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Overview of fitting variable frequency drive (VFD) to a Myford ML7

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choochoo_baloo30/06/2020 00:59:08
252 forum posts
54 photos

Morning chaps. Whilst undertaking overdue spindle/bearing maintenace on my Myford ML7, I started to entertain the idea of a variable frequency (VFD) motor upgrade.

I've read a few posts in forums/youtube comments about the numerous benefits of replacing the original single phase motor (small-ish Metropolitan Vickers no less) with 3 phase VFD controlled. For starters:

  1. What exactly is on paying for in getting a plug and play Newton Tesla unit vs a Chinesium white box and standard looking mtor?
  2. Does the Newton Tesla unit simply offer pre-wired + fancy control panel, or is there more to it?

Therefore I'm hoping for a concise summary of the advantges (and there any disadvantges, cost aside?) of this popular-ish upgrade. Please advise.

Thanks in advance.

Nigel Graham 230/06/2020 02:21:03
655 forum posts
15 photos

I fitted my ML7 with a Newton-Tesla set, which is electronics plus motor.

My version is just a straight swap plus finding a suitable location for the inverter/controller. If you tell them the machine they know which electronics to pair with which motor.

I say "my version" - I'll go by that to start with. You'll see why, shortly.

The lead from the motor has a special plug for the connector on the electronics.

The main lead is rather short, at least on mine, so I have to use a short distribution-board. That though is a matter of workshop geography so may not apply to yours.

I placed the inverter on the cabinet below the headstock, but that is in the way of oil and swarf so I made it a cheap-and-cheerful plywood shelter that sits in the chip-tray above it. It's there because although I am right-handed, the disposition of the controls is better for using left-handed on the inverter I have. In particular, reducing the risk of accidentally using the wrong Stop button.


I stressed that clause because the Newton-Tesla systems I subsequently bought for my other machines differ, by having two separate electronics units. Those do need more wiring - not difficult if you are reasonably happy with such work; but it is vital you put the right wire in the right place, of the mains lead and of the cable linking the inverter itself to the control "pendant". Which isn't really a pendant but a box with lugs for screwing it to a surface.

If the set you buy is of that pattern, put the inverter somewhere well out of the way of swarf and oil-spray, as it is not fully-enclosed.

That on my Harrison lathe is high on the wall above the tail end of the bed, with the controller just below it, still well clear of the muck. It also keeps me clear of rotating things - which can't be said for the rather dubiously-designed clutch lever a feature of the L5! Similarly with the set on a BCA JIg-borer - on the wall a bit above and in front of my shoulder when sitting at the machine. The set destined for the milling-machine will also be similarly elevated to a higher plane.


One thing to watch (having just given myself an expensive repair!).....

If the motor is the type with open ventilation holes in its ends, fit a shield to protect it from swarf, unless your lathe already has that luxury. Turning some bronze, most of the swarf "corkscrews" were falling harmlessly to the front, and I failed to see one sneak round the rather inadequate shield, and enter the motor. The resulting short to earth did not hurt the motor but damaged the inverter. I can say N-T's repair service is prompt, but obviously equipment like this is not cheap!

While the motor and inverter were away I fabricated a complete back-panel and motor shield - I've put a photo of it on the "What I Did Today" thread.



Advantages? There are three, really.

- Very much smoother and quieter running than with the single-phase motor, which tends to make the cabinet (standard Myford one) resonate.

- Better speed control, especially for operations like screw-cutting up to a shoulder. By still using the back-gear, you can have everything moving at a less nerve-wracking rate.

- Ability to adjust the speed during the cut, as sometimes useful such as when noise or chatter may indicate wrong speed for the other conditions. Also when paring-off large diameters.

NB: 1. These motors do not like being run too slowly, and the warning colours on the speed control are for low as well as excessive speed. (Used in conjunction with the headstock gears, I can run the Harrison at about 60rpm with the motor still happy at nearly 1000 rpm.)

NB 2: Don't use the Emergency stop-button as normal stop. The makers warn its frequent use can harm the electronics.


I've not found any.

So, I hope this answers your query!

Ray Lyons30/06/2020 07:39:58
166 forum posts
1 photos

I went the cheap way of installing a VDF on my Super 7 about 15 years ago. Bought a used Lens controller on eBay for about £5 and a new 1HP 3P motor. A bit of a tight squeeze getting the motor in but just fitted. Fitted the unit on the wall behind the lathe and brought a remote control to the leg of the bench.

Agree with everything Nigel has written about the advantages and would add that in my case with the S7 clutch and gearbox it is a step change over the old drive. The larger motor enables the speed changing to be kept to a minium I put the drive belt in the middle range and have not had to change it for years.

Robert Atkinson 230/06/2020 20:33:47
651 forum posts
16 photos

This is just based on review of the material on the Newton-Tesla website, but their ML7 Super7 prewired kits look quite good. They appear to have the inverter in a proper enclosure which is a safety requirement and not met by just buing an inverter, Chinese or otherwise. It also comes properly set up for the motor. Unless you are reasonbly skille with electrical systems I'd strongly recommend buying a pre-made unit like their AV750.
Manny home inverter installations are at best non-compliant with regulations or just plain dangerous, Even Newton Tesla' pre wired packages are not compliant unless they are properly installed in an enclosure with strain reliefs etc. An inverter, motor and box of bits from ebay may have a lower ticket price, but even aside from safety, the time spent selecting parts and buliding it up soon adds up. Even our non-work time costs, either in time taken from other aspects of the hobby or family and friends.

Robert G8RPI.

Emgee30/06/2020 21:23:03
1497 forum posts
218 photos

Both the .5hp and the 1hp motors for Myford on the Tesla site are vented motors, not the ideal choice for a machine that's making swarf and chips, better to have a totally enclosed fan cooled version IMO.


Harry Wilkes30/06/2020 21:34:58
898 forum posts
61 photos

Fit a Transwave kit on my S7 couple years back the only problem I had was removing the motor pulley, I purchased a remote control unit for the VFD I collected it from Transwave as it was not that far the whole lot came with idiot proof installation guide. I have the expertise to have purchased motor and VFD independantly and made up a remote unit but I didn't have the time and to be honest the inclination to source the parts.


Alan Gordon 402/07/2020 06:43:11
85 forum posts
3 photos

I fitted the Tesla CL unit four years ago with absolutely no problems.

Just recently however despite having a perspex guard ( which i made) over the rear of the motor a small amount of swarf manage to get into the motor. I contact Tesla and took advice on how to strip down and clean out the motor, I have to say that the advice and help received was excellent resulting in the motor being stripped and cleaned (easy job) I guess this is the advantage in buying from "local" company. When i bought the unit it came with 10 year guarantee on the electronics don't know if this still applies though.

Steviegtr02/07/2020 23:47:14
1234 forum posts
115 photos

The 3ph motor on my S7 is from Clarks machine mart. There is a cooling fan & guard, but the motor is sealed. The fan is only blowing on the casting. A few times a bit of swarfe has found it's way in there & rattled about before getting spit out. I now have a bit of hardboard bent around the back to stop this. A bit tacky, i need to make something better. When i fitted this setup it was not too expensive. From memory the whole thing with my own made panel / inverter & motor was around £250. Picture of my setup.


speed 2.jpg

on the bench.jpg

Nigel Graham 203/07/2020 01:06:45
655 forum posts
15 photos

I think I am right in saying that Newton-Tesla do now sell totally-enclosed motors for the Myford lathes (or presumably any lathe).

It did surprise me though that whilst the first set I bought - for the ML7 - has a fully-enclosed inverter / controller (it has vents but at the back of the box and fitted with internal mesh) the sets I bought later for other machines all have separate inverters and controllers, and the former are not all that well enclosed. I think they are really designed to be fitted inside cabinets.

Philip Burley03/07/2020 08:32:55
180 forum posts
1 photos

The motor on my S7 gave up the ghost a couple of years ago and I fitted the newton tesla kit . No problems whatever and much better to use than the single phase motor , ( mind you that was goodness knows how old ) For screw cutting , it.s great using the "jog" control and easy reversing . I would recommend it ( not cheap however )

regards Phil

Andrew Moyes 103/07/2020 18:14:57
113 forum posts
19 photos

I fitted Newton Tesla plug-and-play VFD packages to both my ML7 metalwork and ML8 woodwork lathes. That on the ML8 developed a fault after a couple of years; the speed potentiometer became noisy and the speed became uncontrollable. I took the sealed unit in person to the firm in Warrington and was told that the 10-year guarantee only applied to the inverter and not the peripheral switches and potentiometer. I was asked to pay £26 for the repair. So much for the 10-year guarantee, which I notice they still advertise without any qualification. I would normally replace a noisy potentiometer myself but as it was a sealed unit (pop rivetted), I didn’t want to invalidate the guarantee on the Mitsubishi inverter, so I paid up. Having paid over the odds for the complete package, I was not happy.

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