Starting/stopping the motor
A motor that is started or stopped using a series of linkages that longer to do than if this is done by simply pressing a button.
Fig 52 – start/stop/reverse using a lever 931
Fig 53 – start stop reverse using buttons 932
This might seem to be of little importance and usually it is. But when making large numbers of a particular component every second counts. One second off making a thousand parts is twenty minutes.
Different processes require different speeds. There are three main ways of changing the spindle speed.
Firstly the headstock will normally use either gears of belts, or both, to allow the spindle speed to change.
A lathe with a gear box to change the spindle speed is usually going to be faster than one that uses belts.
A gear box will often provide more speeds than any system of belts. Changing speed might involve moving one, two or even three handles.
Where the headstock uses gears and has 8 permutations selected by 3 levers as useful trick is to find 2 speeds that are useful and can be switched between by changing just one lever.
Secondly, if an inverter is used it often has the ability to have its speed change by using a potentiometer.
Thirdly, it is always possible to put the spindle in neutral and rotate it by hand. This has several advantages. It can just as easily be rotated in reverse without any risk of the chuck coming off. If can be rotated as slowly as required without any limit. By putting a chuck key in the chuck and pulling it round produces more torque than most motors can. This can be useful when using a die to cut bigger thread.
If the speed could be changed automatically for each position of the capstan etc it might be very useful. If the speed has to be remembered by the user it is not so easy.
On most lathes the when the motor stops it does not do so instantaneously. Most users must have, at one time of another, put their hand on the rotating chucks to slow it down more quickly. This could happen several times during the making of one component. If there are hundreds to make this becomes significant.
There are three ways of stopping the motor.
By hand – not recommended.
Mechanically. This involves a pad being applied somewhere against a rotating part. On some lathes a mechanical brake is an option. Often it is foot operated.
Machines that use inverters often have options to control how fast the motor slows down.
There is also the possibility of using a mechanical brake that is applied electrically.
When large numbers of small part are made on a large lathe it is quite possible, when parting off, for them to fall down somewhere and disappear completely. The Colchester Chipmaster is carefully designed so they fall down the back of the machine.
Where the lathe has any sort of tray it still provides a lot of space for bit to disappear in.
One solution to this is to place a smaller tray directly underneath where the parts are parted off. Trays designed for roasting chickens are suitable for this and can be bought very cheaply at Pound type shops.
If coolant is being used it can make picking out the parts a messy business. The trick here is to have two trays, the top one is full of small holes. This collects the parts and some swarf. The bottom one collects the coolant.
Often jobs using a capstan involve small parts and produce relatively little swarf.
Apart from the example already given of using carbide tips for parting it would seem that there is seldom any advantage of using carbide tooling over using high speed steel.
The methods used for sharpening cutting edges are the same as for cutter to be used on the lathe. One difference is that very often swarf is produced in small confined spaces. This can affect the cut or the finish. The solution to this is to shape the cutter so the swarf is broken up or curls up in a way that does not cause it to get trapped.
If swarf need to be cleared away the lathe must stopped first
Setting cutting edges