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Friday, 29 November 2013

Spur Gear Cutting

Spur Gear Cutting Points : what is Spur Gear Cutting Gear cutting is one of the most interesting operations that can be performed on a milling machine. The dividing head, formed tooth cutters, (involute gear cutter), and other features of modem milling machine provide a system of spur gear cutting that is beautiful in its simplicity, the complete set up. This system is not efficient, however for mass production of gears. Procedure Skill in Gear Cutting
  1. Select a fairly short mandrel of a diameter that will fit the hole in the hub of the gear blank.
  2. Wipe the mandrel clean and lightly oil the surface.
  3. Press gear blank on mandrel, using an arbor press or a lead hammer. Wipe a thin layer of white lead over mandrel to avoid scoring the bore of the gear blank.
  4. with the cross feed, run the table as close as practicable to the column.
  5. Fasten the dividing head and tailstock (footstock). Place them on the table of the milling machine as close to the column as the nature of the work and dividing head will permit.
  6. Fasten the dividing head securely in position. Then slide the tailstock forward until the centers just touch. Check head and tailstock centers for alignment before bolting them to table. Allow sufficient adjustment on footstock (tailstock) screw to insert and remove mandrel.
  7. Mount milling cutter (10 pitch No. 5) on machine arbor. Align with center of index centers (approximately). Remove all chips and burrs from the faces of the collars.
  8. Set index head for correct indexing.
  9. Place dog on large end of mandrel and mount mandrel and job between centers with dog toward the headstock. Make sure that the tail of the dog has moving clearance in the slot of the work driver.
  10. Clamp tail of dog with screw of work driver. While tightening the screw, see that the tail of the dog is not forced out of its normal position.
  11. Set the machine controls for proper spindle rotation, spindle rpm, and table feed rate and direction.
  12. Now align the side of the cutter dyer, the side of the gear blank. Move the cross feed screw until the workpiece edge just touches a straight edge held against the far side of the gear cutter.
  13. Measure the width of the cutter and divide it by two. Measure the diameter of the gear blank and divide it by two. Subtract half the cutter width from half the gear blank diameter. This is the amount the workpiece must be moved to place its center line directly below the center line of the cutter. Or: Centralize the cutter with the gear blank by placing the blade of a square tangent with the circumference of the blank and measuring distance from the side of the cutter. Do the same on the other side of the gear blank and adjust until both sides measure the same.
  14. Adjust the dividing head crank and sector to index the required number of divisions, (that is one turn and 22 spaces or (23 holes) on 33 circle).
  15. Run the work under the cutter and raise the table until a piece of paper is torn between the revolving cutter and the blank.
  16. Allow 0.002 in. for paper thickness and set graduated collars on verticals adjustment at zero (0).
  17. Move job clear of the cutter and raise the table to the depth of the roughing cut.
  18. Rough out the first tooth and adjust the automatic feed trip.
  19. Run the tab)e back to starting position.
  20. Index one turn 22 spaces or (23 holes) on 33 circle for the next tooth, and so on until all teeth ate roughed out.
  21. Raise the table to 0.2 16 in. (full depth) and take the finish cut for each tooth.

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