ELECTRICAL MATTERS
Conversions : 3-phase : 1-phase : Inverters
If you have any doubts about your ability to undertake work connected with electrical installations, you should employ an electrician, qualified to work on machine tools, to do the job for you; you will find it money well spent.

For excellent advice on how to use electric motors in the small workshop you need a copy of "Electric Motors in the Home Workshop".
This will show you how to identify and use motors from industrial and domestic sources and how to operate 3-phase industrial motors from a 1-phase domestic supply.
For more advanced instruction the book "Electric Motors" is recommended. This was written with the amateur user in mind and covers motor types, characteristics, operation, installation, speed control, braking and a host of other matters - as well as advice on using and adapting surplus motors from industrial sources. To find out how to prepare a complete workshop for electrical installation try "Workshop Electrics"
Machine-tool switches are often a problem, especially on older examples where the parts are obsolete or don’t meet current regulations. We can supply a reversing and on/off switch that will meet the majority of requirements for motors up to 5 h.p. and can be easily wired to replace built-in switch gear that has become unreliable. Other switches to control 2-speed motors and various kinds of push-button starter can also be provided. Just email your requirements and we’ll try to help

Nearly all larger lathes are equipped with 3-phase motors and to use them without a 3-phase supply requires either the motor to be changed, or the use of a phase "converter" or "inverter". Plug a converter into the single-phase household supply and it will produce an output capable of running a three-phase motor; an Inverter does the same job but the output can also be varied to provide a speed-control effect. Besides getting the machine to work with the minimum of effort, combining an inverter drive with the machine’s own belt or geared spindle drive will, of course, have the added advantage of making an even greater range of speeds available. An inverter conversion recently seen on a Boxford lathe (a South Bend clone) had the bottom speed reduced from 40 rpm to 5 rpm - and the top speed raised from 1450 rpm to the 2000 rpm - the same as the now very hard-to-find version fitted with the maker's original "high-speed" pulley set. A word of caution: many inverters have an “overspeed” function than can allow machines to be run at speeds far in excess of the maker’s intentions. Lathe chucks are always limited in how fast they can be spun; being made of cast iron they will eventually burst and the clamping force of the jaws weakens as the speed rises.

Using a "Converter" or "Inverter" normally allows you to connect directly to the machine’s motor and by-pass the original electrical system with control of stop, start and reverse being by the inverter itself. However, it is important to both follow the maker’s instructions on how the connection should be made and also to be aware that, in connecting directly to the motor, you may well be stopping the action of safety features – for example, when opening a door or moving a handle would normally have stopped the motor. The inverter, once installed in the workshop can also be used to run other three-phase machine tools - a drill, milling machine, saw and shaper for example. A 'converter' can, within the limits of the maker’s instructions, be wired to supply several motors simultaneously; an 'inverter' can also do this but, as you vary the output to change speed, the other motors connected to it will change speed as well. If you plan to use a machine tool equipped with auxiliary motors (to power a coolant supply, or milling machine table drive, for example) it is worth bearing in mind that it would be possible to use an inverter for the main drive motor, and a separate (small and relatively inexpensive) Converter to run the auxiliary motors.
If you intend having several 3-phase machines in your workshop a "converter" or "inverter" is almost certainly a more economical way of running them than changing the motor on each; additionally, some machine tools have motors so tightly integrated into their construction that finding a single-phase motor to replace them is impossible - and, unless you take out a bank loan and have the original motor reconstructed as a single-phase unit, using a 'converter' or 'inverter' is the only practical solution.
An important part about the conversion - and often overlooked - is that 1-phase to 3-phase converters or inverters usually produce 3-phase output at the input voltage. So, if you want to run a 3-phase 440 volt machine, you must reconnect the motor in 240 volt "delta" configuration (as distinct from 440 volt "star") which often involves just following the simple instructions printed inside the lid of the terminal case - but can sometimes involve first removing the motor from some dark, oily and inescapable corner of a cabinet stand and having the local motor-rewind shop conduct internal surgery on it. However, some of the recently produced converters and inverters units have a transformer built in (though at considerable extra expense) to provide a 440 volts (or other) output, which of course can save a huge amount of time and frustration - you just configure the inverter, hook up and switch on. 
Today inverters have fallen in price dramatically (ranging in price  from around £90 to £250 covering motor from 0.25 to 4 h.p. and larger) and if the 3-phase motor on your machine is in good order it’s now hardly worth changing it for a single-phase unit. We stock inverters by SIEMENS - please Email for details and the latest prices.

Changing Motors
Should you decide to change a 3-phase motor for a 1-phase one some thought is necessary to get the best out of the conversion. It is as well to bear in mind that a single-phase motor is not the direct equivalent of a three-phase type. A 1-phase motor is best run near its rated capacity all the time (i.e. worked nearly flat out); if the motor is switched on and off frequently against “no load” the windings will be damaged and, if run through a cycle where it is started, worked briefly, stopped and started again, the capacitor will fail prematurely. 
A machine tool with a one horse-power 3-phase motor should, in theory, run just as well with a one horse-power, 1-phase motor - but, life's not like that. If you need your machine to perform as well as it did with its original motor (and it is by no means certain that you will) you may find that, for power for power, for ease of starting and long-term reliability, a successful and reliable conversion to 1-phase requires a motor which is marked as being some 30% to 50% more powerful
When changing the motor(s) leave the original 3-phase wiring and switchgear as intact as possible and store the old motor safely inside the machine’s stand - where it should be impossible for it to be lost. Do not waste time trying to modify any of the original electrics; it is much simpler, and a lot safer, to fit new wiring, a new switch and a "no-volt" safety cut-out. Should the machine ever be put back on 3-phase,or wired with an inverter to give a variable-speed drive all you (or the next owner) needs to do is bolt back the original motor - and hook up the wiring.

If you have any doubts about your ability to undertake work connected with electrical installations, you should employ an electrician, qualified to work on machine tools, to do the job for you; you will find it money well spent.

Motor Power - a Word of Warning
A note of caution might be appropriate here for the owners of smaller machine tools. If you are going to replace the electric motor on your lathe, miller or drill, etc. - think carefully about on how powerful it needs to be. Modern motors are very compact - and it is now all too easy to fit a massively powerful unit in a tiny space.
If you have a "dig in" when turning, milling or drilling - or other accident - instead of coming to a dead stop as the load overcomes the motor power, the machine may continue running and do itself, and you, serious damage.
I remember a little Grayson lathe that the owner had converted to chain drive via a motorcycle gearbox. He hooked it up to a 1 h.p. motor from a Bendix washing machine and revelled, for a time, in the slip-free, powerful drive he had constructed. When, as was inevitable one day, he allowed the cutting tool to run into the chuck the lathe failed to stop. Indeed, the irresistible forces being so efficiently transmitted by chain ripped the entire headstock assembly from the bed and proceeded to smash it to pieces as it hurled, at great speed, round and round the countershaft unit.
For lathes up to 3.5" centre height it is surprising what a 0.25 h.p. (one-quarter horse power) motor can achieve. 0.33 hp (one-third horse power) is probably a safe compromise (that’s the size Myford fitted for many years to their ML7). Anything over 0.5 h.p. (half-horse power) and you need to be aware of the fact that you are driving a powerful little beast - that can have a savage bite.
Lathes between 3.5" and 5" centre height often have more complex drive systems - with the motor inside the cabinet stand - or with variable-speed drive, and require more power to overcome the frictional losses in the transmission. Unfortunately, modern motors do not seem nearly (subjectively) as powerful as their rating would suggest, especially the more affordable ones, and the starting characteristics of single-phase motors often demand an excess power rating to get the spindle turning - especially on top speed and when no clutch is fitted. Thus, it becomes difficult to say exactly what size of motor you should fit to obtain the best compromise between starting, turning performance and safety. The maker's original advertising or maintenance literature will provide a guide of course, or, if that is missing or unobtainable, there is often a plate on the machine that lists the original electrical specification. If the only clue is the existing 3-phase motor, replacing it with a single phase one of the same nominal horse power will almost certainly leave the machine underpowered; instead, as previously advised, something 30% to 40% more powerful would be a good starting point. Single-phase motor can often be obtained in two types: low starting torque and high starting torque with the latter often referred to as “capacitor start - capacitor run” (cap-start-cap-run) types. The high-starting torque variety, though a little more expensive, are to be recommended and are generally more reliable where the motor might be switched on and off frequently.
There are a couple of very useful books to help sort out motor problems: "Electric Motors" and "Electric Motors in the Home Workshop".
If you are in the UK we can supply a range of good quality electric motors from 0.25 to 4 h.p. and a selection of (often hard-to-find) reversing, 2-speed control and other switches. Email for details.
Belts
If a motor is changed, or the drive system otherwise modified, ensure that the pulleys and belts receive proper attention. Pulleys, preferably in cast iron (for grip), should be a close fit on their shaft, secured with a key, locked securely and run without wobbling. If the pulley has to be changed, and the correct replacement cannot be found, the solution lies in the industry-standard but more expensive “Taper lock” type. These are made in two parts: a split centre, tapered on the outside, and an interchangeable outer rim held on by 4 bolts. The tightening action of the bolts compresses the inner section to grip the shaft. The locking force to the shaft is so great that no key is required.
Whether V or flat, belts need to run in line and the easiest way to check this is to lay a long steel straight edge across the full width of both pulleys. Assuming the pulleys to be of the same type - and thickness - the edge should make contact at all four points on the rims. The drive belts also need to be in good condition. V-belts often wear in patches (or develop hard and soft spots through standing) and when the different sections run over the pulleys they either  “fall into the groove” or “climb the hill” and so continuously alter the drive ratio. This speeding up and slowing down of the drive results in a cyclic motion that can create interesting vibrations, especially at higher speeds, with the result that marks are passed to the workpiece and show as vibration bands. New belts are inexpensive and can make a remarkable difference to the smooth running of a machine tool.. A supply of belts – V, flat and round, can be found here.

 

Detailed advice is given on how to identify and make good use of discarded and surplus motors from domestic and industrial sources - and also how to operate 3-phase motors from a single-phase supply. Lots of money-saving advice.
144 pages.
UK £8.75 inc. P & P
Europe £9.75 inc. P & P
World-wide air-mail post £14 inclusive

 

Principles, characteristics, operation installation, speed control, braking, etc. Generators, safety considerations, testing and a useful section on identifying and using 'scrap' motors. An excellent primer on the electric motor.
136 pages.
UK £8.75 inc.  P & P
Europe £9.75 inc. P & P
World-wide air-mail post £14 inclusive