Machine lathe


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Machine lathe

  1. 1. Shop Safety with the Machine LatheIntroduction The machine lathe is a very important tool. It is said that the lathe is capable ofproducing all other machine tools because it can perform a great variety of operations. But thelathe is also a very dangerous machine as there are a lot of high speed moving parts. It isparamount that the lathe is operated at all times to prevent injury and possible death. This reportis intended to help you operate the machine lathe safely.1.0 Function of the Machine Lathe1.1 Principle of operation All the lathes in the shop are driven by electric motors that, through gearing, rotate achuck holding the piece of metal (stock) to be turned. The gearing in the newer models are toothto tooth connected, while the older models are belt connected. By shifting gears you can producedifferent speeds of rotation for the chuck. The speeds required are determined by the type ofmaterial, operation, and type of cutting being done. The metal is mounted and secured in a 3 or 4 jawed chuck. Prior to turning the lathe on,the chuck is rotated by hand to ensure freedom of movement. Longer pieces, like shafts, aresupported by a turning centre also known as a live centre or a dead centre, one that can not turn,in the tail stock (Fig. 1) during cutting. For additional support a steady rest and a follower restcan be added to the lathe (Fig. 2). The tail stock can also mount drills as well as centres. The lathe carriage (Fig. 3) is the centre of the operation and is where the carbon tool bit ismounted in the tool rest. In our shop, the supervisor will grind these tool bits for our use or helpyou to grind one that is needed. Tool bits are used for cutting, facing, parting, boring, andthreading. Each one is used for a different specific operation, for example the Roughing Tool bitis used to take deep cuts and removing most of the stock material, the V-Type Threading tool isused for threading, and there are many more different bits (see Fig. 4). After the tool bit neededis ground, it is mounted into the tool mount or a turret on the carriage. The carriage moves thelength and width of the lathe and the tool rest can be moved on an incline for cutting. It can bemoved either automatically, by internal gearing attached to the carriage and controlled by thelathe speed and feed rate, or by manual hand control done by turning control knobs specific fordirection.1.2 Typical parts and shapes which can be machined A lathe can face end pieces flat or make a cubed piece by facing all sides. Cylinders ortubes can be shaped by the long cutting of a stock piece utilizing lathe feed to move the carriageand then drilling the centre out. Internal and external threads can be cut by boring, or by cuttingusing specific speed and rates of cut. Taper cuts are done using an inclined setting on thecarriage. Specific combinations of methods can produce crankshafts, bolts, nuts, cylinders,
  2. 2. eccentric cams, and more. Surface measurements are very important here for flat and squarepositioning of pieces, to ensure a quality finish.2.0 Safety Considerations2.1 Preparation and set up Before starting, be sure that you wear safety glasses. If you forget your own, an extrapair can be found at the shop door. Ensure you have no loose clothing, hanging items such asjewellery, or dangling hair (use a hair net). Be familiar with the equipment before you startusing it and know what you want to do. Begin by mounting your piece in the lathe chuck. Always remove the chuck key afteruse and never take you hand off of the key while it is in the chuck. Turn the chuck to check forfreedom of movement and clearance of tool rest, chuck jaws, and lathe parts. Determine your required speeds and set the gearing. Finding the turning centre of yourpiece by hand rotating the chuck and set the tool bit to cut, with rotation into the bit, just a littlelower than centre. Move the cutting bit out and position it for stock cutting. Ensure the machineis in neutral before engaging the drive and know where the emergency STOP button is located.All this is done before turning on the power. If you are unsure of anything, ASK FOR HELP.2.2 Operation Ask the shop supervisor if the speeds, and the long and cross feeds are correct. If themachine is belt driven (Fig. 5), it is possible to start the machine in neutral and then engage thedrive. The chuck will not spin until the drive is engaged. If the lathe is gear driven, then themachine must be put into the correct speed setting before being turned on. If a different gearingis required, wait until the chuck comes to rest before changing gears. As cutting is taking place, long pieces of metal will stream off (Fig. 6). Do not grab orpull these as they are sharp and often hot. The piece may also pull back which can cut badly ifyou are holding the metal cutting. In high production or very fast cutting cooling fluid is used tolubricate and cool. In our shop, since we do not make deep or fast cuts frequently, we usuallywill not use cooling fluid. However, we will use fluids like oil when doing a deep cut or aspecial operation like knurling or boring.2.3 Clean up After you are finished cutting, shut off the lathe and remove your piece from the chuck.Do not take you hand off the chuck key while the key is in the chuck. Remove the tool bit.Clean all cuttings and deposit them in a scrap metal bin. Do this by brushing off the lathecarriage, tail stock, and bed with a brush. Using gloves pick the pieces out of the bottom tray. Ifcooling fluid was used, most of it will drain into a reservoir. Clean the remainder up with rags.
  3. 3. 3.0 Safe Machine and Tool Operating Parameters Only use the lathe for what it is intended, cutting rotating metal, facing or drilling. Whenoperating the lathe use the proper speed, long and cross feed settings, as determined by theproper charts and tables. Never distract anyone using a lathe or interfere with its operation. If atany time you are unsure, do not know, or need help, ask the shop supervisor.4.0 New Developments (recent improvements) The lathes in our shop are older models, newer models have CNC (Computer NumericalControl) ability; these are better suited for production needs and processes. Specific machiningrequirements have progressed to more accurate measurement by digital readings and control,compared to calipers and scales.5.0 Environmental Concerns5.1 Lubricant use and disposal The lathe is lubricated internally on a regular maintenance schedule. For our cuttingpurposes we only need to be concerned with cooling fluid. This is, for the most part, recycledwhen it drains back to its reservoir. Rags used in clean up are disposed of in specific, notedcontainers.5.2 Chip disposal and recycling During clean up all chips and cuttings are to be put in a scrap metal container forrecycling. The same applies to scrap stock.5.3 Used tool disposal or refurbishing Tool bits can be re-sharpened or reground for continual use. Broken tool bits or unusabletook bits are disposed of in scrap containers as indicated.6.0 Information for Design of Parts for Safe Machining6.1 Pre-processing of parts Before you start cutting, a lot of thought should be put into what you are doing and whatyour next step is. For example, there is no sense in heat treating your part only to machine offthe heat treated surface in the next step. You should always work from the rough details into thefine details, such as turning your part down then cutting or drilling. This should help to preventcrushed or misshaped parts. Work smarter not faster.
  4. 4. 6.2 Post-processing of parts It is in this step where you will do the finishing touches. Be careful that all your work isnot ruined with one wrong move. As mentioned earlier, removing burrs could remove thatvaluable heat treated surface. Also, handling of mild steel can cause quick corrosion soprecautions should be taken to prevent this. Protect your piece from damage to carefully madecorners and edges. Dents can cause miss-fitting and leaks or incorrect tolerance levels.