Basic speed problems on a new VEVOR MX-7x14lathe

[homebrewed]

Examination of literature for their 7x14 on the Vevor web store shows that the lathe doesn't have a high/low transmission. This suggests that the 500 Watt motor is brushless. My experience with the 500W brushless motor on my mini mill (also sans transmission) has shown that it it has good torque at low RPMs, so it is possible that the controller in your friend's lathe is either defective or is incorrectly adjusted so it can't maintain torque under load.

 

[markba633csi]

That's what I was thinking- that the factory that puts these together doesn't adjust the controller at all, just does a basic on/off test (if that) and ships them. It's quite possible that they don't even realize they need to adjust them or maybe they just run out of time on some batches and have to get them out the door?

Some of them must work ok as shipped, but some don't apparently
If they at least provided a schematic one could "reverse engineer" it enough to figure out the adjustments- but manufacturers are terrified of liability issues- mangling your fingers is one thing but fatal electric shocks are another- "no user serviceable parts inside"

 

[RJSakowski]

Can you give me any information about the motor and encoder and the controller you used? Thanks, it was I thinking about but have yet to find the pieces.


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I used a 2.5 hp 130 vdc 4090 rpm treadmill motor from surpluscenter.com. I chose that motor because it would fit the space occupied by the OEM motor. I seem to recall that that particular motor isn't available any more though

I made my own encoder using a Hall effect switch with 40 neodymium magnets embedded into the intermediate pulley on my G0602 lathe, providing me with 10 pulses/rev of the motor. I already had an encoder for the electronic lead screw but that one us tracking the spindle rather than the motor so any changes in pulley configuration would have to be accounted for. In retrospect, a higher resolution would be preferable as when I get down to a few rpm, the motor will cog much liked a stepper.

I designed and built my own controller using a MOSFET driver. The controller uses feedback from the encoder to increase the pulse width when the motor slows down under load. I haven't done a final tune yet but as it currently stands, my useful operating range is from 10 rpm to 800 rpm on the medium-low (5.75:1) belt configuration. On the low-low (11.5:1) belt setting it would be 5 - 400 rpm and on the medium-high ( 1.44:1) it is 40 - 3200 rpm. The original rating on the lathe was 2400 rpm at the spindle and in practice, I rarely need to run higher than 800 rpm so I use the medium-low configuration. The lathe uses a 3L drive belt to the spindle so the torque limiting factor is the drive belt. In the medium-low configuration, the drive will develop 12 lb-ft. of torque at 10 rpm, at which point the belt slips. Although there is still plenty of torque at 4 rpm, the motor cogs. In the low-low configuration, the motor runs smoothly at 4 rpm at the spindle with a 12 lb-ft. load.

The controller overshoots slightly when first started but settles within a second. My design criteria included having a circuit with simple readily available components rather than more complex circuitry using parts that might become obsolete in in the future. I also decided to use analog rather than digital circuitry. I think that a microprocessor based design might offer some advantages though.

 

[JustSomeHuman]

Thanks for your complete description of how you managed your motor and controller upgrade. This VEVOR lathe currently has a half hp (500 watt) 120 volt AC motor. It does not look like there is any sort of feedback or servo control. A request was made for some pictures, so I got some today. Here’s the controller.

And here’s the motor and controls. All there are an on-off a forward-reverse switch, and a pot to control speed. The controller is sort of odd. If the lathe is running at a significant speed and the pot is set back to minimum, the motor will stop. But 30 or 40 seconds the motor resumes turning at 30 rpm. I think we will rip out the existing controller and replace it with a recognizable controller. There seem to be a lot available.

Thanks again for everyone’s thoughts.

 

[markba633csi]

Looks like a brushed DC motor, but the big cap on the controller tells me it's a mosfet/pwm type. I do see two trimpots on it- it's possible one of those is
the torque compensation. It may be using armature feedback in which case you wouldn't be able to tell just by looking. I see 3 ICs on it and at least 5 transistors plus the power devices so it should be sophisticated enough to give good speed regulation with varying load.

I would mark the pots with a sharpie and one at a time try different settings- you might get lucky- might be all it needs is a tweak
but if not you could substitute a KB electronics control like KBIC-125 or similar

I hope that ground lug normally goes someplace-?

This is what you have now: (I asked 3 of the vendors if they have any documentation- we shall see)
I think they mean "PWM" not "PVC" LOL slight difference there

Universal Lathe Control Circuit Board PVC Motor Speed Regulator for Househould | eBay

Find many great new & used options and get the best deals for Universal Lathe Control Circuit Board PVC Motor Speed Regulator for Househould at the best online prices at eBay! Free shipping for many products!

www.ebay.com

And this is a typical SCR control: --- (Note the 5 devices on the heatsink)

Mini lathe Main Control Board CJ0618-182R Circuit Board 110V | eBay

If you are not sure how to connect the wiring.

www.ebay.com

I'm not endorsing either of these, I would buy an american made unit like KB that has support and documentation

 

[markba633csi]

I found something here that might help you:
If you look closely at the two adjustment pots in the picture the one on the right has the letters IR next to it.
That one is your torque compensation. Try small adjustments on that one and see if your motor performs better. Put a sharpie mark on the pot so
you know where you started.
You should be able to take fairly heavy cuts without bogging if the setting is right. The speed should stay fairly constant under varying loads.
During your tests it's possible you might blow the fuse. Have a couple spares handy.
If it shows a tendency to speed up under load you've gone too far- too much IR comp. Back it off a little.
The one on the left is (I think) the max speed adjust. Shouldn't need to touch that one.
-Mark

 

[markba633csi]

These controllers need to be adjusted/tuned to the motor they are used with- the factory probably doesn't bother and just
puts the adjustment at the midpoint and ships it. If that
The heatsink on these is pretty marginal, especially if it's in an enclosure with limited airflow. I would add a small fan to blow on it, make it live longer

 

[riversidedan]

Examination of literature for their 7x14 on the Vevor web store shows that the lathe doesn't have a high/low transmission. This suggests that the 500 Watt motor is brushless. My experience with the 500W brushless motor on my mini mill (also sans transmission) has shown that it it has good torque at low RPMs, so it is possible that the controller in your friend's lathe is either defective or is incorrectly adjusted so it can't maintain torque under load.

the price we pay for these cheap lathes the motors are definitely brushed......or atleast mine is
I fly model airplanes and use BL motors all the time and thier cheap ! but you have to use a 3 wire BL ESC for speed control

 

[mbemy]

Hello,
I have a good friend who has a brand new VEVOR MX-7x14 lathe. When he turns the speed all the way up he gets 2250 RPM. But if he sets it for 1000 RPM and tries to take a light cut, the machine slows down to almost nothing. A couple of questions, if I may.
1. What type of motor is used in this lathe? Brushed or Brushless? Does the motor operate with any feedback to the controller?
2. How does the controller adjust the speed? Is it voltage, PWM or something else?

I am a retired electrical engineer. I would appreciate any thoughts about this problem.

Thanks!

Experiencing the same issue. "brand new VEVOR 7X14 "550w" model. Though the motor is around 80mm X 125mm long with a 20mm long output shaft leads me to belive it is a 400 or 450W motor. (Can't read the label looking at aliexpress motors) Here is a picture of the controller. No inductor in site can't see how this combo could give torque even adjusting the IR. (The pot down by itself). Did you end up replaceing the controller? I'm thinking the motor is not worth perservering with even with a better controller.

 

[Smithdoor]

Hello,
I have a good friend who has a brand new VEVOR MX-7x14 lathe. When he turns the speed all the way up he gets 2250 RPM. But if he sets it for 1000 RPM and tries to take a light cut, the machine slows down to almost nothing. A couple of questions, if I may.
1. What type of motor is used in this lathe? Brushed or Brushless? Does the motor operate with any feedback to the controller?
2. How does the controller adjust the speed? Is it voltage, PWM or something else?

I am a retired electrical engineer. I would appreciate any thoughts about this problem.

Thanks!

I would check all connections. Next the pots.
Note they use very cheap pots even on board.

After that I would look a new board.
You can wast a lot time on board and on ebay they are cheap

Dave