Explanatory Information (NOT PART OF ANSI STANDARD)

Transcription

1 3 General machine conditions 3.1 Grinding machine design and maintenance This standard recognizes that a wide variety of machines use bonded abrasive wheels. In this section the term grinding machine will refer to any machine, portable or stationary, that may use a bonded abrasive wheel. Where an application requires differentiation in the standard for a machine type, the difference will be described Supplier's responsibility It shall be the responsibility of the supplier (e.g. manufacturer, reconstructor, modifier, installer, integrator) to design, build and label grinding machines in accordance with this and other established standards, to provide for the safe use of bonded abrasive wheels Owner's responsibility The user/owner shall use and maintain grinding machines in a manner that provides for safe operation in conformance with this standard. The user/owner shall not convert, change, or otherwise alter the original design of the machine without the permission of the machine manufacturer. The user/owner shall train all personnel in the safe use, operation and maintenance of the machine and shall follow the recommendations of the manufacturer Operator's responsibility Each operator shall be responsible for following the safety and training rules and procedures established and provided by the user/owner [employer]. 3.2 Safety guards Grinding machines shall be equipped with safety guards in conformance with the requirements covered in section 4, page 50. Explanatory Information (NOT PART OF ANSI STANDARD) E Supplier's responsibility Grinding is a safe operation under normal conditions. Severe stress can be set up in the wheel if established safe operating practices are not maintained. Only machines designed in accordance with this and other established standards, which provide for the safe operation at the required grinding speed and are able to take the pressure and thrust of the grinding operation, are recommended. E Owner's responsibility Proper maintenance of grinding machines is very important to ensure safe operation. Grinding machine maintenance should be performed by qualified personnel only. E 3.2 Safety guards Safety guards are used on grinding machines to provide protection in case of an accidental wheel breakage. (See paragraph 4.1, page 50, for exception.) 31

2 3.3 Spindle Diameter of spindle The spindle shall be designed and sized to support and drive the wheel under the intended conditions of use. Table 1, page 34, shows the minimum diameter of spindles which should be used for wheels of various sizes. It applies to machines where wheels are not mounted between bearings. The use of heavier spindles than those listed in this table is often desirable. See section 6, page 87, for tolerances for arbor holes. Exception: On bench grinders with wheels not greater than 5 inches in diameter operating at peripheral speeds less than 5,000 SFPM, with rated outputs not greater than 1 /10 horsepower, the spindle diameter may be 3 /8" for wheels no more than 1 /2" in thickness. E Diameter of spindle Standard machine design generally conforms to the minimum spindle diameter requirement in table 1, page 34. Experience has shown that requests for wheels with undersize holes often result from the desire to use larger diameter wheels than were originally intended for the machine Tolerance of spindle or mount, up to 3 inches Abrasive wheels shall fit freely on the spindle, wheel sleeves, or adaptors, and remain free fitting under all grinding conditions. To accomplish this, the spindle or wheel mount shall be made to nominal (standard) diameter plus zero, minus inches, measured at 20 C (68 F). E Tolerance of spindle or mount To avoid rupturing pressure in the wheel hole, the diameter of the spindle or wheel mount must be as specified so that there is clearance between the wheel hole and the spindle or wheel mount under all operating conditions. The wheel hole should be made suitably oversize to assure safety clearance under the conditions of normal operating heat and pressure Tolerance of spindle or mount, 3inches and larger Abrasive wheels shall fit freely on the spindle, wheel sleeves, or adaptors, and remain free fitting under all grinding conditions. To accomplish this, the spindle or wheel mount shall be nominal diameter or less while the wheel shall have a bore greater than nominal. See paragraph 6.3, page 90 for tolerance of holes in wheels. 32

3 3.3.4 Length of machine spindle thread If wheels are mounted by means of a central spindle nut and flanges, two conditions shall be maintained (see illustration 37): 1. Spindles shall be of sufficient length to allow all the threads of the nut to engage the spindle. 2. The threaded portion shall extend from the spindle end to inside the outer flange, but not more than halfway within the arbor hole of the minimum width wheel for which the machine is designed. If threaded hole wheels are of cone or plug shape with blind holes, the length of the spindle and the depth of the hole shall be such that the end of the spindle shall not touch the bottom of the wheel hole (see illustration 38). ANSI B E Length of machine spindle thread Illustration 37 The spindle is of sufficient length to accommodate the wheel and flanges Illustration 38 Correct and incorrect mounting of cone wheels with threaded holes 3.4 Direction of machine spindle rotation Direction of machine spindle thread If wheels or flanges are secured by means of a central spindle nut, the direction of the thread shall be in such relation to the direction of rotation that the nut will tend to tighten as the spindle revolves. On machines with spindle reversal capability, and machines where flanges are interchanged from one end of the spindle to the other, means shall be provided to prevent the wheel and flanges from loosening as the spindle revolves Direction arrows An arrow, visible to the operator, shall be displayed indicating the intended direction of grinding wheel spindle rotation. An arrow shall also be used to indicate the intended direction of rotation of any other rotating device where a hazard may be created by improper direction or rotation. (See illustration 39.) E 3.4 Direction of machine spindle thread When reassembling double ended machines which have a right hand thread on one end and a left hand thread on the other, care must be used to replace the spindle properly with respect to the direction of the threads. Illustration 39 The direction of rotation of the cutting-off wheel is indicated by the arrow on the guard. This is also the direction the nut must be turned for removal. 33

4 Table 1 Recommended minimum diameters of machine spindles at point of mounting for wheels of various diameters and thicknesses operating at standard speeds as listed in table 23 (1 Diameter of Wheel Thickness of Wheel, Inches < 1/4 1/4 3/8 1/2 5/8 3/ /4 1-1/ /4 2-1/2 2-3/ /4 3-1/ /8 3/32 3/32 3/32 3/32 1/8 1/8 1/8 1/8 1/2 3/32 3/32 3/32 1/8 1/8 1/8 1/8 3/16 3/16 3/16 5/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 3/16 3/16 3/16 3/4 1/8 1/8 1/8 1/8 1/8 1/8 1/8 3/16 3/16 3/16 1/4 3/8 3/8 7/8 1/8 1/8 1/8 1/8 1/8 3/16 3/16 3/16 3/16 3/16 1/4 3/8 3/8 3/8 1 1/8 1/8 1/8 1/8 1/8 3/16 3/16 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1-1/8 1/8 1/8 1/8 1/8 1/8 3/16 3/16 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1-1/4 1/8 1/8 1/8 1/8 3/16 3/16 3/16 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1-3/8 1/8 1/8 3/16 3/16 3/16 3/16 3/16 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1-1/2 1/8 1/8 3/16 3/16 3/16 3/16 3/16 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1/2 1/2 1-5/8 1/8 1/8 3/16 3/16 3/16 3/16 1/4 1/4 1/4 1/4 3/8 3/8 3/8 3/8 1/2 1/2 1-3/4 1/8 1/8 3/16 3/16 1/4 1/4 1/4 1/4 1/4 1/4 3/8 1/2 1/2 1/2 1/2 1/2 1-7/8 1/8 1/8 3/16 3/16 1/4 1/4 1/4 1/4 5/16 3/8 3/8 1/2 1/2 1/2 1/2 1/2 2 1/8 1/8 3/16 3/16 1/4 1/4 3/8 3/8 3/8 3/8 3/8 1/2 1/2 1/2 1/2 1/2 1/2 5/8 5/8 3 1/4 1/4 1/4 3/8 3/8 3/8 3/8 3/8 3/8 1/2 1/2 1/2 1/2 1/2 1/2 5/8 5/8 5/8 5/8 4 1/4 1/4 3/8 3/8 3/8 3/8 3/8 1/2 1/2 1/2 1/2 1/2 5/8 5/8 5/8 5/8 5/8 3/4 3/4 5 3/8 3/8 3/8 1/2 1/2 1/2 1/2 1/2 1/2 1/2 5/8 5/8 5/8 5/8 5/8 3/4 3/4 3/4 3/4 6 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 5/8 3/4 3/4 3/4 3/4 3/4 3/4 3/4 3/ /2 1/2 1/2 1/2 1/2 1/2 1/2 5/8 5/8 5/8 3/4 3/4 3/4 3/4 3/4 3/ /2 1/2 1/2 1/2 1/2 5/8 5/8 5/8 5/8 3/4 3/4 3/4 3/ /8 5/8 5/8 5/8 5/8 5/8 5/8 3/4 3/4 3/ /4 1-1/4 1-1/4 10 5/8 5/8 5/8 5/8 5/8 3/4 3/4 3/4 3/4 3/ /4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 12 5/8 3/4 3/4 3/4 3/4 3/4 3/4 3/ /4 1-1/4 1-1/4 1-1/4 1-1/2 1-1/2 14 3/4 3/4 3/4 3/4 3/ /4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/2 1-1/2 1-1/2 16 7/ /4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 18 7/ /4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/4 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 1-3/4 1-3/ /4 1-1/4 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 1-3/4 1-3/4 1-3/ /4 1-1/4 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 1-3/4 1-3/ /4 1-1/4 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 1-3/4 1-3/4 1-3/ /2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-1/2 1-3/4 1-3/4 1-3/4 1-3/ /4 2-1/4 2-1/ /2 1-3/4 1-3/4 1-3/4 1-3/4 1-3/ /4 2-1/4 2-1/4 2-1/2 2-1/2 2-3/4 2-3/ / /4 2-1/4 2-1/4 2-1/4 2-1/2 2-1/2 2-1/2 2-1/2 2-3/4 2-3/4 2-3/4 2-3/4 2-3/ /2 2-1/2 2-1/2 2-1/2 2-3/4 2-3/4 2-3/4 2-3/ /2 3-1/2 3-1/2 3-1/2 3-1/ /4 2-3/4 2-3/4 2-3/4 2-3/4 2-3/4 2-3/ /2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/ / /2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/ / /4 3-1/2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/ /2 4-1/ /2 3-1/2 3-1/2 3-1/2 3-1/2 3-1/ /2 4-1/2 4-1/2 4-1/2 4-1/ NOTE: For speeds exceeding those listed in table 23, page 99, for usually severe operations and for wheels with heavy mountings (such as bolted-on-abrasive discs), the spindle sizes shown in the above table may not be adequate. Inasmuch as the proper spindle size is dependent upon many factors, such as general design of the machine, type of bearings, quality of materials, workmanship and application of wheel, a simple table is not practicable. Wheels larger than specified by the machine manufacturers shall not be used. (1) This table is not intended for use with steel-centered diamond cutting-off wheels used for concrete or wall sawing. 34

5 3.4.3 Machines using threaded hole wheels The direction of the thread shall be such that to remove the wheel, the wheel must be turned in the same direction it rotates when in use. 3.5 Flanges All machines which mount grinding wheels or cutting-off wheels shall be equipped with flanges in accordance with the requirements listed in section 5, page Diameter and speed control for grinding machines Abrasive wheel grinding machines shall be provided with a means of limiting the diameter of the wheel that can be mounted, or shall display instruction and warning plates which clearly state the maximum wheel diameter which shall be permitted to be used A grinding machine shall not be operated at a speed exceeding its rated speed No grinding wheels shall be mounted which have a greater diameter than the machine is designed for and/or the maximum size displayed on the nameplate Grinding machines using a single wheel spindle speed The safety guard is satisfactory as a device for limiting the wheel diameter, and hence surface feet per minute (measured in SFPM or m/sec) of the abrasive wheel on single speed machines Stationary grinding machines using variable wheel spindle speed controls Variable speed machines shall have additional means to prevent the wheel from operating above the maximum rated wheel speed. On variable speed machines where the speed is controlled by a direct mechanical link, such as floor stand type machines, the speed ANSI B E 3.5 Flanges Proper selection, use, and maintenance of flanges are all essential factors in the safe use of abrasive wheels. See section 5, page 72. Flange design must be such that flange distortion will not occur under all operating conditions. If distortion occurs, flat flange bearing surfaces must be maintained a failure to maintain flat flange bearing surfaces will result in a dangerous operating condition. E 3.6 Diameter and speed control for grinding machines Mounting and running a wheel larger than the machine was designed to operate with is an unsafe practice and can result in wheel breakage. E Stationary grinding machines using variable wheel spindle speed controls On variable speed machines, the speed control device must be maintained in proper working condition. Overriding these controls is dangerous and could result in a severe overspeed condition which, in turn, could cause a wheel to break. 35

6 adjusting device shall be connected to an adjustable guard or another diameter limiting device to prevent the mounting of a larger diameter wheel on the machine when it is set to operate at higher speeds for smaller diameter wheels. This direct size relationship will prevent the wheel from being operated at higher than the intended Surface Feet Per Minute (SFPM). On other machines, which use electronic or other wheel speed control devices, a means and procedure shall be provided to ensure that the maximum SFPM established by the manufacturer is not exceeded. All such limiting devices, should they fail, shall not cause the wheel to overspeed Permanent speed marking for single speed machines The spindle RPM of single speed grinders shall be permanently marked on the machines and shall be readily visible to the operator(s) Permanent speed marking for variable speed grinders The governing factor on variable speed machines is the peripheral speed which is normally rated in surface feet per minute (SFPM) or meters per second (m/sec). The range of the spindle RPMs and the relative wheel sizes shall be permanently marked on the machine and shall be readily visible to the operator(s). 3.7 Work support on stationary and bench grinders A grinding machine shall be designed so that work support mechanisms can be used and adjusted to support the workpiece without compromising the safety of the operator of the machine for its intended purpose (see illustration 40). In the case of floor stand type machines, if the speed control device is inadvertently ground while adjusting the wheel speed, care should be exercised and the machine repaired so it performs as originally designed and provided by the manufacturer. E 3.7 Work support on stationary and bench grinders Illustration 40 Floor stand grinder with a properly adjusted work rest 36

7 3.7.1 Work support for off-hand grinding The work support for off-hand grinding, typically referred to as a work rest, shall be provided to support the workpiece. These work rests shall be of rigid construction and adjustable to compensate for wheel wear. Exception: Swing Frame Machines Work support for cylindrical grinding machines Work support for cylindrical grinding machines, made up of a variety of devices that hold and drive (turn) the workpiece, shall be provided to support the workpiece. Devices that drive the workpiece, including headstocks and workheads, shall be designed with controls compatible with the machine application. Devices that hold the workpiece, including work centers, chucking mechanisms, and spindle noses, shall be designed to properly hold the workpiece during grinding operations. Other support devices, including steady rests and center rests, shall be designed to properly support the workpiece during the grinding operation Auxiliary work support for cylindrical grinding machines Cylindrical grinding machines may require auxiliary support devices to support the workpiece when it is being loaded or unloaded. Such devices are commonly called work cradles. When the workpiece weight, configuration, or other characteristic requires auxiliary support, the grinding machine manufacturer shall provide cradles specifically designed to facilitate handling of the workpiece when it is loaded or unloaded. When auxiliary work support devices must be used on the grinding machine, the user shall establish procedures to ensure that the workpiece is supported properly before the work support mechanisms engage in the workpiece. 3.8 Portable grinding machines Spindle and flange design for threaded hole wheels Portable air grinders shall be manufactured and operated in accordance with ANSI B186.1 (see paragraph 1.5, page 26). ANSI B E Work support for off-hand grinding Care should be exercised with variable speed grinders, where the work rest is part of the variable speed control linkage, that a U is not ground in the work rest, creating the possibility that the recommended maximum operating speed of the abrasive wheel is exceeded. 37

8 3.8.1 Spindles A grinder shall be equipped with a spindle which will properly accept the type and size of grinding wheel for which it is intended and rated Design consideration for spindle thread directions are defined in section 3.4, page Spindles of grinders for mounted wheels shall be equipped with collets. The collet shall have precision such that the runout on a test pin mounted in the collet shall not exceed the following total indicator reading when measured at a distance of one inch (twenty-five mm) from the front end of the collet, or at a distance equal to the depth of the collet, whichever is shorter..007" Grinders below 25,000 RPM (.178 mm) Grinders 25,000 to 40,000 RPM.005" (.125 mm) Grinders over 40,000 RPM.003" (.076 mm) Flange design The back flange shall be flat, unrelieved, securely fastened and square to the spindle axis. The back flange shall be of sufficient diameter to ensure proper support of the wheel. (See table 17, page 83). A relieved back flange shall not be used. E Flange design If a relieved back flange is used, it will cause the bushing to be pulled out of the wheel, as shown in illustration 41. The back flange should be flat and heavy enough to prevent distortion. Flat Flange No relief Provides proper support for steel bushing and wheel Relieved Flange Does not provide proper support CORRECT INCORRECT Illustration 41 Unrelieved and relieved flange 38

9 3.8.3 Side handles Portable vertical and angle grinders 4" and larger shall be equipped with a side handle for operator control and safety. The operator shall not remove the side handle from the tool. 3.9 Mount design for abrasive discs (inserted nut, inserted washer and projecting stud type) Machines on which abrasive discs are mounted shall be provided with a disc mounting plate equal to or larger than the nominal abrasive disc diameter and of sufficient thickness to provide necessary support. Minimum disc mounting plate thickness for disc grinders are given in table 2 below. Table 2 Minimum thickness of machine face plates (steel disc wheels) for mounting abrasive discs Diameter (Inches) Minimum Thickness (Inches) 14 & Smaller 1 / 2 Over 14 to 18 5 / 8 Over 18 to 26 3 / 4 Over 26 to 36 7 / 8 Over 36 to 40 1 Over 40 to /8 ANSI B E Side handles The side handle is normally placed at 90 degrees to the switch handle and provides the operator with a means of maintaining secure control of the tool at all times. Operation of the tool without the side handle can result in loss of control and is hazardous. Most side handles must be assembled to the tool when it is received, because installing the handle greatly increases the size of the shipping container and handles can be broken off during shipment. E 3.9 Mount design for abrasive discs (inserted nut, inserted washer and projecting stud type) Illustrations 42 and 43 and figure 5 will serve to clarify the difference which exists between the three types of mountings for abrasive discs; the inserted nut type, the inserted washer type and the projecting stud type. (See ANSI Standard, Machine and Plate Mounted Discs, ANSI B5.35.) The machine face plate (steel disc wheel) must be maintained true, flat, and clean. When regrinding the face plate, caution should be taken to ensure that the X dimension (figure 4) is not ground so small that, when mounting, the screws could touch the bottom of the hole. If this condition occurs, the wheel may be damaged. Based on material of minimum 60,000 psi tensile strength steel, other material or design may be used that will provide equivalent or greater strength and stiffness. Screw holes in the machine face plate shall be accurately located to match the threaded holes in the inserted nuts in the abrasive disc and shall be large enough such that the screws will not bind. Dimension X (figure 4) shall be uniform for all mounting screws so that the screws can be interchangeable. 39

10 Figure 4 Screws shall be of sufficient length to properly engage the threads in the inserted nuts, yet not so long that there will be any possibility of the ends touching bottom. The disc mounting surface of the machine face plate (steel wheel) shall be flat and perpendicular to the axis of the spindle rotation and support the disc concentrically when mounted. Illustration 42 Inserted nut type abrasive disc Figure 5 Various methods of mounting projecting stud or stud mounted type abrasive discs Illustration 43 Inserted washer type abrasive disc 40

11 3.10 Mount design for plate mounted type discs Screw holes in the plate mounted disc mounting plate shall be accurately located to match the threaded holes in the mounting plate and shall be large enough so that the screws will not bind. If the mounting plate attached to the disc is as thick or thicker than shown in table 2, page 39, there are no special requirements regarding the diameter and thickness of the machine face plate (steel disc wheel). If the mounting plate attached to the disc is thinner than shown in table 2, page 39, the machine shall be equipped with a machine face plate (steel disc wheel) of sufficient diameter and thickness to provide adequate additional support. Minimum specifications are given in table 3 for disc grinders. ANSI B E 3.10 Mount design for plate mounted type discs A typical method of mounting plate mounted type discs is shown in illustration 44. Note the additional reinforcement to the abrasive disc and the mounting plate by the machine face plate (steel disc wheel). Even when plate mounted discs are used, the machine face plate (steel disc wheel) should be the full diameter of the disc where possible. The original thickness of the machine face plate should be thicker than the minimum in table 3 to allow re-machining to correct for wear. Table 3 Minimum thickness and diameter of machine face plate (steel disc wheel) for machines using plate mounted discs having thin mounting plates Abrasive Disc Diameter D (Inches) Minimum Thickness P t (Inches) 12 and Smaller 3 /8 14 to 16 (over 12 to, and including, 16) 1 /2 17 to 18 (over 16 to, and including, 18) 5 /8 19 to 26 (over 18 to, and including, 26) 3 /4 27 to 36 (over 26 to, and including, 36) 7 /8 D H Illustration 44 Plate mounted type discs P t Mounting Plate P d Machine Face Plate (Steel Disc Plate) P d shall never be less than D+ H 2 nor shall the difference between D and P d exceed 2 inches. It is recommended that P d equal D wherever practical. 41

12 THE FOLLOWING SECTIONS APPLY TO STATIONARY MACHINES 3.11 Stationary machines, excluding bench and pedestal grinders, using wheels smaller than 10" in diameter Power Grinding machines shall be provided with sufficient power to maintain the rated wheel spindle speed under conditions of operation for which the machine is designed Exhaust provision Where the level of airborne fumes or particulates can create a hazard, grinding machines shall have a provision for, or connection to, an exhaust system unless a zone exhaust system is used Moving parts Hazards to personnel associated with moving parts shall be safeguarded Machine components, fixtures, and workpieces shall not constitute a hazard to the operator or other personnel, provided other safety procedures are followed No protective device shall of itself create a hazard to the operator or other personnel nor shall it restrict his ability to observe and control the machine cycle Power transmission All mechanical power transmission components shall be enclosed so that access to any moving parts can be gained only by the opening or removal of a guard, door or cover When guards, doors and covers enclosing power transmission components are not interlocked with mechanical or electrical devices, a warning legend shall be displayed that states: DO NOT OPERATE MACHINE WITHOUT ALL GUARDS IN PLACE AND SECURED When guards, doors and covers enclosing power transmission components are not interlocked with mechanical or electrical devices, they shall be fastened with a device that requires a tool to open the enclosure. E A warning is required since non-interlocked guards, doors or covers could be removed without stopping the machine, leaving dangerous moving parts exposed. The warning legend should be attached at the exposed danger zone and not on any guard, door or cover that can be removed. E Guards, doors and covers enclosing power transmission components should only be opened by qualified maintenance or supervisory personnel. The requirement of a tool is to keep operators and others out of these enclosures. 42

13 No protective device enclosing the power transmission components shall of itself create a hazard to the operator or other personnel nor shall it restrict his ability to control the machine cycle Grinding tools Personnel associated with grinding tools shall be safeguarded against hazards. Abrasive wheels shall be used only on machines constructed in accordance with section 3, page Honing tools Honing tools shall be operated within the tool manufacturer's specifications for speed and direction Honing tools connected to drive shafts having universal joints, or honing tools containing abrasive tools or guides, or both, not rigidly attached to the tool shall not be allowed to rotate under power outside the workpiece or a guard Means shall be provided to absorb rotary forces on the workpiece resulting from the honing operations Sharp corners and edges Machine components, assemblies and guards shall be designed to minimize or eliminate all sharp corners, and edges that may constitute a hazard to the operator or maintenance personnel Direction of controls Whenever grinding machine component movement can be controlled in one or another of two opposing directions, the design of the controls shall attempt to follow the conventions in this section. Exception: It may be that in certain cases these conventions should not be applied. A departure from these conventions should then be made clear by showing on the machine the directions of operation of the control and the corresponding directions of movement of the controlled component. ANSI B E In the event that stones or guides, or both, are not securely retained in the honing tool, the tool should be located inside the workpiece before the tool is rotated at honing speeds. This will, in effect, allow the workpiece to then be utilized as a guard. E A gripping fixture, or radial extension of the workpiece, should be supported by the machine so that the operator is not required to manually resist the rotational forces. Hone truing devices are not considered workpieces. 43

14 Lever controls (a) For control of linear movement, the movement of the lever in either direction from the neutral or center position shall result in a machine motion in the same direction (see figure 6). Figure 6 Control of linear movements (b) For control of circular movement, it is recommended that the plane of rotation of the control lever be parallel to the plane of rotation of the component, and that the movement of the lever shall produce a movement of the controlled component in the same direction (see figure 7). Figure 7 Control of circular movement Push button controls Placement of push button controls shall be configured so that the operation of the righthand button, the top button, or the button furthest away from the operator is to produce a movement to the right, upward or away from the operator when the operator is standing in the normal operating position. This recommendation is applicable for the control of both linear and circular movements (see figure 8). Figure 8 Relationship of rectilinear and circular movements and location of push buttons 44

15 Hand wheel controls The clockwise rotation of the hand wheel (the operator facing the shaft end on which the hand wheel is mounted) shall produce motion so that: (a) The linear movement of the component is to the right, away from the operator, or upwards when the operator is standing in the normal operating position (see figure 9). ANSI B Figure 9 Handwheel control resulting in rectilinear movements (b) For a rotational movement, the component being turned moves in a clockwise direction (as viewed by the operator when facing the end of the spindle or shaft on which the controlled component is mounted) (see figure 10). Figure 10 Handwheel control resulting in rotational movements (c) A movement toward the center of the component (clamping a chuck) Special cases If the direction of the movement of the controlled component can be varied by a preselector device, the conventions given in through apply to the direction which is most frequently used. If the same control is used for starting both cutting and the feed movement, the recommendations in apply to the feed movement Tripdogs/foot controls Tripdogs and foot controls shall be designed and mounted in such a manner that they 45

16 cannot be accidentally tripped, causing the machine to cycle or move unexpectedly Work holding and driving (loading) Work holding and driving devices shall be designed to hold the part securely and not allow it to become loose or be ejected from the machine during the grinding cycle Loading of parts into the machine Loading of parts into the machine can be accomplished either manually or automatically as follows: (a) Manual loading shall be accomplished without placing the operator in a hazardous position. Initiation of the machine cycle after manual loading shall require a deliberate action by the operator such as activating the cycle start device. (b) Automatic part loading mechanisms may require guarding if they create potential danger zones. This may be accomplished by fixed or removable guards requiring tools for their removal, or by electrically and/or mechanically interlocked guards which can be removed without the use of any tools. In the case of interlocked guards it shall be insured that the potential danger has been eliminated before the interlock is opened and the guards are removed. Restarting of the automatic operation shall require the initiation of the normal machine cycle start control. In no case shall the closure or the replacement of the guard cause the start of any machine or loader motion Fire prevention and protection When magnesium, aluminum, or similar pyrophoric or explosive particles are generated during grinding, or where ignitable fumes are generated from the grinding fluids, measures shall be taken such as explosion relief, automatic fire extinguishing and manual wetting to minimize the risk Hydraulic and pneumatic pressure protection Protection for the operator or maintenance personnel shall be provided where excessive pressure, inadequate pressure, or loss of pressure would create a hazard. This would 46

17 also include circuits that contain trapped pressures after power is turned off Lighting Adequate lighting shall be supplied by the employer as required for the safe operation of the machine. Where machine structures or guarding obstructs the normal shop illumination, additional machine mounted lighting, supplied by the manufacturer, may be required Control systems Electrical All new and rebuilt grinding machines as defined in section , page 3, shall be in accordance with the latest revision of NFPA79, Electrical Standard for Industrial Machinery General construction Operator controls, control enclosures, wireways and disconnects shall be located or protected to prevent electrical hazards Disconnect A main power disconnect switch, when supplied, shall be capable of being locked only in the "off" position Operating control Any operating control (button or lever) that could initiate a hazardous motion shall be protected against unintended operation Low-voltage protection All grinding machines shall incorporate a means of disconnecting the power source from all motors in the event of a controlvoltage or power source failure. Restart of the machine shall require deliberate action that shall not in itself create a hazard Voltage All AC control circuits and solenoid-valve coils shall be powered by not more than a nominal 120-volt AC supply obtained from a transformer with an isolated secondary. Higher voltages that may be necessary for operation of machine or control mechanisms shall be isolated from any control mechanisms handled by the operator, but motor ANSI B

18 starters with integral start-stop buttons may utilize line-voltage control. All DC control circuits shall be powered by not more than a nominal 24-volt DC supply isolated from any higher voltage Grounds All grinding machines shall be protected against the possibility of an accidental ground in the control circuit causing false operation when such operation would create a hazard Component failure Circuits shall be so designed that hazards will be minimized in the event of overload, component failure, or improperly sequenced operations Emergency stop A control shall be provided at each normal work station that will stop machine motions without creating a hazard Identification All operator selector switches and push buttons shall have their functions clearly identified Control component location The location of the operator control components shall not create a hazard to the operator Unintended operation Machine controls shall be located, designed, interlocked or guarded to inhibit unintended operation that would create a hazard Foot-operated tripping controls shall be protected so as to prevent accidental actuation A machine or machine cycle that has been stopped or interrupted shall require deliberate action by the operator to restart the machine Guards that are interlocked with the machine cycle, when opened, shall stop the related components, interrupt the machine cycle, or shut down the machine without creating a hazard. Closing the guard shall not be an acceptable method of restarting the machine cycle. 48

19 3.13 Airborne contaminants, flying particles and sparks Particles and sparks shall not present a hazard to the operator or other personnel. The employer shall install and operate grinding machines so that the airborne contaminants caused by the grinding operation shall not exceed the permissible limit established by the authority having jurisdiction Flow slopes and discharge port openings, including exhaust outlets for dry grinding, shall be designed to provide for the movement of particles to the designated point of removal or exit Spark hazard prevention The spark shower should be directed downward and away from the face and body of the operator. Prior to grinding sparking materials, care shall be taken to shield any nearby flammable materials to prevent ignition from the spark shower or from latent sparks Coolant, lubrication, hydraulic fluid, compressed gas Loss of coolant and lubricants from the machine shall be minimized by system design or installation of suitable shields or enclosures Each flexible pressurized line shall be suitable for the conditions under which it is used and restrained or confined if its failure would constitute a hazard Noise level The noise level of grinding machines shall not exceed the limits stated by the applicable regulatory agency. The noise level of the grinding machine shall be measured with the machine operating without a workpiece at those normal speeds and cycles that would be expected to produce the highest noise levels. ANSI B