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Pp mills

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Unit /012 Topic - Milling machines

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Pp mills

  1. 1. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Preparing and using milling machines
  2. 2. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Working safely with milling machines Milling machines produce plane surfaces using rotating multi-tooth cutting tools. When using milling machines: • Suitable guards should be used with horizontal milling machines. • Rotating cutters are far more dangerous than the fixed tool on a lathe, so extra care needs to be taken. • You will need to use heavy vices, rotary tables and dividing heads.
  3. 3. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Vertical mills
  4. 4. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Horizontal mills
  5. 5. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Vices and clamps for milling machines What workholding devices are shown here? What uses do these have with milling machines?
  6. 6. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted The dividing head A dividing head provides a circular division to produce components such as hexagonal nuts or gear teeth around a circular blank. Dividing heads can be angled to produce tapered sections or angled faces on cylindrical work.
  7. 7. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Cutting tools Milling machine cutting tools are made from different materials, such as cemented carbides or high speed steel (HSS). Check any cutting tool to make sure it is sharp and has no points or teeth missing as damaged cutters can give a poor finish or fail. Cutters should be stored individually and lightly oiled so they do not corrode or get blunted by rubbing against each other.
  8. 8. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Setting a machine vice true Before milling a component, set the fixed jaw of the vice true to the axis of the machine. Before setting up: • clean the machine table and underside of the vice making sure there is no swarf or grease • check there are no burrs on the table or underside of the vice • make sure the tee bolts are the correct length and the washers, if used, are thick enough and do not distort when tightened.
  9. 9. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Mounting the cutter (vertical milling machine) Most vertical milling machines use the R8 system of mounting tools in the spindle. To mount an 18 mm end mill using an R8 collet: • Isolate the milling machine. • Slide the correct R8 collet into the spindle of the milling machine, making sure the groove in the collet lines up with the location pin inside the spindle. • Start to tighten the draw bar by hand to hold the collet in position. • Slide the cutter into the collet and position correctly. • Engage the spindle brake and tighten the draw bar using a spanner.
  10. 10. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Mounting the cutter (horizontal milling machine) Most cutters for horizontal milling machines have a hole through the centre and are mounted on an arbor. To mount a side and face cutter: • Isolate the milling machine. • Slide spacing collars along the arbor to enable the cutter to be fitted correctly. • Slide on the cutter, making sure you align the teeth in the correct direction to suit the work you are doing. • Fit more spacing collars and the running bush, tightening the arbor but by hand, checking there are enough spacers to clamp the cutter. • Slide on the arbor support and position. • Fully tighten the arbor nut and check the arbor support.
  11. 11. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Feed rate for mills The feed rate on a mill is measured in mm per minute. This is calculated for the amount of cut each cutter tip can make. Cutting tool material Feed per tooth (chip thickness) in mm for Mild Steel Face mill Slab mill Side and face Slitting saw Slot drill End mill HSS 0.1 – 0.4 0.1 – 0.3 0.07 – 0.2 0.025 – 0.05 0.05 – 0.1 0.05 – 0.2 Carbide 0.07 – 0.3 0.06 – 0.2 0.05 – 0.15 N/A 0.03 – 0.08 0.03 – 0.15
  12. 12. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Up cut milling Up cut milling is where the work is fed into the cutter in the opposite direction to the rotation of the cutter. This prevents the cutter snatching the work. Workholding devices must be very tight as there is a lot of strain placed on them.
  13. 13. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Down cut milling Down cut milling is where the work is fed into the cutter in the same direction as the rotation of the cutter. The cutter can snatch and ride over the workpiece.
  14. 14. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Making the first cut Method Advantages Disadvantages Touch the tool onto the work with the spindle running, set to zero and skim cut the surface. Must be done for all 3 machine axis Quick and easy, the most accurate method as the cut surfaces are used as a datum You may not want to cut or re-cut the datum surfaces and it may be hard to hold the work and machine 3 sides even partially. Use a feeler gauge in between the cutter and the work with the machine isolated, moving the cutter slightly as the feeler gauge is checked. Does not mark the work so settings can be taken from finished surfaces This technique needs lots of experience and practice to be accurate and needs a flat or convex surface allowing easy access for the feeler gauge Use a small bit of thin paper stuck to the work with a drop of coolant, if you measure the paper first when the rotating cutter flicks the paper away you are that distance from the workpiece. Quick and simple method that is quite accurate and does not mark the work. Paper may be blown off by draught from moving cutter or paper may swell due to coolant. Use a wiggler or edge finder to indicate when you are half the diameter of the ball or roller away from the datum surface. Very quick and easy to use, does not mark the work and is very accurate. The process is repeatable so can be easily checked. Does not work in the Z axis so another method will need to be used here.
  15. 15. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Milling steps or shoulders • Clamp the workpiece to the machine table using a workholding device. • Position the side of the cutter to the face of the workpiece and zero the machine. • Wind the table to the required width of the step, allowing 0.3 mm less for the finishing cut. • Position the bottom of the cutter against the top of the workpiece and zero the machine. • Machine out the shoulder, taking roughing cuts until you are 0.3 mm away from the required depth. • Check the dimensions of the step/shoulder and set the machine for the final cut reducing the feed rate to give a good finish.
  16. 16. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Enclosed slots, pockets and recesses Different slots require different milling machines. • Clamp the workpiece to the machining table. • Position the side of the cutter to the face of the workpiece and zero the machine. • Wind the table to the correct position for the cutter to start the slot/pocket. • Zero the cutter to the workpiece. • Machine out the closed slot.
  17. 17. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Drilling and boring using the milling machine Drilling operations can be carried out on the vertical mill by unlocking the vertical quill and using the drilling handle to feed the drill into the work. Boring heads can be mounted on the spindle of milling machines and allow accurate holes to be created.
  18. 18. Chapter 7 Preparing and using milling machines © Pearson Education 2012 Printing and photocopying permitted Checking work Checks need to be carried out on work to: • notice problems during the production plan, giving you the chance to put it right • make you aware that tools are blunt or damaged • highlight shortages of materials, tools and equipment • see errors accumulating • save wastage • reduce costs.

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