12" x 36" metal lathe VFD conversion and upgrades
Description
When the motor died on our Craftex CT041 12" x 37" gap bed metal lathe my brother and I took the opportunity to make a few planned upgrades including converting the lathe to a 2 HP 3 phase motor with an AT1-2200X variable frequency drive for greater speed control and low end torque. Such a lathe conversion required the addition of a SPDT switch to turn on power to the VFD drive. The switch needed to be mounted somewhere, and a 3D printed control box seemed the logical choice of locations. The VFD control box being 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. So now we have a box with a LED latching switch 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 can also easily swap an Arduino microcontroller for the tachometer and then also calculate the workpiece surface speed and feed rates. I will design a new front panel for Arduino in advance and upload it too. So we now have an LED power switch, a potentiometer and a tachometer display in the 3d printed VFD remote control box. The box will be 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 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 As previously mentioned the tachometer display is mounted on the lathe headstock via a detachable VFD remote control box. Ultimately this box will have the VFD power switch, an Arduino controller, an LCD keypad shield and the potentiometer. I will only need to modify the control box with a new front panel once I am ready to swap out the original tachometer. I can also upgrade to a magnet disc with many magnets instead of one for much finer speed resolution at very low rpm. Having a VFD drive with fast DC braking presents an opportunity to add micro limit switches to the forward and reverse controls to stop the carriage travel automatically such as when the tool reaches a thread relief groove. So I made two carriage end stop clamps to shut off the lathe motor instantly in conjunction with DC braking found on the VFD. I made one for forward travel and one for reverse travel. The two main bodies have mirrored holes to allow for left and right facing switches. 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. 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
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