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Thread: VFD for Lathe

  1. #1
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    Default VFD for Lathe

    Hi All

    I've picked up a used HAFCO AL900A 1HP single phase lathe for $300. All looks micky mouse apart from the stripped back gear which means I cant do the low revs and there's a bit of pucker factor when thread cutting. I can obviously have the helical back gears rebuilt or remade (parts no longer available according to H&F) but I thinking a single to 3 ph VFD and new 3ph motor might be a better option.

    What I know about electricity would fit on a postage stamp but I'm interested in opinions on this option and what gear is suitable eg motor and VFD rating, features, brands etc.

    TIA

    Lathe



    Damaged back gears


  2. #2
    BobL is offline Member: Blue and white apron brigade
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    I'd get the gear fixed.

    VFDQuestion.jpg

    The gear ratio between the Small motor pulley and direct drive is 4:1 and from that to the top of your range is ~3:1 - overall range is 12:1.

    A VFD can do at best about 2.5:1 (50 to say 125 Hz) at full power.
    If you double your motor power you can go 5:1 (25 to 125) at original power.
    Other people might but I wouldn't go more than double the original HP.

    If you look at still swapping the motor pulley you'll need 560:90 or ~6:1 - you could do that with a Vector drive VFD but then you'd be up for a bunch of money.
    I'd get the gear fixed first.

  3. #3
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    I agree with Bob. You need to get that gear repaired. The mating gear is not looking too flash but is probably serviceable. Sometimes I see damage like that and wonder how on earth the user managed it. In that case maybe a jammed chuck?

    Michael

  4. #4
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    Thanks gents. Dont know how they managed it. Crashed it I guess.

    Any thoughts on where I can get the gear repaired?

  5. #5
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    Someone here could well do it. First step is to get it out and cleaned up so that it can be looked at. If you can determine what the material is that would be helpful too (it will be either steel or cast iron).

    Michael

  6. #6
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    Apart from some varitation in the head and the paint colour, that lathe looks a lot like my McMillan which is a rebadged Lontain.
    Funnily enough mine also had a busted tooth on the backgear. I inherited mine from my Dad but I can't remember if he busted the tooth or if it was like that when he bought it. Mine has been repaired by drilling and pegging then filled with braze and filed to shape. Works fine.
    At a guess I'd save the likely cause is using the back gear to lock the spindle to remove the chuck. (which I am also guilt of)
    I dont have a pic atm but can take one during the week if you want.

    peter

  7. #7
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    Fun fact about vfd's - you lose power when you go slow. Gears are always better.

    A motor has a set vf (voltage frequency) relationship so when you decrease frequency you decrease power. Most vfd's have a 'torque boost' function that tries to minimize the effect but it's a patch and puts more stress on your motor.

    Most motors will overheat (and degrade insulation etc) under 30% rated speed.

    Above rated freq you saturate the core (causing heating and low efficiency). The vf curve also goes out of wack - you can't make more voltage than line from the vfd.

    You can get away with a larger motor (provided it fits!) and limit max torque in your vfd. This will give you the same torque as original if you size it right. If you don't limit torque you will break expensive/impossible to find bits. Still keep in the range 30-120% of rated frequency.

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Pez View Post
    Most motors will overheat (and degrade insulation etc) under 30% rated speed.y.
    Heat also depends very much on load.

    On my small WW lathe I replaced the 1/2HP SP motor with a 1HP 2P. This is overkill for the small spindle type stuff I usually turn but it means it still generates 1/2HP at 25Hz. I usually use that slower speed when I'm converting square cross section pieces and by using a TC attached to the motor I can monitor the temperature. Because the load is so small the difference in temperature is only a couple of degrees.

    Recently I started making trumpet shaped dust collection ports (Bell Mouth Hoods) from 6 and 4" PVC ducting using this small lathe. There is very little tool contact with the PVC - just a touch to shape the edges. The main shaping is down by running a wooden former in the headstock onto which a 6" length of PVC partially slides and turned at ~ 100 RPM while being heated with a hot air gun. I don't bother to change gears and this works out to about 12Hz on the VFD. Once the of the PVC is heated (monitored with an IR gun) the PVC is then pushed onto the former by an Al disc attached to the live centre on the tailstock. Once again minimal load on everything and the motor does not get warmer by more than a couple of degree. I have made over a 100 of these hoods and no problems with heating.

    I'd attach some pictures but the picture loading service seems unavailable.

    Of course I would not do anything loaded up at these speeds for long periods - just wanted to related my experience at low speeds and low loads. On my Hercus lathe I have a Vector drive VFD and also a 1HP (originally a 1/2HP VFD) and this combo generates the same torque at ~12Hz as a the original motor does at 50Hz and do sometimes run for brief periods at these low speeds.

    It is also easy enough to add extra cooling to motors to help at load speeds. The 1440 rpm 3P motor that runs on my BS has a fan built into it that runs at double the speed of the motor.

  9. #9
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    Quote Originally Posted by Michael G View Post
    Someone here could well do it. First step is to get it out and cleaned up so that it can be looked at. If you can determine what the material is that would be helpful too (it will be either steel or cast iron).

    Michael
    Got the back gears out but still working on the spindle gear. From the research I've done this lathe was also sold as Shen Wai 900B. Probably some other too. It may share similar parts with others like Bollie7 has suggested but its hard to find parts regardless.

    The back gear is a 22/52 configuration, cast iron. The large gear is in good condition but the small one is toast. Specs on the small gear are;
    Module 2
    14.5 helix
    49.3mm dia
    17mm widith
    22 tooth.

    I figure I could have one made up and then braze it to the existing shaft? Shaft dia is 33.90mm

    Images





    Thoughts appreciated.

  10. #10
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    I agree with BobL.

    For the size of motor you use I'd seriously consider a second hand dual-winding aka two speed motor. That would give you a good simple way of getting both speed ranges.

  11. #11
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    Quote Originally Posted by Bidgee View Post
    I figure I could have one made up and then braze it to the existing shaft? Shaft dia is 33.90mm
    That's probably as good a plan as any. Rather than wrestle with the spindle at the moment, wait and see how the back gear repair goes. It may be there is enough tooth left to drive things and removing spindles is something to be avoided if possible. Another reason for leaving the spindle intact is that you may need to give the gear bore and/ or back gear a skim for fit.
    I did not pick that the gears have a helix on them but that only adds a little to the degree of difficulty

    A gear cutting workshop should be able to work off those dimensions. I have a few other things on but could make up a cast iron gear to those dimensions for you in a couple of weeks.

    Michael

  12. #12
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    Quote Originally Posted by Michael G View Post
    I have a few other things on but could make up a cast iron gear to those dimensions for you in a couple of weeks.

    Michael
    Appreciate that Michael. I haven't had much luck tracking down gear makers/repairers so if you could do that I'd be grateful. Obviously happy to pay.

    I've got the spindle mostly out so I'll persist with it for a bit more - frustrating and time consuming without any documentation but if I'm going this route I'll feel better with the spindle gear repaired too.

    Scott

  13. #13
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    those lathes were made and badged by many names,i would chase around and you will find those gears somewhere, i got my metric gears from gumtree 10 klms from home.(hafco AL 330) which i would say could be the same .will keep an eye out for you...bob

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