Hi Secon.58. You might like to consider using a DIAC in your circuit, they are commonly used in dimmer switches for domestic lighting. They minimise 'flicker' at very low light levels, or so I was told many years ago. A bit of RF suppression is a good idea too, as the sharp edges at the top and bottom of the waveforms can cause interference to radio and TV systems.
When the kids were little I used something similar to what you are doing to control the speed of the locomotives on their model railway set. Most of the locomotives used a worm drive between the motor and the wheels, this behaved as one would expect. However, the diesel shunter used spur gears instead of the worm drive and there was a fair amount of play in them. With the shunter set to a very low speed (but not quite off) such that it didn't move, the distorted voltage caused the play in the gear train to produce a sound that was just like a diesel shunter ticking over!
