The 90-volt DC motor provides far more than that of the 1/2 HP AC/DC motor we used to offer prior to 1994. A DC motor offers its maximum torque at low RPM where you need it most, so the full speed horsepower rating of an AC/DC motor can be a little deceiving as far as offering practical, useable power. The DC motor also offers smoother and quieter operation. The motor now features externally replaceable brushes, making replacement of worn brushes a simple task taking just a few minutes.
To power and control the motor a more sophisticated speed control unit is required. The control we have developed accepts any incoming AC current from 100 VAC to 240 VAC, 50 or 60 Hz and automatically outputs 90 VDC to the motor, so this unit can be used anywhere in the world without a transformer. All you need is the correct wall plug or converter. In addition, a load compensating circuit has been designed into the controller. As load is applied, the speed control will add power to attempt to hold a constant speed. Once the on/off switch is switched to the “ON” position, a speed control knob is used to vary the speed over the entire range. With the two-position pulley in the “normal” position on a Sherline headstock, the speed range is about 70 to 2800 RPM. In the “high torque” position the maximum speed is cut in half but torque at any given speed is much greater. If you are using the motor in non-Sherline applications, the maximum no-load speed of the motor shaft itself is 6000 RPM. Complete specs on the motor can be found on the “Standard Dimensions and Specifications” page on this site.
Replacing an Older AC/DC Motor
This unit can be purchased to replace an existing AC/DC motor on an older Sherline machine. This very compact and well-engineered unit costs far less than other DC units of similar power offered in major industrial tool supply catalogs. If you are replacing an older AC/DC motor and speed control you can re-use the same motor mounting bracket, standoffs and drive belt, but you will need to purchase a new stepped spindle pulley, P/N 43230 and the belt guard halves, cover mounting tab and belt cover screws shown in the exploded view drawing below. You could also purchase P/N 3306, which is the complete headstock with DC motor and speed control as is shown below. A version with different pulley ratios and offering a 10,000 RPM maximum spindle speed is available as P/N 3307.
The drawing below shows the components in the 3306 unit and how it is assembled. The 33050 includes only the motor, speed control, power cord and motor pulley.