Intact Stability GM Quick Check: Metacentric Height, Free Surface Correction and a Worked Example

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Every loading condition on a ship or workboat starts with one question: is the vessel stable enough to sail? The fastest first answer is the transverse metacentric height, GM. This post sets out the hydrostatic fundamentals behind it, shows how free surface in slack tanks erodes it, explains how the inclining experiment fixes the lightship KG, and works through a loading condition for a small cargo vessel. It ends with the first checks against the IMO 2008 Intact Stability Code. It is a screening method, not a substitute for a full stability booklet. It also sits alongside our wider overview of marine engineering and naval architecture . Fundamentals: KB, BM, KM, KG and GM A floating vessel is in equilibrium when weight equals buoyancy and both act along the same vertical line. Buoyancy is the resultant of hydrostatic pressure on the hull, a topic we cover in pressure and fluid statics . When the vessel heels through a small angle, the underwater shape changes, and the centre of buo...
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Gear Forming by Machining

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Gear Forming by Machining

Formation of gear through machining consists of following methods:
      1. Form Milling by Disc Cutter
      2. Form Milling by End Mill Cutter
      3. Shaper, Planner and Slotter
      4. Broaching

1. Form Milling by Disc Cutter

It is defined as, "Tooth is cut one by one by plunging the rotating cutter into the blank". 
  • Each gear needs a separate cutter.
  • 8 - 10 standard cutters are available for producing 12 - 120 teeth gears.
  • Used for big spur gears of large pitch.

2. Form Milling by End Mill Cutter

It includes the cutting of tooth at a time and then indexed for the next tooth space for cutting.
  • For a small volume production of low precision gears.
  • Set of 10 cutters  ↠  12 - 120 teeth gears.
  • Used for teeth of large gears/module.
  • To reduce cost, same cutter is often used for multiple sized gears resulting in profile errors.

Characteristics:

  1. Use of Hardened stainless steels (HSS) form milling cutters.
  2. Use of Ordinary milling machines.
  3. Low production rate (need of indexing after machining, slow speed and feed).
  4. Gear having different modules and number of teeth need separate milling cutters.
  5. Low Accuracy and surface finish.

3. Shaping, Planning & Slotting of Tooth Space

  • Shaper  ↠  Linear motion for cutting reciprocates parallel to the center axis of blank and cuts one tooth at a time. It is used for repair and maintenance purpose.
  • Planning  ↠  Machine for large gears.
  • Slotting  ↠  for internal gears.

4. Broaching

Multi-toothed tool in which successive tooth takes a small cut but when all the teeth have passed over the gear blank to be machined.
  • Internal, external spur gears, straight or single helical gears are produced in large quantity.
  • External teeth are produced by broaching in one pass.
Note:

References:

  • Material from Class Lectures + Book named Fundamentals of Modern Manufacturing Materials, Processes and Systems by Groover + My knowledge. 
  • Photoshoped pics are developed. 
  • Some pics and GIF from Google.  
  • Videos from YouTube (Engineering Sights).

Comments

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