Boxford lathe motor replacement

This topic has 41 replies, 12 voices, and was last updated 17 April 2026 at 16:30 by Baldric.

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6 March 2026 at 14:08 #840366
Baldric
Participant
@baldric
I am considering replacing the single phase motor on my Boxford AUD with a 3 phase one with VFD, mainly to reduce vibrations at some speeds but also to make facing off at the correct speed easier as the diameter changes. I have tried to follow lots of threads here and elsewhere, I have a few questions.

1. The existing motor is a Brook Compton 550w motor, would that he totally enclosed? Looking at it I am not sure, but I only see that mentioned on metric motors.

2. I have seen it mentioned that a resilient mount is better, that seems to only be on metric motors and the current one doesn’t have that, does it make much of a difference?

3. Would it be OK to put the VFD in the centre section, where the existing switchgear is, bolted to the back wall of it, or should I expect it will need more ventilation?

4. Are there any pitfalls to avoid?

FYI, I am open to an off-the shelf package or buying the parts from different suppliers, not sure how much difference in cost there will be in the end and if a UK off-the shelf package means a better product.

Mark
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6 March 2026 at 15:32 #840373
Robert Atkinson 2
Participant
@robertatkinson2
Hi,

Totally Enclosed (TE) or Totally Enclosed Fan Cooled (TEFC) are not restricted to metric motors. You can tell if your existing one is by looking to see if there are any ventillation holes that let you se the internal parts. A Under drive set up is less critical in this respect as the motor is not directly exposed.
Resillent mounts are only really needed for single phase motors. The circular ones coaxial with the shaft actully let the body of the motor move slightly. Thi lets it act as an inertial damper reducing torqure ripple. A 3 phase motor has insignificnt torque ripple so mounts are not required.
Brook Compton Gryphon was common model They were availabl enclosed or not Some have it on the data plate. They used TEFV (totally enclosed fan ventillated) rather than TEFC.

The existing switch gear enclosure should be fine to mount the VFD. The manual for the VFD should say how much clearance it needs around it for cooling.

Your 550W single phase motor is about 3/4 HP. You should not need to go any larger than this with a 3 phase motor.

Robert.
6 March 2026 at 15:36 #840375
duncan webster 1
Participant
@duncanwebster1
You’ll probably get a complete package, motor and pendant controller, from Newton Tesla. Probably more expensive than some, but guaranteed to be compatible components and little of no wiring up.

I’ve had 4 VFDs from them and they are very helpful on the phone
6 March 2026 at 15:47 #840379
Bazyle
Participant
@bazyle
Speed control is nice however if the motor is vibrating there is something wrong with it but have you checked the belts and pulleys. I know people say 3 phase motors are smoother than single phase but with various belts and pulleys in between the motor and job I would only expect to see a difference in a large motor being overstretched. I have not ever compared the two on the same lathe.

Because the motor is in the bottom cabinet which should be swarf free there is no need for a totally enclosed motor which might be cheaper if there is an option.

Resilient mount is just some rubber grommets.

You normally need to see the VFD display for speed readout and access to buttons for selecting or modifying performance even if you have a separate control box.
6 March 2026 at 16:32 #840388
Robert Atkinson 2
Participant
@robertatkinson2
I have to disagree with Bazyle. Single phase induction motors inherently have significantly more vibration than a three phase ones all else being equal. This is because of their torque ripple. The size of the motor does not matter. On a lathe or mill this can adversely affect the surface finish. I know the theory but even I was suprised how much difference fitting a 3 phase motor to my lathe made.
Resillient mounting is not “just some grommets”.

You don’t need to see the display of the VFD. The speed control knob can be marked which is good enough. Otherwise the better VFDs provide an output which can be configured to drive an external display. And as there are pulleys between the motor and the head there is a good argument for an independent display with a sensor on the headstock.

Robert.
6 March 2026 at 17:08 #840390
Hollowpoint
Participant
@hollowpoint
Fitted one to my Boxford a couple of weeks ago. I used an Invertek drive. (This is the 3rd one I’ve done since I have been very happy with them). The middle of the Boxford cabinet is the perfect place. I wouldn’t worry about cooling too much, IIRC the only requirement is about an inch gap all the way around. The fan in mine very rarely kicks in so it can’t be getting hot.

I went the whole hog with this setup. VFD, Shielded cable, illuminated buttons, din rail mounts etc and the whole lot came to just over £200. A package would be double that!
6 March 2026 at 17:59 #840393
old mart
Participant
@oldmart
Hollowpoint’s design is excellent and easy to achieve. I used an Invertek optidrive of 750W for a 1hp motor and added an aluminium heatsink to the back just in case to increase the cooling area. The rated heat output of my one was only 40W at 100% output so it was probably overkill. When you also need a new motor, get one with the same power as your old one, but be prepared to deal with mountongs and also the motor shaft may be different in diameter and length.

As always, I recommend the Inverter Drive Supermarket for inverters and motors, especially if you are going to do the electrics yourself. Many of the inverters they sell have the excellent “quick start guides” which can be printed out showing how to wire up the remote butons and controls as well as the programming that is needed, worth its weight in gold.

I have just noticed that the Invertek Optidrive is now made in the UK, a little more costly than the WEG.

https://inverterdrive.com/group/AC-Inverter-Drives-230V/WEG-CFW100C04P2S220G2
6 March 2026 at 18:52 #840396
old mart
Participant
@oldmart
I thought I had used an Invertek VFD, but it was a Schneider VFD, screaming out at me when I checked my photos from when the Tom Senior was first running. That particular model is now obsolete. The other thing I had forgotton is that three phase motors that you would be interested in come in different speed ranges. 2 POLE =3000RPM @50hz, 4 POLE =1500RPM, 6 POLE =1000RPM AND 8 POLE =750rpm. The more poles the slower speed, and they cost more. I used a 6 pole on the Tom Senior with the VFD programmed from 25 to 75 Hz which gave speeds from 500 to 1500 rpm which in addition to the four belt speeds gives a very good total range without loosing too much power at low speeds.You should check the speed of your existing motor before ordering a replacement, it will probably be around 1425rpm. Most of the motors in this power are sealed but with a small cowling and an end fan.
6 March 2026 at 19:23 #840399
Robert Atkinson 2
Participant
@robertatkinson2
Very nice installation by Hollowpoint.
7 March 2026 at 10:40 #840418
Baldric
Participant
@baldric
On 6 March 2026 at 17:08 Hollowpoint Said:

Fitted one to my Boxford a couple of weeks ago. I used an Invertek drive. (This is the 3rd one I’ve done since I have been very happy with them). The middle of the Boxford cabinet is the perfect place. I wouldn’t worry about cooling too much, IIRC the only requirement is about an inch gap all the way around. The fan in mine very rarely kicks in so it can’t be getting hot.

I went the whole hog with this setup. VFD, Shielded cable, illuminated buttons, din rail mounts etc and the whole lot came to just over £200. A package would be double that!

I do like that setup, having the controls mounted like that, rather than on a box/panel sticking out or elsewhere is exactly what I would like. I have a couple of questions from that, was the £200 including the motor? Can you also say what the items are on the DIN rail? It looks like there is 240v going to the front panel, which surprises me slightly. I looks like you have not included the option for forward/reverse, which I assume would just be another switch.

Mark.
7 March 2026 at 13:01 #840431
Martin Johnson 1
Participant
@martinjohnson1
Plus one for an explanation of the DIN rail widgets, please.

Martin
7 March 2026 at 13:14 #840434
Robert Atkinson 2
Participant
@robertatkinson2
Looks like the white item on the DIN rail is a relay / contactor. The coloured items are terminal blocks.
I assume the relay is providing a latch / no-volt release for the stop start buttons. As there are two green buttons I assume one is forward and the other is reverse.

Robert.
7 March 2026 at 13:44 #840438
not done it yet
Participant
@notdoneityet
Hollwpoint’s installation looks neat. My only safety comments would be that of an apparent lack of earth straps (from doors to cabinet) and that technically, the doors should be securely fastened by a lock or other means. Picky, I know, but simple means to avoid of an unwanted shock by anyone at any time.
7 March 2026 at 14:00 #840441
Robert Atkinson 2
Participant
@robertatkinson2
And I’ve been berated for commenting on people having VFDs completely exposed!
While a earth strap o the top panel with the controls would not go amiss, as there are no mains components on that panel one is not strictly required by the standards.
As long as the lower panel is fastened by normal screws i.e. ones that need a tool rather than a thumbscrew that would be compliant too.

We can’t tell if the mains inlet, fusing, isolator etc is OK as its not in the images. Overall it’s a good installation and no glaring safety issues.

Robert.
7 March 2026 at 17:29 #840471
old mart
Participant
@oldmart
That lockable electrical box which I used for the Tom Senior mill has earth straps for the door and extra ones to the mill and motor. All cables except the mains lead are screened with both ends of the screens earthed. All wiring ends either have crimped on connectors or crimp tubes. At the back of the box are three detachable plugs held like Plessey connectors which have different fitting sizes so as not to ever get accidently miss connected. The 230V mains plug has a 5 amp fuse, plenty for a 1hp motor.

Vfd’s have controls built in simply for setting up and programming, anybody using them for machine control is a fool. Robert is absolutely correct.
7 March 2026 at 19:02 #840474
Hollowpoint
Participant
@hollowpoint
OK guys, I’ll try to explain, but please don’t take anything I have done as gospel. I am not an electrician and some of my work may not be best practice.

The £200 figure didn’t include the motor (my lathe motor was already 3 phase). I already had some cable and the potentiometer.

The “DIN” rail is just a standardized way of mounting electrical components. The coloured blocks are terminals – positive, neutral and earth.The earth terminal grounds everything through the rail. The white thing is a latching switch with two positions. The lathe safety interlocks are connected in series with the circuit going through the switch, when the button is pressed the circuit is broken and bypassed. This allows me to override the safety features but still operate the lathe if needed. (Testing purposes).

The buttons are forward, reverse and stop. (Non latching, low voltage). The potentiometer is obviously for speed control. The buttons are permanently illuminated and simply wired to the incoming supply. This is the only part I was a bit unsure about? Though there is no high voltage going through the buttons themselves. The button lamps are completely isolated.

The shielded cable is grounded.
7 March 2026 at 22:35 #840501
Pete
Participant
@pete41194
The usual VFD display will during non programming functions display motor rpm on the VFD’s I’m familiar with. Depending on the machine the motor and VFD is on, that may or may not be enough. For example my mill is a 4 step pulley model and with an extra back gear assembly. There’s of course a known pulley ratio that could be used, and I suppose a hand made chart could be produced to show what the spindle rpm should be for each pulley step versus what the motor rpm might be. I even thought of doing exactly that. Adding a secondary spindle rpm display was much more usable. What the tool or part is turning at is much more important than what the motor might be doing. From what I can gather, your Boxford AUD seems to have at least a 5 step pulley ratio in the lower base.

Most of us would want to turn or mill parts towards the upper end of the maximum recommended rpm limit for HSS or carbide tooling. As long as were below that maximum for the material type being machined, then cutting tool life will be fine. It’s when we might unknowingly go above that limit then cutting tool life which for most of us is very important starts dropping off quickly. But there’s a bit more to those digital rpm displays than just there repeatable accuracy. Some of the cheapest one’s have a very slow update speed before they finally stabilize at what the actual rpm is. When I say slow, I mean a few seconds of lag between the motors + – speed adjustments and what the spindle rpm then shows. The slower that update speed is, the more irritating it is. The better digital rpm displays that are available will all have that update speed listed as part of there specifications.

I would assume your Boxford would use the Imperial standards for your current single ph. motor. The set of pictures I checked on the Lathes UK site for a Boxford AUD seemed to show a single ph. motor with side openings for cooling. A VFD gives the easy availability of running at a reduced rpm sometimes. I think I’d want to upgrade to the better fan cooled or TEFC motor.

My mill has what I’d call a very good industrial quality Baldor VFD. It can use either a remote wireless control which I didn’t buy, separate low voltage control switches on a secondary control panel wired into the VFD, or just using the built in control panel Baldor designed it to have. While that panel is also used while programming. With my mills back gear, I have to have the ability for motor reverse rotation which the VFD’s control panel also allows. That and it’s jog button certainly aren’t used for any programming I’ve needed to do so far. I certainly don’t know everything, but if there are valid and logical reasons for not using it, can you explain why I shouldn’t be using my VFD’s own controls old mart.
8 March 2026 at 10:24 #840530
Robert Atkinson 2
Participant
@robertatkinson2
Hi Pete,
You don’t say what Baldor drive yu are using but I assume it is something like the 15J series. The jog function on thees is used for setting up machines. There are a number of reasons why you should not use the integral panels for routine operation. First is that they are generally not very durable. The main reason is indrect and related to safety. These drives are not designed or constructed to meet the safety requirements for being dierectly accessible to the user of the equipment they are incorporated in. In particulat protection of terminals with dangerous voltages and strain relief provisions for cables.
To be safe they MUST BE INSTALLED IN AN ENCLOSURE. As rule of thumb, if you can see the colour of the insulation of a single conductor of a multicore cable with mains or motor voltage on it (or the bare metal of a terminal) the equipment does not comply. Any cable carrying dangerous voltage which the user can touch must have two layers of insulation. If the unit is in an enclosure you can’t access the integral panel

You could arrange a cutout in the encloseure to allow access to panel but that is not easy and does not address durability issues.

These units are components intended to be designed into compliant products by competent engineers who are aware of the relevant requirements. Just because you can run it screwed to the wall with wires hanging out does not make it right.

Do whatever you like in your personal workshop but don’t tell others it’s OK unless you are competent in the field.
I am competent, trained and authorised in this area as part of my day job.

Robert.
8 March 2026 at 11:30 #840536
Baldric
Participant
@baldric
All,

Thank you for the replies, I have looked at several of the options from inverterdrive.com, the quick-start guides to seem rather useful and buying from someone like them does seem to be worth while, rather than direct from the far-east. I do note they also sell a “kit” that has what I need, but 400v, I am happy to make my own controls, similar to HollowPoint.

One question I have after looking at various options, is a jog function useful? I haven’t had one, so won’t miss it if it isn’t there. The reason for asking is that the Invertek Optidrive E3 only has digital 3 inputs, which will be used up with the stop, start direction controls, if jog is recommended I will look at other drives, although they seem more complex.

I am considering a motor like https://inverterdrive.com/group/Motors-AC/Universal-UMHA-80K-4-B3, these have removable feet, so easy to make replacements to fit the existing base or to modify the base, although it either means modifying the existing pulley, which will have to be on the mill as the later will be out of action, or purchasing a new pully.

Knowing me get in touch with a couple of companies, then I will spend a week deciding…

Mark.
8 March 2026 at 11:32 #840538
Michael Gilligan
Participant
@michaelgilligan61133
Robert’s oft-repeated advice is well-worth heeding !

MichaelG.
8 March 2026 at 11:58 #840542
Robert Atkinson 2
Participant
@robertatkinson2
@Baldric The motor you linked too looks ideal.
I don’t know if a jog function would be of utility on a lathe spindle. You can always add it later if you find a need.

Robert.
8 March 2026 at 12:08 #840548
Baldric
Participant
@baldric
Robert,

Adding jog later would be an issue if not enough inputs, but sounds like you don’t use it. The times I have used that type of thing is when setting up a planner, to machine full size crossheads, or on a shaper, in both cases, rotating by hand was not possible.

Do you use the jog more on a mill? If my static converter ever dies, I will consider a similar change on that.

Mark.
8 March 2026 at 13:16 #840556
Robert Atkinson 2
Participant
@robertatkinson2
I don’t use jog at all. But I’m not the best persion to ask. There are many people on here who use machines more than me who can give better advice on it’s usefulness on a lathe or mill.

Robert.
8 March 2026 at 13:46 #840561
duncan webster 1
Participant
@duncanwebster1
Can’t see a use for jog on a lathe, but what is useful is a switch to select dead slow leaving the main setting undisturbed
8 March 2026 at 15:19 #840567
bernard towers
Participant
@bernardtowers37738
yes i like the idea o a dead slow switch it would be handy for thread milling(I do mine at about 5/6 rpm)
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