bantam 1600 electronic problem

Hi i have just purchased a used colchester bantam that has been converted to single phase.From what i gather the leaver on the apron should introduce power for forward and reverse but my lathe i am having to use the power buttons for what the manual says should be used for the pump.The other problem is i dont have a high or low switch so must of been missing when i purchased it.

Edited By Andrew Cressey on 20/12/2021 08:02:35

Edited By Andrew Cressey on 20/12/2021 08:02:59

Andrew

Sounds like a quick and dirty conversion from three phase to single phase by-passing all the internal factory control gear.

The pump control buttons are independent of the rest of the electrics so wiring direct to the motor power contactor gets it up'n running fast.

As I recall it the apron lever simply operates a motor forward / reverse switch inside the headstock. I have a feeling the 1600 was built with atwo speed motor so lots of wiring on the control side.

Hafta get hold of the manual and start tracing wires to see what you have left. Sounds like that some or all of the complicated gubbins may have been removed. If so probably best to track down the Colchester group on groups.io to find out how other folk have dealt with such defenestration.

I'd swop the single phase motor for a 6 pole 3 three phase driven by a decent VFD and devise a suitable control wiring set to duplicate the factory set up. Which I understand is decent to operate. But I'm confident with such electrics. Selling the 1.5 kW single phase motor should cover a replacement 6 pole three phase as decently husky single phase motors seem to be sought after.

Why 6 pole motor? Lower base speed means more torque in the low speed range as compared to slowing down a conventional 4 pole 1440 rpm motor. Don't need high torque at high speeds so losses when running fast don't matter so much. 8 pole is theoretically even better but spendy. Or you could adjust pulley sizes on the motor to pull the drive input speed down but then the motor pulley will be rather small.

Best to take the trouble to sort it before putting into service or you will make do and curse for fart too long before accepting the inevitable.

Clive

Hi Andrew

Seems your lathe needs the apron lever switch re-connecting to provide control of the spindle, even if you only get fwd control will be a benefit.
You will most likely have to change the contactor coil from 380 to 230v, if it's the OEM Crabtree B15 starter you may have difficulty in obtaining spare parts.

The high/low speed switch was used with the dual speed motor to change pole configuration of the motor for the 2 speeds.
Your single phase motor is only 1 fixed speed, spindle speed range will be as the headstock control levers.

Emgee

Edited By Emgee on 20/12/2021 09:15:09

Thanks for that guys,i wld be happy really just having the apron leaver to start the machine at least my head isnt close to the lathe when starting it.As for the high low will i ever need the high speed for home use on aluminium.

Andrew

Always nice to have more than 800rpm for small diameter aluminium but you can still do good work with less.

Video here with my Bantam cutting 7075T6 aluminium, the work is offset from centre in a 4j chuck so rpm is likely to be 500rpm.

**LINK**

Emgee

It maybe might be a good idea to look at lathesdotco site for info.

You would have found the following:

“with a two-speed motor and marked Model 1600”

That quite possibly means your lathe does not have an original specification motor/?

Edited By not done it yet on 20/12/2021 10:04:23

Great video i didn't know i could take that much material off in a single pass or would my motor struggle.

No the motor is not original it is a single phase motor but thanks anyway

"You can do small work on a large lathe but not large work on a small lathe" they say. Easy to think you don't need high speeds but it depends on what direction your interests take you. Turning small diameter brass (down to 5mm) or reducing silver steel rod from 1/8; or drilling small holes in brass or steel, a high speed is very useful. Not to mention getting the best from carbide tooling which a Bantam should have the rigidity to easily take.

Edited By John Haine on 20/12/2021 09:57:54

Single phase motors can be dual speed. I have no idea whether it may have been single or three phase when new. If it was single phase, it has not been ‘converted’ but just ‘exchanged’ for a cheap alternative or incorrect replacement.

I do have a small lathe as well John so i should be ok for small work.How much can i expect to remove in a single pass with my colchester

ps only ever had small hobby lathe until getting the bantam

Square edge of the drip tray suggests it may be a Mk11 in which case they had two pulley ratios not a two speed motor

Difficult to say Andrew because the motor is unknown. Two things limit the amount of metal that can be removed:

• The power output of the motor. (Assuming it's suitably geared to put the required RPM/torque on the spindle. The latter is rarely a problem: just select the right gears and drive belts.)
• The rigidity of the machine. Too much power bends the structure causing inaccuracy and poor finish, and greatly increases the chance of serious damage in a head-crash or other accident.

If your single-phase motor is of similar power output to the original 3-phase, the lathe will remove roughly the same amount of metal: rule of thumb, about 1 cubic inch per horsepower per minute.

But amateur work is typically much slower than that. We aren't working in a sweat-shop mass-producing junk as quickly as possible: our goal is usually small numbers of parts that fit together. More skill, less rush.

Although my Chinese WM280 with a 1.5kW motor cheerfully takes a millimetre deep cut in mild steel, I rarely push it that hard, preferring to rough out with 0.6mm off the diameter per pass, and reducing to about 0.1mm or less to hit the target dimension.

Your Colchester is more heavily built than my lathe, but I believe they came with smaller motors - perhaps 1kW? The Colchester's design is after reliable accuracy rather than brute metal hacking. In practice, I'd expect the Colchester to cut at similar rates to my machine. The Colchester can probably cope with it's motor at full power, whereas the Chinese lathe is likely to flex when pushed to the limit. But it's probably unnecessary to run either flat out! I'd say anything between 300W and 2500W is sensible, and 1kW is fine for most purposes.

I suggest the best way to find out what your lathe can do is to try it. Set RPM for the diameter of a test mild-steel rod and take a succession of increasingly deep cuts at high feed-rate. Look and listen for signs of distress, especially the motor getting hot. I'd cut dry with Carbine: flood cool if HSS is used.

If the lathe was mine, I'd seriously consider going back to the original 3-phase configuration and driving it with a VFD. The single-phase motor was probably fitted before affordable VFDs existed, and they're OK rather than ideal.

Dave

Hi Jason why would it have hi-lo speed if it had pulleys?

Thanks for that i wouldn't have a clue when it comes to wiring anything like this back to 3 phase plus more money and that is tight at the min especially when building a 1/6th scale tatra from aluminium.I would then need to pay an electrician to do all the work for me.As for my motor it is just over 2hp.

Andrew

The 1.5kW motor fitted on your lathe is more powerful than than the original 2 speed motor when that was used at low speed, you should be able to remove metal at the rate suggested in the lathe manual without problems.
The lathe in the video is running with a single phase 1425rpm motor fitted.

In time no doubt your circumstances will change and you may then decide to go for a 3 phase 230v motor and run from an inverter, you won't need to worry about getting a multi pole low speed motor as the low speed range of the gearbox is more than adequate to keep motor speed high but low spindle rpm.

Emgee

Edited By Emgee on 20/12/2021 13:04:26

The MK1 1600 used a two speed motor to get the two speed ranges and the Mk1 800 just had a single speed motor hence the max of 800

The Mk11 1600 and 2000 used a single speed motor with twin pullies to get the two speed ranges. See third image down this page

What bantam do you have, if a Mk11 then your single speed motor may do.

Cut in aluminium will depend somewhat on the diameter, you should be able to take a 3mm deep cut off 25mm stock eg 6mm off dia in one pass but may not be able to do that on a 200mm dia piece, Feed rate will also come into it as you can go deeper if the depth of cut is less. My similar sized WM280 can cut the full insert width if I wanted but would not want to do that regularly.

Even if it is a MK 1, if using with a VFD I would suggest a 2 pole 2800rpm motor if changing from what you have. This would get spindle up to 2000rpm or more which seems within the capability of the bearings, if somewhat noisy due to straight cut headstock gears. It is useful for small work though probably not used much. Lowest gearbox range is 22 times reduction from that, so a nominal 72rpm, and less than 20rpm available via VFD. Torque clearly is increased by 22 times relative to top speed.

As usual, there should be no switches between the motor and the VFD, so the original wiring is best discarded.

Thank you all for your advice.I believe my lathe is a mk2 i have attached a photo from another thread not my post hope he doesn't mind me using it.