View Full Version : Emco 120 cnc lathe retrofit

11-07-2017, 08:33 PM
This is my diary for the retrofit of a cnc lathe I bought.
It's an emco 120 slant bed 8 tool lathe
My plan was to build a machine small enough to fit in my garage workshop. The lathe was originally designed to run on 3 phase power, I donít have that, and a phase converter doesnít work well with this type of machine, itís very picky about supply voltage and phase balance, The drives are weak and expensive to replace. So I decided to convert the machine to single phase. But hereís the main problem I faced; getting the power requirements required for turning operations from a single phase 240 supply. It wasnít easy, but I managed to equal or better the original performance and specification.

I mostly opted for quality used components. I need this machine to be as accurate and reliable as a typical industrial cnc lathe.
It's complete now and I've taken lots of photos though out the conversion so I thought I would share them, hopefully it could help others.

It had a 5c collet chuck fitted, and one of the step motor drives was missing, I had planned on getting it to work as it was but in the end I stripped out all of the electronics, motors, and hardware to make way for a modern controller, motor, steppers and drives.

I bought most of the parts off ebay, some used, some from China.
Here's my parts :
2.2kw 2 pole 3 phase inverter duty motor
Yaskawa 2.2kw vector drive
A 2x10amp 60v power supply
A pair of digital dsp step motor drives
An szghcnc 1000tdb 2 axis lathe controller
It's basically a clone of a fanuc 21t system, programs the same and has all of the canned cycles you could need. Also supports rigid tapping and fully closed loop axis feedback.
4nm nema 24 step motors
I'm not going to go into great detail about every part but here are pics with short descriptions hopefully they are pretty much easy to understand how ever if you would like any in depth info feel free to message me��

First off, removed everything.22325

I kept the key switch, estop, contactor relay and circuit breakers to be fitted later
Next I fitted my new controller using a piece of abs sheet
Cheap npn proximity switches 5 for 12 quid, I wasn't expecting these to be all that good but they repeat adequately enough for axis limits
The original step motors had a 9.5mm shaft, so made made some bushes to fit the new shafts which are 8mm. Small abs enclosures hide the wires inside which connect to the original stepper cables. I'm running these 2 phase 8 wire steppers in bipolar parallel configuration. I re-used the original stepper mountings, all that was needed was new hols for the bolts.
The steppers are dual shaft type, I plan to add encoders as the controller is able to run step motors closed loop.
So far I've had these motors running rapid moves at 3m/min with no lost steps, I've yet to fully test them to see how fast they will go.
https://youtu.be/qgVIjoiOai4 They are geared 2:1 with a toothed belt system to a 5mm pitch ball screw.
The motor also required a sleeve to fit the main drive pulley,here is a video of the testing the motor and drive on the bench:
Tool turret:

The turret works with 4 opto sensors and has a turthbtable built into the software to find position of the 8 tools. The controller has this ability, that's why I chose it. However the opto sensors are pnp, so I used ic chip uln2803a to make the signal suitable for the controller (npn). I used a small breadboard to prove it out, I have a dip pcbs with screw terminals coming soon. I used a 2 channel arduino relay module for the forward and reverse of the turret a 24v psu and a large ceramic resistor to reduce voltage in the reverse direction. (Add pic here)
I removed the collet chuck for now and added a 100mm 3 jaw Chinese chuck these are only 40 quid and decent quality too.
Spindle encoder22219
The encoder is a hedr55l2 encoder, I chose this model because it has line driver outputs, it has 3 channels and each channel has a plus and minus. The resolution is 3600 ppr. This mounted inside the original emco encoder housing and I used stp cable to connect it. This type of cable can be easily obtained by chopping the ends off good quality network cables.
I used this vfd for my coolant pump22220
I also used line filters with both of my vfd's
When I bought the machine I hired a large van and the fella I bought it from used a forklift to load it, so I took the machine to my workplace and used the forklift to unload it and craned it onto 2 euro pallets and then I had a man with a tail lift Luton deliver it to my home. I borrowed a pallet truck to move it into my garage workshop, however having returned the pallet truck I had no way of moving it around except jimmying it with a long 2x4, it weighs about 370kg! so I ended up getting some heavy duty twin wheeled braked castors, now I can move it around should I need to be in the rear for servicing or repair.

Contactor relay/mcbs/fuses22326

Step motors on mountings22327