Flowering Elbow

You obviously want your classy lathe to have the option of regenerative user control braking right? If not you can skip this step. However, there are significant advantages to having a braked motor, most importantly, you don’t have to wait ages for it to spin down. This spin down time can be quite substantial if your turning something hefty. It also presents a safety hazard as attention is focused on the next task, while the lathe remains spinning and dangerous. 

But it is nice to have the option of braking, rather than have it always imposed… Three reasons:

1. You might not always want it to rush to a halt – doing so puts extra strain on the belt, bearings and other components. In unusual circumstances, It might also endanger your work piece to have a dramatic change of speed.

2. Almost all electronic braking (on series motors) works by shorting the brushes together with a resistor – effectively turning the motor into a generator. This creates a braking force and the energy is dissipated as heat in the armature. Meaning that a lot of stopping and starting with full braking being applied can overheat the motor.

3. It is simply more fun to be able to control things.

One difficulty with this type of motor is that the field coil must remain energized for braking to work.. This is a problem because in general we want braking to coincide with a cut in the power to the unit.

My solution, is to have a push button (S1), normally open, that, when pushed (and held down), makes a separate circuit that both powers the field coil and energizes a solenoid relay (S3), which shorts the brushes through resistor R1.

Key to diagram:
S1 = Push switch – the main switch that the user pushes, and holds, to cause braking.

S2 = A relay that gets power and therefore energizes, when S1 is pressed. It cuts power to the NVRS

S3 = Another relay that, when energized, completes a short circuit between the motor brushes.

NVRS = The main on/off “no volt release switch”.

R1 = A resistor of about 10ohms (the larger the value the more gentle the braking effect)

T1 = Step down transformer 240V to about 9V

D1 = A diode that ensures the field coil is maintained in one direction.