ELECTRONIC LEADSCREW CONVERSION
Part two by Geoff Rogers
The manual provided with the ELS package explains comprehensively what can be controlled. An outline of some options is given below.
Gearbox left or right.
These options enable the saddle to be traversed, for fine feeds, to the left (Gearbox left) or the right (Gearbox right) under the control of the leadscrew stepper motor. Basically these options enable the lathe to simulate normal operation as if the leadscrew were driven by gearing attached to to spindle.
The advantage being that the range of feed rates is much greater and very readily changed by the controller. Also fine feeds are available at wider range of spindle speeds.
Boring
Boring out to a diameter and depth is determined by the controller, such that blind boring is easily achieved. The depth of the bored hole is controlled to a high degree of accuracy (0.005mm) by the leadscrew stepper motor and is repeatable
Threading
Apart from offering the ability to cut threads of a wide range of pitches, the controller also offers the ability to control the tool in-feed, primarily via the cross-slide stepper motor.
The ELS controller offers four different tool in-feed methods:
1. standard radial in-feed with gradually decreasing in-feeds.
2. Simple flank in-feed with even in-feeds. This is the equivalent of setting the top slide over at half the thread angle.
3. Modified flank in-feed with even in-feeds. This is as per 2 above but the tool position is also modified by the leadscrew stepper motor.
4. Alternating flank in-feed with even in-feeds. This option requires the use of a ball screw leadscrew.
The above threading controls apply to external and internal threads, both parallel and tapered (eg BSPT).
Is it difficult to install?
The leadscrew and cross-slide require stepper motors to be fitted at suitable locations and the rotary encoder to be fitted the lathe spindle (photos below)..
As direct fitting of these parts to the lathe is not an option, they were installed using belt drives. After some investigation 3mm pitch, 15mm wide, HTD belt drives of appropriate length were selected. From this and some 3D CAD work, suitable pulley sizes were determined. For simplicity, all three items use a 1:1 pulley ratio.
The existing spindle drive gears for the leadscrew QC gearbox were removed as they were not required. The existing QC gearbox has been left in place and put into ‘neutral’ by keeping the selector lever up. Since installation I have found that the leadscrew stepper motor has sufficient power to drive the gearbox with selector lever engaged. But is not recommended!
As mentioned, all of the CNC parts can readily be removed and the lathe restored to original standard. The only change made to the lathe was to provide a clearance cut-out in the gearbox cover, to enable the cover to be closed with the rotary encoder in place.
More details of stepper motors and spindle encoder next time.