That's a Craftex CT041 12" x 36" gap bed lathe getting the conversion. We installed a new 2 HP 3 phase motor from Hallmark Industries and an AT1-2200X 2.2KW variable frequency drive for more precise speed control and a little boost in low speed torque.
Not my first choice of lathes, but it is what it is. I especially hate the electrical cabinet and all the wiring on this lathe. Total garbage.
DISCLAIMER:
High voltage wiring is inherently dangerous and can kill you. If you are not qualified you should not engage in such activities and instead hire a qualified individual to engage in such work for you. I am not responsible for your stupidity if you proceed with any modifications to your lathe based on what you read here and get dead.
How I modified the wiring to send power to the new VFD circuit.
This lathe normally operated with 3 "power" wires (well really 4 but one is permanently disconnected, go figure) and a ground wire to the original single phase motor. Interlocking 220v contactors toggled between two inputs and a common line in order to reverse the direction of the motor. The switching to affect this is controlled by a low voltage control and safety circuit that goes thru two interlocked NO/NC spindle direction switches.
The variable frequency drive however is operated with only two non-switching 220 volt power wires and a ground wire. I wanted to use the existing wiring to the motor to go to the new VFD, but couldn't have the power toggling as the lathe was currently set up for. So, first up was deciding what is the best way to power the VFD.
I also needed to determine how I would control the motor direction. The first decision was easy. I'd control the motor direction from the VFD using the VFD's low voltage ports x4 and x5.
The next choice was whether or not to use the lathe's existing directional control switches, or a new forward, neutral and reverse 3 way switch I'd add to a new control box on the head stock. As I wanted to retain the existing directional levers I had developed muscle memory for I decided remove the existing control wiring from these switches and replace it with new wires to the VFD.
SO, what I did do to make this work was to leave all the lathe wiring intact EXCEPT FOR the two spindle direction switches. These two interlocked switches have 3 control outputs. The first are the two Normally Closed contacts that simply energize the low voltage circuit required to operate the lathe motor direction circuits. The two Normally Open contacts activate the interlocked 220 volt contactors that toggle the three 220 volt lines to engage the forward and reverse motor operation.
For the new operation I did not need to toggle between three 220 volt mains lines, BUT I needed one Normally Closed contactor to energize the lathe motor circuit, and I needed one Normally Open contact to activate just one of the two lathe direction contactors in order to energize two of the three 220 volt lines to serve the VFD circuit. The remaining third wire to the original single phase motor output becomes obsolete and was terminated with a wire nut.
So I transferred the wiring from the two spindle direction switches to a new single SPDT NC/NO latching switch labeled "VFD Power", except I left off the wire to the Normally Open contact for the reverse side of the two switches.
I was left with the choice of where to mount this switch. I was adding two new control boxes for the VFD, one on the wall for the power filtering circuits and another on the lathe for the speed control and display. The new VFD power switch was initially to be located on a new speed control box mounted on the lathe head stock. But we later decided to locate the VFD power switch in the original lathe control panel, in place of the JOG button. This put the VFD power right next to the main stop switch to keep everything together.
My brother wanted to have a jog function, so I added a forward and reverse jog button to the speed control box that mounts on the head stock.
New sequence of operation
When the original lathe power button is pushed the Normally Closed contact in the new "VFD Power" switch energizes the motor direction control circuit in the lathe. When the VFD Power button is actually pressed the Normally Open switch then energizes the contactor that starts the motor in the forward direction. The wire to engage the reverse motor direction is left unconnected and capped.
SIDE NOTE:
You can see from these images what a dog's breakfast the lathe's electrical box is as it comes from the manufacturer. It is too cramped, poorly laid out and uses a hodge podge of connector types. The ground terminals particularly suck, the manufacturer should have added proper DIN rail mounted ground terminals instead of installing a loose plate onto the rail. Grizzly made the manufacturer do this on the lathes they distributed.
I also don't like that the lathe's original (and current) 28 volt transformer actually puts out 34 volts which does not suit some of my new components which required the purchase of a new DIN rail mounted Meanwell 24 volt transformer I've mounted in a separate electrical box that serves the VFD.
Lessons Learned
IF I had to do this conversion all over again I'd gut the lathe's entire wiring scheme and rewire from scratch with all new components.
I'd run a single 24 volt circuit thru the chuck guard switch, the change gear safety switch, the power indicator light and then the emergency stop/main power switch.
I'd still eliminate the motor "jog" switch from that 24v safety circuit and instead convert that button to a VFD power switch. I'd also eliminate the interlocked spindle direction switches from the lathe's 24v circuit as I did. This would eliminate two superfluous contactors from the electrical box freeing up space.
When all the safety switches are in the closed position the 24v would then activate a simple 2 pole contactor with thermal overload to send 220VAC to the VFD electrical box with it's noise suppression circuit etc. A single new transformer would then power the tachometer and surface feet per minute calculator in the speed control box.
I'd then use the VFD ports to control the motor direction by wiring the two forward and reverse signals thru the two spindle direction switches. I'd still use the 10K potentiometer to control the motor speed in conjunction with the lathe gear box. I'd add the same two jog buttons to the control box as well
I have modified the controls I designed a few times now... but this is the last iteration.
A control box located on the lathe headstock as opposed to the VFD drive located on the wall behind the lathe meant that remote speed control would be convenient. This required the addition of a 10K potentiometer to control box. The final version of the box has two LED momentary jog switches and a potentiometer.
Of course I also need to know the spindle speed, which meant that I would either need to manually calculate the spindle speed based on the motor frequency (or rpm) and the selected lathe gearing, or I'd need to install a tachometer. Math in my head is unreliable and slow, so I went with a tachometer which is instantaneous.
In future I plan to swap an Arduino microcontroller for the tachometer and then also calculate the workpiece surface speed and feed rates. I will design yet another new front panel for Arduino.
The box is mounted on two legs that hold the box at a 10 degree upward angle for better viewing, but the box can be quickly detached for mounting elsewhere if desired.
See this link for the VFD's control box component details and files. I have three iterations of the front control panel if anyone wants a similar project done slightly differently than I've done mine.
https://www.thingiverse.com/thing:5178575
A tachometer also requires mounting some sort of sensor to register the spindle speed. My tachometer comes with a 12 mm diameter hall effect sensor and a magnet to activate the sensor switch. Both need to be mounted within the head stock.
The best place for the sensor bracket, sensor and magnet where those components wont interfere with anything on my lathe is on the outboard end of the lathe spindle. This also happens to be where I wanted to install an indexing system.
This meant designing a multi-purpose mounting hub that could be used to mount various types of discs such as a balanced magnet disc, slotted optical sensor discs or various indexing discs.
It also meant designing a corresponding bracket to mount either the 12 mm diameter hall effect sensor or a 1/2" threaded indexing pin. For the indexing function I elected to go with a retractable spring plunger from McMaster Carr part #8507A12.
This sensor and indexing mounting system is covered in much greater detail on my multi-purpose lathe spindle mounting system thing page at the following link:
https://www.thingiverse.com/thing:5173084
When I convert to an Arduino controller I will upgrade to a magnet disc array with many magnets instead of one for much finer speed resolution at very low rpm.
I also made two carriage end stop clamps to shut off the lathe motor instantly. I made one for forward travel and one for reverse travel. The end stop clamps have attached micro-switches whose NC terminals are wired in-line with the 12 volt forward and reverse inputs for the VFD. Upon contact the circuit opens and the motor stops. The two main bodies have mirrored holes to allow for left and right facing switches.
These same stops can be wired into the conventional lathe spindle direction control switches to interrupt the low voltage safety circuit of these lathes as well. With the single phase motor the lathe is just slower to stop and the carriage will travel a bit after hitting the switch as a result.
See this link for the carriage stop clamp component details and files:
https://www.thingiverse.com/thing:5185523
I'll post more photos later
