Alignment pins serve a variety of functions with jigs and fixtures. Most commonly, these devices align the workpiece to the workholder, or position removable workholder elements. Alignment pins come in many types, styles, and sizes for many applications.
Plain Alignment Pins
Plain alignment pins, Figure 7-57, are the simplest form of alignment pin. The five primary types are L pins, T pins, jig pins, shoulder pins, and clamping pins. Each is made with a precise-diameter locating pin to ensure proper alignment. All but the clamping pin have a bullet-nose end for easy insertion into the mounting holes. The clamping pin has a threaded end to permit a fixed installation. It also comes with a bushing that is positioned and fixed at assembly.
The specific mount for the alignment pins is determined by the application. In some cases, the pins are installed in drilled and reamed holes. For more precision or for longer production runs, they are installed in hardened bushings. Slotted locator bushings, Figure 7-58, are used to line up two sets of holes without binding. The design of these bushings is similar to that of floating locating pins and permits movement in only one direction. As shown, the bushings are installed and correctly aligned in the mounting plate with a dowel pin.
Slotted bushings are also available with a knurled outside diameter. These bushings can be either cast in place or potted in a plastic compound.
Locking Alignment Pins
In addition to the plain style, L pins, T pins, and clamping pins are also available with locking bushings. As shown in Figure 7-59, locking-pin bushings are installed in the mounting plate and securely attach the alignment pin to the plate. The spring clip ring in the locking-pin bushing holds the alignment pin in its retracted position by engaging the groove at the end of the pin. The ring also puts spring pressure on the pin at any intermediate position. This is useful for holding the pin in position if the workholder is turned upside down.
Quick-Release Alignment Pins
Quick-release pins have an integral locking mechanism in the pin itself, which retains it in the hole. The simplest quick-release pin is the detent pin, Figure 7-60. It has a simple spring-loaded dual-ball arrangement. The pin is simply pressed in or pulled out, against light spring force, which extends the balls. These detent pins are available in either zinc plated steel, or stainless steel. Marine Detent Pins are made of 316 stainless steel for extra corrosion resistance. Economical solid alignment pins with a ground shank, this type of Detent Pin has a ring instead of a solid shoulder, for applications where exact grip length is not important. Threaded Detent Pins are solid alignment pins with a ground shank and a threaded end for a knob handle. The threaded end accepts virtually any type of knob handle. These handles are available in steel, stainless steel, and several different plastics. Knob handles can be permanently secured with thread-locking adhesive if desired. Threaded Detent Pins are available in 300 series stainless steel only.
Another variation is the Ball Lock Pin. This group includes single-acting Ball Lock Pins, double-acting Ball Lock Pins, adjustable Ball Lock Pins, and Lifting Pins. These pins are similar to the detent type, except they have a positive ball locking mechanism. Single-acting pins, Figure 7-61, are installed and removed by pushing a button to unlock the balls. Double-acting pins, Figure 7-62, are released by either pulling or pushing the handle. Double-acting pins are available with a “drive out” feature. This allows removing the pin by driving it out of the hole with a hammer blow to the end of the activating spindle, which protrudes from the body of the pin for this purpose. Both single- and double-acting Ball Lock Pins have a fixed grip length. They are available in a range of standard lengths from ½” to 6”, in one quarter inch increments. Special lengths are also available made to order. When grip length must be fine-tuned while in use, the adjustable Ball Lock Pin, Figure 7-63, can be used. This pin’s grip length is adjusted ±1/4” by turning the handle, then locked in place with a knurled lock nut. Marine Ball Lock Pins are similar to standard single-acting Ball Lock Pins in stainless steel, except this
type has its handle and button made of 300-series stainless steel (instead of aluminum) for extra corrosion resistance in marine environments. Marine Pins come in three handle styles: Button (B), Recessed Button (M), and Ring (R). Heavy Duty Ball Lock Pins are a larger, heavier handle for rough service. These pins are only in stainless steel and the handles are made of solid stainless steel for maximum impact strength, and are specially shaped to prevent accidentally pressing the release button. Ball Lock Receiver Caps are ideal for securing Ball Lock Pins used in clevis applications, especially when the through-hole has excess clearance. The Receiver Cap’s inside diameter fits the Ball Lock Pin exactly, and is stepped to provide a perfect locking surface for the balls. The Receiver Cap is tapped to allow fastening the terminal end of a standard Ball Lock Pin cable assembly, and includes a fastening screw. Using a Receiver Cap reduces the Ball Lock Pin's
effective grip length, so this must be included in the grip length calculation.
Another specialized single-acting ball lock pin is the lifting pin, Figure 7-64. Lifting pins have a solid, one-piece
body with four locking balls and a forged shackle for heavy lifting. As with all lifting devices, please observe the
The Carr Lock® System, Figure 7-65, is a combination locator and clamp based on ball lock pin principles. Each mount consists of three components: (1) a Carr Lock® pin/clamp with a precisely ground shank; (2) a liner bushing in the top plate, either plain or slotted; (3) a receiver bushing in the subplate. Turning the clamping screw with a hex wrench advances the large center ball, pushing the three clamping balls outward. The combination precision locating and quick-locking features enable their use for mounting tooling plates. For more information on the Carr Lock® System, please see Chapter 5 on Quick Change Fixturing.
Yet another type of quick-release pin is the expanding pin, Figure 7-66. Expanding pins are precision alignment pins that expand up to .006” to tighten up hole clearance. The pin is actually an assembly of female split bushings separated by male segments, on a center spindle, that expands when drawn together. This assembly provides excellent shear strength, comparable to a solid pin. Expanding pins are available in two versions, actuated either by cam handle or by tightening with a wrench.
Cable assemblies attach alignment pins and other items to a workholder. Attached to the workholder, as shown in Figure 7-67, the items remain handy and less prone to loss or misplacement. Cable assemblies and their individual parts are available in many types, sizes, and lengths to suit almost every application. These cable assemblies are available in a variety of sizes, lengths, and with various cable rings or tabs attached to either end.
The nylon lanyard has one eyelet end and one loop end (Figure 7-68). The eyelet end can be fastened with a screw. The loop end is supplied open – simply snap together to create a permanent assembly. Snap assembly allows on-site attachment without a crimping tool. These economical lanyards are ideal for applications where the attached item is occasionally removed, by cutting the lanyard, and replaced. They are made of Zylex high strength nylon. A minimum pass-through diameter of 3/8" is required for attachment.