Lathe Has a Mechanical Brake ... Should I Use a Braking Resistor in the VFD Circuit
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    Question Lathe Has a Mechanical Brake ... Should I Use a Braking Resistor in the VFD Circuit

    My Nebel lathe has a mechanical brake. Some of the lathes shown on YouTube that have VFDs also have braking resistors. When I wire up my VFD should I include a braking resistor? The motor is a 3 HP 240 volt three phase. The VFD is rated at 5 HP.

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    Quote Originally Posted by FLASH GORDON13 View Post
    My Nebel lathe has a mechanical brake. Some of the lathes shown on YouTube that have VFDs also have braking resistors. When I wire up my VFD should I include a braking resistor? The motor is a 3 HP 240 volt three phase. The VFD is rated at 5 HP.
    No need for the VFD to have any braking.

    The brake needs to be able to tell the VFD to stop powering the motor though!

    On my HBX-360, when you tread on the brake-bar across the front of the lathe, the linkage first action as it starts to take-up slack to apply the friction is to lift a spring-loaded toggle switch that cuts-off power to the 7 HP motor. Not VFD'ed, so the OEM controls are still OEM.

    One can de-power - "no hands" - WITHOUT actually "braking" and let it coast - if that's what you want to do.

    I like it that way. Seems a fairly common setup, European and Asian lathes, but most don't have VFD's?

    Up to you and the VFD manual whether you want to wire it to resume turning as you come off the brake - or do a full stop and require a fresh "RUN" command input before it begins again, much as an E-Stop would do.

    If you do not HAVE a foot treadle, they are not hard to add.

    See also knee-lift and shin-kick bar or taut cable for E-Stops.

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    I always use a braking resistor when installing VFD's on lathes, if one hits the E-Stop one wants the lathe to stop as soon as possible without triggering a VFD over voltage error. Depending on the VFD, I also use a switch to select different acceleration and deceleration curves, and an E-Stop can be wired in for a fast stop input if available. There are also parameters on some VFD models to prevent an over voltage buss error kicking the VFD into a free run mode. In addition with routine turning and threading, I use electronic braking to give predictable and quick stops. Doing work with larger chucks and/or higher speed one may select longer braking times if the VFD does not have the ability to modulate the braking to preven an over voltage error.

    In either case when using the mechanical brake you need to issue a free run (base block) command to the VFD so it will not interfere with the mechanical braking speed. Additionally, once the mechanical foot brake is engaged, you want the lathe to come to a halt and require a rest (typically by moving the spindle switch through the stop position) in order to restart the lathe. I do not know of any lathe that resumes running after engaging the mechanical brake . You need to design a control system, typically with interlocked latching relays to implement this correctly.

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    Quote Originally Posted by mksj View Post
    I do not know of any lathe that resumes running after engaging the mechanical brake .
    Wellll.. are you confusing "brake" with a "spindle lock"? They can be separate. y'know.

    And at least until "electricity" was discovered? They ALL "resumed"!
    Presuming one RELEASED or "feathered" it!

    Waterwheel and lineshaft thing.. but not-only.

    And they remained that way for plenty of electrically-powered lathes that had/have constant running motors, mechanical CLUTCH as well as BRAKE, and even mechanical reversing. Often on the same mechanical ONLY lever, not electrical switch:

    REV [Brake-Neutral] FWD.

    And we PREFER it that way. And even replicate it with "creep" rather than "jog" for easy positioning of our workholding.

    Even in CNC to high degrees of positioning accuracy that are part of the spindle's routine Day Job, often every cycle.

    Even a basic Parker-SSD? Exactly ONE potentiometer:

    REV (and how fast) <- BRAKE/IDLE -> FWD (and how fast)

    No relays. Configuration options, rather.
    VFD have configuration options, too. Plenty of them!

    E-Stop?? A relatively "new thing", as machine-tools go.
    And exactly what it says it is. EMERGENCY Stop.

    AND NOT a normal operating control. A different animal entirely, IOW.
    Spindle lock CAN be yet-another animal. Or integrated.

    Why would one confuse these distinctly identifiable functions, even where one MIGHT choose to correlate, even integrate?

    Or not.

    You should get around ...more than just the one or two lathes? It can be educational. Even fun.

    ADDING E-Stop is nearly always a good idea.

    Screwing-up a(ny) machine tool's designed flow of operation philosophy may NOT be a good idea. Think it through. Plan and review. If it doesn't suit? Fix it so it does do.

    Tailor your controls to suit the OPERATOR according to the need. The flexibility is THERE. And already paid-for. So use it.

    The rest is up to your preferences as to how you NEED it to work.


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    Have to say, I don't follow what you are trying to say, riddles upon riddles. Built 100's of lathe systems, 99% with relays. Your life and your fingers, do what you want, but not for others.

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    Quote Originally Posted by mksj View Post
    Have to say, I don't follow what you are trying to say, riddles upon riddles. Built 100's of lathe systems, 99% with relays. Your life and your fingers, do what you want, but not for others.
    No foul. Everyone has to "run what they got" at whatever speed it has built-in.

    I've known lots of folks who did shit wrong-way-round for over fifty years, believed their way was the only way the whole damned time.

    Machine is meant to obey the needs of mankind.

    Not the reverse.

    I surely wouldn't want some safety Nazi designing P-47's, Claymore mines, nor even bayonets!

    Not understanding what the end USER has to DEAL WITH is how to lose the f****g WAR, Pilgrim!

    Commerce has days like that, too. So-called "brilliance" being bypassed or disabled, all-too-often on the shop floor!

    A(ny) machine is either operator-compatible at "JFDI" ... or it sucks badly enough it falls out of USE.. gets modified.. ELSE some OTHER machine gets the job.

    We JFDWT and "Run what we got" with a greater ration of common sense and sanity ....than misplaced arrogance.

    Not as if machine operators had higher rates of suicide than average, is it?
    Cannot, actually.

    Designers have already et up our share.



    BFD They were the expendable ones, anyway. Ask any operator of an end-luser-hostile machine what he thinks about that tribe ... and OSHA-Nazis!
    Don't expect to win a lot of praise.

    We've got s**t to DO!

    Fingers? Mine are into their 77th year. Let's revisit this at 95 or so?

    Last one of my tribe to be buried, maimed "on the job", was Colonel Rowland Hacker. Lost a hand, age 24. August. 1644. Lived another thirty years, anyway.

    It does HELP if a person keeps their HEAD out of their ass?

    You got a "relay" that can assure that?

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    I believe the idea is that if the brake has been used, someone wanted the machine to STOP. (Same with the E-stop, only more-so).

    Therefore, it should require an action to positively start it again, as opposed to just having the release of the brake bar automatically start it again.

    You do not want it to start as soon as you release the "stop" button either. Same idea. Makes sense to me, no idea what the long dissertation was saying.

    That's how all my machines are wired, and it's never been an issue.

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    Quote Originally Posted by JST View Post
    That's how all my machines are wired, and it's never been an issue.
    And you make your living in the electronics trade.

    Not by running machines 8-plus hours a day for years on-end.

    Pay more attention to what the job and operator actually NEED to complete the work with minimal stress and distraction - select wiser and less intrusive methods, and you can have ALL OF. .

    - safer operation

    - better productivity

    - happier operators who leave shift less tired and grumpy.

    Why is that so hard?

    ..because the insensitive interlock designers have not had to LIVE with the results of their own work all day, every day for all their days.

    Others do have to.

    Take their input on-board.

    You'll get better systems, not worse.

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    Quote Originally Posted by thermite View Post
    And you make your living in the electronics trade.

    .............
    Including safety systems...........

    Just 'cos the operator can make better time if he does not have to hit both buttons to start the press does not mean it's a good idea to short out one of them. Better time does not pay the OSHA fine, nor the court judgement when a safety system is bypassed and causes an injury.

    You have to hunt where the deer are, not where you think they should be.

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    Quote Originally Posted by JST View Post
    Including safety systems...........

    Just 'cos the operator can make better time if he does not have to hit both buttons to start the press does not mean it's a good idea to short out one of them. Better time does not pay the OSHA fine, nor the court judgement when a safety system is bypassed and causes an injury.

    You have to hunt where the deer are, not where you think they should be.
    Been trying to get that across to yah. Lack of buttons wasn't what took down Rome, though, was it?

    Every bite of Venison I ever et was kilt with a lethal weapon in expert hands.

    Nary a one of 'em was put on the table, dead of aggravation over some distant desk-jockey's idea of how that hunter shudda had multiple pushbuttons instead of but the one trigger or bowstring.

    And a brain that knew the meaning of it.

    So now what? Convert the nation to majority Idiots to prove your systems ARE idiot resistant?

    The machine work goes to China.

    The trained-up irresponsible Idiots are left behind.
    Simply vote themselves an income.

    Chinese who took their jobs going to pay the taxes for that?

    It would seem fair, but how can yah collect?

    Dunno about "moderation in all things".

    Sure wouldn't hurt to try for "good sense" now and then.

    Has EVERYBODY MISSED where we came in?

    His machine HAS a brake. Already. However it is arranged, it worked.

    So all he has to do with a VFD is "let it know" ....to not make war on the brake by treating it as a heavier load and trying to power-up to overcome the drag.

    That should not need a roomful of so-called safety systems engineers nor a box full of relays.

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    China is, slowly, going the same way. No-one wants to win a job purely in cost; it's a crap market to be in.

    So your guns don't have a safety on them?

    But yeah, chances are the machine already has a way to drop out the contactor when the brake is applied. Simply ensure that it still affects the VFD.

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    Quote Originally Posted by SomeoneSomewhere View Post
    So your guns don't have a safety on them?
    I don't personally traffic in "fossils". All my slabsiders have ambidextrous safeties. Because I am.

    But a rather large percentage of wheelguns never did have a "proper" safety, no.


    But yeah, chances are the machine already has a way to drop out the contactor when the brake is applied. Simply ensure that it still affects the VFD.
    More than "chances are".

    If it was a serious-enough attempt to bother being furnished with a brake? Whether a grand-old dinosaurian or a modern Asian "LSO" it will have whatever it needed for sanity already "there".

    No need to re-engineer it just to sell more relays and add more failure modes.

    Just "tell" the VFD to not introduce a problem where there had not BEEN one.

    See FIRST response, Post #2

    BEFORE the "usual" bored and habituated kibitzniki brigades piled-on to make yet-another problem out of a simple-dumb solution, IOW.



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