[QUOTE=m_c;92790][pedant mode] The motor should have the same torque at any speed provided the VFD is not limiting current. It's the lack of gearing that means there is insufficient torque at the spindle[/pedant mode]

While I don't claim any expertise on inverter drives, I've been using them for the last 20 years and my understanding and experience is that torque falls off either side of the nameplate frequency. Modern motors designed for inverters and "vector control" improve the flatness of the torque curve but the reason machine tool manufacturers using this type of drive specify such huge motors is due to the drop-off in torque. As an example, one of the Swiss firms I represent in the UK make a plain lathe of 70mm centre height designed for instrument making and horological work. The spindle is belt driven at 1:1 by a inverter controlled 1.1kW motor. In the past this machine was made with multi-pulley drive with a fixed speed motor of 300W!!!

Quote Originally Posted by EddyCurrent View Post
I hadn't understood the four contactors for speed were operating a mechanical device, I thought you were using the inverter digital inputs to select four preset speeds.
You may have provoked me into boring you all with another video! The contactors just control the 4 motor speeds nothing mechanical. The variator (Reedes drive) gives the mechanical variation.