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Little VFD help please

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  • Little VFD help please

    Hey folks. I attended my very first auction the other day and was able to pick up an old power hacksaw. Haven't even been able to scrape off enough grime to find a name. But it was in regular use right up until I moved it. The motor is a GE 3 phase - and I ordered a VFD appropriate for the specs, and I have an experienced friend willing to help with the install.

    I have read several threads that mention never running a drum switch with these VFDs. I am wondering whether the switch in the pic below should be eliminated. It's unfamiliar to me (and doesn't look like the drum switches I've seen) - and I'm not sure if it would cause problems. It was installed between power source and the motor.

    Thanks for any help and advice!

  • #2
    Yes the switch needs to be eliminated, the motor leads will be wired directly to the VFD, the VFD will start/stop the motor, no need for the switch, however you might wont to incorporate an emergency stop switch.....


    • #3
      WOW!! THAT's mixing the new with the old. Great old saw. Yes, eliminate the switch from the electrical circuit. Tha old swiths is called a knife switch. It's kinda cool. I suggest you retain it somehow as an ornament long with a few other electrical antiques as you find them.

      Ever see the original "Frankenstein"? Boris Karloff? The lab scene set has racks of switchboards the same vintage decorated with Jacob's ladders and flashing lights. Keep you old switch on the saw. Call it your "Frankensaw" Ostentatiousl flip the old switch and loudly gloat: "It's alive" if visitors are present when you start it Stained lab coat optional. Hell, it's a machine shop. Have a little fun.


      • #4
        . Thanks so much guys.

        The switch on there reminds me of the circuit breakers is find in old NYC basements. Terrifying really - knowing that the city of New York is run by gear that Frankenstein would be proud of!

        Metalmole: where would you install the safety kill switch in the chain?

        Appreciate the advice.



        • #5
          Real nice saw!! Is that the original colour? Looks to be in nice condition.

          Curious what the name is on it????


          • #6
            Nice find

            You could re-purpose the knife switch to be the emergency kill switch in a steam punky kind of way, or use it to control the start stop on the vfd. Many of the control functions operate at low voltage. Check your docs from the VFD.

            If you really want to step back you are all ready for the line shaft to spin that puppy up.... maybe that's carrying nostalgia to far, but it is nice to see old equipment brought to life again.

            ARS W9PCS

            Esto Vigilans

            Remember, just because you can doesn't mean you should...
            but you may have to


            • #7
              If you cut power to the VFD it will stop!

              A contactor ("manual" or otherwise) on the power input is fine.

              You CAN put the kill switch on the motor side, so long as you remember to close it before starting the VFD again. VFDs don't like having the motor "dropped on the line", they want to slow-start the motor themselves.
              3751 6193 2700 3517

              Keep eye on ball.
              Hashim Khan

              If you look closely at a digital signal, you find out it is really analog......


              • #8
                What I would do is set up three push buttons, stop - start - and a push lock e_stop.
                Ideally you could have a small relay picked up by the start button and retained by a N.O. contact on the relay in parallel with the start P.B. , the stop button would be N.C. and in series with the start P.B.
                You do not want a situation where the saw starts when you release the E-stop.
                The stop start would go to the low voltage input control and the E-stop would control a 3 phase contactor on the VFD input.
                No overload are needed.
                Last edited by MaxHeadRoom; 10-11-2013, 11:41 AM.


                • #9
                  Thanks for all the tips!

                  I want to keep it stupid simple - since this is the first time dealing with a VFD. I think I will set it up with just the VFD at first, so that I can start using it (keeping a close eye on it always of course), and then move into special switches and relays from there.

                  Doubt this is the original color - it's been reprinted several times, based on the layers on the only writing I can find - the patents on the plate that moves back and forth with the cutter. It lists 4 dates, all from the 1890's.

                  My plan was to clean it up "quick" and reprint it with the same grey/green I have for my south bend. But 2 hours, 1 roll of paper towels and several degreasers later, ive barely scratched the surface grease.

                  Got the wheel looking decent.

                  On a whim, I grabbed a bottle of some BBQ cleaner at Big Lots called "LA's totally awesome grill & oven cleaner." It has worked better than engine degreaser - so I'll keep at it...

                  If I unearth a name, I'll let you know.


                  • #10
                    Is the knife switch simply a manual on/off control or part of an automatic trip operating at the end of the cut?




                    • #11
                      It's just a manual on/off switch. And also apparently powers up weird experiments on monster-like creatures

                      I think there may be some type of mechanical shut-off triggered by the plate that slides along with the blade arm. But I haven't been able to figure that part out yet....

                      Still cleaning!


                      • #12
                        I believe I may have found the manufacturer. Some type Miller Falls saw - but of course this one has been modified a ton.

                        Link below shows another couple versions, and some info.

                        Miller falls saw info


                        • #13
                          I believe I may have found the manufacturer. Some type Miller Falls saw - but of course this one has been modified a ton.

                          Link below shows another couple versions, and some info.

                          Miller falls saw info


                          • #14
                            Originally posted by Barrington View Post
                            Is the knife switch simply a manual on/off control or part of an automatic trip operating at the end of the cut?
                            Barrington brings up a really good point. If you do utilize an automatic cutoff switch for
                            end of cut, you are going to need to hook it up to the disable or stop contacts within
                            the VFD itself. The reason everyone is telling you to get rid of the Frankenstein switch
                            is .. its a big no no to break the circuit between the VFD and the motor. Blows the VFD.

                            John Titor, when are you.


                            • #15
                              Thanks mike. I think I understand the idea of not having the machine operate power instead of the VFD. For this situation - the VFD will be in complete control.

                              The only auto "shut-off" that may (or may not be) working on this machine is a mechanical one - not electrical. There is a plate that may slide back when the cut if finished, causing the engage lever to flip back, which effectively triggers a "clutch" of sorts on the large wheel. When I pull this lever back wile turning the wheel by hand, it stops moving the cutting blade arm.

                              It's definitely not like the modern saw that have a tab that flips the power switch when finished. The motor will still be running, but the blade will stop moving. Does that make sense? Hard to describe without some specific photos.

                              I'm now wondering if the line should have some type of fuse between the wall power and the VFD itself...