Machining Operations: Drills Flashcards
What are the primary purposes of cutting fluids?
To reduce heat and provide lubrication to reduce friction.
Cutting oil is generally a mixture of mineral oil with additives like animal oils, sulphur, chlorine, and phosphorus to improve its wetting and lubricating qualities. What are they typically used for?
Low cutting speed applications like tapping, reaming, or broaching.
Emulsifiable (soluble) oils are manufactured by blending oil with an emulsifying agent like soap. The oil can then be mixed with water to form an emulsion of 90- to 98- percent water. What are they typically used for?
High-speed applications such as the lathe operations and milling machine work.
Chemical (synthetic) cutting fluids are mixtures of inorganic chemicals and water. Chemical coolants often contain extreme-pressure (EP) lubricants, which enable severe machining operations to be carried out. What are they typically used for?
Grinding machines.
The following chart details recommended cutting fluid applications. What type of fluid should be used on cast iron?
Cast iron can be cut without fluid.
What type of drill press is shown in the image?
A sensitive drill press.
When using a sensitive drill press, why should you ease up on the hand feed pressure when the drill breaks through the workpiece?
So the drill does not grab the workpiece and break.
What type of drill press is shown in the image?
A radial drilling machine.
What is one of the main benefits of radial drilling machines?
They can drill holes in very large workpieces that are difficult to position manually under the spindle of a standard drill press.
What are the two ways available to designate the size of a sensitive or upright drill press?
- From the center of the spindle to the column.
- The largest diameter of workpiece that can be centered under the spindle axis.
What are the three main parts of a twist drill?
- The shank.
- The body.
- The point.
How can you tell the helix of a drill?
By looking at the side of the drill and determining which side the helix falls towards (The drill in the image has a right hand helix).
The lip or cutting edge extends from the chisel edge to the margin and is the portion of the point that does the cutting. What should its included angle be ground to for general purpose work?
118-degrees.
Lip clearance is provided by grinding the heel lower than the cutting edge. Without this clearance, the drill would not be able to advance into the workpiece. What should the typical lip clearance be ground to?
8- 12-degrees.
What are the two types of drill shanks?
Taper and straight.
Up to what size are straight shank drills usually made?
Up to 1/2-inch in diameter.
A straight shank is less expensive to manufacture but cannot be held as securely as a taper shank.
On what size drills are taper shanks usually found?
Larger than 1/2-inch in diameter.
What are the dimensions of a Morse taper?
About 5/8-inch per foot.
What are high helix drills used for?
For deep holes in softer metals like aluminum, copper, and zinc. These metals tend to jam in the flutes of a normal drill.
What are core drill used for?
To enlarge existing holes.
What are oil hole drills used for?
They are especially useful on deep holes where it would otherwise be difficult to deliver cutting fluid to the point of the drill.
what is a straight fluted drill used for?
Soft materials such as brass, bronze, and plastic. Normal drills tend to draw themselves (dig) into these materials. The straight flute helps prevent this draw down.
What are step drills used for?
To drill and then countersink (or counterbore) a hole all in one operation.
What are center drills used for?
Is a combination drill and countersink used primarily to drill center holes for lathe work.
When are drill sleeves used for?
Drill press tapers are not all the same size. When the taper of the drill is too small for the taper of the drill press a drill sleeve is used to make up the distance.
What are drill sockets used for?
If the tapered shank of a drill is larger than the tapered bore of the drill press.
How are Morse tapers separated from the drill press?
With a tapered tool called a drift.
What tool is used when a sequence of operations must be performed repeatedly, requiring multiple tool changes?
A quick-change toolholder.
How does a power tapping attachment work?
- When the down feed pressure is released (that is, when the tap is finished), the tapping attachment reverses the rotation of the tap, which allows it to turn back out of the hole.
- An adjustable clutch slips if the tap binds. This prevents the tap from breaking.
- The tap is held in a floating head so it can align itself accurately with the hole.
How does a floating reamer holder work?
It reduces the effect of reamer misalignment because it is self-centering. When entering the hole, the floating reamer holder allows the axis of the reamer to move into alignment with the drill press spindle axis.
What two main factors effect cutting speed?
- Type of metal - more heat is generated when cutting a hard metal, so the tool must move more slowly to compensate for the heat that is produced.
- Type of tool - certain types of tools withstand heat better than other types and so have a higher cutting speed.
What is the fastest part of a rotating object (like a drill or milling cutter)?
The outside edge. This is because it has to travel the greatest distance in each revolution.
What is the formula for calculating imperial spindle speed?
rpm = (CS x 4)/Dia
What is the formula for calculating metric spindle speed?
rpm = (CS x 320)/Dia
what is feed rate and how is it measured?
The rate at which the drill is fed into the work and is measured in inches (or millimeters) per revolution (ipr).
How does feed rate vary with drill size?
The larger the drill, the higher the feed rate. Larger drills are better able to withstand the greater stress of high feed rates.
When marking a workpiece with a center punch, how big should the center punch mark be?
At least as large as the chisel edge of the drill.
When drilling a pilot hole, how large should it be?
Just a little larger than the chisel edge of the drill.
If the pilot hole is too large, the drill tends to chatter.
What is the best method for drilling holes in mating parts?
Clamp the two pieces together and drill them as one. This works only if neither piece has been drilled yet.
How are holes transferred to a mating part using the twist drill method?
- Clamp the two pieces together and use the existing hole to guide the drill.
- If the hole to be drilled is smaller or larger than the existing hole (perhaps for tapping or reaming), drill only as deep as the point of the drill.
- Unclamp the workpieces, change the drill, and complete the hole.
How are holes transferred to a mating part using the transfer screw method?
- Transfer screws are threaded through the original piece.
- The two mating pieces are lined up.
- The new piece is tapped with a hammer so the points of the transfer screws mark the new piece.
- The new piece is drilled.
When drilling round work, what must be done when center punching?
The center punch mark must be deep; otherwise, the drill tends to slide off the workpiece.
When holding round work in a vise, what must be considered to keep the work stable?
If the height of the jaws is greater than the radius of the workpiece, then a vise can be used. Otherwise, a V-block must be used.
What factors need to be considered when determining how much material to leave in the hole before reaming?
For reaming a hole, the amount of material to be left for the reamer depends on:
1. Whether the hole is reamed by machine or hand.
2. The diameter of the hole.
What is the included angle on a countersink?
82-degrees.
How much smaller than the hole diameter is a counterbore pilot’s diameter?
Usually between 0.002 and 0.005 of an inch smaller than the hole diameter.
How much larger than the bolt head diameter is the counterbore diameter?
Usually 1/32-inch.
When tapping a hole, what type of tap would be best to pull the chips out of the top of the hole?
A spiral fluted tap.
When tapping a hole, what type of tap would be best to push the chips through the bottom of the hole?
A spiral point (Gun) tap.
When grinding a drill what is the effect on the drill if the cutting lips are not the same length?
The drill cuts oversize.
When grinding a drill what is the effect on the drill if the point angle is uneven?
The smaller angle does all of the cutting and the drill lasts half as long as it should.
When grinding a drill what is the effect on the drill if there is not the correct amount of clearance behind the cutting edge?
If there is not enough clearance, the drill cannot be fed into the work efficiently.
If there is too much clearance, the cutting edges lack sufficient support and chip easily.
The clearance angle for general-purpose work is 8° to 12°.
When sharpening a drill, at what angle to the grinding wheel face should the drill be held?
Approximately 59° from the face of the wheel.
What should the drill point angle be when drilling the following materials:
1. General purpose?
2. Harder materials such as tool steel?
3. Softer materials, like plastic or non-ferrous metal?
- General purpose: 118-degrees.
- Harder materials: 150-degrees.
- Softer materials: 60- to 90-degrees.
When should the chisel edge on a drill be thinned?
The web gets thicker as it gets closer to the shank of the drill. Eventually, as the drill is made shorter through repeated sharpening, the chisel edge becomes unacceptably wide and must be ground away.
