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Instant Reverse ??

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  • Instant Reverse ??

    This term, used in 2005, confuses me. They don't really mean "instant" do they? And if so, why is it so damn necessary to throw all these moving parts into reverse thrust? Maybe for threading, I don't know?

    I don't know for sure but I imagine the term "instant reverse" meant you no longer have to shut down the entire factory so one guy can run his lathe in reverse by switching his belts around. Or, he wouldn't have to wait until lunch time when a shop may have been powered down to make the switch-over. The switch to reverse would be relatively "instant" compared to the alternative of shutting down an entire factory driveline.

    My SB9a has reverse on it. Does that mean I can be smoking along and hit the reverse switch? If so, where the hell do you go to get out of harms way when the chuck comes flying off?

    Maybe this term "instant" should be dropped in this century before some rookie (like me) gets mangled or worse yet, mangles his machine

    Any insite would be appreciated.

    Maybe we should start a movement.

    Hell, we could petition a new law to be written!

    Ray....


    [This message has been edited by Your Old Dog (edited 12-18-2005).]
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  • #2
    thats a good point you have there hehe.
    i to have noticed over the past ten years, that words that once ment something now means something else.
    it looks like good majarity of todays generation is a throwaway sociaty.
    what are they gonna do when their kids decide to throw them away into the trash to

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    • #3
      Nothing in life is instant, except maybe the first time I ... oh nevermind. Maybe we should ban the word altogether? I was in my buddy's shop Thursday and he made me a cup of "instant" coffee; he still had to heat the water

      I have a single-phase lathe and drill/mill. Once it's above a very low RPM, I could throw the forward/reverse switch all day long and the motor would happily keep running in the same direction. To me, throwing that switch and having the machine reverse would be "instant." Instead, I have to turn it off, wait for the spindle to stop and then reverse it.

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      • #4
        I run a three phase motor from an inverter on my lathe and I find the instant reverse very handy when threading with a tailstock die holder. Just flip the switch and the motor ramps down and then ramps up again in reverse.

        Allan

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        • #5
          It does mean instant, in the sense that the motor torque reverses immediately when fed the appropriate power polarities, whether the motor is spinning or not. The standard 3 phase induction motor does it. A single phase motor which has a centrifugal starting switch (such as a split-phase or capacitor start motor) does not. The motor with the centrifugal switch must slow down to the point that the switch turns "on", which connects the start windings. The start windings are what gets the motor going in the other direction, and if they're not in the circuit, the motor will just spin merrily in the same direction no matter what your "reverse" switch is doing. So since you have to let the single-phase motor wind down nearly to a stop before you can reverse it, it's not instant reverse.

          I rarely find "instant reverse" a useful feature, myself. A brake on a motor (that is, "instant stop", more or less) would be more useful.

          [This message has been edited by sauer38h (edited 12-18-2005).]

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          • #6
            Nothing is instant. If you could stand on a nucleus, even the orbit of an electron around it would seem to take a considerable length of time.
            In terms of lathe's, etc, something more 'instant' would be the reversing of a pm dc motor by flipping the switch. Assuming the power supply can handle it, the brushes, switch contacts, et al, that type of motor would reverse very quickly, like maybe in one second it would brake to a stop then wind up to speed again. I've never seen an ac motor that would come up to speed as quickly as a pm dc motor, let alone stop and reverse in an 'instant'.
            Probably the closest thing to instant is when you order a coffee in a restaurant, then promptly fall asleep. The waitress wakes you when the coffee arrives. Now would that make it 'instant fresh brewed coffee'?
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Called Plugging. Or it used to be. You apply reverse torque via the motor to plug the load to a stop.

              Usually it shortens the life of the gear train, the motor keyway, the windings, the

              COntactors used for reversing by pluggin are oversized.

              Inverters have a "starts per minute" rating on them. Any more than spec and they start heating up to "death mode". They charge the capacitors, discharge on startup, recharge, discharge, heat up.
              Excuse me, I farted.

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              • #8
                "So since you have to let the single-phase motor wind down nearly to a stop before you can reverse it, it's not instant reverse."

                The original Westinghouse 1/4 hp single phase motor on my SB9 is "instant reverse". You don't have to let it slow down at all. Flip the drum switch to reverse with the motor at speed and the motor halts within one second and reverses, either direction.
                Free software for calculating bolt circles and similar: Click Here

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                • #9
                  ... Which is why I had the foresight to specify motors with centrifugal switches on their start windings. Permanent-split capacitor motors, induction-repulsion motors, and doubtless a few weirdos I have yet to run into, have no centrifugal switches, ergo do not rely on the state of the centrifugal switch to generate reverse torque.

                  But then, I wasn't entirely sure that these insights into the peculiarities of a tiny percentage of the motors in use today really clarified the answer to the question.

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                  • #10
                    ...Do'h, shaded-pole motors, too. No start windings, no centrifugal switches.

                    [This message has been edited by sauer38h (edited 12-18-2005).]

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                    • #11
                      It really isn't that big a deal. I use "instant" reverse or "plug reversing" all the time when I'm tapping in my Bridgeport. The spindle is rotating in back gear at a relatively slow speed, but yes, that motor really is whizzing when it reverses. If some of the older heads comment about this being a "bad" practice, I may reconsider my tapping technique - but I've been doing it this way for years (although I really don't tap all that many holes, probably less than 50 per year).

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                      • #12
                        Jim I got a milwaukee drill that has been doing that for 25 plus years..
                        Excuse me, I farted.

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                        • #13
                          "I've never seen an ac motor that would come up to speed as quickly as a pm dc motor, let alone stop and reverse in an 'instant'."

                          I have a tapping machine made in Japan by Brother Company.

                          It has two spindle speeds, 1000 & 2000 rpm. In either speed the motor reversal to back the tap out is as close to instantaneous as any I've seen. When I first got the machine I thought the reversal of the tap was by some kind of clutch and gearing mechanism inside the head because it was so fast. Nope, they did it the simple way, by reversing the three phase motor.

                          Rockwell/Delta used to make a drill press designed for tapping, it used a special low inertia motor, long skinny type of motor, to allow "instant" reversal.

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                          • #14
                            "If so, where the hell do you go to get out of harms way when the chuck comes flying off?"

                            That could be why very few "serious" lathes use thread on chucks anymore.

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                            • #15
                              perfectly safe with a 3phase motor.

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