gauges

1. marking gauge:

--it is made of wood and it is used to draw lines parallel to the edge of a piece of wood

-- it has one marking point

2.mortise gauge:

--it is an improved form of marking gauge which instead of one,carries two scribing pins-one fixed other movable

--it has two marking points

--it is used to mark two parallel lines in a single operation on a face

---this is special y used for mark mortises and tenons and other such similar joints which require parallel lines

3. panel gauge: it is used to mark lines across surface

4.cutting gauge: it has a steel cutting knife, held position by a wedge to vary the depth of cut

it is mainly used for cutting parallel strips from thin wooden sheets up to 3 mm an d for making thin deep lines in thicker sections

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trammel points

• these are mainly used for drawing larger arcs and circles
• they are also used for laying out various geometrical shapes such as an ellipse or a multi sided figure
• these have two marking points

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marking knife

• it is also called scriber
• it is generally made up of steel and consists of sharp point at one end and a slating chisel edge at the other end
• it is used for converting pencil lines into cut lines and in other words, we can say it is used for making where accuracy is necessary

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combination square

it is combination of 6 tool

• square
• a 45 bevel
• a set square
• a rule
• a straight edge
• a center finder

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miter square

used to mark and measure the angles of 45

bevel square: it is an adjustable try square having a blade that can be swivel led to measure and mark any angle between 0 and 180 c

it is also called as sliding bevel

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try square

• it consists of a steel blade fixed at right angles to the edge of a machined stock either of metal or wood
• it is used for marking and testing right angles
• 
  

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straight edge

• it is piece of wood or meta, machined perfectly flat and straight on all its edges
• it is used for testing truences of large surfaces and edges

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tools

1. four- fold rule:

as the name implies it contains four pieces made of wood.each measuring 15 cm long and are joined together by means of hinged joint

it is used for measuring and setting down dimensions

2. flexible steel tape:

it is used for measuring longer dimension

by virtue of the flexibility it can be used for measuring curved as well as angular surfaces also

it is usually available in 2 m length

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grinding machines

• rough grinders:
  

1.floor stand& bench grinders
2.portable and flexible shaft grinders
3. swing frame grinders
4.abrasive belt grinders

• precision grinders: are those that finish parts to any accurate dimensions a. cylindrical grinders: it is primarily used for grinding plane cylindrical parts, contoured cylinders,tappers fillets, cams and crank shafts etc
  

-center--type(plain)
- center--type (universal)
centreless

b. internal grinders: used to finish straight ,tapered or formed holes to correct size
----chunking---
----planetary---
-----center less-

c.surface grinders:

---- -reciprocating table
----- rotating table

d. tools and cutter grinding:
-----universal
---special
-----special grinding machines:
eg: crank shaft grinders
piston grinders
roll grinders
thread grinders
key way grinders
toll post grinders

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kinds of grinding

1. rough or non precision grinding:the common forms of rough grinding are 'snagging' and off hand grinding'
2. precision grinding: produce good surface finish and high degree of accuracy
3. external cylindrical grinding:produce a straight or tapered surface on a work piece
4. internal cylindrical grinding: produce internal cylindrical holes and tapers
5. surface grinding: produce flat surface
6. form grinding: done with specially shaped grinding wheels for grinding gare teeth, thraeds, splined shafts , holes, spheres etc
   

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truing

it is the process of changing the shape of the grinding wheel as and when it becomes warn from original shape
it is done to make the wheel true and concentric with the bore or to change the face contour of the wheel for form grinding.

dressing: it is the process of removing the loading of the wheel and breaking away of the glazed surface so that sharp abrasive particles are again presented to the work
A tool known as star-dresser us generally used to perform this operation

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glazing

when the abrasive grains become dull and stop cutting the wheel is said to be glazed

loading: when the abrasive particles at the cutting face of the wheel become embedded with the material which is being cut , the wheel face is said to be loaded

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Grit,grade and structure of grinding wheels

1. Grit or grain: it indicates the size of the abrasive grains used in making a wheel

• coarse wheels are used for fast removal of materials and for soft and ductile materials
• fine grain wheels are used to grind hard and materials.

2. Grade: it refers to the tenacity or hardness with which the bind held the cutting points.

denoted y the 'A' -softest and 'Z'-the hardest .hard wheels are recommended for soft materials and soft wheels are recommended for the hard materials.

3. Structure or grain spacing: the structure refers to the number of cutting edges per unit area of wheel face as well as to the number and size of void spaces between grains.
denoted by numbers.
soft,tough and ductile materials and heavy cuts require an open structure where as hard and brittle materialsand finishing cuts require a dense structure

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Bonding process

1. Vitrified bonding: It is a clay bond base material 'Feldspar' denoted by 'V
2. Silicate bonding: Base materials -silicate of soda or waste glass. it is denoted by letter 'S'

3.Shellac bonding: Abrasive grains are first coated with shellac by being mixed in a steam heated container

• shellac bonded wheels are also known as elastic bonded wheels
• it is denoted by the letter 'E'

4. Rubber bonding: bonding material-pure rubber with some amount of sulpher which act as vulcanizing agent used as anagging wheels in foundries.

5. Bakelite or Resinoid bonding: Abrasive grains are mixed with powdered synthetic resin and a liquid solvent which dissolves resin.

6.Oxy chloride bonding: prepared by mixing abrasive grains with oxides and chlorides of magnesium.
denoted by the letter 'o'

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Abrasives & bond

1. Abrasive : It is the material of the grinding wheel which does the cutting action.
2. Bond : It is the material of the grinding wheel which acts as a binder to hold the abrasive.
3. Types of Abrasive:

1) Natural : examples Quartz,emery,corundum,diamond etc

2)Artificial :

a) Silicon carbide :Trade names: Cry stolon, Electrolon & Carborundum.it is
denoted by 's' it is used for grinding low tensile strength materials like
cemented carbides ,cast iron etc.

b) Aluminum Oxide(al2o3) : Trade names: Aloxite,alundum& borolon.denoted by

'A'

USES: high tensile strength materials like carbon steels,high speed steels,wrought iron,annealed malleable iron etc.

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grinding basics

A metal cutting operation performed by means of rotating abrasive wheel that acts as a cutting tool is called "grinding".

• Action of grinding wheel is very much similar to that of a milling cutter.
• Accuracy in dimensions is in the order of 25 microns . it is the only method of cutting hardened steel.
  

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