[greybeard]

I'd like to run a fractional hp, single phase induction motor to drive a small model makers lathe.
Can I use a vfd to give me speed control ?

If the answer is yes, has anyone built one, as the cost of a new one is several times more than the cost of my lathe and motor.

John

[fkaCarel]

No, phase converters output 3-phase and are to be used with 3-phase motors. However a phase converter for this size can be fed with single phase. A new fractional hp motor will set you back 50-100 euro.

[Geof]

....to drive a small model makers lathe.....speed control ?
John

A small model makers lathe is going to be a small motor. Buy a 1/2" capacity variable speed reversing hand drill. Take the chuck off and figure some ingenious way to attach a pulley and mount the drill in place of your lathe motor. Figure out another ingenious way of using a fairly coarse pitch bolt to depress the trigger on the drill and plug the drill cord into a socket with a switch. The bolt on the trigger presets your speed, the reversing switch gives you forward and reverse and the switch gives you on/off.

[greybeard]

fka - are phase converters the same as vfd's then ? I didn't think so.
Geof - neat, thanks for the idea.
John

[fkaCarel]

Greybeard, my mistake, I meant vfd. The rest still applies. It's just confusing how many flavours of electricity is used on this planet.

Take in consideration that a drilling machine produces a considerable greater amount of noise than a vfd'd lathe.

[fyffe555]

are phase converters the same as vfd's then ? I didn't think so.John

VFD and Phase converter are different animals - almost... VFD changes the A/C frequency to control speed and can be used on Single or Three phase. Commercially the requirement is usually to drive a 3 phase motor from single phase so the 'VFD' actually contains both a VFD AND a phase converter. There are not many pure three or single phase vfd's around for us bottom feeders, those VFD's that are are usually single phase in and three phase out.

To take geof's idea further, the usual solution to speed control on small machines is a DC motor and a speed controller... have any unused treadmills lying around?

Edited; can't type today....

[Geof]

....To take geof's idea further, the usual solution to speed control on small machines is a DC motor and a speed controller... have any unused treadmills lying around? .....

If my idea is not the cheapest solution (excluding all the time spent on ingenuity ) I'll buy greybeard a couple of beers next time I am in England.

[greybeard]

Ok guys, Geof wins on pints ...

One thing though, and perhaps I should have spelt everything out, I did say a single phase motor, so three phase is not in the frame. And I should have emphasised that the reason for choosing the induction motor out of the scrap bin was that it is virtualy silent compared with any brushed motor I have.

John

[handlewanker]

Hi greybeard, be carefull using a VFD on a small (1/4hp) induction motor. As you appear to be into model engineering and are using a table top type lathe, then the "want" from your end is a speed range from about 50 rpm for cast iron etc and 2000 rpm for small drilling and polishing.
The problem is, induction motors run slow get HOT, and as you will be simulating a lathe in back-gear then the torque low down will only be achieved by pumping the amps into the coils in a virtual dead stall situation.
The electric drill method will work but the whining of the motor will drive you nuts. If this is an option then try a vacuum cleaner motor, or angle grinder, modified, with a light dimmer switch rated at about 350 - 500 watts.
Top speed of the vacuum motor is about 10,000 rpm so if you belt this down by vee pullies to 2000 rpm input then the motor will still get some cooling running slow.
The best option for your case is to use the induction motor "as is", and arrange a variable VEE pulley drive to get speed change.
They're not hard to make, and if you use standard vee belts, just use two variable pulleys in compound arrangement. This way you still get "dial up" speed control on the move and plenty of low down torque.
Ian.

[Al_The_Man]

t, I did say a single phase motor, so three phase is not in the frame. And I should have emphasised that the reason for choosing the induction motor out of the scrap bin was that it is virtualy silent compared with any brushed motor I have.

John, Going back to your original question, although there are VFD's out there for 1ph motors they are not very successfull unless the motor is Capacitor start-capacitor run, and even then they tend to drop out of run or will stall at low to medium rpm, especially with a load.
The brushed motors you mention must be Universal type, as a true DC permanent magnet motor is very quiet, apart from a bit of brush noise which should be negligable.
Al.

[greybeard]

Ian - thanks for reminding me about variable vee pulleys. I'd forgotten those as a possibility.
Al - yes, the concensus seems to be that low speed end of the control is the problem area. I think I'd best stick with a mechanical solution. :cheers:

How about a Sturmey-Archer 3 speed hub as a gear box ????
Change the sprocket to a vee pulley ?

John

[handlewanker]

Hi greybeard, "sturmey Archer" now that is cutting edge technology. They're not the easiest thing to mount up and don't give much speed range. Have you thought about a motorcycle gearbox. The four speed one is really compact and gives a speed range from about 1:1 to 1:4.
I would strip the guts out and reassemble in a made up casing.
Ian.

[Geof]

"sturmey Archer"... don't give much speed range... a motorcycle gearbox...gives a speed range from about 1:1 to 1:4.

I thought the Sturmey Archer ratios were: 2:1, 1:1 and 1:2, which, overall, is a range equivalent to 1:1 up to 1:4.

[greybeard]

Ian - if you look carefully at my atavar you'll see where I'm at, re "cutting edge technology"

It just so happens that I'm collecting bits for a tandem trike for the wife and myself, and there's a spare S-A on the shelf.

Geof - I think you're right on the ratios - it's on the next "find out" list.

John

[Geof]

Hey Old Guy get up to date! Go with derailleur gearing, much wider speed range, on-the-fly shifting, almost inexhaustible supply of spare parts, ample power transmission capacity.

[handlewanker]

Hi Geof, would that be overhead de-railer or is the "Dickension" work shop treadle power?
I draw the line at Vee belt drive. Chain drive? UHH UHH. Too messy, dangerous if it snarls up. Flat belt drive? Only if the lathe already has a set of cast iron flat pulleys with back gear built in.
Also it's easy to replace flat belts on headstocks, virtually impossible without stripping the spindle out with Vee belts, except for those special segmented belts.
The motor bike gearbox that I mentioned earlier measures 100mm long X 100mm high X60mm wide, that is the steel box made to contain the two shafts stripped out and meshed together, and has 4 ratios.
I think the 'bike was a Java or AJS from the '60s. I got it from a scrapyard in Bristol, UK.
I think Honda moped gearboxes are even smaller, once they are removed from the casing, or as the engine and 'box are one, then a swift attack with a drill and hacksaw will lighten it up a bit, and leave the clutch and gear change mechanism intact as well, and I would definately get rid of the CHAIN sprocket output and fit a vee pulley.
As it only has 4 speeds then a double vee pulley should be added to give a high/low range as needed.
BTW what's an "atavar"? Sounds like something an old geezer would wear to keep the chips out of his gumboots. blol.
Ian.

[handlewanker]

Hi Geof, would you also include the front wheel mag-dynamo in that set-up so that you could power a bike head lamp to see the job while you're working the treadle?
Beats candles any day.
Ian.

[Geof]

......BTW what's an "atavar"? Sounds like something an old geezer would wear to keep the chips out of his gumboots. blol.
Ian.

An atavar is a typographical error; an avatar is that funny picture people put beside their nom de plume.

Didn't treadle power predate Dickens? I thought he was age-of-steam; overhead line shafts with fast and loose pulleys. Place I served my time in NZ actually had a working system used by an old guy who refused to operate any other machine. He let them replace the donkey engine out in the little shack with an electric motor driving just the segment of shaft over his machine.

And if Greybeard pops his head up and complains about thread hijackers I will tell him to stop being a grumpy old man that is reserved for me.

Java? AJS? Yikes talk about going back; what about Matchless, Ariel and a few other names that elude me at the moment.

[greybeard]

oops (chair) - atavar = incredibly tiny variable, not be confused with avatar = fairly tiny pic of vole apprentice.

Any spare deraillers will be reserved for the various bike/trike projects, so I'll go with the belts!

John

[Geof]

oops (chair) - atavar = incredibly tiny variable,....
John

No, that would be atovar(chair) (chair) (chair) (chair)