Change old AC motor to BLDC motor in Sieg C6

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Hi folks here!

I am looking for a new brushless DC (BLDC) motor with speed control to replace an old 550-watt, single-phase electric motor. There are so many variations of BLDC motors with speed control available on Alibaba that it is difficult for me to determine which one would be suitable. I am looking for an 1100-watt motor with a 14 mm shaft diameter and a shaft length of 20–30 mm. If the shaft diameter is slightly larger than 14 mm, I can machine it down to 14 mm, provided the length is sufficient for attaching the pulley. The price is well within my budget.

Does anyone here have experience installing a BLDC motor from Alibaba on a Sieg C6 lathe?

 

Regards Jens Eirik

 

[John HaineParticipant @johnhaine32865]

Several people have successfully used the Jack sewing machine motors to drive machine tools. A search (try Google Gemini) on this forum should bring up some posts.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Does this brushless motor have dimensions roughly the same as the old 550-watt one—such that I could install it in the same spot without major modifications—and does it have a 14 mm shaft diameter and a length of 25–30 mm?

There isn’t much information in the link, and the speed controller unit lacks a reverse function.

[Jens Eirik Skogstad 1]

On Jens Eirik Skogstad 1 Said:

[…]   and the speed controller unit lacks a reverse function.

You might want to ask these people about that ^^^

Servo-Motor 550 Watt JACK JK-513A

[see feature 3.]

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

… or watch this:

.

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MichaelG.

[Clive FosterParticipant @clivefoster55965]

Deleted.

[HollowpointParticipant @hollowpoint]

Why brushless? Why not 3 phase with a VFD?

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Can you explain how do?

[Robert Atkinson 2Participant @robertatkinson2]

Couple of comments, probably not what you want to hear though. These sewing machine BLDC motor kits do not meet UK / EU safety requirements despite what the sellers say.
You cannot easily machine the shafts on these. disassembling the motor is not recommended. It is hard to get them back together within tolerances without tooling.

 

[Hollowpoint]

On Hollowpoint Said:

Why brushless? Why not 3 phase with a VFD?

Yep, I reckon might be the better solution.

[HuubParticipant @huub]

I have mounted a Lichuan AC servo on my Lathe (C-axis) and have bought a HLTD T3D AC servo for my mill. I prefer the HLTD because it is cheaper and all cables have connectors so it is easier wiring.

I prefer the AC servo above a BLDC motor because a servo can run from 0 RPM to Max RPM. Speed can be controlled by a pot meter, buttons, step/dir or PWM signal and a servo can be run as C-axis so you can use the spindle as dividing head, something I use often.

Mounting a stronger motor is easy. But if the rigidity of the machine can’t handle the extra torque you will not benefit.

Beware, a servo needs to be tuned and that can be more complicated then setting a few parameters on a BLDC driver.

 

 

[Clive SteerParticipant @clivesteer55943]

Robert. In what way do these sewing machine motors and controllers not meet UK/EU safety requirements?

Clive

[Clive Steer]

On Clive Steer Said:

Robert. In what way do these sewing machine motors and controllers not meet UK/EU safety requirements?

Clive

Hi Clive,

Two issues. The first is easily seen in the photos. Th connectors are not suitable for mains voltage when accessible to the user. They use either “molex” or “avionics” style connectors. The molex have retecangular plastic insulation and a flexible rubber “boot” on the back. These are not “touch-proof” i.e. recessed contacts, do not have a make first, break last protective earth contact and don’t have a cable strain relief. The avionic connectors have a round metallic body and screw-locking. The are also used on CB radio microphones. The are not touch proof, don’t have proper earth contacts and the metal shell is not earthed. This is important for both the motor and control connectors as the circuits in these drives are not isolated from the mains.

Second issue is interference. These units don’t meet emissions for residential / domestic use.

Robert.

[Clive SteerParticipant @clivesteer55943]

Many thanks Robert. All valid issues and a good reason for those inexperienced in electrical safety to cautious of using these products without supervision or a check over.

[Nigel Graham 2Participant @nigelgraham2]

Irrespective of motor and electronics, I would suggest it better to modify the pulley than the motor spindle.

[mgnbukParticipant @mgnbuk]

I would suggest it better to modify the pulley than the motor spindle.

Agreed. As a general rule, don’t modify expensive “standard” parts to fit cheap, easily replaceable, parts.

If (and it is a big “if”) I really wanted a BLDC motor & drive I would look to get it from an established seller like stepperonline rather than from an unknown source on AliExpress.

stepperonline list an 1100w 6000rpm motor with a 14mm keyed shaft, but the driver is currently on back order. More chance of getting some form of back-up from a source with warehouses in various locations (including UK and DE).

Why not a standard 3 phase motor & VFD as a solution ?

Nigel B.

[duncan webster 1Participant @duncanwebster1]

If the 5000 rpm motor speed is needed can you get that from a normal 3 phase motor? I know you can run the vfd at more than 50 hz, but is the rotor safe  at more then 3000 rpm?

[HuubParticipant @huub]

is the rotor safe at more then 3000 rpm

I am more worried about the chuck. If you run a chuck faster than it limit, the centrifugal forces could rip it apart.
My 160 mm chuck can handle 2500 RPM and I think 2000 is a safer limit because it is a Chinese chuck.

Most AC motors can handle a higher RPM and a VFD running at a higher frequency is the way to go. Beware, the motor could heat up faster and the in case of a disaster the damage will be greater. The lathe could also suffer from vibrations.
A higher RPM can be achieved by changing the pulley (gear ratio).

 

[duncan webster 1Participant @duncanwebster1]

If the present motor does 5000 rpm, the belt of gear ratio must be such that the spindle goes at a safe speed.

 

[Michael GilliganParticipant @michaelgilligan61133]

A useful benchmark:

https://www.siegind.com/shop/c6-bench-lathe

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

SIEG’s specification should be a useful benchmark:

https://www.siegind.com/shop/c6-bench-lathe

MichaelG.

[duncan webster 1]

On duncan webster 1 Said:

If the 5000 rpm motor speed is needed can you get that from a normal 3 phase motor? I know you can run the vfd at more than 50 hz, but is the rotor safe  at more then 3000 rpm?

Induction motor speed depends on the number of poles and the frequency.  A 4 pole motor runs at a nominal 1500 rpm on 50Hz.  A 2 pole motor will run at 3000 rpm on 50 Hz.  A VFD can then be used to adjust that to the desired rpm, which is how I have set up my Pultra lathe.

Rod

[mgnbukParticipant @mgnbuk]

but is the rotor safe at more then 3000 rpm?

Modern motors are built to much tighter tolerances than earlier models. Partially this is to improve efficiency, but also for “inverter rating”.

Squirrel cage motor rotors are aluminium cast onto the compressed rotor lamination pack, with the shaft then pressed though the unit & finished turned on the shaft between centres before balancing. I don’t see much room here for the rotor to come apart at high revs. Limiting factor is most likely the bearing rating and the quality of the balancing.

During the rebuild of a CNC router for aerospace machining at a former employment (wing ribs from solid billets on this machine) the spindles were basically squirrel cage induction motors with the “shaft” being the 40 ISO taper spindle held in precision angular contact bearings. Part of the rebuild was to re-engineer the spindles to fit power drawbars and increase the speed as far as possible – up to 12,000 rpm, which was the limit of the bearings & driven by Siemens inverters. The rotor castings were the originals.

In service, bearing life was around 9 months use – the machines were pushed hard, with the operators having to use a welding glove to hold cutters when they were taken out of the spindle after use. Customer had spare heads converted, so the machine could be kept running when the worn out heads were returned to us for rebuilding and running in – which took around two days to get them to run at full speed without overheating.

Nigel B.

[Robert Atkinson 2Participant @robertatkinson2]

For a small lathe you would be better using a 4 pole 1500 RPM motor and VFD and turning the frequency up to 100Hz to get 3000 RPM than using a 2 pole and turning it down for lower speed. You can’t increase the current at lower speed due to resistive losses so will get much lower power and torque. A modern small motor design will use the same bearings etc across 2, 4 and even 6 pole models. Thus you can happily double the speed of a 4 pole motor.  you also get smoother running.

Robert.

[duncan webster 1Participant @duncanwebster1]

But I think the OP is trying you get 5000 rpm out of the motor, unless the belt? Drives can be altered

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