Problems in Speed Control

Speed control largely consists of reducing the base motor speed. Two methods are currently available: mechanical or electronic. The mechanical method of speed reduction is done quite simply through varying the ratio of pulleys or gears. If you want to cut the speed of your work in half, you would drive the work with a pulley whose diameter was twice that of the motor pulley. Simple. And as a bonus you would get twice the torque at the spindle. This arrangement is fine until you decide that you want additional speeds. The next option is the 4-step cone pulley or a variable pitch (diameter) pulley. Now you will need to modify the basic drive train - the motor mount must be moveable to allow selection of the various diameter pulleys. This will change the overall design, shape and size of the machine. More importantly, using different pulley diameters to change speed has an inherent limitation: The maximum practical reduction is quite low To get an 1800 rpm motor down to say 300 rpm (a 6:1 reduction), a 3” motor pulley and an 18” spindle pulley. are needed. Even if you would build such an arrangement the center distance would become prohibitive. With high reduction ratios and short distances, the amount of belt in contact with the pulley falls off and you loose power transmitting ability. So now you get into jack-shafts and other contrivances - all workable and inexpensive, but messy to use and maintain.
The next mechanical option is the variable pitch pulley (the famous Reeves drive is an example). Things get better here - it is easy to change speed, but the price goes up. And you still cannot get the super wide range of speeds the artisan turner could use. The final mechanical option for speed control is the gear box. Here you can get ease of use - just pull the shift lever and you have another speed/torque combination. But the price goes up and you can only get at most 4 speed choices.

The other major category for speed control is the electronic drive - either AC or DC. Here you can get a wide range of speed in a small easy to use package. There are also some bonus features in these drives. Instead of slamming the 220 VAC across the motor as is done with a manually switched system, the drive ramps the motor up to speed , providing a softer start (and stop). The rate at which the motor ramps up to speed and down to a stop can be adjusted in the drive. Also, dynamic braking becomes available.
Every silver lining has its cloud. With the electronic drive it is cost and constant torque. Remember the plus side of reducing speed with pulley diameters - the torque increase? Well - this does not happen in an electronic drive. They are called constant torque devices. With a 2 hp drive you get 72 lb/ins of torque no matter what speed you are running. With a pulley system , if you reduce the speed by 6:1, you get 6 times the torque or 432 lb/ins of torque! This is why electronic drives have gotten a bad rap with wood turners.
So what I have done with the L-1 is to set aside the cost factor and design a machine that would marry the best of mechanical and electronic speed control. A 2-hp AC drive provides all the rotational control and a two-speed gear-box provides the additional torque. Due to the fact that the drive train does not have to be physically modified, the motor mount has become a simple rigid plate. Since the drive belt is never moved, a gearbelt can be used. They are lighter, allow shorter center distances , are nearly frictionless and require very low belt tension. With a fixed drive train, the layout can be designed for ease of access when repair or replacement does become necessary

When you have to stop your work, and swap pulleys, if not for a major change, you will just say the heck with it and work at the current speed. This may be OK, but the speed could be a little too fast or slow. When you can simply reach out to the control panel and tweak the speed with barely a shift in your tool position, you suddenly have a new range of capabilities at your command. When you are working on a new piece which is a bit larger than you are used to, or a bit more out of round than you had planned, how quickly can you drop the speed to a level at which you feel comfortable? Or do you hold your breath, and just “go for it”? With the L-1 you have other choices!