[millman52]

A bit OT need a variable speed control for a 12V DC brush type permanent mag motor. Motor is rated at .4A no load to 3.4@ max 7200RPM Planning on using this on a 2 axis CNC controlled Ox/Acet burning table for manual torch height control. Any help much appreciated.

[NC Cams]

There are a number of 'model train throttles' that will readily do what you want to do. However, to retain torque, you're probably better off with a PWM based throttle.

Do a web search for an NE544 IC. THis is a servo driver IC that has been used to make PWM bidirectional speed controllers for a number of hobby uses over the years.

If you're electronic literate, you can create a wein bridge oscillator to make a saw tooth generator with two stages of a 324 op amp. You can then feed the saw tooth into a comparator circuit made from the remainder of the 324 and drive a mosfet (IRFZ40 or 44). The whole circuit takes residence on half a business card.