Traditionally, in the metalworking industry, machinists were prized for their ability to achieve precision results through their creative fixture construction and their ability to maximize output. One of the shortcomings of this approach was the very individualized results achieved this way. This methodology had numerous limitations including the need to build the fixturing each time the job was run, resulting in variations in output and quality. Setup time was a serious limitation in overall productivity, as well. With the growth in the popularity of CNC machines, much of the variability was removed; however, setup was still a serious concern.
In recent years, a new approach to fixture construction and change out has been developed. The Carr Lock® System is an approach that takes advantage of the features of the newest machine tools, such as extreme accuracy and high speeds-high forces, and the increased emphasis on maximizing spindle utilization to dramatically improve productivity. See Figure 5-1. Using this system allows fixture change out to be completed in minutes (or even seconds) rather than hours, since the fixture is always in the same location on the machine table as it was the last time it was run. This setup reduction becomes very powerful in maximizing machine utilization as well as facilitating smaller run quantities to aid in creating a lean environment.
The clamps have precision ground shanks available in sizes 13mm, 16mm, 20mm, 25mm, 30mm, 35mm, and 50mm. They come in lengths for standard plate thicknesses, (two lengths for each diameter) in either metric lengths from 13mm to 25mm for metric plates, or 0.50” to 2.00” for inch dimension plates. Carr Lock® Clamps are actuated by turning the clamping screw with a hex wrench, which advances the large center ball, pushing the three clamping balls outward. These balls engage the angled ID section of the Receiver Bushing, pulling the clamp firmly downward. See Figure 5-2. Clamps with 16mm and 20mm shank diameter are optionally available with a Knurled Head Screw for quick, tool-less actuation.
The Carr Lock® System requires that each fixture plate have one mounting hole designated as the primary reference hole (Primary Liner Bushing) and one mounting hole designated as the secondary reference hole (Secondary Liner Bushing or Slotted Locator Bushing). All other mounting holes should be drilled clearance holes not locating, .015-.030" over nominal size used for clamping only.
Secondary Liners have slight ID clearance (+.0010/+.0020" tolerance) to avoid binding. Slotted Locator Bushings have a tight ID tolerance in one direction and full relief in the perpendicular direction. Slotted Locator Bushings provide better accuracy than Secondary Liners, but take a few extra steps to install, and are not available in all sizes.
The accuracy and the holding force of the Carr Lock® System require the clamps be used with the appropriate receiver bushings. Receiver bushings come in two styles, face mount or back mount. The face mount bushings (Figure 5-3) are a slip fit into a precision bored hole and are held in place with three Socket Head Cap Screws, while the back mount bushings (Figure 5-4) are a light press fit installed from the bottom of the fixture plate.
With either bushing type, the installation holes must be jig bored for accurate size and location. Installed bushings will be approximately .012" below the subplate’s top surface.
Due to the highly efficient design of the clamps, the torque required to clamp them is fairly low – one foot pound of torque on the 13 mm diameter clamp delivers 750 pounds of hold down force. On the largest size, 50 mm, 38 foot pounds of torque will result in 20,000 pounds of hold down force. Given the low amounts of torque required, preset torque wrenches are available to prevent the application of excess torque, which can break the clamps. These wrenches, with attached hex driver, are available for the 13, 16, 20 and 25 mm diameter clamps. See Figure 5-5.
For reasons of simplicity, pre-assembled kits are available for many machines, from table sizes of 12” X 14” to 500mm X 1000mm (20” X 40”). These kits include not just the subplate, fixture plate(s), and the appropriate number of clamps, but also all items needed to mount the subplate on the machine, T Nuts, Socket Head Cap Screws, and Sure-Lock™ Fixture Keys. Two locating holes for Sure-Lock™ Fixture Keys are provided for alignment with a slotted machine table. Fasten to the machine using the four, six, or eight mounting slots provided, with Socket Head Cap Screws and T Nuts to match the machine table.
VERTICAL QUICK-CHANGE SYSTEMS
VERTICAL QUICK-CHANGE SYSTEMS
These quick change systems can be applied to either horizontal or vertical machines. We will first discuss the vertical application. The Carr Lock® system for verticals utilizes a subplate with high-precision bushings installed and interchangeable fixture plates that can be mounted and removed quickly.
The subplate is essentially permanently attached to the machine table. Once it is properly located and fastened, it is ready for the mounting of the fixture plates. Each subplate is made from A-36 precision ground plate, and contains a series of highly accurate receiver bushings to allow the mounting of different sizes and styles of fixture plates. These plates, and their associated kits are readily available for many popular machine table sizes, from 12” X 14” up to 500 mm X 1000 mm (20 in. X 40 in.). Different subplates have varied sizes and arrangements of receiver bushings allowing the installation of different fixture plates, including multiples, up to four vise plates on the largest subplates. Using multiple fixture plates, or vises, allows the machining of two or more different parts in the same machine cycle.
Made from MIC-6 aluminum, fixture plates are available to fit any of the various subplates, from 12” X 14” to 500mm X 1000mm (20” X 40”). As shown in Figure 5-6, each plate has two bushed holes, one a primary liner, and the other a secondary liner. The other two holes in the plate are clearance holes which are used for clamping, but not location. Carr Lock® Fixture Plates also have two fixture-key holes for conventional mounting directly on a slotted machine table using Sure-Lock™ Fixture Keys. Vise fixture plates for mounting vises are also available in a design that allows the maximum utilization of the machine by mounting up to four vises on one subplate. (Figure 5-7.)
Fixture Plates are also available for use with vises, when shorter run jobs are necessary. Called “Jigsaw Plates,” these vise plates nest, or interlock, to maximize the number of vises that may be mounted on one subplate. See Figure 5-8.
As with most tooling items, these plates can be produced by capable machine shops, but are probably more economically obtained commercially. Still, it may be necessary to construct a custom fixture plate that takes advantage of the accuracy and quick-change features of the Carr Lock® System. Each top plate should have one Carr Lock® Mount designated as its primary reference point, and one as its secondary reference point. These two mounts should be as far apart as possible. The secondary reference point should have a relieved liner to avoid redundant location, which can result in binding. Additional Carr Lock® Mounts can be used for more clamping force, but these should be installed in clearance holes, .015”-.030” larger, not locating liners. Note that the same Carr Lock® Clamp fits any type of liner or a clearance hole. (Still use four Receiver Bushings in the subplate.)
When making your own fixture plates, plate thickness must be ±.005 inches to achieve proper clamping force. Extra-thick top plates can be counterbored to achieve proper clamping thickness Special-length Carr Lock® Clamps are also available, as specials. See Figure 5-10.
Fixtures built on these plates are easy to install and remove, simply tighten or loosen the four Carr Lock® clamps, as appropriate. The precision of the clamps and bushings in the system provides highly repeatable location of the fixture in a minute or less, allowing the operator to move from one job to another quickly.
Given the high precision inherent in the Carr Lock® System, it is often ideal to machine the fixture plate on the machine on which it will be run, or, at least, another precision machine with a Carr Lock® subplate installed. A consideration to keep in mind in these cases is avoiding damage to the subplate, which can be caused by drilling or milling through the fixture plate. An easy way to avoid this is through the use of a Carr Lock® Machining Kit. The kit consists of four extra-long Carr Lock® Clamps, used together with four precision-height spacers, providing ample clearance underneath the fixture plate to allow through-hole machining without damaging the subplate. The kit also includes an extra four spacers to use as additional supports under large plates. See Figures 5-11 and 5-12.
One concern that may arise when using a fixture plate or plates on a larger subplate is the propensity of chips to collect in unoccupied receiver bushings. An easy solution to this condition is the use of Carr Lock® plugs. See Figure 5-13. These plugs are designed to close off the hole, and prevent chips from packing into bushings and necessitating lots of work to clean them out so they may be used for the next setup, thus negating much of the “quick change” aspect of the system. These inexpensive plastic plugs are easy to install and remove since they are a light press fit in the bushing. They are available for all sizes of receiver bushings.
The adaptation of Carr Lock® fixturing for horizontal machines has a different approach. Here, the fixture plates are mounted on a tooling block (tombstone) that contains four receiver bushings and acts as the subplate. See Figure 5-14. The one-piece cast aluminum alloy construction provides superior accuracy, dimensional stability, and vibration dampening. These columns are available for 400mm and 500mm pallet sizes, with universal mounting holes to fit almost any inch or metric slot spacing. Dual mounting capability allows both JIS mounting (locating from two reference edges) and DIN mounting (locating from a center hole and radial slots) with excellent accuracy. The material is A713 Tenzaloy aluminum alloy, aged to T-6 condition.
Carr Lock® Horizontal fixture plates are available in plain steel or aluminum, with multi-function steel plates, or aluminum vise plates. Carr Lock® Blank Fixture Plates (Figure 5-15) provide an excellent base for most dedicated fixtures. These 1.250"-thick steel plates provide sufficient depth for tapping and other machining required to mount fixture components, while also providing excellent rigidity. Each fixture plate has four mounting holes for Carr Lock® Clamps – two with liner bushings for fastening with accurate location, the other two for fastening only. All three styles of fixture plates are available for 400mm and 500mm pallet sizes.
Carr Lock® Modular Fixture Plates are identical to blank Carr Lock® Fixture Plates, except with added multipurpose mounting holes in a standard 2.0000" grid pattern. Every multipurpose hole has a .5000" precision alignment bushing on top, with a 1/2-13 thread below it. Multipurpose holes accept Locating Screws (with a ground locating diameter), Socket Head Cap Screws, clamping studs, and many other threaded components.
Carr Lock® Aluminum Blank Fixture/Vise Plates are ideal for mounting vises or existing fixtures on a Carr Lock® Tooling Block. These lightweight, .750"-thick plates are machined from MIC-6 cast aluminum alloy.
The machining of horizontal fixture plates is best done with the use of a machining kit to avoid damage to the tooling block when building the fixture plate. Again, fixture accuracy is increased by machining the fixture plate on the machine on which it will be run.
FIXTURING FOR 4- AND 5-AXIS MACHINES
FIXTURING FOR 4- AND 5-AXIS MACHINES
The increasing popularity of machines designed to perform operations on four or five sides of a part in one setup has fostered demand for a way to securely hold the part while it is machined on all of those surfaces. Machining in this way simplifies the problems associated with maintaining a tight tolerance relationship between features on more than one side of the part without extensive setup.
One of the primary concerns is preventing interference with the machine quill when working low on the part. This necessitates raising the part off the machine table. The CL5® system achieves this with a riser. These risers can be “zero point” devices, which are also quick change devices.
Subplates. The foundation for this system is one of three subplates, 250mm and 310mm round plates and a 630 X 500 subplate, which is round with flat sides for the 500mm dimension. See Figure 5-16. Each of these subplates is also a multi-function plate, and so would allow the construction of a fixture directly on the subplate, if desired.
These subplates can be precisely located by first installing a Center Locating Key that matches the table’s center-hole diameter in the plate’s 25mm bottom center hole. For exact radial orientation, install a Step Fixture Key that matches the table's slot width in the plate’s 20mm bottom slot. Fasten the plate to the machine table with four 1/2-13 x 1.50 or M12 x 35mm Socket Head Cap Screws and T Nuts to match the table slots. Following these steps will allow exact location of the riser and top tooling every time it is placed on the machine, simplifying setups and increasing accuracy.
Riser Blocks. The best way to raise parts to be machined off the table is through the use of a riser block. There are two styles of risers, a simple riser and a quick-change/zero-point riser. The simple risers are made from cast sections machined to mount on either the machine table or a modular subplate. These risers come in five sizes from 3 X 3 X 3 to 4 X 4 X 11. While the four largest are able to be attached to a multi-function subplate as well as the machine table, the smallest is made to attach to a multi-function subplate. The two smallest risers are blank on the top, allowing you to build your fixture directly on them, the three largest are pre-machined for mounting a vise. See Figure 5-17.
Figure 5-17. Riser blocks for 5-axis machining.
To locate the Riser Block at the exact center of a rotary table, first install a Center Locating Key that matches the table’s center-hole diameter in the riser's 25mm bottom center hole. For exact radial orientation, install a Step Fixture Key that matches the table’s slot width in the riser's 20mm bottom slot. Fasten the riser to the machine table with two 1/2-13 x 1.25 or M12 x 30mm Socket-Head Cap Screws and T Nuts to match the table slots.
Quintus Quick-Change Risers provide accurate location and secure clamping while also providing quick-change capability and elevating the workpiece for improved spindle access – all in one compact unit. To locate and clamp a fixture, the Quintus 1 riser utilizes two integral locating pins, a round pin for zero-point centering and a diamond pin for single-axis centering, and a single pull-down bolt that provides 2,700 lbs. of pull-down force. See Figure 5-18.
There are two other sizes of the Quintus riser, Quintus 2 and Quintus 3. The Quintus 2 riser utilizes two pull down bolts – one with zero-point centering, the other with single-axis centering – providing 2 x 4,500 lbs. of pull-down force. To locate and clamp a fixture, the Quintus 3 riser utilizes three pull-down bolts – one with zero-point centering, one with single-axis centering, and one without centering – providing 3 x 4,500 lbs. of pull-down force.
A key feature of the Quintus riser is that it does not require any adapter plates, the fixture plates or vises attach directly to it. See Figure 5-19. Designed for quick change, as well as zero point accuracy, fixture change takes only seconds. Fixture plates are available, also, to mount directly on the Quintus 1 or 2 riser. Simply screw the Quintus pins to the bottom of the plate, place it on the Quintus riser, and tighten the locking mechanism. Round fixture plates to mount on the Quintus are available either as blanks, or multi-function plates in 130mm, 160mm and 250mm. Rectangular plates are available in sizes 100mm X 250mm or 150mm X 250mm, also as blank or multi-function plates. The Quintus 3 Riser will serve as the riser for larger vises, or custom fixture plates. The Quintus pull down pins are available to facilitate adapting your custom fixture plates to the Quintus.
Accessories. Necessary accessories for the CL5® System such as Center Locating Keys, step fixture keys, T Nuts, Quintus pull down pins and vise locating pins are available separately. Center Locating Keys are used to precisely center a fixture on a rotary table. They are used for mounting Quintus Quick-Change Risers. Riser Blocks, and Round Tooling Plates, which all have a standard 25mm center hole. See Figure 5-20.
Figure 5-20. Quintus Center Locating Keys.
A step fixture key provides radial orientation when mounting a plate or riser on a rotary table. Use together with a Center Locating Key. Keys are available for machine-table slots either larger or smaller than the fixture slot. Top and bottom of key are centered within .0005" of each other. Fasten with a Socket Head Cap Screw. See Figure 5-21.
Fixtures attached to the Quintus Quick Change Riser require the appropriate number of pulldown pins to enable the quick change and zero point features of the riser. Due to the differing sizes of the three risers, each has a different requirement for the pull-down pins. With the smallest Quintus riser, the pull down pin performs only the pull down function, since the zero point function is provided by the round and diamond pins in the riser. For the Quintus 2 and 3, the pins perform both the pull-down and zero point functions. The Quintus 2 pull-down pins are one zero point, and one radial alignment style, while the Quintus 3 uses one zero point, one radial alignment and one pin whose only function is to provide pull down force. See Figure 5-22.
Figure 5-22. Pin options for Quintus 1, Quintus 2, and Quintus 3.
Vise Locating Pins. Vise Locating Pins are round and diamond pins, which are used together to locate a 5-Axis Vise on a Vise Adaptor or Riser Block. They are available in 6mm and 10mm diameters.
ZERO POINT SYSTEMS
Speedy Zero Point
Speedy Clamping Plates are subplates for mounting on a machine table or tooling block. These plates have two clamping modules to simultaneously locate and clamp a fixture that has pull-down Locating Posts. Hydraulic connection is required only while changing fixtures. Applying hydraulic pressure releases locking balls in both clamping modules to allow the fixture to be changed. When hydraulic pressure is released again, Belleville springs re-engage the locking balls to pull the fixture down securely into position. The pump unit can then be disconnected for machining.
contains all items needed to implement this system, Speedy clamping plate, air powered hydraulic pump, locating posts and all hardware necessary to mount and connect the unit. See Figure 5-23.