Schematic

Schematic produced by Hackspace member David Smith: Schematic

Functional Description

Three-phase power arrives at the input on M1, M2 and M3. The 440 V primary winding of transformer TX1 is wired between phases 1 and 3.

Transformer TX1 has two secondary windings. One 50 V winding powers the working light on top of the lathe via fuses F1 and F2. This light fitting uses a 50V incandescent bulb.

The second secondary winding on TX1 generates 230 V for powering the lathe's control gear.

One end of the wiring is connected to net 8, which is effectively the “neutral” for the lathe control gear. It is not connected to the neutral of the 3-phase input.

Start/Stop control

The START and STOP buttons are wired in such a way that, when the START button is pressed, this makes net 3 live. Net 3 is a main supply signal for the control gear that is live once the lathe is enable (START button pressed). Net 3 is then daisy-chained through the three thermal override relays via nets X1, X3 and 4, then to the coil of contactor 1M, which turns on three-phase power to the main three-phase power bus (M4, M5 and M6). The fourth contact of contactor 1M is wired in parallel with the START button, so that once the button has been pressed, the contactor keeps net 3 live. If the STOP button is pressed, the circuit is broken, and contactor 1M both disconnects the three-phase supply and stops bypassing the START switch.

If any of the thermal override relays trip, contactor 1M automatically disconnects three-phase power and disables the control gear.

Cam Auxilliary Switch

The main control gear live (net 3) is connected through an auxilliary contact on the main cam switch to net 6. Net 6 is a main supply signal for the control gear that is live when the main speed control lever is in one of the “running” positions (high or low speed)

Coolant Motor

The coolant pump is connected to the main three-phase bus via contactor 5M and a thermal override relay. Contactor 5M's coil is powered via net 18 from a switch in the control stalk. The switch connects net 18 either to net 3 (so that the pump is running continuously when the lathe is enabled), net 6 (so that the pump runs only when the lathe is running) or disconnected (so that the pump is off).

Spindle Motor

The spindle motor is powered through contactors 3M and 4M.

Firstly, contactor 4M switches the main three-phase bus onto net M14, M15 and M16. The coil of this contactor is effectively wired in parallel with the main contactor 1M (so that it is switched on whenever the lathe is enabled), except that there is an additional switch on the spindle lock to ensure that the motor cannot be switched on when the lock is engaged.

Contactor 3M is used to provide directional control for the motor. Unlike most of the other contactors, it contains two Normally-Open (NO) contacts, and two Normally-Closed (NC) contacts. These are wired so that, when the contactor is energised, phases 1 and 3 are swapped, reversing the direction of the motor. The coil of contactor 3M is controlled by the third contact of the FWD/REV switch.

The outputs of contactor 3M (M18, M15 and M17) are then connected through a thermal override relay and on to the large cam switch. This connects the three phases onto the spindle windings in one of two ways (for slow and fast speeds). The spindle motor is switched off when the cam switch is in the central position, which leaves the motor disconnected.

FWD/REV Switch

The forward/reverse switch has three single-pole contacts. Two of them are wired in parallel; one of theese is closed in the FWD position, and the other is closed in the REV position. This means that net 1 is normally connected to net 1X in both positions, but the connection is temporarily broken whilst the switch is being moved. This prevents the user from going directly from “powered forwards” to “powered reverse”, since the disconnection will interrupt the power feed to the control gear, switching off contactor 1M.

Speed Change Motor

The speed change motor is powered through contactors 2ML and 2MR. These connect the three-phase bus to a thermal override relay and on to the motor either directly (in the case of 2MR), or with phases 1 and 3 swapped (in the case of 2ML). Thus, they allow the motor to run in either direction.

The fourth contact of contactor 4M is used to provide a switched version of net 6 that is live when the spindle motor is turning (i.e. the speed control lever is in one of the running positions and the spindle is not locked). This is net 7A, and it is used by the speed change motor control gear, to ensure that the motor is only operated when the spindle is turning (to avoid damage to the variable transmission hardware).

If the SLOWER button is pressed, power from net 7A is fed to net 12, which is connected through contactor 2ML to net 14, which eventually powers the coil of contactor 2MR, causing the motor to run forwards.

If the FASTER button is pressed, power from net 7A is fed to net 13, which is connected through contactor 2MR to net 15, eventually powering contactor 2ML's coil, causing the motor to run in reverse.

Feeding the control signal through the fourth (NC) contact of one contactor before powering the coil of the other contactor ensures that both contactors cannot be enabled at the same time (shorting phases 1 and 3 together). The wiring of the FASTER and SLOWER switches themselves also ensures that pressing one button automatically disables the other.

Two limit switches are also used to prevent the motor from running the speed change hardware beyond its limits.

Brake

The spindle brake consists of a spring-loaded brake pad which automatically rubs against a drum on the main spindle motor unless the solenoid is energised to pull the brake pad away from the drum.

The brake is controlled by contactor 1CR which switches the 230 V supply from net 3.

When the BRAKE switch is in the OFF position, the contactor coil is also energised by net 3, causing the brake to be held off continuously.

When the BRAKE switch is in the ON position, the contactor coil is energised from net 6, meaning the brake is only held off when the speed control lever is in the HIGH or LOW position; when the lever is moved to the OFF position, the contactor is de-energised, and the brake is automatically applied.

Powerfeed Motor

The Powerfeed Motor is supplied from net 6 (so that it is enabled when the speed control lever is in the HIGH or LOW position). The internal wiring of the powerfeed module is not covered by this description.

  • archive/hardingedocumentation
  • Last modified: 13 months ago
  • by felix.h