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Projects

Project to implement an inverter drive for the BH600G lathe

GWH Engineering

creative engineering in a home workshop

The BH600G is a basic belt driven lathe with back gear arrangement exactly the same as in the Myford.  The only problem is the changing of the motor belt from large to small pulley was difficult as I had no access to the rear of the lathe.  The best solution is to incorporate an inverter drive unit which then gives easy speed changes.   Where very slow speeds are required it is best practice to allow the inverter to operate at a medium to high frequency to prevent over heating of the inverter.  The change of spindle belts is quick and easy and for very slow speeds the back gear is used. I normally have the motor pulley drive set to high speed and the spindle pulley to middle which at full frequency gives 900rpm.   Installation of the inverter unit is relatively straight forward.  The first stage was to remove all of the electrical contents from the existing lathe  cupboard at the rear.  I had started to experience some intermittent contact failure with the original set-up so it was probably only a matter of time before the contactors failed completely.  The cupboard is now used to hold the mains feed to the inverter including a no volt release switch with LED incorporated into the door.  Other basic transformers for the lighting and suds pump are now in the box and a connect strip to include the safety switching. I was keen to continue the BH600G safety concept which prevented the motor running if a door was open etc and the use of an emergency stop button near by.  This was relatively easy to set up as the inverter I bought had a safety option which could allow a set of control switches daisy-chained together to ensure all was correct before the motor started.  The inverter incorporated a no re-start following the stop control so this added exactly the type of safety switching needed. I bought from the inverter supplier their control unit which provided start, stop, forward, reverse, run and jog controls.  The best place to position this control unit was based on use to be at the RH end of the lathe and to the back so it was fitted to the rear splash guard.  The safety features as mentioned were all inter-connected so the lathe motor would not start unless all were in the safe position and in the event any one was, say in the case of the chuck guard, raised the motor would stop and remain stopped unless made safe and the control unit start button pressed. The safety switches include: chuck guard pulley top cover gears door carriage lever previously  now stop only carriage stop Emergency Stop The emergency stop button is now at the front LH side and I have added a tachometer display.  The tachometer pick-up is at the rear of the spindle.