Renovating a Hardinge HLV-H

[BillTodd]

I may have misunderstood the logic...

No, it's my fault for not making it clear :)

For those unfamiliar with the Hardinge drive train; The lathe has a dual speed (480/1480 rpm - 0.5/1.5hp) three phase drive motor and a 8:1 variable V-belt system (driven by a motorised jack with up/down buttons - see attached picture) that gives it two ranges of 125 to 1000 and 375 to 3000rpm.

The dual speed motor is controlled directly by a lever switch giving Low/Stop/High speeds. The motor is sufficiently robust to withstand the current surges caused by abrupt speed changes when connected to a three phase supply. (i.e. it is possible to switch high>Low or Low>High without stopping)

I'm going to drive my main motor from a 1.5kW electronic variable frequency drive (often called an inverter or a VFD). These convert the single phase mains to a variable frequency three phase. They can ramp the motor speed up and down, slow it quickly with DC injection braking and all sorts of clever tricks.

I want to keep and use the Hardinge Low/Stop/High Lever control. However, the VFD will not take kindly to the power surges if I leave it connected as it it now - it will just stop with a fault code or worse, go bang.


I will switch the motor connections to the VFD with a dual contactor (one for high one for low), changing the range only when the VFD says it is at 0Hz (stopped). These contactors have to be a mechanically interlocked pair to ensure that both cannot be 'ON' at the same time. These are a fairly expensive and awkward to find item . Fortunately, there is already a pair of these in the control box, used to control the variable speed jack. I'll use another small (100W) VFD to drive the jack up and down.

The main VFD has enough power to drive both the jack and the main motor. However, using a separate VFD for the jack means I can also dispence with the fwd/rev contactor allowing the main VFD to reverse without upsetting the jack motion.

I'll make a simple control circuit* (it only needs to be two small relays) that will take the input from the existing lever switch. If/when the lever is moved directly from one speed to another it will; tell the VFD to STOP, and once the VFD says it is at 0Hz (stopped) it will change the range contactors then tell the VFD to ramp back up to speed (50Hz).

I wont be using the VFD to change the motor speed, it'll simply start,stop and reverse it smoothly [although, as you say Mike, using it as an electronic back gear might be useful]


*I cut my teeth on a microprocessor controlled motion sensing logic for a 24trk tape recorder, but I don't want it to make this that complicated.
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Yesterday I tested the new VFD. Typically, after searching everywhere to find a cheap step-up tranformer and ordering a new one (80 sobs! :(), I remembered I had a 1kVA tranformer that would do the job perfectly !!! (Kip, of this parish, will be laughing at this point because I sold him the other one of the pair I had)

It took about a hour of playing with the up/down speeds, adjusting the brake, oiling the pulleys etc. to get the lathe to run smoothly. The attached picture shows a penny balanced on the head stock while the spindle is spinning at 3174rpm, unfortunately the camera flash has frozen the motion.