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ELEMENTARY PRINCIPLES OF CONE PULLEYS AND BELTS

ELEMENTARY PRINCIPLES OF CONE PULLEYS AND BELTS  Everyone knows that cone pulleys are usually made with regular steps; that is, if it is one inch from one step to the next, it is also one inch from the second to the third, etc., the reason being that when the centers of the shafts on which the cones run are a fair disance apart, the belt will pass very nearly half way around that part of each cone on which it is running, and the length of the belt will consequently be approximately equal to twice the distance between the shafts, added to half the circumference of the grade of one of the cones on which it is running, and half the circumference of the grade of the other cone on which it is running. As the steps are even, the half circumference of any two grades of each cone will, when added together, produce the same result. For example, if we had two cones, the diameters of the several grades of which were 6, 8, 10 and 12 inches, it is evident that the sum of half the diameters taken anywhere along the cones, as they would be set up for work, would in every case be the same. If the diameters are the same, it follows that the circumference must also be the same, and, of course, that half the circumference must be the same, so that when the centers of the shafts are a fair distance apart, and the difference between the largest and smallest step of the cone not too great, the same belt will run equally well anywhere on the cone, because it runs so near half way around each grade of the two cones on which it is running, that the slight difference is within the practical limit of the stretch of the belt.  But when the shafts are near together, and when the difference between the largest and smallest step of the cone is considerable, the belt is not elastic enough to make up this difference. Fig. 1 shows a three-step cone, the grades being 4, 18, and 32 inches diameter, respectively, there being a difference of 14 inches on the diameter for each successive grade, and the step being therefore 7 inches in each case. Of course, it is not likely that such a cone as this would be made for practical use, but it is well to go to extremes when looking for a principle. Now, it is evident that two cones, even if like the one shown in the cut, were set up far enough apart, they would still allow the belt to run very nearly half way around each grade of the two cones, the angularity of the belt would be slight, and the length of belt would therefore still be as mentioned above.  But (again taking an extreme case) by reference to Fig. 2, which is intended to represent a belt running from the largest grade of one cone to the smallest grade of the other cone, we see that the belt runs three quarters of the way around the large pulley, and only one quarter of the way around the small one, the distance between the shafts in this case being 19% inches.  The length of this belt will evidently be equal to three quarters of the distance around the large pulley, plus one quarter the distance around the small pulley, plus the distances A and B, which we find to be each 14 inches. The circumference of a 32-inch diameter pulley is 100% inches, and the circumference of a 4-inch diameter pulley is 12% inches (near enough for our present purpose); three quarters of 100% is 75%, and one quarter of 12% is 3%; the length of a belt, then, to go around a 4-inch pulley and a 32-inch pulley, running at a distance of 19% inches apart, is 75% plus 3% plus 14 plus 14; total, 106% inches.  Now, let us take the middle cone, when the belt is running on two pulleys, both 18 inches diameter (see Fig. 3), and, of course, the same distance apart as before. The circumference of an 18-inch pulley is 56% inches, and half the circumference of two 18-inch pulleys is evidently the same as the whole circumference of one 18-inch pulley; the length of belt in this case will then evidently be 56% plus 19% plus 19%; total, 96 inches. It is therefore evident that a belt long enough to run on a 4- and 32-inch pulley, 19% inches apart, is 10% inches too long to run on two 18-inch pulleys 19% inches apart, and, of course, it is therefore 10% inches too long to run on the middle grades of such a cone as we have under consideration.  The thing to do, then, is to make the middle grades of these cones (or the two 18-inch pulleys) enough larger than IB inches diameter to just take up this 10% inches of belt, and if this were the only case we had to deal with, it would be very easy to settle it by saying that as half the circumference of two 18-inch pulleys is the same as the whole circumference of one 18-inch pulley, we should make the two 18-inch pulleys enough larger in diameter to make an additional circumference of 10% inches; and as 3% inches is nearly the diameter of a 10%-inch circumference pulley, by making the middle of both cones 18 plus 3% inches diameter (that is, 21% inches diameter) our trouble would be ended in this particular case. It is easy enough to see, by looking at Fig. 2, that the belt being obliged to go three quarters of the way around the large pulley, is what makes it so much too long to go around the two middle pulleys, where, of course, it goes but half way around each. But, of course, what we want is some way of calculating the diameters to turn any pair of cones, running at any distance apart.  If we were to draw these same 32- and 4-inch pulleys twice 19% inches apart, and then three times 19% inches apart, and so on, until we got them far enough apart so that the belt would practically run half way around each, and should calculate the diameter of the middle grade of the cone to fit each distance, we would probably formulate a rule that would work for any distance apart, with this particular cone; but as it is evident that the further apart the cones are to run, the nearer to the nominal diameter of 18 inches must the middle of the cones be turned, so also must it be evident that the less difference between the largest and smallest diameter of the cone, the less must also be the excess over nominal diameter of the middle of the cones.  Any method, then, of calculating such problems must take both of these things into consideration. The nominal diameter of the middle of any cone will be equal to half the sum of the diameters of the largest and smallest part respectively. This is almost self-evident, and no proof of it is necessary in this connection. What we want, then, is some way to find out how much larger than the nominal diameter to turn any one cone or cones to fit the conditions under which they are to run. The following formula is the result of a thorough investigation of this subject by Prof. Rankine, and has proved itself to be practically correct in the shop, as well as satisfactory to those mathematicians who are competent to criticise it.  STRENGTH OF COUNTERSHAFTS There is scarcely a shop in existence which has not had a more or less serious accident from a countershaft some time in its history. It may have been caused by a heavy pulley running very much out of balance, or the shaft may have been bent in the beginning. Possibly the shaft was too light, or too long between hangers. The latter is responsible for most of the trouble, and is the one with which this discussion is principally concerned.  There are two methods in vogue for turning cones and pulleys; one is to set the rough casting to run true on the inside, and the other on the outside. This latter method makes a cheaper and an easier job, but when turned, it requires an enormous amount of metal to balance it. And here is the source of considerable trouble. We may balance a large cone perfectly on straight edges, but that is a standing balance only; and when the cone is put in place and speeded up to several hundred revolutions per minute, it shakes, and shows that it is decidedly out of balance. The trouble is that we have not placed the balance weights directly opposite, or in the plane of the heavy portion of the cone. The result is that neither weight, when rotating, has its counter balance pulling in the same line, and, of course, the pulley is sure to be out of balance. All cones and all other pulleys which have a wide face should be set to run true on the inside before turning.  A certain countershaft failed because it had been welded near the center. The weld twisted and bent open, and someone was badly injured by the fall. A weld in machine steel is so very uncertain that it should never be trusted for such a purpose. The extra expense of a new shaft would not warrant the hazard of such a risk.

tool die design

Our tool die design handbook and reference books show you the way how the precision high speed metal stamping tool die making being performed in a simple self explained format. Miniature and high precision sheet metal stamping no more a secret in the precision metal stamping trade.

Precision metal stamping tool die design book was written in a simple 2D diagrams. Illustrated the way how the professional tool die makers arrange the strip layout, deep draw sequences, forming sequences and it technique in precision die making. See how the professionals overcome the metal spring back and how to achieved the tight tolerances in stamping ferrous and non ferrous materials. High speed die making tool design technical reference handbook make it simple for tool die makers.

Jig & Fixture Design Tools

Design jigs and fixtures with the power of NX

Advanced solid modeling and assembly design aids in NX are ideally suited for general tool, jig and fixture design. Designers begin with solid models of parts, in-process workpieces, or product assemblies, using associative capabilities to directly relate tooling models to the geometry of the workpiece.

With feature-based modeling, component libraries, and assembly design aids, tool designers can quickly model workholding fixtures, jigs and other production tools, ensuring accurate fit and function of the tooling to the workpiece. NX provides powerful capabilities for creating jigs and fixtures that are associatively matched to the design parts or assemblies.

• Knowledge driven automation to update fixture designs to match new product arrangements
• Rapidly perform design changes with associativity
• Validate and guarantee the design
• Connect seamlessly to NX’s simulation products to analyze geometry and check for strength, distortion, modes of vibration, as a part of the fixture design process – all in NX
• Connect directly to NX CAM to prepare NC programs to mill, drill and turn fixture components – all in NX

The NX Advantages:

Assembly design context: With NX Assembly's modeling approach, it is natural to design fixture components around the part or assembly the fixture serves.

NX Assembly mating conditions allow a new or updated part of the same type to be positioned in the fixture automatically.

NX Mold Design has increased our productivity by 100% allowing us to create mold designs twice as fast as before.

NX offers the powerful capabilities in geometric and large assembly modeling making it ideal for all types of fixture design.

Associative surfaces for easy, fast updates: With the Wave Link technology, jigs and fixtures can contain the geometry of the held part.

Full associativity between the product model and the fixture can ensure fast, accurate updates..

Utilize fixture assemblies across many manufacturing applications: The careful design work you perform to get precise and careful work holding can be carried on to various manufacturing applications.

NX CAM can use fixtures directly in the machining environment, including fixture collision avoidance and detailed machine motion simulation.

Assembly fixtures and other positioning aids can be deployed in your work cell or factory simulations or in your human modeling analysis.

Simulation: Easy to use kinematic software can be used to display and check mechanisms and NX offers a wide range of tools for stress analysis.

Welding fixture complete with clamps and welding guns for an automotive assembly.

Assembly fixtures and other positioning aids can be deployed in your work cell or factory simulations or in your human modeling analysis.

Complex configurations: Using Teamcenter extensions to the NX Managed Environment, an unlimited range of alternative configurations of fixtures can be defined and recalled as required.

NX can display multiple arrangements of fixtures that have different conditions, for example, opened or closed positions.

Fixture (tool)

A fixture is a workholding or support device used in the manufacturing industry. What makes a fixture unique is that each one is built to fit a particular part or shape. The main purpose of a fixture is to locate and in some cases hold a workpiece during either a machining operation or some other industrial process.^[1] A jig differs from a fixture in that it guides the tool to its correct position in addition to locating and supporting the workpiece.^[1][2]

The primary purposes of jigs and fixtures is to:^[1]

• Reduce the cost of production
• Maintain consistent quality
• Maximize efficiency
• Enable a variety of parts to be made to correct specifications

Types of Fixtures: General Purpose - They are usually relatively inexpensive and can be used to hold a variety and range of sizes of workpieces (examples: Vises, chucks, split collets).

Special Purpose - They are designed and built to hold a particular workpiece for a specific operation on a specific machine or process.

What is a Fixture

The fixture is a tool which holds the work piece with the machine bed precisely at the desired location. The fixture also reduces the nonproductive loading, unloading, and fixing time of the work piece. For example, you need to use a milling machine for giving a chamfer at the corner of rectangular work pieces. You can use a vice to hold it in the desired position, but in that case every new work piece will take lots of time for fixing it. On the other hand if you can make a milling fixture like the one shown below and bolt the fixture to the milling machine bed, then you need not waste much time for fixing the work pieces every time:

You just place the work piece and it will automatically aligned to the required angle, and straight away you run the machining operation, no need to measure the angle, and no need to be worried about the accuracy.

What is a Jig

In simple terms, the jig is a tool that guides the cutting (or machining) tool. The most common type of jig is the drill jig, which guides the drill bit for creating holes at desired locations. Using drill jigs increases production rate drastically by eliminating the time spent using a square scriber, height gauge, centre punch, etc. The picture below shows the functionality of a simple drill jig:

Like drill jigs, welding jigs and wood working jigs are also used in industry quite extensively. Wood working jigs are useful for creating intricate wooden profiles.

Jigs and Fixtures

Jigs and fixtures are production tools used to accurately manufacture duplicate and interchangeable parts. Jigs and fixtures are specially designed so that large numbers of components can be machined or assembled identically, and to ensure interchangeability of components.

The economical production of engineering components is greatly facilitated by the provision of jigs and fixtures. The use of a jig or fixture makes a fairly simple operation out of one which would otherwise require a lot of skill and time.

Both jigs and fixtures position components accurately; and hold components rigid and prevent movement during working in order to impart greater productivity and part accuracy. Jigs and fixtures hold or grip a work piece in the predetermined manner of firmness and location, to perform on the work piece a manufacturing operation.

A jig or fixture is designed and built to hold, support and locate every component (part) to ensure that each is drilled or machined within the specified limits.

The correct relationship and alignment between the tool and the work piece is maintained. Jigs and fixtures may be large (air plane fuselages are built on picture frame fixtures) or very small (as in watch making). Their use is limited only by job requirements and the imagination of the designer.

The jigs and fixtures must. be accurately made and the material used must' be able to withstand wear and the operational (cutting) forces experienced during metal cutting

Jigs and fixtures must be clean, undamaged and free from swarf and grit Components must not be forced into a jig or fixture.

Jigs and fixtures are precision tools. They are expensive to produce because they are made to fine limits from materials with good resistance to wear. They must be properly stored or isolated to prevent accidental damage, and they must be numbered for identification for future use.

INTRODUCTION TOOL DESIGN

INTRODUCTION

In 2006, the U.S. Department of Education developed a Tool Kit on Teaching and Assessing Students with Disabilities (Tool Kit) to support the Department’s initiative to improve outcomes for students with disabilities. The Tool Kit focused on increasing states’ capacity to provide rigorous assessment, instruction, and accountability for students with disabilities.  The Tool Kit on Universal Design for Learning is an additional component of the original Tool Kit, and offers a compilation of current information on universal design for learning (UDL).

What is UDL?

UDL is a framework for designing educational environments that help all students gain knowledge, skills, and enthusiasm for learning.  The concept of UDL was inspired by the universal design movement in product development and architecture, which calls for the design of structures that anticipate the needs of individuals with disabilities and accommodate these needs from the outset (Orkwis & McLane, 1998; Rose & Meyer, 2002).  Elements of universally designed buildings might include levered door handles, widened bathroom stalls that can accommodate wheelchairs or other assistive devices, and tables and countertops at a variety of heights.  The tenets of universal design also can be applied to teaching and assessing, and in these contexts, a universally designed curriculum includes goals, methods, materials, and assessments, and supports all learners by simultaneously reducing barriers to the curriculum and providing rich support for learning (Rose & Meyer, 2002). In a classroom using a universally designed curriculum one might find books on tape, interactive software, magnifiers, or highlighted materials.  UDL can be used operationally to provide access to the general education curriculum and maximize learning for the greatest number of students (Access Center, n.d.).

UDL is a framework with three guiding principles that parallel three distinct learning networks in the brain:  recognition, strategy, and affect (Rose & Meyer, 2002).  This framework is important because it reflects the ways in which students take in and process information. Using this framework, educators can improve outcomes for diverse learners by applying the principles below to the development of goals, instructional methods, classroom materials, and assessments.   Use of these principles leads to improved outcomes for students because they provide all individuals with fair opportunities for learning by improving access to content.

1. Provide multiple and flexible methods of presentation to give students various ways of acquiring information and knowledge. Technically sophisticated (hi-tech) examples of this include using digital books, specialized software, and Web sites.  Low-technology (low-tech) examples include highlighted handouts, overheads with highlighted text, and cards with tactile or color-coded ink.
2. Provide multiple and flexible means of expression to provide diverse students with alternatives for demonstrating what they have learned.  Hi-tech examples of this include online concept mapping software, which provides students with a graphic map to demonstrate learning, speech-to-text programs, and graphing to a computer, which collects data regarding students’ learning progress.  Low-tech examples include cooperative learning (asking the student to demonstrate his/her learning in small groups), think alouds (encouraging the student to talk about what s/he is learning), and oral tests.
3. Provide multiple and flexible means of engagement to tap into diverse learners' interests, challenge them appropriately, and motivate them to learn.  Hi-tech examples include interactive software, recorded readings or books, and visual graphics.  Low-tech examples include, games or songs, performance-based assessment, and peer tutoring.

UDL can incorporate the use of digital materials and be implemented in a broad range of educational settings. Research has shown that digital materials, such as automated speech to text, provide powerful learning supports in the universally designed classroom.  Well-designed, digital materials can sometimes be more flexible than conventional classroom tools such as printed text, printed images, and lectures (Center for Applied Special Technology, n.d.).  Digital materials can be modified easily and efficiently from one media type to another instantaneously.  For example, one might modify text to speech, speech to text, image to text, depending on the needs of the student.  Such materials make it easier to customize and individualize learning materials and methods.  This transformational capability of digital media is, in part, the impetus for the Individuals with Disabilities Education Act (IDEA) of 2004 regulations related to the National Instructional Materials Accessibility Standard (NIMAS).  Students with disabilities that make it difficult to read printed materials may require Braille, e-text, audio or large print versions of core learning materials.  All of these can be created from a single NIMAS-compliant digital source file.   NIMAS is a technical standard used by publishers to produce source files (in XML) that may be used to develop multiple specialized formats (such as Braille, audio books, electronic text, large print, etc.) for students with disabilities related to accessing printed materials.  NIMAS enables states and school districts to leverage the flexibility afforded by digital technology to develop those multiple specialized formats quickly and efficiently.   .

UDL Teaching Methods

The Center for Applied Special Technology (CAST), funded by the Office of Special Education Programs (OSEP), at the U.S. Department of Education, has devised three sets of broad teaching methods that support each of the three UDL principles.  These teaching methods draw on knowledge of the qualities of digital media and how recognition, strategic, and affective networks operate.  The UDL teaching methods (Rose & Meyer, 2002) are listed below. .

To support diverse recognition networks:

• Provide multiple examples;
• Highlight critical features;
• Provide multiple media and formats; and
• Support background context.

To support diverse strategic networks:

• Provide flexible models of skilled performance;
• Provide opportunities to practice with supports;
• Provide ongoing, relevant feedback; and
• Offer flexible opportunities for demonstrating skill.

To support diverse affective networks:

• Offer choices of context and tools;
• Offer adjustable levels of challenge;
• Offer choices of learning content; and
• Offer choices of rewards.

Benefits and Examples of UDL

UDL is a framework for providing instructional content in a variety of formats that respond to student learning differences and, therefore, make curricula more accessible for students (Orkwis, 2003).  With UDL, educators can still individualize learning, while maximizing the consistency of educational goals, by developing a flexible curriculum that supports all learners (Hitchcock et al., 2002).  UDL also provides for delivering instruction using a variety of teaching methods.  Technology provides one means of changing instruction and engaging students in digital learning formats (Abdell & Lewis, 2005); however, there are a variety of additional ways that UDL can be incorporated into education, such as the following:

• Building accessibility into design helps to ensure that features meeting the needs of the widest range of students are incorporated integrally into the curricula.  Such designs can prevent the need for adaptations or retrofitting.  For example, electronic curricular material that is designed to be compatible with assistive technology devices allows paraprofessionals, parents, or teachers to more easily program these devices with appropriate content.
• Providing adaptable materials and media allows students to choose and customize formats suited to their learning needs.  For example, using digitized text, students can change text to speech, speech to text, font size, colors, and highlighting.  Digitized materials also can support students through built-in scaffolding to assist with activities such as word recognition, decoding, and problem solving.  There also are non-digitized materials, such as highlighted passages or overheads, that can provide support to students.
• Using multiple media, such as video and audio formats, provides a variety of ways to represent a concept and allows students to access the materials through different senses.  For example, computer-based simulations that include video description can help students with and without disabilities to visualize difficult concepts.  A more low-tech example might be using a book with large print or providing books on tape for students.
• Providing challenging, salient, and age-appropriate materials to all students motivates students who may not otherwise be able to access curricular content they need given their age and developmental level. For example, a student with a learning disability can use decoding supports and text-to-speech features incorporated into digitized history or science books, enhancing his or her ability to access grade-level content.
• Presenting information in multiple, parallel forms help to accommodate diverse learning styles.  For example, information can be presented orally in a lecture, visually through pictures or readings, kinesthetically through a model demonstration, and using technology-based programs that further allow students to interact with the concepts