Variable speed control for a small lathe

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

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  1. Nov 26, 2019 #41

    nurd77777

    nurd77777

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    Hi there
    The motors I mentioned are universal brushed they are used on front loading washers. I can get loads I know a guy that scraps washers. They have a flat belt pulley and are designed to turn a big pulley which turns the drum. For machines its best to use the drum gear and cast another pulley where the internal drum was. On my lathe the total reduction is around 40 to 1 and this divides the 500-12000 rev range. With tacho feedback the speed is constant with load .
     

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  2. Nov 28, 2019 #42

    almarghi

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    I have successfully used one of those on a BF20L for about 2 years, but upgraded to a 3-phase motor + VFD, due to noise :(
     
    Last edited: Nov 28, 2019
  3. Nov 28, 2019 #43

    nurd77777

    nurd77777

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    Hi Almarghi I only have small machines which are lashed together with bits I have accumulated. I would not have a lathe or a Gingery imitation mill if it was not for the versitility of motors. The type of controller I have/make feeds back speed info so the speed is constant at setting unless its overloaded in which case it limits at 20 amp. It does sound like a vacuum cleaner so I suppose it is noisy.
     
  4. Dec 7, 2019 #44

    velocette

    velocette

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    Hi Shop Geezer " Prying the belts off to change speeds gets old real fast" Have you considered using an Eccentric or over centre belt tensioner on the motor to loosen the belts and just lift them between grooves. Loads of ideas posted that all require a considerable expense and modifications. Treadmill DC motors are fine but run at 4000 to 6000 RPM so require a sizable reduction ratio. A couple of Photos of the tensioner - clutch on my wood lathe may explain better.
    DSCF0986.JPG DSCF0984.JPG
     
  5. Dec 7, 2019 #45

    Shopgeezer

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    On my lathe the motor is firmly bolted to the frame. The belts are tightened by eccentric pulleys that are also bolted to the frame. They can slide in slots when loosened, so changing the belts requires digging out two different sized wrenches and loosening everything, prying off the belts and rearranging them (or swap them for longer or shorter ones) and using a bar to retension the pulleys while bolting them back down. Clever engineering insures that over centre levers would require some major re-design of the belt system. Just turning a knob on a VFD sounds sooo much better. But it would require bypassing all the safety relays that prevent the spindle from turning if the cover is up and I am guilty of leaving the key in the chuck and trying to turn the lathe on. So I leave it set at 520 rpm for everything. Too slow for aluminum and way too fast for reaming and tapping.
     
  6. Dec 7, 2019 #46

    TonyM

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    No need to worry about incorporating old safety features Shopgeezer. I changed my Warco 240 to three phase motor and VFD, kept all the original safety switches and even added another emergency stop near the VDF . bottom left of VDF in pic 2
    IMG_1.JPG IMG_2.JPG
     
  7. Dec 7, 2019 #47

    nurd77777

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    Hi The problems of providing a wide speed ratio with VFD have all ready been out lined earlier in this thread. I am sticking with my triac controlled washing machine motor 500 to 12000 RPM since I also get a free drum pulley off the donor washing machine for 10 to 1 reduction.
    Regards Keith
     
  8. Dec 7, 2019 #48

    TonyM

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    My point was that all safety features are easily retained or even improved which was what shopgeezer was concerned about.

    I can't compare my set up to a washing machine motor or treadmill motor so I have no idea if they are better or worse so I do not decry the use of scrap yard bits and pieces. .

    I do know my lathe does a lot of work. It has better power and control than the original setup without the need for belt changing. It runs with more power than I need from 40 rpm to 1800 rpm. It rarely takes 8 amps even when starting and the cooling fan on the VFD rarely runs. I have retained all of the safety features plus one more. Work involved was minimal. However the cost was substantially more than a second hand washing machine motor and control from a scrappy.

    We all do what we can with the resources we have.
     
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  9. Dec 13, 2019 #49

    velocette

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    "Just turning a knob on a VFD sounds sooo much better". Variable spindle speed with independent variable speed power feed lets you find the "Sweet Spot" for machining all materials. The development of VFD drives has come a long way since I first experienced them used in industry in the early 1990's.
    Eric
     
  10. Dec 13, 2019 #50

    Shopgeezer

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    The power feed is another question. My lathe has the two selector knobs at the bottom of the front panel that gives different speeds. Even on the slowest setting speed is still relatively fast. Since the gear train driving the lead screw is driven by the motor, slowing down the motor will also slow down the lead screw. Good unless you want high spindle speeds and slow speed rates as I would for aluminum. I have seen You Tube videos for electronic lead screw drives. That is really next generation but would be great to have.
     
  11. Dec 14, 2019 #51

    velocette

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    I had a similar setup and changing gears from roughing cuts to a fine finish cuts a pain. So fitted a 24 Volt DC gear head motor with a Poly Vee belt to drive the lead screw.
    The motor speed is controlled with a PWM unit with a reverse switch. Ten years of use and so much easier to use the lathe would recommend it to anyone.
    Eric
     
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  12. Dec 15, 2019 #52

    chrsbrbnk

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    for a kinda cheapo variable voltage supply for dc motors I'v used light dimmers and a bridge rectifier they make some pretty good wattage ones for fairly cheap at the home supply stores
     
  13. Dec 15, 2019 #53

    velocette

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    A problem with this setup you get very little torque at low speed with a large diameter work piece in a lathe chuck.
     
  14. Dec 16, 2019 #54

    TonyM

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    You are right about that. I tend to leave mine set on the slowest feed and rough by hand feed. What power motor and controller did you use. It seems like a good idea to me.
     

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