mounting hole or slot.
Common flat washers are not suitable for die clamping. Use only large, thick, carburized-steel washers designed for die setting. Recommendations for a ¾-in.-dia bolt are a ¼-in.-thick washer and a 1-in.-dia. T-bolt, which requires a 9/32-in.-thick washer.