ELECTRONIC LEADSCREW CONVERSION
Part 6/6 by Geoff Rogers
Taper turning
Taper turning is normally achieved by setting the top slide at an angle. As a last resort the tailstock can be off-set (a small amount) - not my favoured option.
With the CNC facility two options are available. First is to specify a length and reduction in diameter at the small end and secondly to specify a cone ratio.
The first option applicable to specific cases, while the second option is much more versatile. When the cone ratio is defined, specified as part of the parameters applicable to taper turning, setting the taper results in the controller automatically calculating the small diameter. This means that a specific angle can be applied regardless of length. The angles given for taper reamers, for example, are 1 in 50 (metric) and 1 in 48 (imperial). For the CNC controller these would be set as 1:50 or 1:48.
Likewise, an angle of 45 degrees gives a cone ratio of 1:0.5. So a chamfer of set length can be easily machined and if necessary, easily adjusted.
Emergency Stop
The operation manual recommends (stipulates!) an emergency stop feature be included in the installation and a level 1 type stop is required.
This led to an exploration of the topic. What did level 1 mean? How many levels are there?
There is an ISO standard for this subject. Makes for interesting reading and is only really applicable to industrial setups with complicated machinery.
I found some assistance regarding the ES from the Model Engineer magazine CNC forum from David Smith.
The complete machine must have an emergency stop device in which the ELS control must also be integrated. The ELS has inputs and outputs for this purpose.
An automatic restart after the emergency stop has been triggered must be safely prevented!
An emergency stop of category 1 - controlled shutdown while maintaining the power supply is required to carry out the shutdown.
The energy supply is only to be interrupted after the machine has come to a standstill.
This procedure brings the spindle and drives to a standstill as quickly as possible. Only then can the power supply be interrupted.
With most model engineer machine tools, a simple ES is all that is required and when activated it switches off the drive motor.
The ELS installation puts in place separate drives for the cross-slide and leadscrew.
The solution is to install a double pole stop switch, which stops the lathe motor and the ELS drives at the same time.
The ESL controller has a 24V output for connection to the stop switch.
NC (Normally Closed) and NO (Normally Open)
The ELS requires the lathe spindle to be rotating before the stepper motors will operate.
The S7 clutch disconnects the spindle from the motor and this stops the stepper motors.
With most model engineer machine tools, a simple ES is all that is required.
When activated it switches off the drive motor.
The ELS installation puts in place separate drives for the cross-slide and leadscrew.
The solution is to install a double pole stop switch, which stops the lathe motor and the ELS drives at the same time.
The ESL controller has a 24V output for connection to the stop switch and can be switched between NC and NO.
However, the ELS requires the lathe spindle to be rotating before the stepper motors will operate and the S7 clutch disconnects the spindle from the motor and hence stops the stepper motors.