Variable speed control for a small lathe

[cds4byu]

Seems like your VFD is exactly perfect for driving the lathe -- 120V 1 phase is limited to about 1.5 HP, so it ought to work.

A 4 pole (1725 RPM) 3-phase motor would be ideal. Here's one (new) from eBay for $170 shipped: General Purpose Electric Motor 1 HP 3 Phase 56C Frame 1725 RPM TEFC 230/460 Volt | eBay

And here's one for $160: ebay link

I *love* my VFD on my lathe. I think it's a great upgrade.

Carl

 

[retailer]

For those contemplating a repair on their small lath/mill motor speed controller I found a comprehensive repair document on an electronics forum and uploaded it in the downloads section, it may be helpful.

 

[TorchHypnosis]

I am inclined to agree with you Carl, having a VFD that can be controlled by a computer is best, especially when dealing with harmonics. Being able to set the RPMs on the lathe has enabled me to eliminate chatter and get really nice looking mill marks. Integrating PLC control on a VFD will most certainly give me the control I need to attain the finish I am looking for. I will look at those motors, and will post the results once I get the hardware integrated. It might take me a minute(I already shut down production for about 4 months while we performed some major mechanical upgrades) but as soon as I install a new motor I will be sure to post my findings. We work daily, but as soon as I get the new controller in I will be using it for manufacturing, so upgrading the motor will go onto the back burner. But I will have to deal with our issue during the next 10 months. I will let you know the results of what I come up with as I test solutions out. Thanks for the recommendations, and thanks for the input!

 

[Richard Hed]

Mark, good point. The first time it went out I thought it may have been a fluke so I just bought another. In retrospect I should have bought another one with the replacement to keep on hand, but hindsight is always 20/20.

Carl, it is not direct drive. The motor drives a belt which turns adjustable gears. I don't even know where to start to look for a motor and VFD...I have an extra 120V 1 phase to 230 3 phase VFD I am not using ATM...that kind of power seems a bit overkill...I will look to see what I can find as far as a low RPM 230 3 phase motor. Any suggestions would very much be entertained! But you both are right....just replace the da*# controllers as I need to. Still, there's always the desire to make your machine better...

Keep an eye on recycle junk places -- that's where I got a treadmill motor. There were thrown away treadmills all the time. Sold to me by weight at steel scrap prices.

 

[ignator]

I am inclined to agree with you Carl, having a VFD that can be controlled by a computer is best, especially when dealing with harmonics. Being able to set the RPMs on the lathe has enabled me to eliminate chatter and get really nice looking mill marks. Integrating PLC control on a VFD will most certainly give me the control I need to attain the finish I am looking for. I will look at those motors, and will post the results once I get the hardware integrated. It might take me a minute(I already shut down production for about 4 months while we performed some major mechanical upgrades) but as soon as I install a new motor I will be sure to post my findings. We work daily, but as soon as I get the new controller in I will be using it for manufacturing, so upgrading the motor will go onto the back burner. But I will have to deal with our issue during the next 10 months. I will let you know the results of what I come up with as I test solutions out. Thanks for the recommendations, and thanks for the input!

As for resonance, i.e. harmonics, every VFD I have in my shop has the ability to skip over these by simple front panel programming. I'm looking at my Hitachi VFD manual, and 3 areas can be programmed with jump through those frequencies.
As odd as it seems, I've removed single phase motors and replaced them with 3 phase and a dedicated VFD. The feature I like, I can program a Hz to spindle ratio, and have the LED display on the front panel indicate spindle RPM. As the RPM range is so great, I leave the belt setting in the mid range reduction, and have all the torque needed both at low and high spindle RPMs. I can thread using taps and dies, without back gear on my 10x24 lathe. Having that stop button where I can hit it, is my only issue.
Just make sure the VFD is of the sensorless vector type, as this gives high torque at low Hz operation. The motors are all 4 pole, so I program the max Hz to 120, as this will give 3600RPM operation, which the rotor is capable of.

 

[Steamchick]

Good morning all, I just wanted to chime in to this convo and bring up a few talking points.

I'm actually in the same boat as the OP. I have a small parts lathe, which I use daily for my business. The controller dies religiously once every 12 months. At the moment, I'm looking at 12 days down time while waiting for a replacement controller to arrive, which is unacceptable. I have orders that need to go out yesterday.

I have a 480 3 phase motor and inverter that would be perfect for my application, a SEW Eurodrive...$4000 of motor for a $1000 lathe, but I cant use it until I get 480 3 phase into the shop. Would be great as the inverter is an explosion proof sealed unit that can provide excellent torque at 1RPM, but I cannot satisfy the power requirements at this time.

That being said, I am looking for alternatives to replacing my motor controller every year. Someone said use a treadmill motor/gearbox/controller. That seems like a very realistic alternative as you can still receive a decent amount of torque at low RPM's while not risking burning out the motor. I noticed a lot of folks here are recommending VFD's. I cant help but notice that not much attention has been drawn to the fact that you drop the RPM's too low(reduce the Hertz) you will burn out the windings in your motor. While the VFD solution may be fine and dandy for folks who keep their RPMs up, I typically run at 80 RPMs. Super slow. If I were to try and use a VFD to operate a motor that wants to run at, oh, I dunno, say 1000 RPMs, and dropped it down to what I need(80), I would burn out the windings in my motor. Not only that, but lose torque. So, anyone correct me if I am wrong, but a VFD is not going to be a permanent solution for me. I'm thinking something like a treadmill motor with a reducing gearbox would be best to maintain the motor torque and still provide the motor RPMs I need.

But the single phase motor that I have and am currently running at low RPMs does not seem to be experiencing any issues. This motor is 120VAC, controlled by a small PCB with a potentiometer. The motor isn't the part that is burning out...it seems to be the controller. There are 2 black wires and 2 white wires going to the motor, then 3 ground wires going from the motor controller to the lathe chassis. I have to wait 5 more days before my new controller gets here, but the symptoms I am experiencing are the exact same as those I experienced last time I had to replace my controller. I will update when I install the new board, but it seems to me that the motor is still fine and the controller is burning out. Always seems to go out in the winter time, and the lathe is in an un-heated shop so the electronic components of the PCB might be failing due to freezing temps. I would definitely be interested in hearing anything anyone else has to say on the topic.

Regardless, I just wanted to throw in my 2 cents, and would welcome any knowledge any of you might like to share. Still trying to find a cost effective solution that will not require me to replace parts every year. I have two conveyor belt motors with controllers but I am not sure what their power requirements are. I can do 230 3 phase, just not 480. I also have extra 120 single phase to 230 3 phase VFDs. It's just going to take me too much time to make the mounting, program the control, and wire up all the parts when I can just spend another $160 to get another controller and work for another year.

Thanks for reading!

I am not an Electrical Engineer, but my experience with small brush motors says you can get all the torque you want with gearing, but direct drive of any electric motor will either run too low for torque at low spedds, or cook, due to high electric current with near no cooling. (SLOW fans). So the compromise is some gearing and some VSC. I have 2 speeds (belt pulleys) and Variable speed DC PM motor. Very poor min speed torque, and overheats if on continuous use below half speed of the motor. So I need more pulleys! A 6 speed gearbox (very traditional, pre-electronic VFD, etc.) Was always good enough for speed and torque. Just costs more initially! And people buy cheap, so why make "good"?
K2

 

[Iampappabear]

When converting my lathe and mill to inverter driven 3 phase motors I gave serious consideration to mounting one inverter on the wall then with a set of cheap relays sending the output to each machine along with a light duty wire for for/rev (would double as start stop) and potentiometer.

When it comes to motors, there is nothing cheaper or more reliable than a 3 phase motor and partnered with the Powerflex you have an amazing drive system. I particularly like the "ramped up" start & stop, so nice to get away from that harsh stop start most small AC motors have.

The only drawback from this system is having the same max current for all machines which for me means the 2hp motor on my mill has to have the same max current as my Emvcomat lathe 1/2hp motor as I am not a big fan of thermal overloads.

Colin

 

[Steamchick]

Just spotted Richard's post #64: What a good idea! I didn't know treadmills used these motors.
Some of these 1HP~3HP motors are essentially the same design as my Lathe motor - 1HP 4500rpm 180V DC - with a variable speed (DC voltage variation) control. I don't think I need a replacement motor (yet) but have had issues with it - the carbon dust from the brushes shorts the brush holder and flashes over with some frightening loud bangs at random times. (Makes me jump - which isn't a good idea when doing a careful cut by hand feed!). The brush holder has sharp corners and gaps to earth as small as 1mm (0.040") - which show signs of flash-over as well. The Original brush-holder resin/fibre board had burnt away with repeated flashes: Having replaced that, it still flashes from the sharp corners - I guess when a bit of carbon dust get in the gap? I have tried removing sharp corners to double the gap and give a rounded edge, and filling gaps with silicon sealer, but all to no avail. It Still pops occasionally! The control board is a common type - but is limited to the 1HP motor (current) - even so I have burnt-out the switching thyristors and had them replaced (professionally). And even had some of these short (flash) to earth at the mounting bolts. All-in-all I am not impressed with reliability from these Chinese designs. But that is all that will fit in the motor space on my lathe.
As to usage, with a 4:1 reduction gear to the lathe main-shaft, at lathe 50rpm, I can stall the motor with a 1/4" Whitworth taper tap in mild steel. As that is at the full 5A that the VSC can deliver, the torque is NOT impressive, compared to my mate's 1HP AC motor and GEARS. He gets 30:1 increase of motor-torque at his lowest speed, but I am not sure how the motor-torque compares to mine.... - maybe 3/4? - as he is at 240V and so "3/4" of the current than my lathe for the same HP rating... (But rotor diameter, field strength in the motor based on current and number of windings, all go to define the torque).
My lathe is good for small model stuff, as I generally only make 0.010~0.020" cuts in most materials. Having started taps/dies larger than 1/4", I have to do the job by hand. It also gets awkward when trying to de-scale cast iron or steel at over 2" diameter, as the slow speed needed and lack of torque sets a limit to what I can machine. - My next plan is to make new pulleys for the belt drive to get maybe 10:1 ratio - which would give me 2.5 x torque compared to now at up to ~500rpm. So while the treadmill motors are cheap - as are the second-hand controllers, you really need to consider the limitations of 1HP motors and I suggest gearing is the way to get the torque and power needed for mild steel above 2" and up to 6" diameter.
How about the lads with 3-phase and VFD? Can these do better with a 1HP motor? - So far I have priced a package at over £200 - but the motor is too large to fit inside my lathe!
Hope this helps?
K2

 

[dnalot]

I didn't know treadmills used these motors.

I repowered my old Atlas 10" lathe about 6 years ago with a treadmill motor and it is still running great. My only expense was a $10 pot to control the variable speed. and a few more dollars for an E-Stop switch.

Here is a link to my conversion thread treadmill repower

Mark T

 

[SmithDoor]

I agree
Simple controls and low cost too.

Dave

I repowered my old Atlas 10" lathe about 6 years ago with a treadmill motor and it is still running great. My only expense was a $10 pot to control the variable speed. and a few more dollars for an E-Stop switch.

Here is a link to my conversion thread treadmill repower

Mark T

 

[Richard Hed]

Just spotted Richard's post #64: What a good idea! I didn't know treadmills used these motors.
Some of these 1HP~3HP motors are essentially the same design as my Lathe motor - 1HP 4500rpm 180V DC - with a variable speed (DC voltage variation) control. I don't think I need a replacement motor (yet) but have had issues with it - the carbon dust from the brushes shorts the brush holder and flashes over with some frightening loud bangs at random times. (Makes me jump - which isn't a good idea when doing a careful cut by hand feed!). The brush holder has sharp corners and gaps to earth as small as 1mm (0.040") - which show signs of flash-over as well. The Original brush-holder resin/fibre board had burnt away with repeated flashes: Having replaced that, it still flashes from the sharp corners - I guess when a bit of carbon dust get in the gap? I have tried removing sharp corners to double the gap and give a rounded edge, and filling gaps with silicon sealer, but all to no avail. It Still pops occasionally! The control board is a common type - but is limited to the 1HP motor (current) - even so I have burnt-out the switching thyristors and had them replaced (professionally). And even had some of these short (flash) to earth at the mounting bolts. All-in-all I am not impressed with reliability from these Chinese designs. But that is all that will fit in the motor space on my lathe.
As to usage, with a 4:1 reduction gear to the lathe main-shaft, at lathe 50rpm, I can stall the motor with a 1/4" Whitworth taper tap in mild steel. As that is at the full 5A that the VSC can deliver, the torque is NOT impressive, compared to my mate's 1HP AC motor and GEARS. He gets 30:1 increase of motor-torque at his lowest speed, but I am not sure how the motor-torque compares to mine.... - maybe 3/4? - as he is at 240V and so "3/4" of the current than my lathe for the same HP rating... (But rotor diameter, field strength in the motor based on current and number of windings, all go to define the torque).
My lathe is good for small model stuff, as I generally only make 0.010~0.020" cuts in most materials. Having started taps/dies larger than 1/4", I have to do the job by hand. It also gets awkward when trying to de-scale cast iron or steel at over 2" diameter, as the slow speed needed and lack of torque sets a limit to what I can machine. - My next plan is to make new pulleys for the belt drive to get maybe 10:1 ratio - which would give me 2.5 x torque compared to now at up to ~500rpm. So while the treadmill motors are cheap - as are the second-hand controllers, you really need to consider the limitations of 1HP motors and I suggest gearing is the way to get the torque and power needed for mild steel above 2" and up to 6" diameter.
How about the lads with 3-phase and VFD? Can these do better with a 1HP motor? - So far I have priced a package at over £200 - but the motor is too large to fit inside my lathe!
Hope this helps?
K2

Remind me what kind of lathe you have? Can you send a photo and a photo of the motor area? Could you mount the motor on the outside of the lathe?

 

[Steamchick]

Hi Richard,
It is a Chester DB8VS Lathe. 700W motor. Chester machine tools version of many lathes based on a Chinese supplied lathe.
As I have a tiny space for my workshop, there is no space behind, above, or beneath my lathe for an external motor. The internal space is only 6in. max height, for the current 4in diameter motor.

Cheers!
K2

 

[Vietti]

K2

Don't give up hope. One of my treadmill motors is less than 6" in dia. I suspect it came from an inexpensive treadmill. I wonder if other exercise equipment might have smaller motors?

John

 

[dnalot]

One of my treadmill motors is less than 6" in dia

I have two treadmill motors in my shop. Rated at 2.25 HP. They are 9" long overall including stub shaft and a little under 3.5" in diameter. 300 RPM to 4600 RPM

Mark T

 

[Steamchick]

I think I can fit a 2 1/4 hp. motor that is on E&@y.... which should give me double torque, but I would need the controller as well as my controller cannot deliver the current. (I am sure the smoke would leak out if I tried it! Or the current limiter would stop me gaining the torque the more powerful motor will be capable of supplying!). The cost would be the same as 3-phase VFD, But I haven't seen comparitive torque figures, nor found a 3 ph motor small enough. Yet! The only advantage I can see between 3 PH AC with VFD and DC PM with VSC is that the 3 PH motor has no brushes! It does seem that the 3ph motors have a slower "sync" speed but larger armature diameter. I don't know about field strength comparison between the electromagnets in a 3 PH motor compared to field in the DC PM motor...? But it all combines to define the torque from the motor.
I think the pulley change can give me double torque, at low cost and complexity. So that's my first step, I think?
K2

 

[Randoo]

When converting my lathe and mill to inverter driven 3 phase motors I gave serious consideration to mounting one inverter on the wall then with a set of cheap relays sending the output to each machine along with a light duty wire for for/rev (would double as start stop) and potentiometer.

When it comes to motors, there is nothing cheaper or more reliable than a 3 phase motor and partnered with the Powerflex you have an amazing drive system. I particularly like the "ramped up" start & stop, so nice to get away from that harsh stop start most small AC motors have.

The only drawback from this system is having the same max current for all machines which for me means the 2hp motor on my mill has to have the same max current as my Emvcomat lathe 1/2hp motor as I am not a big fan of thermal overloads.

Colin

You can set the drive for the highest max current then add individual overload blocks between the relays and the smaller motors.

 

[Steamchick]

Aha! - A 3Hp DC treadmill motor for £60 - Not bad.
But £150 for the treadmill controller and stuff to make it go? And I doubt my knowledge of eletrickery is adequate to re-wire the whole thing for the existing rev. meter /speed-feedback etc. - so I'll research this a bit more. Makes a pair of pulleys sound tempting?
K2

 

[Bentwings]

Good morning all, I just wanted to chime in to this convo and bring up a few talking points.

I'm actually in the same boat as the OP. I have a small parts lathe, which I use daily for my business. The controller dies religiously once every 12 months. At the moment, I'm looking at 12 days down time while waiting for a replacement controller to arrive, which is unacceptable. I have orders that need to go out yesterday.

I have a 480 3 phase motor and inverter that would be perfect for my application, a SEW Eurodrive...$4000 of motor for a $1000 lathe, but I cant use it until I get 480 3 phase into the shop. Would be great as the inverter is an explosion proof sealed unit that can provide excellent torque at 1RPM, but I cannot satisfy the power requirements at this time.

That being said, I am looking for alternatives to replacing my motor controller every year. Someone said use a treadmill motor/gearbox/controller. That seems like a very realistic alternative as you can still receive a decent amount of torque at low RPM's while not risking burning out the motor. I noticed a lot of folks here are recommending VFD's. I cant help but notice that not much attention has been drawn to the fact that you drop the RPM's too low(reduce the Hertz) you will burn out the windings in your motor. While the VFD solution may be fine and dandy for folks who keep their RPMs up, I typically run at 80 RPMs. Super slow. If I were to try and use a VFD to operate a motor that wants to run at, oh, I dunno, say 1000 RPMs, and dropped it down to what I need(80), I would burn out the windings in my motor. Not only that, but lose torque. So, anyone correct me if I am wrong, but a VFD is not going to be a permanent solution for me. I'm thinking something like a treadmill motor with a reducing gearbox would be best to maintain the motor torque and still provide the motor RPMs I need.

But the single phase motor that I have and am currently running at low RPMs does not seem to be experiencing any issues. This motor is 120VAC, controlled by a small PCB with a potentiometer. The motor isn't the part that is burning out...it seems to be the controller. There are 2 black wires and 2 white wires going to the motor, then 3 ground wires going from the motor controller to the lathe chassis. I have to wait 5 more days before my new controller gets here, but the symptoms I am experiencing are the exact same as those I experienced last time I had to replace my controller. I will update when I install the new board, but it seems to me that the motor is still fine and the controller is burning out. Always seems to go out in the winter time, and the lathe is in an un-heated shop so the electronic components of the PCB might be failing due to freezing temps. I would definitely be interested in hearing anything anyone else has to say on the topic.

Regardless, I just wanted to throw in my 2 cents, and would welcome any knowledge any of you might like to share. Still trying to find a cost effective solution that will not require me to replace parts every year. I have two conveyor belt motors with controllers but I am not sure what their power requirements are. I can do 230 3 phase, just not 480. I also have extra 120 single phase to 230 3 phase VFDs. It's just going to take me too much time to make the mounting, program the control, and wire up all the parts when I can just spend another $160 to get another controller and work for another year.

Thanks for reading!

We have a stock grizzly BFF motor on our small lathe it has great pier for a small piece so far no problems. There is a reduction belt rive before the main gear train so it runs a bit faster motor rpm than some I think. There is electronic tach that give chuck speed I think . Generally 1000 rpm or more the little other cuts through 4130 and 4150 like butter it’s hard to stall it electrically it does not he hot at all. 480 vac is way beyond my level actually if I can’t just plug I in nd use it I’d call the electrician LOL I DONT LIK MESSING WITH LINE OWER ANY MORE THAN NECESSARY

BYON

 

[animal12]

Treadmills can be picked up for free quit often . After they sit doing nothing folks just want them gone . You can use the controller that in in the treadmill to run the motor , & there's several Youtubes on how to make your own controller for @ $30.00 .
animal

 

[SmithDoor]

I agree

They get motor and most buy treadmill and use it one or two times and then the belt goes bad from lack of use.

Dave

Treadmills can be picked up for free quit often . After they sit doing nothing folks just want them gone . You can use the controller that in in the treadmill to run the motor , & there's several Youtubes on how to make your own controller for @ $30.00 .
animal