NewtonTesla systems

I am thinking about fitting a Newton Tesla motor system to my Myford ML7 lathe.

Do I go for 0.5 HP or 1.0 HP motor?

What speeds will I get with this system?

Most people fit the 0.5hp system, I think.

You will get normal speeds set at 50Hz, but you can easily run up to 60Hz (and may get away with 70Hz) so top speed of each range is 120 - 140% of normal.

Minimum speeds are silly slow, but still best to use back gear as otherwise overheating is likely. If the inverter has the motor ratings properly programmed in it will reduce power/stop rather than allow the motor to overheat but still best to avoid running too slow.

Neil

Stephen,

I would advise you to go for the larger capacity system, more power is better than not enough. The standard Myford supplied motor is nearer 3/4 HP than 1/2.

Speeds will be determined by the motor that is mated to the control system. Being frequency controlled, in theory the motor speed can be operated from zero rpm to an upper limit which might be preset at 100 Hz; ie twice standard mains frequency. That would give a motor with a rated 1425 rpm shaft speed at 50 Hz a new shaft speed of twice that when running at maximum frequency. In between those limits the motor speed is variable and under your control.

Generally, an upper limit is preset at a lower value of maybe 80 Hz. This would give the same motor a shaft speed of 2300 rpm.

So it is just a case of you doing the maths on the spindle speed table so helpfully provided by Myford on the belt cover to establish a new set of maxima for the various belt arrangements. What you will find useful is the smooth variable control of spindle rpm that you don't have at present and because of this the need for belt shifting will become largely redundant. I would also be cautious about using the higher spindle speeds that become possible as the bearings may not be able to support those for extended periods. A bit of common sense and judgement is called for.

Do also bear in mind that motor power is not maintained at a fixed value throughout the speed range and the use of back gear for low spindle speed/high torque work is much kinder to the motor and control system than expecting it to crawl round at a few rpm and put up with huge cuts on big jobs in the chuck. That way is an abuse of the system and invites expensive damage.

I hope that answers your question

Regards Brian

Edit    I have just seen Neil's reply which while suggesting different upper values of frequency control endorses all the other things I have said. I would still use the upper motor power if the cost is within reason.

Edited By Brian Wood on 03/11/2017 09:56:38

The normal single phase motor is 3/4 hp, so a 1/2 hp three phase should equate; but better to have more power than too little. As LONG AS IT DOES NO DAMAGE TO THE MACHINE (Gears being the main vulnerability, although usually it takes brutality on the part of the operator to break them!)

Often the safety device is that the belts slip before much mangling of the "works" happens.

VFD is a boon, (for the lazy like me) but as Neil says, for protracted work at low speeds, use back gear, so that the motor runs at a speed where the fan moves enough air to keep it reasonably cool.

Howard

Agree with most of above. I fitted a 0.75 kw motor and VFD to my 5" Boxford about a year ago. Previous motor was 0.5 hp SP. Very pleased with the outcome. I've set the max. speed at 75 Hz, ie 50% above standard so the motor will turn at 2100 rpm. If I turn the speed down the motor tends to lose torque, so I think that the larger motor would be better in that respect, but as said, you should change drive ratio for any long period at low speeds.

FWIIW, the components for my system, including wiring, remote push-buttons etc cost ~£230 UK source.

I have a .75kw TEE 4 pole motor and Siemens Micromaster Vector VFD on the Super 7, if I was doing it again i'd have gone for a bit more power to provide a bit more torque at lower speeds to give a greater usable RPM range with each belt ratio.
I've been running the motor at up to 120Hz for over 10 years now so I can confirm that decent industrial quality motors will handle 200% of standard speed comfortably.

Early ML7 were fitted with a 1/3 HP motor, later ones with 1/2 HP. Mine ran for years on 1/4 HP. However running with VFD at less than 50 hz gives reduced power. I'd go for 0.5 kw, which is 0.67HP, then you'll get 1/3 HP down to half speed.

A four pole motor will quite happily run a 3000rpm as that is just what a two pole machine does, the bearings are the same usually and I doubt that the rotor construction is any different, the only uncertainty will be how well balanced a 1450rpm rotor will be at 3000rpm. So far I have not had a problem with over speeding a motor up to 100hz but as some inverters can go much higher perhaps someone would like to report back on how long their motor lasted at 300hz.

Mike

Using the kit supplied by Transwave (usual disclaimer but service was 1st class), it's advisable to set the Cub's read-out to amps rather than the default. The motor was a 1hp and prior to purchase Transwave's comment was words to the effect "don't think you can forget about changing the belt/pulleys from now on, you will have to !". The motor will stop by the thermal cut out if more than its stated 2.6A is being consumed so regualr belt changing is still needed to keep below that 2.6A figure (for my motor).

I have a cheap desk fan playing across the motor when in use because being of the enclosed type, its own fan isn't very effective at cooling.

Nevertheless, it is one of the best purchases I've made, especially when using a multi-link Fenner belt to the mandrel on my Myford.

From lathes .co.uk:

"It is very important not to "over-motor" a Myford (or indeed any other lathe); any accident or dig in will have far more serious consequences - and if the machine is worked beyond its capacity, excessive wear will occur. Early ML7s were fitted with 1/3 hp motors, later ones with 1/2 hp - the latter a figure that should not be exceeded. Apart from the very first examples, the Super 7 has always been equipped with a 0.75 hp motor (necessary to pull the top speed of over 2000 rpm) and this too should be respected as an absolute maximum. "

Clearly adamant that an ML7 shouldn't be over 0.5hp and an S7 over 0.75hp.

The upper frequency of 70% was based on a discussion with Transwave at a show. Higher frequencies increase inductive losses (heating) in the motor and used for extended periods can cause overheating.

Neil

The makers of my motor, TEC, specify 70 Hz for continuous operation and 100 Hz for intermittent, but I don't know the duty cycle though. These same limits seem to apply to both their 2 and 4 pole motors, so the max. allowable rpm for the 2 types will differ.

P.S. earlier should've said my motor was 0.75 hp, not kW.

I've found the belts tend to slip if I have a serious dig in on my Super 7. I have the Newton Tesla set up with a 1 h.p motor and definitely see the benefit at lower speeds. If they don't slip, it's very easy to quickly hit the kill switch. You can always still swap the belt positions if you need more torque and if all else fails, kick in the backgear although I very rarely need to do this except for those situations where you would use backgear anyway.

Then that is a Transwave shortcoming with their inverters and/or chosen motors, I run a little CNC mill with a Siemens 440 drive and an Electro Adda compact frame .75kw 2 pole motor, it's run for hundreds of hours at 7000rpm with no temperature or other issues and at 8000rpm for several hours too.

- Nick

See Clive's comment above, the TEC motors they supply are specced for 70Hz continuous, 100Hz intermittent.

Your motor is rated 75Hz at full power, and up to 80Hz, but you need to derate it to 60% power at 80Hz. That catalogue also says it should NEVER be run faster than 7,000 rpm.

In short, Transwave are being conservative as you would expect any manufacturer/distributor to be. There's no big difference between TEC and Electro Adda.

They would be unwise to suggest running outside manufacturer's specs given that they offer a 5-year warranty on their inverters.

Neil

I suggest you get yourself Huanyang inverter 2.2 KW which some of my friends have, for around £100, not one has experienced any trouble or problems. As for a motor running at high speed and not over heating, when you double the speed you square the volume of air the fan is pulling through the windings, but what about the bearings, some cheap motors have phosphor bronze bushes, especially on the non drive end. If the lathe is under powered take many small cuts, its easy to get ambitious taking heavy cuts on a hobby lathe and break some thing There is always tomorrow round the corner. John

I recently purchased the cl750 1hp Newton Tesla motor package for my Boxford. Excellent product, only let down by the poor customer service. My controller came labeled up as a cl400 and the motor was missing the key which was supposedly taped to the shaft, no sign of tape or key on mine. When queried the response was more or less "we ran out of the correct labels , so stuck the cl400 one on, and we might have some spare keys" It took nearly 3 weeks for them to send the key out, by which time I'd sourced another.

See post 5 here -

https://www.rcgroups.com/forums/showthread.php?880024-over-clocking-3-phase-motors

Guided by excellent engineering practice, empirical proof and a quick chat to confirm I erred on the conservative side and decided not to exceed 8k with a Compact Frame so the same size as 3/4hp :D

- Nick

EDIT: The motor does not misbehave or run hot, had it done either I was advised to desist if I didn't have the sense to work that out for myself  

Edited By Nick Hulme on 03/11/2017 22:20:16

I don't say you can't do it, but my point is a seller/manufacturer isn't going to endorse it

Neil

All this talk of speeds and motors is near irrelevant if you ask me. The answer is, however fast you like - change your pulleys and shoot for 10,000rpm!!

Or not....... because you'll melt your spindle to your bearings, and this is really the limiting factor, nothing to do with which motor you've gone for, you can always change a motor, you'll probably be able to pick one up from a junk sale for a fiver as a spare just in case.

You need to identify if you're running the original white metal bearings and soft spindle, or the newer bronze type bearings with a hardened spindle, then look up the maximum surface speed for your bearing material, and measure the size of your bearing and take it from there, if you think you think you can hit 2000rpm I'd say gear for it with your VFD at 100%, and I'm sure an occasional blast to 120% won't hurt anything, adjust your driver or driven pulley size to suit and make sure you're oil cups are working well (although I think these run significantly more oil than is required anyway, it was slightly comforting to see it pooling on the drip tray... oil cooled bearings would be a more accurate description of my old setup!

On the subject of motor ratings, it’s worth noting that 3 phase motors have improved performance compared to their single phase equivalents. As noted in an earlier post, Myford specify a 3/4 hp single phase motor for the Super7. However for 3 phase use they specify a 1/2 hp motor. When I converted my own Super 7 to VFD I used a 1/2 hp motor (because I had one on the shelf) and it’s always seemed perfectly adequate.