Lathe Drive Motors, 1ph or 3ph?

[Peter GainParticipant @petergain89847]

There are currently 2 advertisers in ME extolling the virtues of 3ph drive motors. One advert claims that a superior finish can be obtained due to a decrease in vibration. As I am no craftsman, anything that may improve my turning is welcome.

  

Please – no theortical dissertations. Does anyone have practical experience of replacing the single phase motor on a Super 7 with a 3 phase version? Useful comments will be appreciated.

 

Peter Gain.

[Peter GainParticipant @petergain89847]

[Clive FosterParticipant @clivefoster55965]

Peter

 

Although a three phase motor is smoother to the touch than a single phase one when installed on a machine I’ve never seen any difference in finish directly and specifically attributable to the motor change.  If everything were on top line you might be able to measure a variation with a Talysurf or similar but I doubt if you’d see it.  Diamond turning of optical quality surfaces or fine tolerance grinding might well show a visible difference but that isn’t Super 7 territory.  The drive belts do a good job of vibration isolation anyway.

 

Probably a different story if you put a nice new three phase motor on good anti-vibration mounts in place of a knackered old single phase motor with half the balls in the bearings worn square and held on to a home bodged mount by two bolts and a wood screw.  But that’s hardly a fair comparison.  You do have to take a bit more care over mounting a single phase motor as sometimes they will excite a resonance mode on the machine but that’s easily dealt with.

 

There are a lot of reasons for poor finish which should be attended to as appropriate.  Changing the motor will have little effect unless you inadvertently fix the, or one of the, underlying problems whilst doing the motor change job. 

 

Clive 

[Fowlers FuryParticipant @fowlersfury]

Have to agree with CF’s reply.

I’ve just installed a Transwave kit & 3ph motor and cannot in all honesty say that the surface finish is improved. However, I don’t think that’s the main issue.

I also installed a Fenner (breakable link) drive belt on the mandrel and that combined with the 3ph motor has made an unbelievable improvement in smooth running & quietness on a fairly new S7.

The new set-up makes me run the S7 at a speed more suitable for the different materials & diameters I am turning. That improves the finsih because I was usually too lazy to keep changing the 2 belts to run at the ‘correct’ speed. Anyway at the fastest speeds, the S7 used to sound rough & it vibrated with the 1ph motor & original belt. Not so now, it’s a joy to use at high speed.

I’d put the change-over as one of the best workshop  investments I’ve made.

(Transwave provided excellent service at a good price)

[CirclipParticipant @circlip]

There’ll be lots of suppliers extolling the virtues of 3phase Peter, all the better to prise pictures of HRH out of your pocket.

 

  What MOST seem to forget is that the use of 3phase machinery in the home workshop started because some of us realised that there was an alternative, in buying ex-industry machinery which was USUALLY 3phase, to having to change to a single phase motor for home use USUALLY single phase, by the addition of a rotary or static convertor. Second hand (or prior user) 3P machinery WAS cheaper, but with the advent of solid state electronics giving vari-speed etc. the market has changed.

 

  Any one for tennis???

 

  Regards  Ian.

[Ian S CParticipant @iansc]

All my machines are single phase. I think the main advantage of 3ph is the ease of contrlling the speeds rather than improved finish through reduced vibration.3Ph motors tend to be lighter and cheaper than single ph, and they often have better bearings-designed for industrial use. Ian S C

[KWILParticipant @kwil]

All my in use machines are 3 phase run through inverters. 3 were originally 3 phase however my Myford S7 was changed from single phase. Better? Yes, for a start there is no need to have a resilient mount motor.; Why was it resilient mounted when single phase,? Simple, single phase motors are at best a jerky drive machine so Myford chose to smooth the drive vibration by resilient mounting the motor. The belt does not seem to have any significant effect on the smoothness of drive, but the 3  phase motor does. On top of that you have the conveniences of inverter drive. Incidently the res mount motor on my original (now retired) ML7 had plain sleeve bearings, ball bearings would have been better but cost more!

[John HaineParticipant @johnhaine32865]

Can anyone recommend a supply for the Fenner drive belts for the S7 please?

 

John.

[Chris HillierParticipant @chrishillier27195]

One of the advantages of a 3 phase motor is that it enables variable speed to be fitted to a lathe. Before  I bought the Newton Tesla conversion, changing speed to get the optimum speed, and hence a good finish, was time consuming, and I normally didn’t bother. Since fitting the Newton Telsa conversion kit with its variable speed control to my Chinese lathe, setting the optimun speed is very easy.  I think that the finish achived when turning is greatly improved. The kit comes with a replacement 3 phase motor and a control box, installing it was simple. 

regards Chris Hillier

[WALLACEParticipant @wallace]

Don’t touch a modern single phase with a bargepole. One I brought from a major supplier litterally buzzed itself around the workshop floor when first wired up to test  – the noise when actually bolted into a Harrison lathe was undescribable !

 

The older Brook -Crompton ones are a lot better – but a 3 phase one is so much quieter with less vibration – and that’s not even mentioning the varying speed advanatages, quicker overload cutout (useful for the odd dig in) etc etc .  . 

 

Also – though probably due to the way I butcher cutting tools on the grinder – is the fact that you can vary the speed during actual cutting if it all starts to ring due to chatter. Wouldn’t care to say what this does to the finnish though .  .!

 

W.

 

  

Edited By WALLACE on 30/04/2010 16:15:15

[_Paul_Participant @_paul_]

Changed my ML7 to three phase using a 2HP E2 Teco Tverter inverter and a resilient mount Brooke Crompton 1425 rpm 1HP motor very smooth almost no vibration at all, £120 second hand off Ebay for both.

 

What a difference with speed changes no stopping the machine or swapping belts and also never quite getting the RPM you want with single phase.

 

With my three phase setup speed changes are now as simple as turning a knob plus as the inverter can run the motor up to 200hz that means I can get almost 6000 rpm at the motor if I need it (yes I know thats 4x it’s rated speed).

 

Not that I am interested in the really high speeds but the ability to turn work at very low rpm (1 rpm is possible) really is a great help.

 

Other niceties are adjustable slow acceleration – deceleration,  torque boost & DC braking.

 

Sorry if this sounds like an advert but it really has made a difference in the quality of my work .

 

Paul

 

[Peter GainParticipant @petergain89847]

Thanks for your replies. I am in the process of assimilating the useful advice.

Peter Gain.

 

[Fowlers FuryParticipant @fowlersfury]

Attn: John Haine.

 

Just put “Fenner drives” into Google and find a stockist near to you.

On the Myford website, they list a Fenner-type belt but it’s expensive at over £42. In addition it has much less thickness than a real Fenner.

I run my Fenner belt a just little slack and a dig-in will cause it to slip yet no problems with a heavy cut.

This is what Myford say about their belt:-

 

Power Twist Plus V Belt to fit the primary drive on all ML7-R and all
Small Bore Super 7 lathes.  This belting is particularly useful
for eliminating inherent single phase motor vibration which can be
transmitted via the primary drive belt upto the countershaft.

 

I can’t remember what I paid for the Fenner belt a few years ago, but it was nothing like £42 !

[John CParticipant @johnc47954]

Hi Peter,

 

I have 3 ph motors on an ML7, Super 7 and a Dore-Westbury mill.  The ML7 was a swap from the original 1ph to  a new 3ph motor and inverter from Drives Direct (no connection). I wanted the speed control and have not been disappointed. I had to modify the mounting plate slightly for the replacement motor.  The Super 7 came with a 3 ph motor and I fitted an inverter (from e-bay – getting clever now!)

The mill was 1 ph but I changed the motor to 3 ph from a pillar drill that was the same spec, and fitted an inverter (e-bay again).

The improvement in flexibility is, to me, outstanding.  I have remote speed controls with fwd/off/reverse fitted to all. I was thinking, afterwards, that I could use one inverter with a trailing output lead and just plug in each device seperately as required – but I’d bought the other inverters by then!  I made my own remote controllers for the second two inverters.  Very well worth the change to 3 ph in my opinion. I have seen good comments regarding the after sales support from both inverter suppliers. Drives direct were very helpful to me.

It is worth noting the difference in inverter types – with lower spec ones you lose torque at low speeds, with higher spec ( and therefore price..) you keep the torque and can turn at very low speeds as stated by Myford Paul above.

Hope this helps,

John  

[NJHParticipant @njh]

The advantage then seems to be flexibility and ease of use. I have been contemplating a change to 3ph. for a while on my Super 7 –  engaging the high speed range is a pretty noisy and vibrating experience!

As a birthday is approaching and a change of government to Gordon Clegg-Cameron

(or  David Brown -Clegg or whatever) almost certainly means an increase in price of such goodies now might be the time.

Question then for S7 owners. With  variable speed drive fitted where do you put the drive belts? Can you get all the required speed / torque requirements without moving belts or do some operations still require belt changing? I guess backgear may still be needed for some applications but I don’t envisage a need to exceed the placarded top speed.

 

( Last time I read a thread on tooling I was persuaded to buy  a Diamond Toolholder – I’ve not been disappointed. This though is a rather more serious investment ! ) 

 

 

[John Wood1Participant @johnwood1]

I recently installed a Newton Tesslar speed controller and 3-phase motor to my Warco Chinaman and the difference in smothness and noise is remarkable. I can easily change speeds now over the complete range I require just by turning a knob, no more belt changing. The new motor retains its torque over the range pretty well and the ‘jog’ facility is also useful.  A 3-phase motor doesn’t mind the frequent stop-starts on the amateur’s lathe whereas a single phase motor doesn’t appreciate it. No real difference in finish noticed here.

 

All the best

John

[haroldParticipant @harold]

Remember that your motor has an integral cooling fan. When you run the motor slowly, using the VFD/inverter, the motor won’t be turning the fan quickly enough to shift enough cooling air and so the motor can overheat if run for enough time (thanks, messrs Navier and Stokes). Sounds implausible, but it does actually happen this way. So now I use a small additional fan if I’m de-rating the speed to any less than 50%.

 

HTH

 

[Fowlers FuryParticipant @fowlersfury]

NJH – snip “Question then for S7 owners. With  variable speed drive fitted where do
you put the drive belts? Can you get all the required speed / torque
requirements without moving belts or do some operations still require
belt changing? I guess backgear may still be needed for some
applications but I don’t envisage a need to exceed the placarded top
speed.”

 

Transwave (usual disclaimer) told me straight off, “don’t think you can just forget to change the drive betls with an inverter. You have to consider motor heating (as ‘harold’ points out) and  also that your chosen spindle speed should really be about the half-way point on the potentiometer” ~ or words to that effect.

I chose a big 3 ph motor (1.5 hp) and have never found any overheating even at low speed.

And, if I’m honest, I only change the belts if I’m turning small stock held in a collet at high speed.

 

The other hitherto unmentioned advantage of 3 ph running is that I can carry on lathe work after SWMBO has gone to bed without hearing complaints later of her being kept awake by the noise

 

[David Clark 13Participant @davidclark13]

Hi There

I have an inverter on my Tom Senior Light Vertical Mill.

The speed is set to what it would be if it was a normal speed machine and the inverter is programed to vary between 50% and 100% of speed.

This gives me overlap of the ranges but I still change the belt on different ranges.

This works for me.

regards David

 

 

[KWILParticipant @kwil]

Myford-Paul,  I personally would not run the ML7s plain bearings at anything like that top speed of 6000RPM !!

[Steve GarnettParticipant @stevegarnett62550]

It’s a shame that Peter said “Please – no theoretical dissertations”…. because that set me thinking about the differences in finish you might get from running the coolant pump (if you have one) with 3-phase rather than single phase. What I was wondering initially was whether having the coolant pulsing ever so slightly over the work rather than flowing more smoothly would make any finish difference…

 

I blame Peter for this entirely, because if he hadn’t said that, I would never have started thinking along those lines!

 

KWIL, the one thing I discovered very early about running three phase motors at four times their rated speed is that for a whole raft of reasons, you don’t get much work out of them. Primarily the eddy current losses reduce the efficiency to the extent that although it might spin unloaded at that rate, it certainly won’t remain at it if you apply any significant load. I would imagine that just the couplings and bearings themselves would take care of this for starters, and you’d probably not achieve 6000 rpm anyway. Given a sufficient supply of lubricant, I can’t see any inherent reason for not running a plain bearing at this sort of speed though – on a similar sort of scale, isn’t that exactly what happens with a car crankshaft?

 

 

[Ian S CParticipant @iansc]

Just don’t over speed the chuck, they can be burst. Ian S C

[CirclipParticipant @circlip]

Nicely pointed out IanSC

 

  “Forgive them lord for they haven’t a b****y clue”  

 

  Regards Ian.

[KWILParticipant @kwil]

Steve,

 

Car crankshafts are usually pressure lubricated.

[Steve GarnettParticipant @stevegarnett62550]

I know – that’s why I said “Given a sufficient supply of lubricant…”

 

I’ve never found the need to spin a lathe chuck at 6000 rpm, I must admit, but the point about chuck busting is timely – probably a rather more cogent reason for not doing it, in fact. Even though it’s easily possible with an inverter to get a lathe running at somewhere near this sort of speed, there are now several good reasons mentioned for not doing it, I’d say.

Edited By Steve Garnett on 02/05/2010 20:50:49

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