Thread: C6 Lathe 3 Phase + VSD Conversion

Guys,

I've just recently got to a working stage the conversion to 3 phase motor with a VSD for my C6 lathe.
The VSD I am using is a Danfoss VLT 4kVA unit which requires 3 phase 415V input. Inspired by an old post by Brobdingnagian, I have successfully powered the VSD from 240V single phase through a 240V to 415V 1.5kVA step up transformer with the two wires connected to L1 and L2. Phase imbalance trip setting was changed to warning only. As the motor I'm using is only 0.75 kW (at the moment, for testing purposes) the derating of the VSD still provides plenty of capacity.

The lathe controls have been transferred to a new control box with push-buttons for FWD, REV, JOG and STOP buttons, with a speed control pot. Additionally, I have included switches for the coolant system pump and the worklight. The lathe internal safety interlocks and emergency stop button have been included in the controls, and drop power to the control box VSD controls.

Latching relays for FWD and REV were needed with this VSD to allow push button control.
The Stop button can be momentarily pressed for coast-down to stop, or held in for DC braking stop.

The motor was mounted externally to the lathe to minimise disturbance to the original parts (in case I need to restore the original setup), and so the original motor has been replaced by an idler shaft driving the original pulley arrangement of the lathe.

The setup seems to have adequate power for this lathe from about 25Hz to 100Hz (lathe rigidity seeming to be the limiting factor with metal removal rate). This gives a speed range in the outer high speed pulley position of 350 RPM to 1400 RPM, and in the low speed outer pulley position of 70 RPM to 280 RPM.
The transformer and VSD should have enough capacity to upgrade the motor to about 1.5kW
The larger motor would give better overlap of high/low speed ranges, but presently I can use the other 4 pulley positions if needed.
The new drive runs much more smoothly and a bit quieter at all speeds than the original drive setup.

Some picture attached showing the setup, rough electrical schematic, and the temporary belt tensioner...

Andrew.
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Hi Andrew,
My main reason for wanting to replace the motor with a 3ph (or brushless DC) motor is to get away from changing belts to adjust speed - as far as that is possible without fitting a gearbox.
I already have a VFD as part of my CNC router so I just have to find a cheap 3ph motor.

Another thing I've been looking into is to replace the thread cutting gears with a stepper motor setup. There are a few ready made options for this ELS which is quite old now and this one I found yesterday, ZyklenAutomatik
The web page for ZyklenAutomatik is all in German but the Youtube videos are in English. I've sent him an email to get more details on the release of the latest version.
Fitting a stepper motor should be straight forward, lots of space once the gears are removed. Fitting a sensor to the spindle will require a bit of planning to avoid damage when changing belts. Industrial strength rotary encoders are available but not really affordable!
Let me know if you're interested in this and I'll forward details as I get them.

Originally Posted by snowyskiesau

Hi Andrew,
My main reason for wanting to replace the motor with a 3ph (or brushless DC) motor is to get away from changing belts to adjust speed - as far as that is possible without fitting a gearbox.
I already have a VFD as part of my CNC router so I just have to find a cheap 3ph motor.

Another thing I've been looking into is to replace the thread cutting gears with a stepper motor setup. There are a few ready made options for this ELS which is quite old now and this one I found yesterday, ZyklenAutomatik
The web page for ZyklenAutomatik is all in German but the Youtube videos are in English. I've sent him an email to get more details on the release of the latest version.
Fitting a stepper motor should be straight forward, lots of space once the gears are removed. Fitting a sensor to the spindle will require a bit of planning to avoid damage when changing belts. Industrial strength rotary encoders are available but not really affordable!
Let me know if you're interested in this and I'll forward details as I get them.

1) If your variable speed aim is to get rid of belt changes, you may have to take out a mortgage on your kids. It is doable, but pretty expensive. Because for every single belt step that you do away with, you will have to nearly double the size of your variable speed drive in order to maintain the metal removal capacity that you had with the belt steps. Or to put it in other words, nearly all home shop owners are happy to keep their belt drive gearbox as is along with a variable speed upgrade. If we are talking about a 1HP 6 speed belt drive hobby lathe, the price difference between a 1HP/6speed VFD drive upgrade and a 6HP/1speed VFD drive upgrade is probably more than the whole lathe costs in the first place.

2) ELS fore home use is good enough if all you want to do is cutting fastener threads. If however you want or need to cut accurate pitch threads, like needed for making replacement leadscrews for machine tools, you will find that all these homebrew ELS available today are just not good enough, and by very far not nearly as accurate as the good old and simple changegears or norton gearboxes.

Snowy,

The only times I have needed to change the belt drive to a different ratio in the last six months of use was when I used a parting tool on a piece of 3" diameter steel bar, and when I was taking heavy cuts on the outside diameter of a piece of 6" diameter 1045 steel while making the slimline 4-jaw chuck for my rotary table. Both of these operations stalled the motor.
Picture below:
Picture 002.jpg
The added functions of the VSD, including variable speed, DC braking, push button operation and jog functions, and also the smoothness and quietness of the drive have transformed the lathe.
The motor I have installed on the C6 is 0.75kW, only slightly larger than the original motor.
I have a 1.1kW motor ready to install, but haven't found the need to be great yet.

I am not sure if there would be any large benefits (to me) in using an electronic leadscrew as I regularly do screw cutting at various pitches which needs to be fairly accurate, and I normally hand feed the carriage when turning.
This gives me a better feel for avoiding chatter etc., particularly as I use various turning tools with different cutting characteristics.
It also means I am not changing the leadscrew gearing all the time, and also wearing out the leadscrew.

Andrew.

If by installing a VFD/3ph motor combination I can reduce the number of belt changes to get the speed range I need, that will do me.
As for an electronic leadscrew, it would be accurate enough for any use I'd put my lathe too. Perhaps a first step on converting it to CNC

It's a hobby, it's done for fun!

Nice job mate. I'm going to do this for my drill press when I get time.


Sent from my iPhone using Tapatalk

I've decided to go ahead with the electronic lead-screw, it's nearly winter and I need an indoor project
Most of the parts I have been able to get on eBay or through Element14 (Farnell) but finding a suitable spindle encoder from a local supplier is proving difficult. I object to buying a $35 encoder from Digikey and then paying an extra $35 for shipping.

PCB's have been ordered,. Minimum order quantity is 5 and the price for 10 is only $3 more so I got 10. This means I'll have a few spares if anyone else wants to give it a go.

I'm still going through the source code to get familiar with it, comments in German don't help a lot!

Originally Posted by snowyskiesau

I've decided to go ahead with the electronic lead-screw, it's nearly winter and I need an indoor project
Most of the parts I have been able to get on eBay or through Element14 (Farnell) but finding a suitable spindle encoder from a local supplier is proving difficult. I object to buying a $35 encoder from Digikey and then paying an extra $35 for shipping.

PCB's have been ordered,. Minimum order quantity is 5 and the price for 10 is only $3 more so I got 10. This means I'll have a few spares if anyone else wants to give it a go.

I'm still going through the source code to get familiar with it, comments in German don't help a lot!

With the weather we have had of late, that sounds like a good plan, it sure has been cool up in the North West of the state. Here is some "German" for you to practice with before you get right into that code, its old but good, and probably quite relevant. Good luck with the project,
Rob.

ACHTUNG!

ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKEN.IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN

Originally Posted by snowyskiesau

.............

I'm still going through the source code to get familiar with it, comments in German don't help a lot!

I am native in German, feel free to send a PM if you need some comments in that code translated.

Originally Posted by cba_melbourne

I am native in German, feel free to send a PM if you need some comments in that code translated.

Thanks, The designer's coding style is not unlike my own and comments are few.
So far, Google translate has been up to the task of translating the words if not their meaning in context. Unfortunately, this means I have to work out what the code does by understanding it.