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Running Lathe With VFD?

read your post from 2019
My neighbour just made me shut my genset down, which I use to get 3ph for the lathe
I do not use all hp on the lathe doing light stuff, I took the big 4 jaw off because it takes a lot to wind it up
how many hp is your Mazak, could you give me advice on vfd, I have one running my press and one on my bandsaw, working fine
thanks Stuart
Hi Stuart

I have lately purchased an old COLCHESTER MASCOT 1600, 80 inch Gap Bed Lathe. Specs attached. I intent to machine stainless steels, nickel and cobalt based super alloys on this machines. I own a foundry and machine shop where I make these alloys (www.acmelloys.com) and parts.
Could you suggest way forward to put a VFD on this 12.5 HP, 16 speed (40 RPM-1600 RPM), 3 phase, 50 Hz, 220 V system. Though I am mechanical engineer and a metallurgist by profession, I have good understanding of electricals.

The newer models of COLCHESTER machines all have variable speed drive spindles. My thinking is to study the electrical circuit and manuals of Colchester VFD lathes to have an understanding, find the gap and then try to attempt converting the lathe machine to VFD...

Sincerely Vishal Kumar [email protected]


  • Colchester-Mascot-1600.pdf
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What is the voltage of the machine and what is the voltage and phase of the shop panel? Why not use a Phase Perfect or an RPC to run the machine and not rewire everything. My concern with using a VFD is that the mechanical pressure lube system needs to operate within a certain speed range if you add a VFD and change the speed then it would effect the lubrication pressure and flow. I just did a install on another lathe with a mechanical lube pump, we kept the speed range of 30-90Hz based on a number of factors. Since it is a clutch machine we just used a simple 3 wire VFD control to turn the motor on/of and there is a VFD reverse, but there is an issue of using an electrical motor reverse with a mechanical oil pump. Newer lathes I have worked on have an electric oil pump with a safety oil pressure switch to shut down the VFD in case of low oil pressure.

Newer machines that use VFD's have vector motors that are oversized to handle a wider operating speed range and I would assume having an electrical pressure lube system.
Why not use a Phase Perfect or an RPC to run the machine and not rewire everything
Because ACMECAST already has three phase. They don't want or need a phase converter. There are other reasons to use VFDs, hence why practically all large VFDs are three-phase input.

They result in cost savings based on the load put on the machine
I am not exactly sure that is accurate. On a machine tool, you'll never make back the energy costs unlike with pump/fan loads running 8x5 or 24x7.

The primary advantage is the speed control. Do you really need to go below minimum speed, above maximum speed, or between the 16 speeds? On the fly speed changes are nice too...
A VFD also provides lower starting torque that's nicer on gearboxes and motors, but the machine was built for direct-on-line starting. The gearbox can handle it.

There's no need to change the motor; even older motors can take the harmonics from drives fine, especially when properly installed. You may need an extra cooling fan if you intend to run for sustained periods at high torque and low speed - unlikely.

You would only put the spindle motor on a drive; the lube pumps can continue to be supplied by utility 3~, although it sounds like the intention is to install variable speed pump with onboard VFD.
It was not stated what the panel voltage and phase was, as well as the lathe voltage. The lube pump is mechanical not electric on this model of lathe, so running the motor at low speeds would be damaging to the lathe lubrication system if the pump is run off the motor speed. It would be foolish to run the motor so low that it would need fan cooling and there is also the issue that Hp falls off in a linear fashion below the motor base speed as well as the loss in torque due to the mechanical advantage of the gearbox. Older motor, torque often falls off below 20-30Hz. There is little reason to go to a VFD with a lathe 16 speed gearbox.
They stated in another post that they have "3 phase , 220-440V, 50 Hz." - obviously something is off with the voltage spec, but being India, it's certain to be UK colony standard of 240/415 or thereabouts.

I was thinking coolant pump, not lube... lube pump could be an issue, though your suggestion of minimum 30Hz is probably fine.
Given the cost of electricity in Bethel( have worked there many times over the years ), a rotary phase converter would be my last choice. A Phase Perfect would be just the ticket for your situation, given you don't want to fool with converting the lathe for a VFD. Feed an appropriately protected 1P circuit from your breaker panel to the Phase Perfect input, and it's 3P output to your lathe( via a disconnect of some sort, which could be as simple as a twist lock outlet ) and your done. Your electrician friend can handle it no sweat. That's my 2 cents.
Can we assume you have 3ph mains, and that 1ph to 3ph conversion is not among your needs?

Identify a suitable VFD (there are so many good ones). I have good luck with Toshiba and Siemens.
Don't be afraid to oversize! But money is money.
The lathe has a gearbox! My opinion is USE IT!
Use the VFD for fine tuning between 25 and 75 Hz/ Some gearbox selections are "sweeter" than others, so I tend to use those and then play with frequency to get Surface speed and finish.

All the switches and contactors in the lathe controls can be used to control the VFD (if a suitably sophisticated unit was selected) Running control wires out to the VFD location is not hard, Just make a map and pre purchase a selection of colors. Wire labels work also.
I added a pot at an available location on both the MAZAK and the Weiler to control VFD output frequency. Other than that, The only "controls are "on and off". I select VFD braking in the VFD parameters, and change the values to those appropriate for chucks or collets. Most good VFDs would accept alternate configurations that would accommodate Acel/decel and braking etc. by a selector input.
On the Mazak, I run a braking resistor box. On the Weiler, I use DC injection braking . (That sheared a key on the gearbox when I first set the Weiler up. I've modified my stopping expectations since ;-)