bantam 1600 electronic problem

[EmgeeParticipant @emgee]

Andrew

If you purchase an original 2 speed motor you will need 400v 3 phase supply, if not a rotary converter or similar to run at the 400v required.

It would be less cost to get a 230v 3 phase motor and VFD plus it would give a greater stepless speed range.

Emgee

[Andrew CresseyParticipant @andrewcressey80402]

Thanks Emgee starting to wish i never bloody bought it.Can't use hi-lo speed can't use the apron leaver to start the machine plus need to get re-wired and new parts lol story of my life

[Andrew CresseyParticipant @andrewcressey80402]

If i do manage to get a motor will it use twice the electricity?

[not done it yetParticipant @notdoneityet]

Posted by Emgee on 20/12/2021 17:05:39:

Andrew

If you purchase an original 2 speed motor you will need 400v 3 phase supply, if not a rotary converter or similar to run at the 400v required.

It would be less cost to get a 230v 3 phase motor and VFD plus it would give a greater stepless speed range.

Emgee

Will it? Plenty of single phase motors were two speed. Just choose the number of poles.

[JasonBModerator @jasonb]

Anyone know what the original two speeds were that the motor ran at? could be the one you have is somewhere between the two so may give a useful range eg 60-1500rpm

[Andrew CresseyParticipant @andrewcressey80402]

Could i use a two speed pully from the motor or is that defeating the object of purchasing this lathe ?

[EmgeeParticipant @emgee]

Posted by JasonB on 20/12/2021 17:31:44:

Anyone know what the original two speeds were that the motor ran at? could be the one you have is somewhere between the two so may give a useful range eg 60-1500rpm

On my Mk1 1600 motor speeds were 1425 and 2800 changed by the pole changing switch, this gave max 800rpm in low speed and 1600rpm in high.

Emgee

[JasonBModerator @jasonb]

You probably could convert to a pair of pullies but obviously not as simple as a switch to go through the full range of speeds. Another option may be to change the existing pully from the motor to the input shaft to get a mid way spread of speeds and just leave in at that. If the input speed were upped by 50% rather than double you would have something like 50-1200rpm in eight increments just by using the headstock gears

Thanks Emgee, sounds like Andrew will just get the 800rpm with what he currently has.

[Chris GunnParticipant @chrisgunn36534]

Andrew, please do not get disheartened, there are several ways to sort it out, when you do you will have a super machine, that is as good as you can get in the size range, I have had mine for 35 years or more, and a delight to use. It has many features that do not appear on hobby machines that make life easy. If it were mine I would bring it back to original specification, as the apron lever is so handy. As you can see from the other posts, plenty of folk have converted theirs to VFD drive, so could well have original parts available. I have the original switchgear on mine, plus the original 3ph 2 speed motor, and run it from a Transwave converter. This means I can use the original suds pump as well, which I find really handy. I did burn the motor out about 15 years ago, and got the original rewound.

Chris Gunn

[Andrew CresseyParticipant @andrewcressey80402]

Thanks everyone for all your help i think i will try to obtain an original motor and VFD drive.And i agree Chris the apron leaver is a handy thing to have.When would this machine of been produced is it the 80s ?

[SillyOldDufferModerator @sillyoldduffer]

Posted by Andrew Cressey on 21/12/2021 08:59:52:

Thanks everyone for all your help i think i will try to obtain an original motor and VFD drive…

Don't rush into anything yet. Although the single-phase motor and peculiar controls aren't ideal, they may be 'good enough' for whatever it is you intend to use the lathe for. If the motor runs the lathe should cut metal. Possibly the eccentric single-phase conversion is merely irritating rather than a serious problem. I'd use the lathe for a few months before deciding what to do next.

Two reasons for slowing down:

• To assess how much the single-phase set-up matters in practice. Much depends on what the lathe is for. A business wouldn't mess with a lathe like yours: cheaper and quicker to replace it with a machine in Good Working Order. But the lathe may be absolutely fine for home-workshop duty, or for learning on. What type of work do you do?
• Before fixing the electrics, you need to assess the lathe's mechanical condition as well. With the power off, spin the chuck by hand and confirm everything moves as expected: at this stage look for gross issues like jambs. Once reasonably confident, run the motor and cut metal. Turning, facing, drilling, boring and threading reveal problems like nothing else! All being well, the lathe's controls will work as expected, with no smoke, electrical tingles, crunches or wobbles! The machine will cut straight and produce an acceptable finish. In the worst case, cutting metal will reveal serious bed-wear, broken gears, knackered bearings, worn-out lead-screw, done for half-nuts, cracked castings, bodged repairs, a bent-spindle, missing parts, and headstock and tailstock misalignments etc. The cost of fixing a thoroughly decrepit industrial lathe is shocking: a few new spare parts may cost more than the second-hand value of the whole lathe! Best not slide into throwing time and money at a total lemon by accident.

Don't panic! Most lathe problems can be fixed without breaking the bank, or worked around by the operator. It's amazing what's done with less than perfect machine tools. But best to identify all the big nasties, if any, before ordering a spendy new motor and VFD or headstock bearings. The forum is better at answering questions about specific nasties than generalisations.

Dave

[Andrew CresseyParticipant @andrewcressey80402]

Chris if i have all the original parts what motor would you recommend and what transwave converter

[Andrew CresseyParticipant @andrewcressey80402]

I have machined some aluminium bar and drilled holes with no problems.I mainly machine aluminium but i just wish i had full use of the lathe hi-lo speed and the use of the apron leaver to power up the machine.But it all seams abit to complicated for someone with my knowledge of electrics and would probably cost a fortune to put back to 3ph.

[Andrew CresseyParticipant @andrewcressey80402]

If i purchased a transwave rotary converter is it just a case of getting a 2 speed motor and wiring it in

[Chris GunnParticipant @chrisgunn36534]

Andrew, I am using the original 420v 2 speed 3ph motor as supplied with the original machine. I am using a 3 KW Transwave capacitor type static converter, which I bought when I got the lathe. I fitted a 3ph plug to the original machine lead and plug it in. I use the same converter to run my Bridgeport. I have blown a capacitor a couple of times, and I took it to Transwave who are not too far away, and they repaired it while I waited. They told me my unit predated their numbering system, so it is an old one, but cannot fault it and the service. EmGee gave the motor details in his post. Good luck.

Chris Gunn

[Andrew CresseyParticipant @andrewcressey80402]

Thanks Chris but they are not cheap from what i have seen but you get what you pay for.

[John HaineParticipant @johnhaine32865]

Just buy a modern single-speed motor and a VFD. Rotary converters are obsolete.

[Andrew CresseyParticipant @andrewcressey80402]

Everyone is saying the same John go for a 3ph 240v motor with a VFD i should be able to control the forward reverse with that setup.Would i be able to use the hi-lo or does the VFD make it variable speed ?

[Clive SteerParticipant @clivesteer55943]

If anyone has motor/electrics problems on an old machine and especially those with a two speed motor I would recommend buying a modern 240V 3 phase induction motor and a VFD. However, having said that, I believe that there are some 3kW brushless DC motors available that have superior driving capabilities than an induction motor when operating at slow speed. Even if these motors are optimistically rated ie described as their peak rating rather than their continuous rating they are seriously powerful. Also, having permanent magnet rotors, rotor heating when operating at low speed and high torque isn't as big a problem as it is with an induction motor. Most induction motors are fully enclosed to prevent the spread of fire in the event of a motor overload and rely entirely on a shaft mounted cooling fan blowing air over external cooling fins. However at low speeds this would provide far less cooling so for continuous use at low speed a fixed speed electric fan should be used to cool the motor or use a much larger motor and use the VFD to limit the power it can provide.

Since the electronics of a VFD and a BLDC motor controller are virtually identical only the extra cost of a BLDC motor may be an issue. However their higher efficiency and their capability to produce high torque at low speed , I believe, gives the BLDC motor the edge. From an historical perspective DC motors have always been the favourite for traction applications and brushless motors will hasten their return.

[EmgeeParticipant @emgee]

Posted by Andrew Cressey on 22/12/2021 10:56:11:

Everyone is saying the same John go for a 3ph 240v motor with a VFD i should be able to control the forward reverse with that setup.Would i be able to use the hi-lo or does the VFD make it variable speed ?

Andrew

Yes, speed control is one of the features of a VFD (Variable frequency drive), increased frequency will increase motor speed and conversely reducing the frequency will reduce spindle speed.

The choice of 2 pole or 4 pole is debateable with a geared head lathe such as the Bantam, you have many choices of spindle speed, 35-800, via the gearbox so the motor can always be running fast enough to provide cooling so if your use will be for speeds between 800-1600 or greater then I would prefer the 2 pole motor so at 50Hz you will be in the range 72-1600 from the gearbox, increasing frequency will take you up to 2000 without issues, going much above this you have to consider chuck max speed and other rotating mass, don't forget the Bantam was designed to work happily up to 1600 or 2000 for later versions.

Emgee

[Andrew CresseyParticipant @andrewcressey80402]

Thank you Clive and Emgee you are all very clever when it comes to this kind of stuff,me on the other hand know some but not gears and speeds and so on.Emgee you said what range will i be using well i tried 800 rpm today on some 40mm bar and i found that to be to quick for my liking so i wonder will i ever use 1600 rpm it would be nice to have all the speeds through the gearbox using all the lathes leavers but it would appear that's not going to happen.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Andrew Cressey on 22/12/2021 15:27:33:

… i tried 800 rpm today on some 40mm bar and i found that to be to quick for my liking so i wonder will i ever use 1600 rpm …

A handy rule of thumb for guesstimating RPM for cutting mild-steel with HSS is:

rpm = 10000 / diameter in mm

40mm would suggest a speed of 10000/40 = 250rpm, so as you say, 800rpm is too fast. It would be about right for 12mm or 1/2" diameter rod.

4mm diameter rod would be happy at 2500rpm.

Those speeds are for HSS, but carbide cuts better at much higher rpm – 2 to 10 times faster than HSS. So your spinning 40mm at 800rpm is reasonable when the lathe is fitted with a carbide insert.

Don't get too hung up on cutting speeds. I use the formula to get into the right ball-park, but speed up or slow-down as necessary to get a decent finish. The material matters as well a diameter, but the mild-steel formula still helps:

Aluminium, Brass and many plastics cut faster than mild-steel

Free cutting mild-steel (recommended!!!), bit faster than mild-steel

Copper, Bronze, Gunmetal and some cast-iron cut at about the same speed as mild steel

Tool, Cast, Silver and Stainless Steels cut slower than mild-steel

Most cast-iron cuts much slower than mild-steel

Three factors to experiment with:

1. RPM (as formula)
2. Depth of cut (not normally critical, but light cuts need a sharp edge)
3. Feed rate. (worth experimenting with: counter-intuitively fast feed rates sometimes produce better finish than slow.)

Beware scrap metal! Quite a lot of it doesn't machine well. I recommend starting with known metal where the description includes words like 'free-cutting' or 'good machinability'. Move on to unknown scrap when you know what to expect: lots of trouble is caused by beginners trying to learn on metal that would test an experienced machinist.

Have fun,

Dave

[JasonBModerator @jasonb]

Posted by Andrew Cressey on 22/12/2021 15:27:33:

i tried 800 rpm today on some 40mm bar and i found that to be to quick for my liking so i wonder will i ever use 1600 rpm it would be nice to have all the speeds through the gearbox using all the lathes leavers but it would appear that's not going to happen.

You don't say what material or what cutting tool so hard to comment.

Was it the rotational speed that was not to your liking or the speed the tool moved on autofeed, if the later you may simply have had too high a feed rate selected.

[Andrew CresseyParticipant @andrewcressey80402]

Thank you for answers i should of stated what material and cutter.It was aluminium with a carbide cutter and it was the speed of travel that put me off.I have just used a dial indicator for the first time on the test piece and the dial hardly moves so i am happy with the results on a slower speed.

[JasonBModerator @jasonb]

With that combination you were running quite slowly, even your to speed of 1600 is about half the minimum book cutting speed.

You may want to select a finer feed rate say half of what it's set at at the moment but depth of cut can be increased so you end up taking a similar amount of metal off in the same time.

Small amount of paraffin or WD40 will give a better finish and also stop metal sticking to the tip of the insert.

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