Description of LATHE

Description

The purpose of a lathe is to rotate a part against a tool whose position it controls. It is useful for fabricating parts and/or features that have a circular cross section. The spindle is the part of the lathe that rotates. Various workholding attachments such as three jaw chucks, collets, and centers can be held in the spindle. The spindle is driven by an electric motor through a system of belt drives and/or gear trains. Spindle speed is contolled by varying the geometry of the drive train.The tailstock can be used to support the end of the workpiece with a center, or to hold tools for drilling, reaming, threading, or cutting tapers. It can be adjusted in position along the ways to accomodate different length workpices. The ram can be fed along the axis of rotation with the tailstock handwheel.
The carriage controls and supports the cutting tool. It consists of:

• A saddle that mates with and slides along the ways.
• An apron that controls the feed mechanisms.
• A cross slide that controls transverse motion of the tool (toward or away from the operator).
• A tool compound that adjusts to permit angular tool movement.
• A toolpost T-slot that holds the toolpost.

  Choosing a Cutting Tool

  The figure above shows a typical cutting tool and the terminology used to describe it. The actual geometry varies with the type of work to be done. The standard cutting tool shapes are shown below.

  • Facing tools are ground to provide clearance with a center.
  • Roughing tools have a small side relief angle to leave more material to support the cutting edge during deep cuts.
  • Finishing tools have a more rounded nose to provide a finer finish. Round nose tools are for lighter turning. They have no back or side rake to permit cutting in either didection.
  • Left hand cutting tools are designed to cut best when traveling from left to right.
  • Aluminum is cut best by specially shaped cutting tools (not shown) that are used with the cutting edge slightly above center to reduce chatter.

    Installing a Cutting Tool

    Lathe cutting tools are held by tool holders. To install a tool, first clean the holder, then tighten the bolts.
  • The tool post is secured to the compound with a T-bolt. The tool holder is secured to the tool post using a quick release lever.

  • Positioning the Tool

    In order to move the cutting tool, the lathe saddle and cross slide can be moved by hand.
    
    There are also power feeds for these axes. Procedures vary from machine to machine.
    A third axis of motion is provided by the compound. The angle of the compound can be adjusted to allow tapers to be cut at any desired angle. First, loosen the bolts securing the compound to the saddle. Then rotate the compound to the desired angle referencing the dial indicator at the base of the compound. Retighten the bolts. Now the tool can be hand fed along the desired angle. No power feed is available for the compound. If a fine finish is required, use both hands to achieve a smoother feed rate.
    The cross slide and compound have a micrometer dial to allow accurate positioning, but the saddle doesn't. To position the saddle accurately, you may use a dial indicator mounted to the saddle. The dial indicator presses against a stop.
    
    

    Feed, Speed, and Depth of Cut

    Cutting speed is defined as the speed at which the work moves with respect to the tool (usually measured in feet per minute). Feed rate is defined as the distance the tool travels during one revolution of the part. Cutting speed and feed determines the surface finish, power requirements, and material removal rate. The primary factor in choosing feed and speed is the material to be cut. However, one should also consider material of the tool, rigidity of the workpiece, size and condition of the lathe, and depth of cut. For most Aluminum alloys, on a roughing cut (.010 to .020 inches depth of cut) run at 600 fpm. On a finishing cut (.002 to .010 depth of cut) run at 1000 fpm. To calculate the proper spindle speed, divide the desired cutting speed by the circumference of the work. Experiment with feed rates to achieve the desired finish. In considering depth of cut, it's important to remember that for each thousandth depth of cut, the work diameter is reduced by two thousandths.
    

    
    

    
    
  
  

Penstock Protection and Supports | Steel, PVC, HDPE Pen stocks

Pen stock are to be considered one of the most important component of any hydro power project and act as key member between the reservoir and power house. Pen stock may be of different materials and each type has its own protection technique and Support anchorage system in the following article two there different of pen-stocks are discussed along with their protection measures and Standard requirements. Protection of Steel Penstock 1. Above-ground steel pen-stocks should be clear of the ground to avoid corrosion and to allow easy access for paint.

2. Steel pipes must be given two coats of paint on the outer side and the maintenance plan must include regular repainting. Internal painting is recommended. Standard metal oxide paint can be used, although the recommended paints are:

• Romate primer followed by polyurethane enamel top coat.
• Inside: Bitumen (easier to apply, use rag or brush); or lead oxide (more difficult to apply).

3. If steel pen-stocks are buried, they must be coated with bitumen. It is preferred that they are galvanized, and double-coated with either bitumen or high zinc content paint.

4. Tar paper or bitumen must be used between steel pipe work and supports/anchors to exclude water and air which may collect in inaccessible areas and promote corrosion. Rubbing plates or tar paper are recommended between pipe work and support piers to prevent abrasion due to thermal expansion and contraction. Rubbing plates should not be used if they pose danger of air and water entrapment which may lead to corrosion. Tar paper or bitumen may be needed on either side of a rubbing plate to avoid this.

5. Expansion joints are recommended on steel pen stocks:

• One immediately below forebay tank or integrated into forebay tank wall

• Between each anchor block one below final anchor block on sites of more than 10 kW with a high head and complex manifold which may be vulnerable to stress. When visiting verify the above and in addition:

6. Over ground steel penstocks should be inspected to ensure that there are no areas where rain water can accumulate and cause corrosion. Check that this is being done as part of a routine maintenance schedule, and that corrective action is routinely taken (i. e. clearing of plant growth touching the penstock); and that repainting is undertaken periodically.

7. Over ground penstocks should be checked to ensure that thermal expansion will not cause wear at any sliding support.

8. During commissioning check that expansion joints are not closed up tight to one end of their movement as this may cause leaks and failure. Check that operators know how to reset expansion joints after works are carried out on the pen stock.

Protection of PVC and HDPE penstocks

1. PVC and HDPE pipes often give good service without special protection from either sunlight or thermal expansion and contraction forces. Nevertheless it the following precautions can improve the cost effectiveness of the scheme:

a. PVC penstocks can be protected from sunlight by paint or some other sort of effective and durable covering; or by burying.

b. Expansion/contraction. PVC pipes with spigot and socket joints can accommodate thermal forces without special measures. If a glued PVC pipe is not buried and is straight, a socket and spigot joint is recommended between anchors and at the forebay to accommodate thermal forces; alternatively some inclusion of flexibility in the run of pipe.

2. If PVC penstocks are buried they must be laid on sand beds without danger of stress points occurring below or above the pipe surface due to objects such as stones butting against the walls of the pipe.

Penstock supports and anchors

1. Anchors and supports must be sized and designed to reliably accommodate all possible sliding, toppling, and sinking/lifting forces.

2. Supports should be designed to allow some longitudinal sliding between the pen-stock and the support. Supports must be fitted with a vertical movement retention method, to accommodate lifting forces.

3. Anchors should be constructed from concrete, preferably reinforced. Special attention should be given to ensuring that their foundations are sound and not likely to move (as this will cause severe difficulties in handling the turbine manifold, and jeopardize the forebay and penstock).