BMFS 3373
CNC TECHNOLOGYLecture 3
Lecture Objectives
At the end of the lecture, you will be able to: Understand the engineering drawing terms and to
interpret various projections Identify the various types of systems and practices
used in basic blueprint drawing State the various tooling and their applications in
milling and lathe operation Explain the meaning of tool speeds and feeds for
milling operations Understand the difference between climb milling and
conventional milling & various cutting fluid application
Drawing Formats
Title Block: placed in the lower right-hand corner of the drawing form. It shows the company’s name and address, drawing title, scale, drawn and checked by, etc.
Part list: also known as the Bill of Material (BOM) is located above the title block.
Revision block: placed in the upper right-hand corner of the drawing. Indicates the zone where the correction takes place and the description of correction.
Notes block: is located to the left of the title block. Contains Tolerances, Material, Finish, Next assy, Used on
Visualization
1. Parallel projection:a. Multiview orthographic projection present the minimum views needed to completely describe a 3-D object Auxiliary views Sectional views- Commonly used as working drawing
b. Oblique projection
c. Axonometric projection Isometric Dimetric Trimetric
2. Perspective projection
Drawing Codes
Other aspect to be understood when reading a blueprint:
DimensioningTolerancesThread forms and dimensioningSurface finish symbols and notes
Tooling for Drilling
Twist DrillMost important tool used is the twist drill.Comprise of 2 helical grooves/flutes that cut
around a center (web), shank (straight/tapered)The web gives strength to the drill in resisting
deflection.Accuracy tends to decrease when either the drill
length or drill size is increased – less stiffness and more torsional deflection.
Metal cutting twist drills are made from a wide range of material ranging from carbon tool steel to solid carbide.
Tooling for Drilling
Tooling for Drilling
Center DrillTo better locate a hole center, center drills are
used due to its short and stubby character as compare to twist drill.
The initial work is used to guide the twist drill into the material
Good practice: the countersunk portion is approx. 0.003 to 0.006 in. larger than the twist drill diameter
Tooling for Drilling
Tooling for Drilling
Spade DrillConsists of a blade holder to which one of several
different size drill point blades can be bolted in.The larger web of the spade drill ensures that during
drilling penetration less flexturing occurs and thus more accurate hole results.
Spade drills are designed to machine a hole from the solid in one pass - no need for center drilling or multiple pass drilling. However the hole depth is limited because flutes does not exist to carry out the cut chips.
To fully utilize the cutting tool, a 50% or greater torque machine is required with increased machine rigidity.
Tooling for Drilling
Tooling for Drilling
Indexable Insert DrillMade of carbide that helps penetration into the
hardest of material. It offers a penetration rates of 5 to 10 times that
of a twist drill or spade drill.However it requires a machine to have higher
spindle horsepower, pressurized cooland system and rigidity
Tooling for Drilling
Tooling for Hole Operation
Boring: enlargement of existing hole & accurate readjustment of the center location of the enlarged hole
Reaming: increase the accuracy of a hole dimension size
Tapping: cutting threads on the inside of a holeCounterboring : enlargement of a hole to a depth
slightly larger than the head of a specific bolt/pin to allow the head to burried below the machined surface.
Countersinking: enlargement of the top end of a hole in the form of coneshaped depression to allow a flat or oval head machine screw to be flush or slightly below the surface when inserted.
Tooling for Hole Operation
Cutting Parameters
Cutting speed is defined as the speed of any point on the circumference of the tool (surface feet per minute/sfpm)
Cutting Parameters
Cutting speed selected for a particular tool will depend on several factors, some of which are: Type of hole operation, material hardness, hole depth Type of tool used and type of lubricant or coolant used Type of hold-down fixture and CNC machine used
Cutting Parameters
Tool feed (Hole Operation) is defined as the rate at which the tool advances into the work per revolution (inch per revolution/ipr)
Cutting Parameters
Tooling for Milling
End Mill:2 flutes vs 4 flutes :Different hardness of materialPlunging directly into center of solid materialSuitable for rough drilling hole, counterboring
and boring, as well as slotting and cavity cutting
Tooling for Milling
End Mill:
Tooling for Milling
Shell End Mills:Several cutter sizes can be fitted to one mounting arborFacing uses this cutter
Tooling for Milling
Carbide Indexable Insert End Mills:
Cutting Parameters
Cutting Speed for milling is the same as previous explanation
Tool Feed for milling
Cutting Parameters
Correct feed for milling also depends upon another parameter known as chip thickness. This is not the chip load (feed per tooth) but the actual thickness of chip resulting from a given feedrate
For general purpose milling, the chip thickness must be within 0.004 to 0.008 in. or it will cause premature wear and breakdown of the carbide insert cutters.
Cutting Parameters
Feed Direction for Milling Operations
Climb Milling (Down) The tool to make a chip of maximum thickness at
the start of the cut at and near the part surfaceLess clamping and horsepower is requiredRecommended in order to get a more accurate
roughing cuts with minimum machining marks and machining thin parts or parts that are hard to hold down
Cutter are less prone to be dull as the chips are pushed behind and away
Conventional Milling (Up)
Feed Direction for Milling Operations
Conventional Milling (Up)The tool starts with a cut of chip of no
thickness before attaining maximum thickness at the end of the cut near and at the part surface
High clamping and horsepower is required especially for hard outer scales material.
Recommended in cases where the a tool length used may cause unacceptable chattering of the cutter if using climb milling
Cutter are prone to be dull as the cut can create high tool impact
Feed Direction for Milling Operations
Cutting Fluids
Cutting fluids are essential in order to minimize the heat built up during the shearing action of the tool towards the workpiece.
The phenomenon known as Built Up Edge (BUE) can result in the tool’s edges becoming dull.
Cutting Fluids
Water based solutions of cutting oil are the 2 most commonly used cutting fluids. They can be divided into 4 categories: Nondilutable straight oils – provides best lubrication but
poorest cooling Water soluble oils – provides both good lubrication and cooling Semi-synthetic fluids – lubrication and cooling falls between
synthetic and soluble oil fluids Synthetic fluids – provides best lubrication and cooling of all
fluids
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