Machining Operations: Mills Flashcards
What tasks are mills generally used for?
- Machining flat surfaces.
- Machining parallel surfaces.
- Cutting keyways.
- Cutting key seats.
- Drilling holes.
- Boring accurate hole sizes.
What are the main features of a plain horizontal milling machine?
- The main spindle is horizontal.
- The table does not swivel; instead, it moves at only right angles to the spindle.
Can horizontal milling machines be converted into vertical milling machines?
Yes, with the use of a vertical milling attachment.
How is a universal horizontal milling machine different from a plain horizontal milling machine?
The universal horizontal milling machine is essentially the same as a plain horizontal milling machine, except the table can be swiveled.
How does a vertical milling machine differ from a horizontal milling machine?
Other than the orientation and construction of the spindle, a vertical milling machine is the same as a horizontal milling machine.
What are the advantages of vertical milling machines versus horizontal milling machines?
Vertical milling machines are more versatile than horizontal machines. Vertical mills can do any operation that can be performed on a horizontal mill, as well as pocket milling and drilling hole patterns.
What are the disadvantages of vertical milling machines versus horizontal milling machines?
Vertical milling machines are not as rigid as horizontal mills of the same size and cannot remove metal as quickly or as accurately.
What feature makes ram-type milling machines the most versatile of all?
The milling head can be positioned relative to the workpiece by moving the ram forward or back.
What is a downside to a ram-type milling machine?
They are lightly constructed and lack the rigidity of other knee and column type milling machines.
How are knee and column type milling machines sized?
Range of movement possible and the horsepower rating of the main motor.
What are the main parts of a vertical knee and column milling machine?
There are five basic components to a vertical knee and column milling machine:
* Base,
* Column,
* Saddle,
* Knee, and
* Table.
What main part of knee and column milling machines is only found on horizontal milling machines?
The overarm.
What is the purpose of the overarm?
To support the arbor support, which in turn supports the free end of the arbor. The overarm can be moved in and out to accommodate different arbors and set-ups.
Why do milling machines use a backlash eliminator?
To control the backlash in the table lead screw.
It tightens before climb milling in order to prevent the workpiece from being drawn into the cutter. The backlash eliminator should be loosened when it is not being used in order to prevent unnecessary wear on the lead screw.
How does the backlash eliminator work?
It consists of two nuts that can be tightened against the lead screw in opposite directions. That way, clearance between the screw and the nuts is cancelled.
What are the various feed mechanisms on a vertical mill and where are they usually located?
- Longitudinal traverse handle - usually found on the saddle and moves the table left or right.
- Vertical feed handle - usually found on the side of the knee and moves the knee up or down.
- Cross-traverse handle - usually found on the side of the knee and moves the saddle toward or away from the column.
What is the typical size of the spindle tapered bore on a milling machine?
3-1/2 inch per foot.
On mills with a gear box to control the spindle speed, when should you change the speed?
When the machine is stopped. Stop the milling machine before the speed is selected; otherwise, the gears will be damaged.
On mills with a variable speed drive to control the spindle speed, when should you change the speed?
When the machine is running. Never rotate the variable speed hand wheel when the spindle motor is stopped; otherwise, the mechanism will be damaged.
What type of cutting machine is shown in the image?
A portable keyseat mill.
What size shaft diameters can portable keyseat mills be used on?
From 0.5 inch to 24 inches.
Horizontal milling machines are of the arbor-mounted type. They have a bore and a keyway and must be fastened to an arbor or mandrel before being installed in the spindle of the milling machine. How is their size designated?
The size of an arbor-mounted milling cutter is designated by its outside diameter, the width of the cutter and the diameter of its bore, in that order.
The cutter in the image is called a 5 × 3⁄4 × 1 inch cutter.
Used on a vertical mill, what is the name of the cutter in the image?
A solid endmill.
What is the maximum depth of cut for a solid endmill?
Half the diameter of the cutter.
What are the four different types of shank styles for endmills?
- A straight shank.
- A Weldon shank.
- A threaded shank.
- A double ended endmill.
What is the name of the cutter in the image and what is it used for?
A Woodruff keyseat cutter.
It is used only to cut keyseats in shafts.
The size of Woodruff keyseat cutters is determined by the number code on its side.
The code on the cutter in the image is No 608, what does this stand for?
The first number, 6, is for the width and it indicates that the width is 6/32-inch (6 x 1/32).
The second number, 08, is the diameter and it measures 1-inch (8 x 1/8).
What is the name of the cutter in the image and what is it used for?
A fly cutter.
Fly cutters are especially useful for producing very flat surfaces with a good surface finish and can take the place of more expensive cutters.
What is the name of the cutter in the image and what is it used for?
A face mill.
Used to machine flat highly accurate surfaces.
What is an arbor?
A long or short bar that holds the milling cutter in place while cutting.
What is a collet?
Collets are hardened steel bushings with a series of slits running almost their entire length. The outside of the collet is tapered to fit the tapered bore in the collet holder. The inside diameter is parallel and fits the shank of the milling cutter. When the collet is forced into the collet holder, the taper squeezes the collet onto the shank of the cutting tool.
What is an R8 collet?
An R8 collet fits directly into the spindle of the milling machine and is held in place by the spindle draw bolt. The cutter is held closer to the spindle and is therefore more rigid.
Friction collets grip the cutter with friction only, which is adequate for most milling operations, but not heavy duty operations. What are the different parts of a friction collet?
A friction collet consists of:
* Chuck body - which is mounted in the spindle bore and held in place with a draw bolt.
* Collet nut - which turns onto the threaded part of the chuck body.
* A set of collets which snap into the chuck nut and then fit into the bore of the chuck body; and
* A wrench to tighten the chuck nut.
A heavy-duty collet chuck has a thread that mates with a thread on the cutting tool shank, so the cutter will stay in the same place cut after cut. It is good for heavy duty cuts. How does this collet maintain rigidity?
The chuck body mounts in the spindle bore and held in place with a draw bolt.
How is the cutting speed for a milling machine measured?
The speed at which the periphery of the cutter travels through the workpiece, measured in meters (or feet) per minute.
What variables must you know to calculate the feed rate for a given cutter and workpiece material?
- The spindle speed of the cutter.
- The number of teeth on the cutter.
- The optimum chip load per tooth.
What is chip load?
The amount of metal removed by each tooth per revolution.
What is the formula for calculating mill cutter feed rate?
Feed = Chip load x Spindle speed x # of teeth
What is conventional milling?
The workpiece feeds against the rotation of the cutter, so the cutter tends to push the workpiece away and lift it off the table.
What is climb milling?
The workpiece feeds with the rotation of the cutter, so the cutter tends to draw the workpiece in and push it down toward the table.
In conventional milling, the chip is very thin when the tooth enters the material and gets progressively thicker as the tooth exits the material. The cutter tooth starts the cut in clean machined metal rather than in the hard scale found on the outside of many materials? How does this effect the cut?
- The cutter lasts longer.
- The set-up for conventional milling must be rigid because the cutter tends to lift the workpiece off the table.
In climb milling, the thick end of the chip is at the beginning of the cut and at the end of the cut, the tooth scrapes and burnishes the workpiece. how does this effect the cut?
- It is easy for the tooth to bite into the material.
- the burnishing action leaves a good surface finish.
When aligning the vertical mill head for perpendicularity to the table, what amount of total runout is required for good machine performance?
A total runout of 0.001 − 0.002 inches.
When aligning a mill vise what should be clamped between the vise jaws to make the alignment easier to measure?
Clamp a parallel between the jaws so the parallel extends above the top of the jaws. The parallel should be long enough to cover the entire width of the jaws.
What type of mill cutter is shown in the image?
A face mill.
What are the three different types of mills used to cut keyseats?
- Side milling cutters.
- Endmills.
- Woodruff keyseat cutter.
How is the depth of a keyseat measured?
The depth of a keyseat is always measured from the flat. The small distance between the flat and the outside of the shaft must be taken into account.
What is the usable length of a keyseat?
The length of a keyseat is its usable length. It does not include any runout or radius left by the cutter at either end.
How do you center a shaft using a strip of paper?
- Tear off a strip of paper at least six inches long.
- Hold the paper between the rotating cutter and the workpiece. Keep your fingers away from the cutter. Hold the paper loosely so it slips out of your fingers easily. If in doubt, moisten the paper with coolant or cutting fluid and stick it to the shaft.
- Move the workpiece toward the cutter until the cutter grabs the paper.
- Lower the workpiece so it clears the cutter and move it over by a distance equal to half the diameter of the cutter plus half the diameter of the workpiece.
What is spotfacing a workpiece for a bolt or screw?
The process of squaring the surface of a workpiece to a drilled hole. It is most often used on castings. See letter C in the image.
