View Full Version : lathes and tubes?

tony ennis
04-25-2009, 10:07 AM
Why does a Monarch lathe (10EE?) have vacuum tubes?

Spin Doctor
04-25-2009, 10:09 AM
Because that was the only way to get the vairiable speed back then?

04-25-2009, 10:30 AM
Why does a Monarch lathe (10EE?) have vacuum tubes?

Older Monarchs has a variety of different drive systems:


Early 10EEs were built during WW2 and, with a shortage of materials and components, differed from month to month in their detail specification. Some, close together in serial number, will have V-belt drive others flat-belt (though this may have been a customer preference). A number of different of DC control boxes were employed and variations on the complex drive system persisted for several years with the types coexisting side by side until a full change-over was accomplished. On the earliest machines the spindle was driven by a V or flat belt from a massive hydraulic/hydrostatic variable-speed unit of Sundstand manufacture that provided a speed range of 25 to 2500 rpm. In 1941 this was replaced by a three-phase motor driving a 3 h.p. DC generator that provided power for an electronic variable-speed drive system - a not dissimilar arrangement being used on the English Cromwell toolroom lathe. However, some experimentation appears to have been conducted by the factory (or a shortage of components encountered) as subsequent changes involved three versions of the Reliance VS Motor Generator unit, then a "WiaD" drive, a Module Drive and finally the Monarch DC type. Some details: in 1949, in line with new developments in electronics, the Reliance rotating motor-generator set (DC) arrangement was replaced by a system (WiaD) that used electronic-tube controlled thyratrons to rectify AC current to a variable DC voltage to drive a DC motor (multiple vacuum tubes being used to control the rectifier tubes). This set-up became better known as the "works in a drawer". In 1950/51 the drive was again redesigned and improved and then, in 1960, the WiaD superseded by fitting of a more powerful 5 h.p. motor and a "module drive" that used an all-solid-state electronic module to control the electronic components, with the exception of the thyratrons - around 3,000 lathes being built with this system. In 1984 further alterations were made with an entirely solid-state DC armature regenerative drive replacing the now old-fashioned thyratron tubes and finally, in 1995, a change to one of the increasingly popular and less-expensive AC-inverter types finally ousted the DC system. The lathe was now equipped as standard with a 7.5 HP AC TEFC motor and this unit was also made available for field retrofits and factory rebuilding. Today, when a machine is factory refurbished, it will be fitted with either a 5 h.p. 3-phase motor with backgear, or a 10 h.p. - both types having their speed varied by a modern inverter (VFD). For home-shop use the most convenient drives are the early Sundstrand, WiaD and Module types. A single-phase motor can be used to power the Sundstrand whilst both the WiaD and Module drives would have been be fitted with single-phase motors as standard when new. Only the coolant pump on the latter two types is 3-phase - and this can be ran from a simple and inexpensive static converter. The motor generator units need to be powered from a proper rotary-phase converter (a static unit will be unhappy) whilst the Monarch Electronic DC drive will only run on a true 3-phase supply (either from the mains or a phase-perfect electronic phase converter). The drive motor (integral to the motor generator) is about 6.5 h.p. - a figure to use when working out the RPC size required. One unit recently tested with the MG unit was fitted with a 15 h.p. RPC and was pulling 20 amps at 240 volts out of the wall - and that was without the spindle running. It was promptly exchanged for an AC brushless servo drive. No matter what the system, all older electronic drive systems eventually prove troublesome and some recent successful conversions have been achieved by using a Baldor "Smart Motor" - though a small amount of machining is necessary to adapt the Baldor motor to the Monarch gearbox (including a spacer plate & spine shaft).

- Bart