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Thread: Granite surface plate lathe

  1. #41
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    Thanks for pointing out another supplier and another vote for switching PS.

    CNCrouterparts 380oz-in: 3.15V, 3.5A/phase,4.1mH
    Kelling KL23H2100-35-4B 381oz-in: 2.55V, 3.5A/phase, 2.8mH

    Anything to worry about with the higher inductance in the cncrouterparts motor? The G540 manual states that inductance should be between 2.5mH and 3mH if maximum power is required which I'm not sure it is here.



  2. #42
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    Hi,
    Here's my view on it - If you're going very close to the voltage limit of the drive then a regulated supply is the correct choice. However, a linear, non regulated supply can usually supply 150-200% (the voltage will sag a bit though) of it rated current during short periods of time which a typical switching supply usually can't. Once it reaches its rated output current it'll shut down with an overcurrent fault - at best. Some try to restart automatically which can result in some interesting results.

    This means that the switching supply needs to be sized for peak current while a non regulated linear supply can be sized for continous current.

    That 7.3A switcher will (hopefully) live up to its specs and supply 7.3A but probably not more. Meanwhile you can count on the the 7.5A linear supply to easily give you 10 or 15A for short periods - a couple of seconds each minute etc.

    If the switcher is 50% oversized as it is then I don't see any problems with using that though.

    Well, that's my €0.02

    /Henrik.



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    Quote Originally Posted by will gilmore View Post

    CNCrouterparts 380oz-in: 3.15V, 3.5A/phase,4.1mH
    Kelling KL23H2100-35-4B 381oz-in: 2.55V, 3.5A/phase, 2.8mH

    Anything to worry about with the higher inductance in the cncrouterparts motor? The G540 manual states that inductance should be between 2.5mH and 3mH if maximum power is required which I'm not sure it is here.
    That is a good question. I guess you would be right. Maybe you would get better power using a lower mH motor. What I can tell you is that I am using these motors on my CNC router and it is moving a much heaver gantry than you will be moving on your lathe. I would think you would have plenty of power on a small lathe.

    At work I find myself taking faster smaller cuts on the CNC lathe than heavy slower cuts I used to take on the old manual lathe. This said I think you can go with the motors that make you feel better and not go wrong. The CNC router parts motors work. If the Kelling motors make you feel better then with their mH ratting go for those. Hopefully if someone knows more about the power difference they will let us know.



  4. #44
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    Nice work! Great concept.

    I wouldn't worry too much about this PSU/motor thing. Your lathe will work fine whichever way you go.

    I used puny 167 ozin unipolar steppers geared 2:1, driven bipolar half winding, from a 36V PSU on my 7x12 lathe conversion, which must be about the same size as your lathe. This set up has provided sufficient power for cutting. The VFD controller 3/4 HP 3 ph motor direct driving the spindle bogs down before either axis.

    The limitation I have is rapid speed, at about 1m/min. If you look at what some of the routers are doing with G540's 50v psu's and low impedance motors, I think you will find that rapids will not be an issue for you, with your ballscrews direct driven with NMA 23's and a 50V PSU.

    For X at least, you might well have greater total performance with a lower inductance motor like the KL23H276-30-8A, as the cutting loads tend to be smaller on X.

    I have my doubts about these stepper ratings. I wonder what the manufacturing tolerances means to actual motor performance. In the really world I can imagine there being bigger differences within batches of either of those motors you have listed than between them.

    What are you intending to cut? What will your spindle drive system be? What will be your lathes swing? If you are going to cut batches of 5" diameter slugs of Stainless, then you may well need the G201's and Nema 34 motors. If you are going to be mainly turning Aluminium and diameters less than 30mm, then cutting force is not going to be an issue. One advantage of a CNC lathe is that you can take two finer cuts in little more time than it would take to do one hogging pass. Unless you are doing production runs of thousands, the cycle time is not a huge factor to us hobbiests.

    Regards,
    Mark


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    Lower inductance motors will give better high speed performance - less torque will drop off at high speeds because the driver will be able to pull enough power quickly enough before it's time to change polarity on each phase.

    I used to think Keling had the best deal, but then I saw some higher performance motors here: http://www.homeshopcnc.com/RSstepperMotors2.html

    Maybe a few bucks more, but the specs look better than the Keling motors.
    I picked up one of their motors but haven't gotten it running yet. It's a Nema23 570 oz/in and wow is it hard to turn the shaft by hand.

    -Matt



  6. #46
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    Thanks for all the comments.

    Quote Originally Posted by RotarySMP View Post
    Your lathe will work fine whichever way you go.
    Yeah...I think I'm unnecessarily splitting hairs now with the motors and psu.

    I'm not sure what I'm going to be making with this lathe. It has a 4" swing over the tool plate and around 8" in front of the tool plate. I'm sure I won't be able to use the full swing for spindle power and ridgidity reasons.

    I would like to be able to turn hard materials. For example I made these dies for a planishing hammer. Each face has a different radius that I ground by hand on a belt sander. They are 1.5" (the big one is 3") diameter S7 tool steel. Cutting the radii on a CNC lathe would be handy.




    I'm trying to get all my electronic ducks in a row and I'll probably order some stuff next week.



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    Quote Originally Posted by Ryobiguy View Post

    I used to think Keling had the best deal, but then I saw some higher performance motors here: http://www.homeshopcnc.com/RSstepperMotors2.html

    Maybe a few bucks more, but the specs look better than the Keling motors.
    I picked up one of their motors but haven't gotten it running yet. It's a Nema23 570 oz/in and wow is it hard to turn the shaft by hand.

    -Matt
    Keling has basically the same 570 oz motor for $11 less.
    http://www.kelinginc.net/NEMA23Motor.html

    But neither is a very good motor to use with the G540, as you'd need to run them bipolar series, which has higher inductance.

    Gerry

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  8. #48
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    A regulated supply,wether linear or switch mode,needs a large cap 2000 to10000Mfd at the output of the supply.The drives and motors work best with an unreglated supply.Adding the cap makes the regulated supply act like an unregulated supply.
    Larry

    Last edited by lgalla; 01-24-2010 at 12:04 PM. Reason: mis
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT


  9. #49
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    Turning 3" diameter steel dies would be no problem on my 7x12, if the steel is not too hard. Otherwise it would be a non-starter, due to machine rigidity rather than power, so it will work fine on your lathe, whichever of these motors you choose.

    If you do the headstock with a big hairy 3HP motor and gearing, then you may well end up being limited by axis power rather than spindle power, but then you just take a few more, lighter cuts and still get the job done. If you use a CNC lathe for making one off work (like I do) then the speed of the machine of no relevance other than bragging rights, as it generally takes way more time to set up on off work than to run the cycle.

    I wouldn't agonise over the motor question. If you are completely wrong and buy the wrong motor, you have a $34 motor you can sell on Ebay with little loss.

    If you buy a 570 ozin motor, but never need more than 200 ozin of torque for cutting , then you have limited your rapids for no gain.

    If you install 270 ozin motors, but occasional need 300 ozin torque for cutting force, you will have faster rapids all the time, including on that one job where you now need two cuts instead of one due to the cutting force limitation.

    Do you have a CAD model of what your lathe will look like finished?

    Regards,
    Mark


  10. #50
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    RotarySMP - No CAD. So far its all been designed with pencil and paper.

    lgalla - First I've heard of this smoothing cap on a switching PS. Sounds reasonable.

    Spindle drive is up in the air right now. Head stock is a Dunham 5C: http://dunhamtool.com/precision_spindle_headstock.html 3600RPM

    Right now headstock has a single V belt pulley so the easiest thing to do would be to use a motor and VFD. I'm thinking 1-2hp so costs would be around $100 for the motor and $150-$250 for the VFD. It would also be easy to have a couple pulleys for the motor if I needed to gear down for more low speed torque if I was turning a big diameter.

    Second option is to use a servo to drive the head stock. In the long run this would add the capability to use live tooling. I would need to change the vbelt to a toothed belt plus, spindle, drive, encoder etc. More $, less power but more functionality.

    I think I'll probably start with the motor/vfd to get up and running.

    Last edited by will gilmore; 01-25-2010 at 12:52 PM. Reason: learned that mfd and uF are the same!


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    more progress. I had a slight detour with some balls coming out of my hsr15 rails but I got them back together and am back on track. I have the Z rails squared to the edge of the granite.




    squaring X rails to edge of tool plate. X was designed with 2" between rails which made it easy to get close.

    Z is 4" between the rails so 2 123 blocks to get close.

    Can anyone recommend a good paint for machine tools? Spray can is nice.



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    Registered lgalla's Avatar
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    Will that sentence was from Gecko design PDF's.The large cap is a reserve.Motors are up and down in current and voltage just like an unregulated supply.Regulated SMPS are like a brick wall when current limits are reached and will shut down.
    SMPS are used in computer supplyes.I have 4 fried PSU'S
    Smps are switched at high K Hz and may be noisy.
    SMPS are multi stacked circuit boards and have hundreds of components.If it fries,time for a new supply,no repairs.
    Alinear supply has 4 or 5 parts an can be serviced.I have never had a linear supply go down.Linear supplies have a good reputation.
    I would spend the extra for the un regulated linear supply.Besides adding a large cap to the SMPS makes it perform like an un regulated supply and brings up the cost to where you should have used the linear in the first place.
    Love your build.I posted too much on the Epoxy granite thread and recomened surface plates as parts of machines.Will follow
    Larry

    L GALILEO THE EPOXY SURFACE PLATE IS FLAT


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    Hi,
    Been following this one since I fell over it, I've also got a 5C "gangster" at design stage, with most parts bought (no granite though!!)
    I decided to put "X" rails as far apart as gang plate allows (100mm on 150mm plate, would've preferred more) reasoning that there'll be lots going on outside the plate area. Thought this would reduce the effect of the tilting moment when using end working tooling.
    Love the Dunham spindle, mine's a Hardinge HSL, meaning I've had to make space for a bed I don't want! Upside may be to use the dovetail piece atop the plate as a tooling mount.
    Curious about collet closer, is it basically air operating a traditional toggle type?
    My old 5C machine hit me with serious tennis elbow after last "earner", need to convert!!
    I'll keep watching the thread, best of luck with the build.
    John.



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    Larry-thanks for the comments. The caps do bring up the cost of the switching PS but not to the level of an unregulated supply. (10,000uf cap for $12.20 http://search.digikey.com/scripts/Dk...me=565-3299-ND) still undecided on this. One nice thing about the Antek unregulated PS is that they can come with a 5V output to power limit switches, relays etc.

    JLSD- The wider the rail spacing the better. I bought ground flat stock for the headstock spacer, the plate that holds the linear bearings, and the tooling plate. They came as 18"x6" plates. The tooling plate is a full one and the rest is made of two plates each cut into two pieces so that dictated the spacing of the Z rails. In practice, the tool that is cutting will almost always be between the Z rails.


    Squaring plate to Z axis

    Finished Z

    Finished Z from the back.

    -Will



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    nice progress, keep up the good work!

    FS: Complete Z-Axis Assembly with THK RSR15WM slide, leadscrew, stepper mount. PM for more info.


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    X axis on for the first time. Its heavy. ~30 lbs. I hope the stepper can lift it I guess with the fine pitch screw it will be ok.



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    Hi, I love your project. I do have a question about the way you mounted the rails. Will the bolds eventually lose there tension because they are so long. I honestly don't know.



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    Steel doesn't creep enough at room temperature to let his bolts get loose. If that was the case, steel bridges wouldn't work. At really high temperatures, this isn't true, but if his lathe gets that hot, he won't care. Here is a link that says it all in the first sentence.

    http://www.engineersedge.com/material_science/creep.htm



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    Quote Originally Posted by chimpera View Post
    Hi, I love your project. I do have a question about the way you mounted the rails. Will the bolds eventually lose there tension because they are so long. I honestly don't know.
    I don't think they will stretch. One concern is that the holes in the granite are bigger than the bolts. If the bolts are slightly slanted in the hole they could shift and be loose. I guess we will find out.



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    I'm going with G540, Keling 381 steppers, Antek 48V unregulated PS
    Questions:
    Do I need a 5A fast blow fuse between PS and drive? (out of curiosity why is a fuse ok when a switch is not ok on DC side of PS)
    Do I need 470uf 100v cap across PS inputs on G540?
    Do I need zener diode voltage clamp across PS inputs on G540?

    Wire questions:
    Stepper motor wire: 22 gauge shielded. right?
    PS to G540 (48VDC,8.3A max): ?
    What size wire for all the 5VDC circuits(estop, inputs, outputs etc)?
    AC to PS: 120V, 400W = 3.33A? I have a bunch of 12 gauge wire laying around.

    Any one have a good idea/source for connectors for inputs? db9 like G540? DIN? ??



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