DIY machining a compression screw

I built a powered milling attachment to replace my toolpost and added CNC control to the spindle of my lathe (carriage was already CNC'd) so that I could machine a compression screw for an extruder. The screw is 25mm diameter, 25mm pitch and the threaded section is 500mm long. It was very slow going, the motor I used on the milling attachment was only 1/4HP, would get very hot after 10 minutes and needed frequent breaks. The channel in the screw is 6mm deep in the feed section, reducing to 2mm in the metering section giving a compression ratio of 2.5:1