Variable speed control for a small lathe

Discussion in 'Machine Modifications' started by Shopgeezer, Nov 19, 2019.

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  1. Nov 19, 2019 #1

    Shopgeezer

    Shopgeezer

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    So my King 10X22 lathe is a traditional belt drive 110v single phase machine. Prying the belts off to change speeds gets old real fast. I know, they won WWII with belt drive lathes. I should just respect the heritage. But Ebay has all these cheap speed controllers........

    The motor shops all tell me that there is no way to install speed control on a 110v motor. Has to be 3 phase they all say. I could easily swap out the 110v motor for 220v if that would help. Motor shops say no, but Ebay......etc.

    So I am thinking maybe a mechanical variable speed arrangement on the belts themselves? Sort of like a split pulley? Anybody have any ideas/experience with this?
     
  2. Nov 19, 2019 #2

    Bully

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    G'day Shopgeezer, If you really want to do the adjustable pulley thing, I would have a look at Google and search for Continuously Variable Transmissions (CVTs). There several different belt and pulley types.
    However, for lathes, the best solution I think is a device called a Variable Frequency Drive. An electronic motor controller that creates a variable AC power frequency allowing the user to control the motor speed. Versions for Single Phase or Three Phase supply are available. If you have a lathe with a Three Phase Motor but no 3P supply then you can use a device called an Inverter to create the 3P to run the motor. There are two types; electronic only (no moving parts) and rotary converters (1P motor drives 3P generator) which are used for higher horsepower industrial type lathes. VFDs are used on most modern small lathes. I have an Optimum TU2506V, (V: read VFD) which has this setup and find it excellent. I can adjust the spindle speed from 120 to 1200 rpm without touching gears or pulleys. PS The supply voltage (110Vac) should not be an issue if the motor size not over 1hp. I am currently restoring a BV-20 lathe and thinking of putting a VFD on it.
    Hope this helps,
    Bully
     
  3. Nov 19, 2019 #3

    BaronJ

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    Hi Guys,

    There is no fundamental way to control the speed of a single phase induction motor without being able to change the frequency of the supplied voltage. That in itself creates a number of problems.

    A three phase motor can be driven from a single phase voltage source by means of an inverter that generates a fixed or variable frequency three phase output voltage ! Variable speeds can be obtained from a single or three phase supply by varying the frequency of the output voltage. These inverters are normally referred to as VFD's.

    Otherwise a single or three phase induction motor driven from a 50 or 60 Hz supply is effectively speed locked to the supply frequency.

    NOTE that the voltage does not vary to control the motor speed. A 110 volt motor still requires 110 volts.
     
    Last edited: Nov 20, 2019
  4. Nov 19, 2019 #4

    awake

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    Another possible option is to re-purpose a treadmill motor and controller. You will want to keep the step pulleys so that you can gain additional torque for slow-speed operation.
     
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  5. Nov 19, 2019 #5

    Shopgeezer

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  6. Nov 20, 2019 #6

    dnalot

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  7. Nov 20, 2019 #7

    dkwflight

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    A VFD is a good way to go.
    Any three phase motor can work. If the motor is rated for electronic controls it will work much better. If not the motor can be noisy.
    Do the research and pick the pulley sizes for the range you really need. better a little on the slower top speed. Remember the chucks have a top speed rating too.
    It would be better if the VFD devise is a little over size.
    Dennis
     
  8. Nov 20, 2019 #8

    lemelman

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    When I converted my lathe from 1ph single speed to 3ph + VFD, I was dismayed when I opened the control box to find a mass of relays and a network of wires. It seemed horribly complicated until I realised that one relay was for implementing the NVR switch, and the other relays were just for setting the 1ph motor direction (forward or reverse). I simply made the NVR outputs to control the VFD, and used the VFD to control the direction of the 3ph motor. So what looked horribly complicated turned out to be quite simple. The relay used is the one for NVR, all the other relays and wiring were just left untouched and do nothing at all.
     
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  9. Nov 20, 2019 #9

    Rickus

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    The only thing I know about electrical is quite "shocking." But what about a router speed controller like the one Harbor Freight sells?
     
  10. Nov 20, 2019 #10

    tornitore45

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    There are only two options:
    DC motor + Controller Controller can be electronic or a simple Variac followed by a bridge rectifier

    VFD + 3 ph motor, is a little more expensive. I have it done for a total of $200 and never regretted. Works great and requires practically no adaptations

    The mechanical approach may work but is just a pile of aggravation, bulky, slipping low torque, needs protection from swarf, and still needs a motor
     
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  11. Nov 20, 2019 #11

    awake

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    That type of controller works on the "universal" type of motor (brushed, very high speed), but not on an induction type of motor. I'm not aware of any lathe that use the former; most use the latter, except for the smaller import lathes (e.g., Grizzly 7x14) that use DC motors.
     
  12. Nov 20, 2019 #12

    Rickus

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    I can manipulate metal to pretty much do what I want, but electrical gets to me. Like nature abhors a vacuum, I abhor electrical stuff.
     
  13. Nov 20, 2019 #13

    SpringHollow

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  14. Nov 20, 2019 #14

    cds4byu

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    I converted my single-phase 13x40 lathe to a 3-phase motor with a VFD and made it so the existing controls all work.
    https://13x40.blogspot.com/2018/11/adding-vfd-to-my-enco-13x40-lathe.html
    I'd be happy to give you personal advice if you'd like.

    I added a VFD to my Bridgeport mill clone to replace a static phase converter. I elected to replace the existing control switch, and just use the VFD panel on that one. One could use the same approach on a lathe.

    I'm happy with my lathe modification, and also happy with my mill modification.

    Carl
     
  15. Nov 21, 2019 #15

    Wizard69

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    There are lots of options if you want to consider them.

    One mechanical solution is to go with a Reeves Drive.

    a second option is a DC drive / motor combination.

    a third option is to consider a 3 phase motor with a VFD drive.

    Considering the 3 phase motor and VFD, this is one of the better options but getting the best results requires a bit of thought. First upgrade the VFD to one affording vector control. Second you need some understanding as to what the ideal speed range will be for this lathe ideally you will work with a 4 pole motor when figuring this all out. You then need to figure out the best belt ratio for the motors ideal operating range. The larger the ratio (speed reduction) The better the low end performance. However you need to consider if you will have suitable spindle speed when the motor is topped out. Topped out depends upon the max recommended motor rotor speed and the VFD’s capability. Also it doesn’t hurt to up rate the motor horsepower maybe as much as 3X the current motor to help with that low end torque.

    without too much effort you can get good results however if you have a back ear option don’t give up on it. Running a back gear or additional speed reduction can really help at the low end especially if your setup isn’t ideal. A low end VFD/ 3 phase motor installation can benefit from keeping the rotor speed up. You get more power but maybe more important you get better motor cooling.
     
  16. Nov 21, 2019 #16

    Ken I

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    You can normally get a single phase rewound to three phase by a competent rewinder. I've done it several times - as long as the number of stator slots can be divided by three it can be done (they normally are as the laminations are invariably used for both single and three phase).
    While you are at it, you can easily double your horsepower by running the motor at double the rpm - see my article on getting more power.

    https://www.homemodelenginemachinis...re-power-from-your-squirrel-cage-motor.25236/

    You can send me a PM for the full article.

    People are forever telling me you can't do this - I do it all the time - I'm in robotics and I invariably need more power to weight than a squirrel cage can provide at 50/60Hz - if you use 200Hz - with an appropriately rewound motor - 4 times faster - same torque = 4 times more power - you do have to gear it down of course.

    Small motors are a doddle - I have pushed 15kW out of a 3kW motor - the biggest was a 5kW 4 pole pushed to 30kW at 300Hz - nearly 9000 rpm - it did require lubricated ceramic ball bearings and fine balancing (it was a replacement for an extremely expensive German import HF fan drive).

    Yesterday I took an out of the box 1.5kW unit to my rewinder - who always rolls his eyes at having to rewind a motor that is not burned out - rewound for 150Hz & 4.5kW - The third such unit for this particular customer - his oldest has been running production for 8 years.

    Do it right - no problem.

    Regards,
    Ken
     
    Last edited: Nov 21, 2019
  17. Nov 21, 2019 #17

    tornitore45

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    Rewinding a 50Hz motor for 200Hz will give you 4 times the power.
    Sure but only long enough to melt.
    The Iron losses will raise 8X (exponent 1.5)
    And that is not counting the effect of the carrier frequency when the drive come from a VFD
     
  18. Nov 21, 2019 #18

    Ken I

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    I am talking from practical experience - Iron losses are 20-25% of all losses and yes they increase but so does the fan speed - which generally more than offsets this.
    There is a lot more to this than my simplified explanation - if you start with a low duty cycle (or cheap Chinese) motor - then yes you can turn it into smoke PDQ.
    But doubling the power is within the realms of reason for almost any motor.
    Torque remains the same, I^2R (copper losses) remain the same - magnetic saturation remains the same - eddy current losses go down, hysterysis losses go up, mechanical losses go up. Cooling increases.
    I ran a 3kW Siemens rewound for 250Hz delivering 15kW - for a robot mounted saw in a continuous production environment - it burned out after 10 years - nothing particularly unusual there. The conversation with Siemens at the time was fun - they told me rewinding the motor would void the warranty - NSS.
    Check out most of your power tools - brush motors - doing 20000 to 30000 rpm - not one squirrel cage in the lot.
    The power comes from more revs - this is an electric motor not your V8.
    I can't argue with the maxim that "if you need more power - buy a bigger motor" - I am simply offering another option if you are stymied by space and weight constraints.

    P.S. Commercial aircraft use 400Hz in order to gain more efficiency from motors etc.

    Regards, Ken
     
    Last edited: Nov 21, 2019
  19. Nov 21, 2019 #19

    awake

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    With regard to rewinding a single-phase to 3-phase, or rewinding for higher frequency, or so on - I've no doubt it can be done, and I'm sure in some circumstances it makes sense due to space constraints or such. Question is, in the situation described by the OP, would it make sense economically to go this route, when there are such low-cost alternatives?
     
  20. Nov 22, 2019 #20

    Ken I

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    Awake - point taken.
    However just by chance I am in the same boat - I am about to upgrade my lathe to VFD.
    Rewinding the single phase motor is cheaper than a new motor - regardless of the frequency its being set up for - the rewind costs the same (less turns of heavier wire is all).
    All other costs the same.
    My lathe is so underpowered it has trouble starting on high speed range.
    So while I'm at it, I'm going to double its power by doubling its output rpm and changing the primary belt ratio 2:1 - that's the only additional cost.
    The VFD has to be sized to suit - which you might consider an on-cost - but you have to pay for more power - you might be able to get 2kW from a 0.75kW motor but you can't get 2kW from a 0.75kW VFD.

    P.S. I use H.F. motors all the time and they are not that different from your run of the mill squirrel cage - except for fine balancing and close spec. bearings needed for 24000 rpm operation.
    Sometimes they use copper squirrel cage bars in the rotor (as opposed to the more commonly used Aluminium) to reduce "copper losses" in the rotor.

    Regards, Ken
     

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