Mini lathe 3 phase AC conversion

[Mark Muller 1Participant @markmuller1]

Jason, I get it… I know Steve Jordan has the “back gear” (it’s not a back gear, but you get what I mean) version. I also understand what the gearing does and what it looks like. Blimey, I could probably replace the bearings on one with my eyes closed by now, I’ve seen so many of them on YouTube! Point is, mine does NOT have this feature. Honest! The other point is, APART from this, there is no difference. Everything else is the same.
Again, I’m really not sure how any of this is relevant! How does it affect my original question?

Edited By Mark Muller 1 on 30/05/2018 18:12:16

[JasonBModerator @jasonb]

Posted by Mark Muller 1 on 30/05/2018 17:59:08:

Bottom line: it's not a bad little lathe. What you would expect at the price point. Mechanically robust and taut as you like after I fine-tuned the moving parts. I get that it's a cheap Chinese knock-off (they all are btw! They all come from the same factory!). That's kind of the point of them… affordable. I thought we all knew this.

That is just so wrong, I think Ketan has given up by now but as someone who has visited the far eastern factories, trade shows etc he will be the first one to tell you how many sources there are for what to the casual observer is just a Mini-lathe.

Yours does sound like the one I linked to above with no handle on the back where they have kept the cost down by not fitting gears and not fitting a brushless motor. How do you know they have not skimped on any other parts to get the costs down?

These shortcuts will affect how your machine can handle being overpowered if you can't see that then I can't be of much help either.

J

J

Edited By JasonB on 30/05/2018 18:30:58

[Mark Muller 1Participant @markmuller1]

Hi Dave, point taken and thank you making it so graciously. For the record, it wasn’t 5″ bar stock, it was a 3/4″ plate with a diameter of 5″. I’m sure the lathe is capable of such a facing operation. I was taking very light cuts at a very slow feed rate. My problem was that my speed was too slow. For that, yes, I accept resposibility.
Point is, the motor has burnt and it needs replacing.
As I said, I am wanting to get my lathe in operational order. I bought a 3hp based purely on a bargain. I totally get that it is way too much for the lathe, but my plan is to moderate that excess both with the VFD settings and the use of extreme operator caution. Perhaps I didn’t make that clear previousy. Being relatively new to machining, obviousy my default position is caution. I know enough about machinery to know they can bite very brutally (I had a cabinetmaking factory, so I’m not a complete novice to machines) and I have at least a few year’s metalworking experience in terms of fabrication. Basically, I am that way inclined.
I realise that is not a qualification, but hopefully this will go some way to allay some of the fears you good gentlemen have concerning my abilities.
With regards to the actual machine, there are no signs to betray any structural defects. As I said, it is level, straight, has almost no runout and the costcuttings are obvious (in other words, in spec rather than quality of production).
I take your point that there is more than one factory (China is a big country!). My point is, the designs are essentially all the same. Visibly at least.
So, in summary of this verbose self-justifying ramble, all I want to do, is get the lathe I bought to do what it says on the tin.
Hoping that’s not asking too much!

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mark Muller 1 on 30/05/2018 17:59:08:

It's not brushless, guys. It is a brushed motor with a toothed belt drive direct to the spindle.

.

A suggestion, Mark … if I may:

Proceed just as you intended, with the overpowered 3phase motor and VFD

BUT, also change the toothed belt drive for a Poly-Vee arrangement giving a substantial speed reduction compared with the toothed belt [giving you a more appropriate range of speeds]. Poly-Vee belts will wrap reliably around very small pulleys … and they also run very quiet.

You will have massive torque available but, simply by running the belt a little loose, you will also have a safety clutch.

MichaelG.

[Mark Muller 1Participant @markmuller1]

Michael, thank you for your very helpful suggestion. As it happens, that is the setup I have decided on. Hopefully I shan’t kill myself and everyone within a 30 mile radius, as seems to be feared.

Edited By Mark Muller 1 on 30/05/2018 19:11:16

[Neil WyattModerator @neilwyatt]

Posted by Mark Muller 1 on 30/05/2018 17:59:08:

(they all are btw! They all come from the same factory!).

No, the original opnes came from Russia, and there are several factories in China producing them.

The two best known factories are SIEG and Real Bull (although I understand Real Bull has split in two?) and the 'Tengzhou Wellon Machinery Co.,Ltd' seems to be a recent entrant to the market. I am sure there are others…

[Mark Muller 1Participant @markmuller1]

Thanks Neil, again, I stand corrected.
In other news, I’ve changed my mind… going for a 5hp…

[Neil WyattModerator @neilwyatt]

Just an observation…

But in the 'old days' entire workshops were run off overhead shafting driven by massive steam engines or electric motors. With only one machine running 100hp or more was potentially available.

As Michael points out it's the ability of the drive belt to transmit this to the machine that determines if there is a risk.

In the old days of flat belts it was very easy for them to slip (in fact you had to dress the belt so it could transmit enough power).

I would suggest using round belting in a v-groove rather than a poly v as its probably going to be easier to set it so it can slip if the machine stalls.

The power applied by the VFD isn't the whole story as a 3kw motor will have about six times the mass and greater diameter so it will store vastly more energy than the 0.45 kW motor I used with its flywheel effect.

Neil

[SamsarandaParticipant @samsaranda]

Mark, just a small point but if you are going to be putting much increased torque through the lathe, bearing in mind that it is for all purposes a budget machine, then the headstock bearings will be of a quality just to cope with the original configuration and in order to avert their failure when your mods are completed, if it was mine I would definitely upgrade the quality of the headstock bearings at the same time.

Dave W

[Nick Taylor 2Participant @nicktaylor2]

The only way to limit the power from the motor with the vfd will be to set a lower maximum current rating for the motor. This will just result in the motor tripping the vfd all the time.

3HP on that lathe is silly and pointless, you’re one crash away from the machine tearing its self apart inches from your face. Even the spindle mounting method on that lathe isnt up to 3HP let alone the saddle or tool holder assembly. You say you’re a beginner and that you understand the risk but I don’t think you do. I would take the advice and get a smaller motor and get some more hours under your belt. This is not us trying to be rude, please understand that people here value our hobby and we don’t want it effected by regulations because some newbie lost an eye in his shed being silly.

[Mark Muller 1Participant @markmuller1]

So… not sure if all my replies were read, but you know what, I’m going to shop for 500W motor. I’ll use the 3hp for a table saw or something… don’t lecture me, I know about table saws!!
I’m upgrading to tapered roller bearings anyway (and “slippable” belts), but to keep the peace, I’ll go for a lower wattage motor. I still think it would’ve been fine (yes, I’m a newbie, but I’m also not daft!), but life’s too short and I’ll just get the darned little motor. Thanks again everyone. M

[RedsetterParticipant @redsetter]

Mark, With due respect, you seem to be digging yourself a very deep hole.

It is always best to use the correct parts if available, and conversions are seldom as easy as they look.

There are plenty of mini lathe spares around. Why don't you just fit a new motor of the correct type?

Machine tools are dangerous, and I think Nick Taylor's post says it all.

[not done it yetParticipant @notdoneityet]

Posted by Neil Wyatt on 30/05/2018 15:31:02:

I would use a 1:1 direct drive with that motor, but limit its power output in the VFD setting – Muzzer posted some advice on this in a recent thread

2.2 kW is overkill, but it will give you nice smooth running at lower speeds with plenty of torque.

A mini lathe can tackle surprisingly hefty cuts, the problems are the temptation to keep cutting with blunt tooling, shock loads or if the cut does stall there can be some nasty straining going on.

Neil

The most acceptable replies on that thread were those from Colin Whittaker. Running the motor in star configuration with a 230V 3 phase supply would reduce the motor power at a stroke.

3HP on a machine like that is, I would say, just plain folly. Even 1.75HP is far too much. But your choice, as ever.

I was not considering using a 2HP motor in place of the 1HP single phase (originally fitted), because I know that would have been just asking for trouble – and I am not that stupid! Running slack belts is not a reliable method of avoiding disaster.

The propensity for belt slip will change, depending on the speed at the time. It may be fair game for a constant speed motor but not, IMO, a satisfactory solution for a variable speed powered drive.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Mark Muller 1 on 30/05/2018 20:23:51:
…

I'll just get the darned little motor. Thanks again everyone. M

Good move, and maybe you can still implement other parts of your plan.

A mini-lathe with only one speed range is somewhat restricting and may have contributed to the burn-out. The job needed you to reduce speed and you could only drop it by overheating the motor. The two speed gearing on my mini-lathe was useful and I sometimes wished for a third to drop the speed even more. Like when screw-cutting and cutting large diameters.

If you're still up for arranging belts as you planned for the 3HP, getting more ratios on the lathe is a good idea. Say 0-50, 0-1000, and 0-2200 rpm. Likewise replacing a brushed DC motor with 3-phase & VFD is also worthwhile.

Let us know how you get on – interesting project in it's own right.

Dave

 

Edited By SillyOldDuffer on 30/05/2018 20:57:32

[John RuddParticipant @johnrudd16576]

Amazing how this thread has come full circle in two pages….

[Anonymous]

Posted by John Rudd on 30/05/2018 21:19:48:

Amazing how this thread has come full circle in two pages….

Not quite, we haven't re-invented the belt drive on multiple pulley sets, or a geared headstock yet!

Andrew

[Mike PooleParticipant @mikepoole82104]

I don't think the motor was the problem, having broken the motor your original plan would have broken the next weakest link in the drive. I would replace the drive with something appropriate, a brushless setup or a VFD in an appropriate size for the machine if you want a mild upgrade. A rethink on your feed and speed rates should get the job done within the capabilities of the machine. Many jobs have been done on home workshop lathes that are too big for the machine but a bit of mechanical sympathy will usually get the job done without breaking anything.

Mike

[Neil LickfoldParticipant @neillickfold44316]

If it were me, I would not get the higher RPM motor, but would prefer to get the lower 1400 or so rpm motor. With the VFD the 1400 rpm motor can be over driven to 2800 rpm or so. But as the RPM increase so does the power needed to spin at that rpm range. But the 1400 rpm motor has a bunch of torque. But at partial RPM it is not so good. The only issue is at slow RPM's. Some motors do not like running below 15 hz for any length of time, as they can over heat. Although you can get to like 4 to 5 hz, based on a 3k motor, that;'s like 300 rpm. For me I use the 200-300 rpm for tapping etc and it really does need torque to tap successfully. But the 1400 rpm motor would be in the 10 z range.

As others have mentioned, the total power can be limited on the vfd to the motor, same as peak current draw. A 2 kw motor can emulate that of a 1kw motor.

A friend of mine was always asking how i was getting better surface finishes yet I was not running anywhere near the rpm he was. It was sharp tools. A sharp tool at 600 rpm will give a better finish than 1600 rpm with not so sharp tool.

Neil

[Ketan SwaliParticipant @ketanswali79440]

Posted by Mark Muller 1 on 30/05/2018 20:23:51:
So… not sure if all my replies were read, but you know what, I'm going to shop for 500W motor. I'll use the 3hp for a table saw or something… don't lecture me, I know about table saws!!
I'm upgrading to tapered roller bearings anyway (and "slippable" belts), but to keep the peace, I'll go for a lower wattage motor. I still think it would've been fine (yes, I'm a newbie, but I'm also not daft!), but life's too short and I'll just get the darned little motor. Thanks again everyone. M

Hi Mark,

Now that everyone understands what you have got, along with an idea of your ability, do consider the various options proposed.

If you are considering Neils route, then do consider a higher wattage motor around 1hp+ route, with appropriate VFD, rather than the 500W motor route, especially as it is not clear if the 500W is 'input' or 'output'. This is relevant because thereafter, you have to consider the torque issues – VFD programing. If you have more power to work with, this can be de-rated via the combination of programming as well as mechanical. If you start with 500W, you may get issues with 'not enough torque' at various points in the speed range. This will be a process of experimentation. I don't know if your original 3hp/2.2Kw idea will or will not be appropriate/suitable for de-rating, or if Neils/Steves routes are the directions. This is up to you to consider, based on your abilities, now that we know what we are dealing with.

For the bearings, in your case, do consider angular contact (AC) bearings in place of taper roller bearings (TRB), as the mechanical torque on the TRB will result in transfer of a slightly higher load onto the motor, i.e. the motor will need to work slightly harder to turn/drive the spindle. Reason: Based on the pre-load on bearings, in AC bearings (7206B-2RS) the balls have a two point contact on the insides of the inner and outer race, where as for TRB – 30206 (for example), the rollers insider the TRB have full contact with the insides of the inner and outer race. The difference in accuracy between the two types of bearings is so marginal when used in a mini-lathe that it is not necessary to consider a TRB, and the use of AC bearings can deliver marginally higher speeds, which is great for getting better finish with the right tools, on non-ferrus material.

Ketan at ARC.

[blowlampParticipant @blowlamp]

Fitting the same type of motor again may not be a good idea because your machine doesn't have any reduction gears in the headstock – it stands a good chance of going the same way as the first one when the going gets tough.

You could do what I did and get yourself one of the new technology BLDC sewing machine motors, which I've seen range in power from around 400w / 750w and are available in various places on the internet at very reasonable prices. Bear in mind they come complete with a suitable controller too.

The advantage of them is they have superb low speed torque – which is what your lathe will need and they have a large speed range making them suitable for small diameter work.

Take a look in my album for some pics of the setup.

Martin.

[oldveloParticipant @oldvelo]

Hi

Many and varied replies to this thread read through with great interest as an owner of several re powered and modified machines.

Running any motor fitted with a cooling fan at way below it's rated speed will run hotter fit an auxiliary fan if this is a problem.

Blowlamp has an excellent suggestion for a re power for the average home workshop machines.

Eric

[RainbowsParticipant @rainbows]

I'm just gonna be unhelpful and butt in here with a semi relevant question, anyone have a wild shot at the upper bound for safe maximum motor power on the lathe? Was wondering of a ballpark of 1000w/1.5 hp to have some -e n h a n c e d- metal removing speed which is a bit above other users of 1 hp. 3 hp seems a bit wild, though I have the benefit of hi lo gears.

[oldveloParticipant @oldvelo]

Hi Sorry for the intrusion this is my slant on Rainbows question

"I'm just gonna be unhelpful and butt in here with a semi relevant question, anyone have a wild shot at the upper bound for safe maximum motor power on the lathe?"

It Depends on the size of the lathe. Pure Guess on my part that you have a far eastern lathe with a Hi-Low ratio gears that are adequate for the motor the manufacturer fitted.

Be prepared for breakages of the gears with a bigger motor fitted.

X2 mill Drill has the same head stock here is a link to the conversion I did six years ago and has run without any problems just a few more alterations.

.**LINK**

Eric

[ZanParticipant @zan]

It's the low speed you have to consider. True, the output speed is proportional to the frequency produced in the vdf, so when going for a low speed it is possible that the motor will not be able to cool itself when the speed setting is low. This however is balanced by the overkill motor, which will have a higher mass. You will need to calculate from the lowest normal speed needed. My S7 has an inverter drive, but I still occasionally change the belt position to the smallest spindle pulley so that the motor runs faster in order to get the cooling. I'm not happy on running it below 20 hz for long periods. Perhaps others would like to comment on this. The overkill of the motor power I think is a red herring, it will cost more to run but won't make any difference to the lathe unless somthing jams up! The limiting factor here will be belt slip, which could be left a bit on the loose side to allow intentional slip in emergency

[Author]

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