D.C. motors are very useful for powering things in your shop. I've built or repowered several things in my shop with them, from the main drive on my lathe to an X-axis power feed for my mill. The main advantage of a D.C. motor is infinite speed control. Another nice feature is instant reverse of rotation.

The most common D.C. motors available on the surplus market are rated at 90 volts. They come in all sizes and shapes. A small 1/5 horsepower gearmotor typically costs $15.00. A large 1 horsepower motor can cost $50.00. If the motors you find don't have a horsepower rating on them it's pretty easy to come up with an approximate figure. 1 horsepower equals 746 Watts. Most motors will have a voltage and current rating in Amps. Since Volts x Amps = Watts that's pretty easy math to do in your head. You should remember though that all motors are not 100 percent efficient, so you should derate that number by about 30 percent. I use 1000 Watts per horsepower and am usually pretty close.

Besides having a D.C. motor you will need some form of a variable D.C. voltage power supply. My basic design for powering 90 volt D.C. motors consists of a Variac and a full wave rectifier bridge. I won't bore you with the math but take it from me, 120 volts A.C. that is run through a full wave rectifier comes out at about 90 volts. No wonder there are all those 90 volt motors out there.

A 10 amp Variac sells on the surplus market for $15.00. A good quality full wave bridge can cost $20. If you do your shopping cautiously you can get a motor and build a power supply for well under $100.00.

Here is a schematic for the basic power supply that I use.

The 'feedrate override' switch is useful on the X-axis drive for rapid travel in the reverse direction, but is not necessary on a main drive motor power supply.

These are pictures of 2 versions I have built. Click on the thumbnails for full sized pictures.

SmallVariac1.JPG

SmallVariac2.JPG

BigVariac1.JPG

BigVariac2.JPG

The small one uses a 2 Amp Variac and is housed in 2 dual gang electric boxes that are bolted together. I use this one for powering the 1/5 HP gearmotor on my power feed. The top right switch is On/Off, the top left is feedrate override, the bottom switch is direction.

The big one is built from a 25 Amp Variac and some 100 Amp rectifiers. I use this brute to run the 3/4 HP motor on my lathe. It's over built by a huge factor, but it was made from parts I got for free. In theory it could easily run a 3 HP motor. The right most switch is On/Off, the switch next to it controls the front panel outlet, the left most toggle switch selects either the top or bottom binding post as the output so I can eventually use it to also power my mill, the toggle switch just to the right of the binding posts is forward/reverse.

There is not much I can say about changing the motor on your lathe or mill. It's pretty simple to find a motor and make a mount. If you are lucky you can find a motor with a shaft size and mount similar to the one you have. I wasn't so lucky with the motor I was given for free to use on my lathe, but making a shaft bushing and mount were pretty simple.

This is a picture of the motor and mount I made for my lathe and a movie of the finished product.

LatheMotor.JPG

DCLathe.WMV

This is a sketch of the gear arrangment I use to build my powerfeed.

The gearmotor is not connected directly to the table screw, but goes through an idler gear that is used as a 'clutch' and can be disengaged. This is a simple system and modeled directly off the quick change gearbox on my lathe. The gearmotor I found was 120 RPM on the output. That figured well for the speed range I was looking for so the gear ratio to the table screw is 1 to 1.

There are a couple of simple tricks that make building this easy. The arm that the idler gear is on rotates around the table screw shaft.The idler gear is mounted on an eccentric bearing, meaning I drilled the mounting bolt hole off center. This makes a simple way to set the lash between it and the gear on the table screw. Then with the clutch engaged, you can set the lash between the gearmotor and the idler with elongated mountings holes for the gearmotor.

These are some pictures of the powerfeed and a movie showing it's operation.

Xfeed1.JPG

Xfeed2.JPG

PowerFeed.WMV