In this article we discuss the Metal Lathe treadmill motor conversion on an Atlas/Craftsman 618 and how to convert an AC 110v Metal Lathe to DC Treadmill motor power with variable speed drive. This conversion is awesome and highly recommended and should have been done by us a long time ago. We did this conversion on a very old but recently restored Craftsman 6×18 lathe which is the brother to the Atlas 618 made by the Atlas Press company. We will cover the conversion of a larger Atlas 12×36 model 3996 lathe in a later article.
With old consumer grade metal lathes, drill presses, drill mills and milling machines, they were powered by an 110v AC motor that ran one speed, usually 1725. Different speeds were achieved by stopping the machine and changing the position of the belts on the different sized pulleys. Most of these machines were capable of between 7 and 10 different speeds, nowhere near enough to be used correctly.
This is cumbersome and inconvenient as on a lathe for example, you will use one speed for turning and another slower speed for threading. Further to that sometimes you cannot get the speed you need for the diameter you are trying to machine. Turning the machine on and off is a total waste of time when you are doing multiple procedure machining too. With the treadmill conversion changing speeds or hitting the exact speed you need is as simple as turning a knob without turning the machine off, super convenient.
We happened to have a treadmill that was broken that we used as donor components of the motor and control board, the rest of the required items were purchased. To complete this project we bought the following items off of Amazon.
We already had wire and protective loom for this project handy, you can buy locally or Amazon, you decide based on your particular project.
The Project; Metal lathe treadmill motor conversion
The donor treadmill has a control board that has a 110 VAC input and converts it to, in our case a 90 VDC output. The control board has a seven connections you will need to make, three terminal connections that a 10,000 OHM rotary potentiometer is connected to. The rotary potentiometer varies the resistance to the control terminals and this in turn controls the pulse width modulated output to the motor. Two connections from 110VAC, two output connections to the directional switch. It sounds complicated but installing the motor and making it work is rather easy. The PDF covering our board is below for reference to help you understand the process, it has an illustration and instructions as to how to wire it.
In our case we chose to mount the motor below the table and run the belt down rather than behind the lathe as was original design shown in the illustration below. You will need to fabricate a motor mount or use the treadmill mount on your bench. We also machined a pulley out of 6061 round stock to accommodate the new motor shaft size, if you are looking at this page you already know how to do that 😉 For the motor drive, we chose to use link belt rather than regular v-belt, it is far superior. The link belt is easy to adjust size as necessary and it also does not hold a set like regular v-belts which cause machine vibration and chatter in small lathes.
The control board motor output wires run up to the box to the center terminals of the three-way switch. Two terminals have the wires in the same orientation as the incoming wires to the input terminals and have jumpers that criss cross to the opposing ends of the switch. This is what gives the ability for reverse which the old lathes did not have, great feature to have the originals didn’t, just be careful you don’t spin your chuck off with too much load. The switch spec sheet is attached for reference.
The tachometer kit comes with the tach, sensor and magnets. You will need to fabricate a bracket for your application and mount the sensor and magnet. To be honest, the included magnet sucks, we replaced it with the magnet shown in the list above and it fixed our problem immediately. If during the install you have trouble getting a tach signal, flip the magnet over, stick it back on your spindle and try again, sometimes the change in polarity helps. Once you have signal, epoxy the magnet in place and let it cure.
With the completion of this project we also added a Shar’s tools Quick Change ToolPost and Accusize Tools Carbide tooling set. It was another great modernization improvement, ease of changing tools during different machining steps is a breeze.