General-purpose workholders are the simplest and most-basic workholding devices. They are also the most-universal workholders. General-purpose workholders include machine vises, self-centering vises, collet chucks, collet vises, and chucks. They usually hold regular or symmetrically shaped workpieces; squares, rectangles, cylinders, hexagons, and similar part shapes. Although they lack the ability to hold specialized part shapes, they are still widely used. With modified clamping elements, many general-purpose workholders can be adapted for special part shapes.
MACHINE VISES AND VISE JAWS
Machine vises are among the most-common workholders used in manufacturing today. Their main benefits include self-contained workholding capability, a relatively fast clamp/unclamp cycle, accurate machine-table mounting, a solid fixed jaw for part location, and good rigidity.
Bench Vise vs. Machine Vise
Bench vises, or Mechanic's vises, are not held to the same standards as a quality Machinist's vise. Bench vises may be constructed from 30,000 psi ductile iron and often have a cast in anvil and pipe jaws for general fabricating. Bench vise jaws are often serrated and may be permanently mounted. Machinist vises will be constructed from stronger materials and have hardened, precision ground guide rails and jaw pockets that are held to higher tolerances for being parallel and perpendicular. Jaws themselves are also held to higher tolerances and are often exchangeable to accommodate different part shapes. Machine vises will not have an anvil and should never be struck.
Although manual vises are still frequently used in some areas of manufacturing, power vises are usually the best choice for high-production machine tools. There are several different types of power actuation, ranging from power assist to fully automatic operation, as shown in Figures 3-1 and 3-2. The following are the basic methods of vise operation.
Manual. Manual vises are found in almost every shop, in many varieties and sizes. Manual vises are the most-common and usually the cheapest type of vise. These vises are hand operated using a crank handle or similar device. Usually a simple lead screw advances the sliding jaw, clamping against the fixed jaw.
Hydraulic. Hydraulic vises provide highly consistent clamping force. After initial adjustment to the workpiece, these vises clamp automatically at the push of a button, powered by an external hydraulic power unit. Hydraulic vises can be used individually or gang mounted for multiple-part setups, Figure 3-3, controlled individually by clamping valves.
Figure 3-1. Hydraulic vises provide automatic power clamping with exact high force at the push of a button (external power unit required).
Figure 3-2. Hydra-mechanical vises are manually operated, but final force is applied easily using hydraulic power assist.
Figure 3-3. Five hydraulic vises mounted side by side, operated independently by five clamping valves (using one hydraulic power unit).
Hydra-Mechanical. Hydra-mechanical vises are self-contained power vises that require no external hookup. Turning the crank handle clockwise moves the sliding jaw mechanically toward the workpiece. Once contact is made, further turning automatically disengages the spindle screw and gradually applies full hydraulic pressure, with relatively little effort. Some of these vises are equipped with a gauge to allow the operator to monitor the clamping force applied, Figure 3-4.
Figure 3-4. Hydra-mechanical vise equipped with a force gauge.
Pneumatic. Simple pneumatic vises are powered directly by air pressure, not hydraulic power. Since typical shop air systems operate at only 80-100 psi, large air cylinders are required, and still provide only light clamping force.
Types of Machine Vises
There are countless varieties of vises, but the following are the major categories of machine vises used in production applications.
Figure 3-5. Precision milling vises are usually mounted directly on a T-slotted machine table. Swivel bases and compound-angle bases are also available.
Precision Milling Vises. This type of vise, Figure 3-5, is commonly used on vertical milling machines and other machine tools with T-slotted tables. These vises are slotted underneath for accurate two-axis positioning using fixture keys. Optional swivel bases and compound-angle bases can be used for machining at angles.
High-Precision Machining-Center Vises. These vises, Figure 3-6, have locating holes to allow mounting vertically or horizontally with excellent repeatability. They are specially designed to mount on horizontal-machining-center pallets, as well as vertical milling machines, providing zero-position referencing in all three axes. Machining-center vises can be mounted in multiples on modular tooling blocks, with up to eight vises per pallet.
Figure 3-6. High-precision machining-center vises have locating holes to allow mounting vertically or horizontally with excellent repeatability in all three axes. They are ideal for mounting in multiples on tooling blocks.
Figure 3-7. Double vises are high-precision vises that allow clamping two workpieces, against a fixed center locator, in about the same space as a normal vise.
Double Vises. These high-precision vises, Figure 3-7, allow clamping two workpieces, against a fixed center locator, in about the same space as a normal vise. This type features the same accurate location in all three axes as high-precision machining-center vises.
Figure 3-8. Modular vises are high-precision vises consisting of self-contained fixed-jaw and sliding-jaw units that mount on modular tooling plates and blocks for total flexibility.
Modular Vises. These high-precision vises, Figure 3-8, consist of separate, self-contained fixed-jaw and sliding-jaw units. The jaw assemblies mount on modular tooling plates and blocks for accurate three-axis location.
Any of these vises can be easily mounted on Carr Lock® Fixture Plates. The jig saw for of the fixture plate enables dense mounting on the Carr Lock® subplate, Figure 3-9. Mounting the vises on the fixture plates allows the operator to take advantage of the same quick change features as other Carr Lock® fixtures.
Figure 3-9. Jigsaw Vise Plates have an interlocking design to allow moutning vises and other narrow fixtures close together.
Selecting appropriate vise jaws is just as important as selecting the proper vise. Figure 3-10 shows some of the types available. The standard jaws on most vises are plain hardened-and-ground flat jaws, sometimes with serrations for extra gripping force. Soft jaws can be machined to make custom vise-jaw fixtures. Optional vise jaws, Figure 3-10, are also available to expand a vise's versatility.
Figure 3-10. Vise jaws are key to a vise's productivity. A large selection of standard jaws reduces the need to machine custom vise-jaw fixtures.
Step Jaws. These jaws allow clamping a rectangular part high up in the vise without using parallel blocks. This raises short workpieces for easier access, and also provides tool clearance between the work-piece and vise bed. Each jaw has both a high and low step. Steps are precision ground to maintain accurate height and positional location. Step jaws should be used only in pairs.
V Jaws. This jaw has precisely ground V grooves to allow clamping cylindrical workpieces in either horizontal or vertial position. A V jaw is usually used together with a standard flat jaw.
Swivel Jaws. This jaw has a swiveling face for securely clamping a workpiece that has nonparallel sides. The contact face swivels up to 5 in both directions. A swivel jaw should be used together with a standard flat jaw.
Dovetail Jaws. Dovetail jaws allow clamping a workpiece (with matching dovetails cut into the bottom of the two sides) very low on the part. Because of the dovetail feature, the vise can apply high clamping force while holding a very small portion of the workpiece. This can allow machining on five sides of the workpiece. When the machining is completed the bottom of the workpiece must have the dovetail portion removed in a separate operation. See Figure 3-11.
Figure 3-11. Dovetail clamping provides full access for 5-axis machining.
Collets and collet vises are another popular form of general-purpose workholder. Like chucks, collets, and collet vises have many design advantages that make them very attractive and cost-effective workholders.
Types of Collet Vises
Collet vises come in two general forms, single collet vises and tripe collet vises. Both styles of collet vises are hydraulically operated and provide adaptable ways to clamp collet-mounted workpieces. Each of these vises can be used with any standard or special 5C collet. This includes standard collets, step collets, expanding collets, and emergency collets. Both vises can be set up individually, or gang mounted for multiple-workpiece machining setups.
Single Collet Vises. The single collet vise, Figure 3-12, is designed for single-part applications where only one collet is needed. These collet vises have two clamping cylinders, one on each side of the collet, to provide a smooth and uniform clamping motion. When the power is released, a dual-spring return mechanism releases the collet. Mounting holes in the vise body permit the single collet vise to be mounted either vertically or horizontally, as needed. An adjustment-screw plug is provided in the base of the vise, Figure 3-13. This plug permits the height of shorter workpieces to be precisely adjusted and set. For applications with longer parts, or for bar feeding, the adjustment-screw plug can be removed, Figure 3-14.
Figure 3-12. The single collet vise is an accurate and versatile fixture for round, square, and hex-shaped parts.
Figure 3-13. The adjustment-screw plug in the base of a collet vise permits workpiece height to be precisely adjusted and set.
Figure 3-14. The adjustment-screw plug can be removed for longer parts or bar-feeding operations.
Triple Collet Vises. The triple collet vise, Figure 3-15, is designed for multiple-workpiece applications. These vises, like the single collet vise, have two clamping cylinders and two return springs for each collet. Like the single collet vise, the triple collet vise also has a removable adjustment-screw plug for each collet in the base of the vise. Both the single and triple collet vises can be mounted together to accommodate multiple-workpiece setups, as shown in Figure 3-16.
Figure 3-15. The triple collet vise.
Figure 3-16. Both the single and triple collet vises can be gang mounted for multiple workpiece setups.
There are several types of collets available for workholding. Of these, the most popular is the 5C style, Figure 3-17. These collets are made in a variety of forms, but the standard round, square and hexagonal are the most common. Standard 5C collets are well suited for workholding applications. Since they are standard, off-the-shelf items, no machining is required.
Figure 3-17. 5C-style collet.
Round. Round 5C collets, Figure 3-18(a), are the most popular collet. These collets are for round workpieces or bar stock. Round 5C collets are made in standard sizes ranging from 1/64" to 1-1/16" in 1/64" increments.
Square. Square 5C collets, Figure 3-18(b), are a variation of the round collet. They are designed for square workpieces or bar stock. Square 5C collets are made in standard sizes ranging from 3/64" to 3/4" in 1/64" increments.
Figure 3-18. Round (a), square (b) and hexagonal (c) 5C-style collets.
Hexagonal. Hexagonal 5C collets, Figure 3-18(c), are for holding hex-shaped workpieces and bar stock. Hexagonal 5C collets are made in standard sizes ranging from 1/16" to 7/8" in 1/64" increments.
Step collets, Figure 3-19, are an enlarged version of the standard 5C collet. Step chucks have a shallow gripping capacity, so they are most commonly used for thinner workpieces with larger diameters. These collets are available in sizes ranging up to 6/00" in diameter.
Figure 3-19. Step collets are available for larger diameters.
Expanding collets, Figure 3-20, are a unique-but-popular collet. Unlike conventional collets that grip a workpiece on the outside and squeeze inward, these collets grip the workpiece in an internal bore and push outward. The machine-mounting end of the collet is the same shape as that for other 5C collets. Expanding collets are used to internally hold parts with diameters up to 6.00". These collets have less gripping force than conventional collets, so they are best suited for medium-duty clamping.
Figure 3-20. Expanding collets are used for clamping an internal diameter.
Emergency collets are another 5C-collet variation. Emergency collets are made with a standard collet mount that is hardened and ground to size. The opposite end of the collet is soft and can be machined to meet individual workpiece requirements. Emergency collets are available in two basic styles, collet and step collet. The collet style, Figure 3-21, externally holds smaller parts and the step collet style, Figure 3-22, is for parts to 6.00" in diameter. The collet type can be used for longer parts, providing the diameter is smaller than 1.063". The step-collet type is for larger-diameter parts that are relatively thin, .50" or less.
Figure 3-21. Emergency collets can be customized for clamping odd shapes.
Figure 3-22. Step-type emergency collets hold larger odd-shaped parts.
These collets must first be machined to size. The collet is mounted in a lathe, or other machine tool, and machined to the desired form. Each of these collets is furnished with three pins between the gripping segments in the soft end, Figure 3-23. The pins must be in place while machining the collets to size. Once the collet is machined, the pins are removed. For most applications these collets are used in their as-machined condition. For longer production runs, they occasionally require hardening.
Figure 3-23. Each emergency collet is furnished with three pins to keep the gripping segments properly spaced and rigid during machining.
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This page contains information originally published in the Jig & Fixture Handbook, 3rd Edition, Copyright 2016, Carr Lane Manufacturing Co., St. Louis, Mo.