Adding variable speed control to my lathe

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Nearly a year ago I bought and restored an old 1980s Woodfast lathe. I realised pretty quickly that constantly changing belt speeds for various operations becomes more and more frustrating, and leads to shortcuts, like sanding at 3000 RPM. I know, it was a simple inconvenience, but given that this is a problem with a solution, I embarked on converting my lathe to variable speed.

The components.

  • Three phase motor. Given that my existing motor was a 1 HP, I upgraded to a 2 HP motor to compensate for the reduced power at lower RPMs. I chose a Weg W21, 1.5 kW, which when wired for Δ (delta) supported 230 Volts. I should note that I searched for a second hand motor for months, with no success.
  • Variable Frequency Drive (VFD). I required a VFD which would convert single phase to three phase (which the motor requires), and as suggested by the name, vary the frequency from the standard 50 Hz, which results in a change of motor speed (RPM). Given the great reputation for both product and support on the Woodwork forums, I purchased a Powtran PI150, 2.2 kW direct from the manufacturer. Given the negligible price difference between the 1.5 and 2.2 kW models, I purchased the larger capacity unit, allowing greater re-use potential in the future if required. I also purchased a matching break resistor from Powtran, which allows the unit to brake heavier loads without overloading the in-built resistor.
  • Multi conductor cable. Whilst any cable with four conductors will suffice, the specialist which supplied my motor strongly advised that I source some shielded cable for connection between a motor and VFD. As is the case when living on an island, some items can’t be had for love nor money without a special order, and so I had to wait an extra week for the shielded cable to arrive.

Programming the VFD

Setting for Vector Drive. Vector drive allows the motor to run with far more torque at lower frequencies than simple variable frequency. The setup is a little more involved, but not enough to not do it. The following parameters were set. Note that all the bx.x parameters were based on the motor’s specification:

  • F0.00 (Motor control more) = 0 (Vector)
  • b0.00 (Motor type) = 0 (General asynchronous motor)
  • b0.01 (Rated power) = 1.5 (kW)
  • b0.02 (Rated voltage) = 230 (V)
  • b0.03 (Rated current) = 5.7 (A)
  • b0.04 (Rated frequency) = 50 (Hz)
  • b0.05 (Rated speed) = 1455 (RPM)

With that set, it was time to run the AutoTune routine, in which the VFD runs a test cycle and determines the exact values to set for a range of additional motor parameters.

  • b0.27 (Auto tune) = 2 (Asynchronous motor parameters comprehensive)
  • Press [Start]

Setup for the remote. Given that the VFD has the capacity for integrating a remote, I took the opportunity to configure it such that I could mount a remote head anywhere on the lathe.

  • F1.10 needs to be set to 2 (three wire type 1).
  • F1.00 set to 1 (forward run)
  • F1.01 set to 3 (three wire control)

Wiring up the Remote Head

I setup the remote to enable me to Start, Stop and Change speed. I had anticipated adding a reverse switch, but after many months of not having the facility, honestly, I have no idea when I would use it. I left a spare wire in the head just in case I want to add that, or another feature down the track.

For the buttons, I chose push buttons with an integrated LED, so that when powered up, the Start and Stop buttons light up with green and red respectively.

Note that the stop button should be normally closed. I didn’t realise when I ordered them. None the less, a pull down resistor and harnessing the 10 V line allowed me to convert my NO stop switch to act as NC.

Magnets epoxied on the back allow it to be repositioned wherever my fancy takes me, and an eight pin DIN socket allow it to be disconnected as required.

The circuit diagram below shows the ports on the VFD to which they connect through the cable.

And then it was done.


I had read comments from people noting that once you have tried variable speed you can’t go back. I am rather smitten. The variable speed, when so quick and simple to adjust makes different operations a joy. I had expected to use it much like I did the belts, having a couple of speeds and switching between them. What I find instead is that I am frequently making small changes as a piece gets closer to round. It certainly encourages me to start much slower, knowing that I can effortlessly speed up as required.

One feature provided by the VFD that I truly love is the soft start and braked stop. Having my lathe set to accelerate over three seconds ensures the start-up is far less violent than 0 to 3000 RPM in an instant!

The braked stop too, means that I no longer put my hand on the piece to slow it down, as it will actively break the rotation to a full stop within three seconds too. All calmly and gently.


May 2021

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