Drilling and Reaming - THY200 - Seneca College - PDF

Seneca College of Applied Arts & Technology THY200 Drilling and Reaming  Drills Great at making holes Efficient at removing material with a high MRR They are available in a range of types, sizes, materials, coatings, geometries, and features...

Seneca College of Applied Arts & Technology THY200 Drilling and Reaming  Drills Great at making holes Efficient at removing material with a high MRR They are available in a range of types, sizes, materials, coatings, geometries, and features Relatively low cost Jobber twist drills Sets, Sizes and Charts Fractional inch: >1/64” Numbered: >#1 (>0.228”) Letter: A-Z (0.234”-0.413”) Decimal inch Metric  Materials/Coatings HSS: general purpose drilling, low cost HSS + Cobalt: Tougher materials, higher hot hardness Caride: Heavy duty, high production, hardest materials  Carbide Drills Can be solid carbide or have carbide inserted tips. Extremely hard: They maintain a sharp edge much longer than HSS. Brittle: Best not to hand-drill or use drill press. Can drill extremely hard, difficult-to-machine materials. Often used to drill steel, cast iron, non-ferrous metals and high-temperature alloys. Spot Drills Creates a starter dimple for precise twist drill location Stubby to reduce deflection Not necessary for carbide drills* Short flutes, not designed to drill past the point angle Point angle must be greater than drill  Center Drills Creates a 60° tapered hole for use with lathe tailstock centres Has a small pilot as well as a 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 Typically used to a depth equal to ⅔ the length of the taper Spade Drill Replaceable cutting insert. Ranges from approximately 0.5” to 4.0” 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 that require a great deal of heat at the cutting point in order to machine efficiently.  Drill Shanks Twist drills may have straight or tapered shanks. Morse taper is the most common. Refer to your Machinery’s Handbook for more info on Morse tapers.  Drill Holders – Chuck A Jacobs chuck is a common drill holding device. The jaws open and close quickly with the use of a chuck key Can hold a wide range of drill sizes Do not leave the chuck key in the chuck! Drill Holders – Morse Taper Use the correct size of Morse taper sleeve to mate your drill bit with the machine. A, “drift” can be used to tap the drill away from the sleeve. Drill Machines Standard drill press. Drill Press - Belt Drive Some drill presses are gear-driven internally. Others, like the one in this illustration, use a V-belt to drive the spindle. The V-belt height can be manually adjusted by hand in order to change the RPM. Only do this with proper procedure and safety training!  Drill Machines Deep hole or gun drilling machine. Radial arm drill Workpiece Holding A vise is used to hold a workpiece in place Ensure the vice is clean before use Do not drill the vice! Drill Geometry  Drill Point Angles Medium Hardness Materials Harder Materials Softer Materials The standard drill point angle is 118 degrees included angle.  Drill Point Angles Drill point angle affects the tightness of the chips. Lip Relief or Lip Clearance Angles Lip relief angles are normally 10º to 15º, standard twist drill is usually 12º. Lip relief for high strength or tougher steels is between 7º to 12º (Stronger backing for cutting edge.) Lip relief for softer materials may be between 12º to 18º. Lip Relief or Lip Clearance Angles Lip relief angles are normally 10º to 15º, standard twist drill is usually 12º. Lip relief for high strength or tougher steels is between 7º to 12º (Stronger backing for cutting edge.) Lip relief for softer materials may be between 12º to 18º.  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 Influences 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. Appropriate for drilling brass.  Drilling Speeds and Feeds Drilling speeds and feed rates can be found in the Speed and Feed charts in your Machinery’s Handbook. Manufacturer-specific information can be found by contacting a sales representative from a cutting tool manufacturer. Cutting RPMs can be 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 be used first, to 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. Unless otherwise stated Drill point length = D/2[Tan(90-A/2)] DPL for 118° drill points = ⌀*0.3  Sharpening a Twist Drill Skilled people can grind drills by hand. Only attempt this after you receive a proper demonstration from your instructor. Do not rush to complete the drill grinding exercise in the shop; this project is a useful filler when you have to wait to use other machines and equipment. https://youtu.be/y0SQkzScQk0?t=85 What Causes Oversized Holes? Drill lips ground to Drill lips ground to Unequal lengths unequal lengths. unequal angles. 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 an 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 Parts of a Reamer 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 thce. e correct reaming allowanapproximately 2% of a given hole diameter. For example, for a 0.5” reamed hole, the reamer should remove ~0.01”. Charts can be found online that suggest drill sizes for proper reaming allowance. End of Presentation