Re-motoring a Smart & Brown Lathe

I recently got a Smart & Brown 1024:
http://www.practicalmachinist.com/v...eiki-lathes/my-new-smart-brown-1024-a-321483/

I was not able to power it at purchase and knew there might be issues...and indeed there were! The motor is a 380 V and is shot...so re motor time!

I'd like to have variable speed on it anyway so I am looking at options.
The orig config was this:
3 speed motor(2400, 1400, 940 rpm, 2.5hp, 2hp, 1.5hp)
Drives a 2 speed gearbox, 1:1 and approx 3.6:1
Gives 12 speeds(with backgear) of 30 to 2500 RPM

I'd like to keep this speed range and I want to retain the 2 speed box, I drive my shop on a 5HP rotary converter now, and I can run a 220V single to this machine.

From reading here and elsewhere this looks like a good drive:
CV73 Series

And I'm thinking this motor:
218OT3E145T-S

I'm no expert on this stuff...so if anyone thinks this is no good I'd appreciate hearing about it.

Lastly...I have another lathe that will sit near this one(a Wade 8a) and I'd like to "share" this drive with that machine eventually, is there some easy way to have 2 "cords" that I can replace from one machine to the other when needed?

Thanks for any help!
Paul

Replacing A 380V 3 Speed Motor With A 1 Speed 230/460V Motor

From the RPM's listed, appears to be a 50Hz motor, which would suggest a metric frame size on the motor.
Does it couple to the gearbox directly? A NEMA motor to metric gearbox shafting could pose a dilemma if direct drive. If that is an issue you may want to seek out a metric frame motor.

To get the equivalent speed range output from a 1800RPM motor you would need to over-speed the motor with the VFD. This can be done, but has some considerations to think about.

Increasing the frequency while holding the voltage steady at 230V max, you will loose HP above 1800RPM base speed. The one you selected is already below the HP of the original unit at base speed. 2HP@ 1800RPM VS 2HP@ 1400RPM. You may want to consider the next size up if you need the full HP at high speed. A smaller rating to begin with coupled with losing HP above base speed may be a bad combo depending on the type of work you do.

To increase HP with speed (above base) you need to increase the voltage along with the frequency, a constant volts/Hz increase. To achieve this you would need a transformer to get 480V and a compatible 480V VFD. 480V VFD's are not designed for 1Φ input applications. Therfore you would need a 480V VFD that is oversized to allow derating for the 1Φ input. Then you need to selet a 480V drive that will run off 1Φ without faulting out on loss of phase.

If you considered such an option, then sharing the drive with another machine would also be problematic.

Just some food for thought...

SAF Ω

sandiapaul said:

I recently got a Smart & Brown 1024:
http://www.practicalmachinist.com/v...eiki-lathes/my-new-smart-brown-1024-a-321483/

I was not able to power it at purchase and knew there might be issues...and indeed there were! The motor is a 380 V and is shot...so re motor time!

I'd like to have variable speed on it anyway so I am looking at options.
The orig config was this:
3 speed motor(2400, 1400, 940 rpm, 2.5hp, 2hp, 1.5hp)
Drives a 2 speed gearbox, 1:1 and approx 3.6:1
Gives 12 speeds(with backgear) of 30 to 2500 RPM

I'd like to keep this speed range and I want to retain the 2 speed box, I drive my shop on a 5HP rotary converter now, and I can run a 220V single to this machine.

From reading here and elsewhere this looks like a good drive:
CV73 Series

Click to expand...

See first alternative motors....

And I'm thinking this motor:
218OT3E145T-S

Click to expand...

I have its bigger brother in 10 HP. Was only another $90, different supplier. They are not Weg's top-of-the-line.

OTOH, mine is for very rare use as an RPC idler for testing only. I already have 3-P off the Diesel and a 10 HP Phase-Perfect soon to be inbound as well.

"Open, Drip Proof" with thin rolled-sheet-steel housing may or may not find a clean-enough place to live long and prosper on your lathe, either. TEFC or even TENV or NV are better-protected.

Take onboard SAF's points as to practical fit-up and power, then also that some motors are happier than others on VFD.

On the website of the supplier you cited, one example can be found in the 'Vector Duty' listings.

And, of course, there is plenty of competition, motor brand as well as supplier.

Likewise USED 3-P motors are generally low-risk compared to 1-P or Dee Cee. New bearings are usually quite cheap. A modest cleaning, perhaps a lead-wire touch-up, and there can be scores of years of life still in them.

Best to come back to VFD selection AFTER you have a more thoroughly researched motor choice.

Bill

Dang it! I posted a long reply here last night and I guess it got lost.
First thanks for the replies. And also I realize I don't know a lot about this subject!

The motor drives the gearbox thru a flat belt, output of gearbox drives spindle in turn thru another flat belt. Orig motor was 50HZ(this machine came from the UK)

Yes a 1800 rpm motor will have to run about 30% faster to get my top 2500 rpm speed. I think rarely(ever really) would anything near full HP be needed at that speed. But the cost to go to 3hp is not much more so that seems to make sense. How much HP is lost per increase in HZ? I am actually more concerned about having adequate torque at the lower speeds and not stalling the machine with a moderate heavy cut or large diam hole drilling at say 200 RPM. At 2000+ RPM cuts are going to be minimal and torque requirements small.

The motor and gearbox resides in a fully enclosed cabinet away from all chips and oil/coolant, so I thought the lesser cost of the open drip proof motor was a reasonable option here.

Lastly, the "sharing" the drive idea is simply that the other lathe has similar HP and speeds. My thought was I could make up plugs( or something similar) and plug either machine into the drive when I wanted to use that machine. But in thinking it thru maybe its just easier to get another drive for the other lathe. The costs are not that much in the end.

Thanks for the help.

Paul

Paul -

I have done the same job for my 1024. It is interesting to revisit all the same problems and maybe a few that you haven't yet found. The good news is that there is a good route through this project and having completed it a few years back, I am very very happy with the results. I was planning to publish the project at one time so started to write a longish report on it. Part way through I realised that hardly anybody would be interested. But I kept it and have included it below. Please forgive the style which is not ideal for a website.

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1024 Electrical Rebuild

About two years ago [actually many years ago now!] I started looking for a good Smart & Brown 1024 lathe for my workshop. I believed that this was the ideal lathe for my size and type of projects, but accepted that there would be one or two challenges in getting such a lathe set up and working. Foremost amongst these challenges was running the lathe from a single phase supply. I hoped to find a VSL model which has a Reeves type variable ratio drive, but despite looking at a couple of these I was unable to find one in good enough condition. In the end I bought a Mk1 1024 (no Reeves drive, just a gearbox) which had been all its life in a university workshop and was in generally good mechanical condition. This meant that I had to find a way to run a lathe with a 3 speed single voltage 415V main motor from a single phase supply.

There were several options:

1. Use a rotary converter, either bought or home built to produce a 415V three phase supply. This would mean that the lathe could be run as-is without any further modification. My experience with these units is that the noise from them although not especially loud is annoying, since it is always present. In addition it can be difficult to get a good balanced three phase supply at varying loads. A transformer would be needed to obtain the 415V supply.

2. Buy a ‘Phase Perfect’ type of unit that would provide 415V three phase supply for the whole of my workshop. This is an attractive option from the viewpoint of simplicity and silence, but a unit that could deliver sufficient power is extremely expensive, and my other machine tools have already been converted to run off single phase, so they would not benefit from this.

3. Convert to single phase motors for the main motor and suds pump. This is feasible, but a bit ‘agricultural’. The 1024 is a really high class lathe and it seemed a pity to inflict a rough running slam bang start single phase motor on it. Even worse, a single phase motor would have a single speed and this would drastically limit the range of speeds available.

4. Replace the main motor with a new dual voltage single speed inverter duty motor and build an inverter based power supply that would provide all the facilities of the original design. This is probably the most expensive option and the most complex by a large margin. It would provide a few major advantages if it could be made to work. The most significant to my mind were sophisticated speed control with good motor protection, soft starting enabling the initial current draw to be kept low, and a smooth quiet drive.

In the end I chose the last option and started a project that took many months to bring to a successful conclusion.

Design Issues

The Mk1 Smart & Brown 1024 has an unusual spindle drive. The main motor is a large, high quality three speed unit with (in my case) a brake. The motor changes speed via some complex wiring and a rotary switch mounted on the front control panel of the lathe. The drive is taken from the motor to an intermediate gearbox by a flat belt drive and crowned pulleys. The gearbox (made by Matrix) has two ratios, mechanically selected via a linkage to a control lever again on the control panel of the lathe. The gearbox can change speeds ‘on the fly’ via a pair of internal Matrix multi plate clutches. The drive is taken from the gearbox to the lathe spindle via a second flat belt drive. This drives a pulley mounted on its own set of bearings to avoid transmitting vibration and belt stresses to the spindle. Although this design of drive might seem archaic in some respects, it does provide a silky smooth and nearly silent drive when in good condition and contributes to the excellent finish for which this lathe is renowned. The design means that six spindle speeds are immediately available from the control panel without stopping the spindle to change speeds. An additional back gear is available selected by a handle on the headstock. This provides a total of twelve spindle speeds from 30 – 2500 rpm.

The original motor speeds are 2800, 1400 and 940 rpm, and the corresponding outputs are 2.5, 2 and 1.5 hp. That means that there is a ratio of nearly 3:1 between the lowest and highest motor speeds. A motor driven by a VFD can provide variable speeds of course, but a range as large as this is rather problematic. A normal 3 phase induction motor has a characteristic output with varying speeds. From zero up to its base speed it delivers roughly constant torque. From its base speed to its rated maximum speed it delivers roughly constant power. The corollary to this is that from zero to base speed the power of the motor rises with the speed, from very low power at low speeds to reach the rated output at the base speed. Over the base speed, the torque drops off as the speed rises, so that at high speeds the torque available is significantly diminished.

The original motor is single voltage – 415V. This has significant implications for a rebuild intended for domestic 240V use. Many modern 3 phase motors of around 3hp are dual voltage. This means that they can be connected to either 415V or 230V supplies. In the case of 415 V supply, the motors are connected in star configuration and for 230V in delta. A delta connected motor is very convenient since it can be driven by a low cost single phase 230V in and 230V three phase out VFD. Unfortunately a single voltage 415V motor cannot be driven in this way – transformers can be used but life becomes a bit more complex. Single phase 230V in, 3 phase 415V out VFDs are available, but they are expensive or the result of local modifications that may not have the manufacturers full approval.

Connecting a suitable VFD to a three speed motor might seem relatively easy – simply mimic the original wiring and feed the VFD provided 415V three phase supply to the rotary switch to allow the three speeds to be switched on the fly. If you read the manuals provided by the VFD suppliers you will find that they specifically warn against this type of arrangement. Any switches between the VFD and the motor that are capable of interrupting the supply under load might cause VFD failures. In reality modern VFDs may be capable of living with this, but the risk is still real, so best avoided.

I could have retained the original motor and used just one winding – say the middle speed. I didn’t do this because the motor isn’t designed for inverter use in this way and I felt that I would be stretching its design far too much to get the speed ratio I needed from it. The difficulty of supplying it with 415V further put me off pursuing this option. I decided to bite the bullet and buy a new, good quality, inverter rated, dual voltage motor.

The motor size I selected was 2.2 kW or 3 hp, so slightly larger than the original motor’s maximum power output. I chose a 4 pole motor, meaning that the motors synchronous speed at 50Hz would be 1500 rpm. The speed under its rated load would be slightly slower, say 1425 rpm. A 2 pole motor would have been twice this speed and an 8 pole half the speed. The choice was an engineering compromise as is often the case. A 4 pole motor favours the lower speed end of the range. I wanted to ensure sufficient torque in the lower spindle speeds, at the expense of torque in the highest speed of 2500, since I did not expect to use this high speed very often, and certainly not with a big chuck.

Modern VFDs have a ‘sensorless vector’ mode. Without getting into the details, this allows the VFD to deliver better performance at lower speeds. I selected a VFD that had sensorless vector control and was confident that with the four pole motor, I could successfully run at 940 rpm (or even less) with no problems. This just leaves the problem of reaching the higher motor speeds needed to deliver a spindle speed of 2500 rpm. That would require a VFD output of about 98Hz. This is well beyond sensible frequency limits for a normal motor. I decided that the maximum frequency I could use (based on some reading and study of motor performance charts) was about 80Hz. I parked this issue for a while as I considered how the new motor could be fitted mechanically.

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See next posting for part2

Part 2
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Mechanical Matters

The original three speed motor is large, very heavy and was suspended by its feet from the underside of the gearbox mounting plate. The modern single speed motor is smaller and lighter, and had completely different foot/shaft dimensions. This meant that some new parts were needed to allow the new motor to line up with the gearbox input pulley. The flat belts used on this lathe are endless so ideally the new motor should be located in such a way that the original belt could be re-used. To get the motor into the required position, I designed a welded framework that dropped the motor by the required amount and allowed the existing tapped holes in the gearbox support plate to be used. The framework also moved the motor sideways so that the shaft would line up with the gearbox pulley.

To provide a bit of added interest, the position and mounting of the motor in this lathe is not user friendly. Getting the motor out safely required a timber framework to be made. I reused this when getting the new motor in position, but the whole exercise of measuring up for the weldment and moving motors in and out (several times) was extremely physical.

The new motor was metric and of course the shaft was a different size – 28 mm compared to 1”. As you would expect, the keyway was metric as well. I decided that it would be simpler to make a new pulley rather than trying to modify the existing pulley. Given this decision, I had the opportunity to change the ratio between the motor and gearbox a little to resolve the problem that I had with the higher speeds. I made the new pulley a little larger than the old one, sufficiently so as to bring the maximum spindle speed within reach of the motor running at 80Hz. This was a balanced change that did not take the lower limit of speed out of reach for the motor.

Electrical Requirements

That took care of the major mechanical problems. What was left was a major electrical re-design. To understand this, a summary of the specification I was trying to meet might be useful. The goals and features I wanted to reach and achieve were:

1. To reuse all the existing controls in such a way that they worked in exactly the same way as they did on the original lathe. This included the speed range switch, jog switch, suds pump control, spindle forward, reverse and emergency stop.

2. To have the best possible motor protection. The motor that I bought had a built in thermistor so I wanted to utilise this as well as all the protection offered by the VFD.

3. To have fully continuous control over the spindle speed from a convenient control OR the original stepped speed control selectable from a switch.

4. To be able to stop the lathe quickly – hopefully as fast as the original motor brake did when new.

5. To make a much more powerful low voltage machine light.

6. To modify the suds pump to run off 230V rather than 415V.

7. To provide a tachometer to display the true spindle speed. This is very important given requirement 3.

8. To provide an ammeter display to show the current being drawn by the motor. I felt that this was important because the new motor is twice as powerful as the original motor in parts of its speed range. I have no idea how much torque the gearbox is capable of handling and do not wish to find out the hard way. The amps drawn by the motor are closely related to the torque it develops.

This all requires a lot of new electrical equipment:

• A VFD for the main motor;
• Brake resistor sized to stop the lathe quickly;
• Thermistor relay to disable the drive if the motor temperature rises too high;
• A small, simple VFD for the suds pump;
• A low voltage supply for the low voltage machine light;
• 240V single phase supply for a DRO;
• An enclosure for the above with fans and filtration;
• A box for the additional controls such as speed potentiometer, switches, power meter etc.

The use of a VFD is a slightly mixed blessing when a significant amount of control logic is required. The blessing is that all the control circuitry is low voltage and is determined, in the main, by the programming of the VFD parameters. The curse is that you have to work through the manual to see how to accomplish what you want and draw up suitable schematics to implement it.

I bought a Mitsubishi FR-D700 VFD. This is a good quality VFD and having reviewed my requirements I was fairly sure that it could do everything I required. This turned out to be true, but not necessarily in the way I had intended. A problem that I ran into was that some of the control terminals are dual purpose. If you use them for one purpose, they are unavailable for the other purposes. This showed up when I needed to implement the 3 switched motor speeds. This on its own is no problem, because the VFD provides just this function and 3 terminals for Low, Medium and High speeds. Unfortunately it turns out that you need to use one of those terminals to implement latched start and stop if you want to use ‘3-wire’ control with momentary contact switches (and I did of course). This stalled me for a while and I resorted to calling the suppliers who were most helpful. They pointed out that for three speeds I needed 3 distinct logical states (say 00, 01, 11) and that this is obtainable from two terminals, provided that I programmed the VFD accordingly. This was really good support and enabled me to work out a schematic which implemented the 3 speed switching. Another problem was to work out how to make the speed control switchable between continuous potentiometer control, and the stepped speed control from the original lathe control panel. In this respect the Mitsubishi control was excellent, since it is able to sense that if the multiple speed control is not in circuit, it should default back to continuous analogue control via a potentiometer. This is precisely what is needed for this bit of logic.

I needed a low voltage regulated supply (5V) for the tachometer that I selected. This was the RevMaster unit, designed by Tony Jefree. I know Tony well and have used this tachometer on other projects, so it was a natural choice for me. I also needed a 12V supply for the fans that I chose for my enclosure. These are standard PC fans that are very good value for money compared to other units. I decided to use 12V for my replacement machine light, so this again needed to be provided. The cheapest way to provide these low voltages is with a PC power supply, so I purchased one at a good price. These switched power supplies can provide more than enough current at these voltages and the voltage is quite closely regulated. They do need a little rewiring to ensure that they switch on and provide supply. Two changes are needed for most of them. The first is to find the wiring that corresponds to the PC front ON/OFF switch and to make this connection permanent. The second is to provide some load that will persuade the power supply to switch on and stay on. In a PC this load would come from the motherboard, but it is necessary to replicate this with a power resistor in other applications. The power resistor does get warm, so it should be mounted inside the power supply case in a position that will get some air from the fan.

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see next post for part 3

part 3
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Wiring

With a full schematic, I could just proceed to wire everything up. Well not quite. There are a few minor problems to be sorted out. The first and biggest is where to put all this electrical equipment. I have faced this issue before when carrying out a similar exercise with my mill. I was lucky in that case because I was able to find a never-used, stainless steel enclosure on Ebay that although apparently rather large was otherwise perfect. The lesson I learned is that an enclosure may look big when you just lay out the equipment that has to go into it, but as soon as you wire it up, it magically shrinks to the point of being awkward. I was determined that I would buy an enclosure that would be easy to work on for my lathe, but for this machine I wanted the enclosure to be physically attached to the lathe, rather than free-standing. On the S&B 1024, there is really only one logical place for an enclosure to go, and that is on the large steel plate that covers up the gearbox and motor at the rear of the lathe. That unfortunately limits the practical size of the enclosure somewhat. Again I bought a box that I thought was big enough, but actually wasn’t.

Laying out the enclosure backplate for all the large bits of kit is made a lot easier with CAD to help assess different options. I used DIN rail to hold relays and terminal strips. Power distribution is made a lot easier with commoning blocks, which are also mounted on DIN rail. By the time everything had been fitted in the enclosure, it was heavy and this presented some problems in finally fitting it to the cover plate and the whole assembly to the lathe. Again, a timber frame proved useful.

I wanted a good low voltage machine light. The lathe had a ‘LoVolt’ light taking power from an isolating transformer. I could have bought a new light, but good quality costs a lot of money. The new 12V high intensity LEDs are very impressive, so I made an adaptor so that one of these could be mounted in the original lamp housing. The 12V DC supply for this came from the PC power supply.

Wiring up the lathe required a significant amount of wire. I used an entire reel of 0.75mm wire for the control circuitry. It is important not to skimp on the wire gauge for connecting the motors and the mains supply, so I was generous with these. Crimp terminals make a good secure termination and a professional result. I also used bootlace crimp terminals for the push in and screw connectors on the VFD control connections. To make future maintenance easier, I labelled all the wiring using a Rhino wire labelling system, bought second-hand. Hopefully this will mean that my successors can see how it all works. All the original switchgear was in excellent condition and was originally designed to switch 415V, so was vastly over-specified for the new setup. I had to modify the rotary switch to get the required logic from it. These switches are designed in a modular fashion to suit many different uses, but it took me a couple of evening with a multimeter and some drawings before I got the switching pattern that I needed.

A small control box was needed to house the speed control, the switch that selects either continuous or stepped speed control, the tachometer display and the ammeter. I used a diecast Aluminium box and machined out the lid to give the required apertures. The labelling of the controls was made easy by printing an acetate slide of the design that I wanted and clamping this against the front of the box with a transparent plastic sheet. This gave an attractive result that can be easily cleaned.

The control box needs to be easy to see and reach, as does the DRO which I also purchased and installed. I selected a Newall DRO, which is easy to fit and gives all the functions that I needed. To achieve this visibility and accessibility, a mounting bracket is needed. I welded one up from box section with swinging arms on which the DRO and control box would fit. My lathe headstock was already drilled and tapped at the rear. This was definitely not original because the threads were M8 and M6 – most unlikely for the Smart & Brown factory. I don’t know what these were used for on my lathe since they were just open holes when I bought it. I suspect it might have had another DRO at some time in its past since there were also drilled and tapped (metric) holes on the cross slide in roughly the right places. I decided to use the headstock holes for my new mounting bracket.


.

Billmac,

I suppose all this is buried on the yahoo forum...but thanks for putting it here...lots to think about!

Right now I just would like to pick the drive and motor that will do the job for me...I'm a bit confused about your "3 switched motor speeds" Do you mean that you were just reusing the orig contacts on the switches for the low, med and high?

I don't nee to retain all of that...I'm happy just mounting all the new remote controls in the original panel area and use a pot for the speed control. This seems like a good plan in this post:

http://www.practicalmachinist.com/v...nd-vfd/vfd-setup-remote-12-x-40-lathe-195492/

Thanks,
Paul

Paul -

I wanted to have my cake and eat it. The original setup with the rotary switch for changing spindle speeds is very convenient, so I wanted to keep it. In addition, the spindle speed chart on the control panel is good for quick reference so I decided to keep that as well. On the other hand, being able to vary the spindle speed continuously is also very attractive, especially for facing, so I wanted that as well. I added a switch that would allow me to change between continuous control or the original rotary switch. This costs nothing but adds a lot of flexibility. You should be able to do this with any recent VFD, but the actual details will vary.

If you follow this route, then the motor choice is simple you will just need an inverter rated 3hp 4 pole motor. VFD choice is also easy and you have much more choice of low cost drives in the USA than here. I would personally avoid the Chinese VFDs and buy a good quality make.

I haven't uploaded this write-up to the Yahoo website, but I might do so if there is any interest.

I have drawings for the motor mounting frame, new pulley and other bits. The schematic is specific to the VFD and other components but you are welcome to it if it would help. I also have some photos.