Drilling Techniques and Tools Overview

Drilling and Reaming

• Drilling is efficient at removing material with high Material Removal Rate (MRR).
• Available in various types, sizes, materials, coatings, geometries, and features.
• Drills are relatively low cost.

Drills - Types, Sizes, and Charts

• Fractional inch sizes: greater than 1/64".
• Numbered sizes: greater than #1 (0.228").
• Letter sizes: A to Z (0.234" to 0.413").
• Decimal inch sizes
• Metric sizes

Materials/Coatings

• HSS: general purpose, low cost.
• HSS + Cobalt: tougher materials, higher hot hardness.
• Carbide: heavy duty, high production, hardest materials.

Carbide Drills

• Can be solid carbide or have carbide inserted tips.
• Extremely hard; maintain sharp edge longer than HSS.
• Brittle, best not to hand-drill or use drill press.
• Drill extremely hard, difficult-to-machine materials.
• Commonly used for steel, cast iron, non-ferrous metals, and high temperature alloys.

Spot Drills

• Create a starter dimple for precise twist drill location.
• Creates a stubby to reduce deflection in the drill.
• Short flutes, not designed to drill past the point angle.
• Point angle must be greater than the drill's point angle.

Center Drills

• Creates a 60° tapered hole.
• Has a small pilot and larger counter sink.
• Stubby to reduce deflection.
• Often used as a spot drill.
• Typically not used on a mill.
• Short flutes (not designed to drill past the point angle).
• Do not break the center drill when drilling.
• Typically used to a depth of 1/2 the length of the taper.

Spade Drill

• Replaceable cutting insert.
• Ranges from ~0.5" to 4.0" in diameter.

Gun Drill

• Straight flutes.
• Large length-to-diameter ratio.
• Has coolant through holes.

Core Drill

• Used to enlarge pre-existing holes.
• Not meant for drilling into solid material.

Stellite Drill

• Used for drilling extremely hard materials.
• Requires great heat at the cutting point to machine effectively.

Drill Shanks

• Twist drills can have straight or tapered shanks.
• Morse taper is the most common type.

Drill Holders - Chuck

• Jacobs chuck is a common drill-holding device.
• Jaws open and close quickly using a chuck key.
• Holds a wide range of drill sizes.
• Do not leave the chuck key inside the chuck.

Drill Holders - Morse Taper

• Use the correct size Morse taper sleeve to mate the drill bit to the machine.
• A "drift" can be used to tap the drill away from the sleeve.

Drill Machines

• Standard drill press.
• Radial arm drill.
• Deep hole or gun drilling machine.

Workpiece Holding

• A vise holds a workpiece in place.
• Ensure the vise is clean before use.
• Do not drill the vice.

Drill Geometry

• Height of point
• Clearance angle
• Flank
• Drill diameter
• Drill Body
• Lead
• Helix angle
• Neck
• Flute length
• Shank length
• Overall length
• Neck length
• Margin width
• Depth of body clearance
• Margin
• Body clearance
• Chisel edge angle
• Flute
• Flute width
• Cutting edge
• Land width

Drill Point Angles

• The standard drill point angle is 118 degrees included angle.

• Medium hardness materials

• Harder materials

• Softer materials

• Drill point angle affects the tightness of the chips.

Lip Relief or Lip Clearance Angles

• Lip relief angles are normally 10° to 15°; standard twist drill is usually 12°.
• Lip relief for high-strength or tougher steels is between 7° to 12° (stronger backing for cutting edge).
• Lip relief for softer materials may be between 12° to 18°.

Drill Web

• The web of the drill holds the two flutes together.
• It thickens as a drill becomes shorter after sharpening.

Thinning the Web

• The web of the drill can be narrowed by carefully grinding it on the corner of a pedestal grinder wheel.
• Do not attempt without proper instruction.

Rake Angles

• Influencing chip flow:
• 18 to 45 degrees (typically 30).
• Larger angles for softer materials.
• Smaller angles for harder materials.

Drilling Brass

• A twist drill can be modified using a pedestal grinder to have a zero rake angle.
• Suitable for drilling brass.

Drilling Speeds and Feeds

• Drilling speeds and feed rates are in Machinery's Handbook.
• Manufacturer-specific information from a sales representative.
• Cutting RPMs calculated using the General Shop Formula or the Simplified Shop Formula.

Pilot Drills

• The web on a drill increases cutting pressure; it doesn't cut; it chisels.
• On larger diameter drills, over 0.5" or 12mm, cutting pressures can be extremely high.
• A pilot drill, slightly larger than the drill web can relieve cutting pressure on larger drill sizes.
• 0.25" or 6mm are typical pilot drill diameters.

Drill Hole Depth

• The depth of a drilled hole is measured to full diameter.
• Drill point length = D/2[Tan(90-A/2)]
• DPL for 118° drill points = Ø*0.3

Sharpening a Twist Drill

• Skilled people can grind drills by hand.
• Only attempt this after receiving proper demonstration from an instructor.
• Do not rush to complete the drill grinding exercise.

What Causes Oversized Holes?

• Drill lips ground to unequal lengths.
• Drill lips ground to unequal angles.
• Unequal lengths and angles.

Characteristics of Drilled Holes to Consider

• Not very round.
• Not very straight.
• Not accurately sized.
• Poor surface finish.
• Poor positional accuracy.

Reamers

• Reamers are used to finish pre-drilled holes.
• Reamed holes are extremely accurate in size and roundness (~0.0002").
• Reamed holes have excellent surface finish.
• Reamers can create very straight holes.
• Reamers cannot correct holes that are out of position.

Tapered Reamers

• Reamers can be tapered to finish-machine tapered holes.
• They can be found in Morse taper sizing.

Types of Reamers

• Reamers are usually made from HSS.
• Reamers are normally made for machines, but hand reamers are also available.

Parts of a Reamer

• Shank length
• Overall length
• Tang
• Taper shank
• Flute length
• Cutter sweep
• Chamfer angle
• Chamfer length
• Chamfer relief angle
• Actual size
• Straight shank
• Helix angle
• Helical flutes
• Right-hand helix shown
• Body
• Land width
• Margin

Reaming Speeds and Feeds

• Ream at half the RPM of drilling.
• Ream at twice the feed of drilling.
• When you ream, "half the speed, twice the feed."

Care and Use of Reamers

• Do not run reamers backwards.
• Remove reamer from hole before stopping machine spindle.
• Protect the cutting edges of reamers.
• Do not use reamers to clean out holes in hardened workpieces.

Reaming Problems

• Surface finish may be poor if too fast a feed is used.
• Score marks may be caused by damaged cutting edges.
• Chatter may be caused by too fast a spindle speed.
• Bell-mouthed holes may be caused by reamer misalignment.

Reaming Rules

• Use spiral fluted reamers for bores with key ways.
• Deburr holes before reaming.
• Leave the correct reaming allowance (approximately 2% of a given hole diameter).
• Charts can be found online to suggest the correct drill sizes for proper reaming allowance.

This quiz covers various drilling techniques and tools, including the types of drills, sizes, materials, and coatings. It delves into the specifics of carbide drills and their applications, providing an essential understanding for those in machining and manufacturing sectors.