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Rpc or vfd on a mill?

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  • Rpc or vfd on a mill?

    I can't rebuild the single phase on the Bridgeport, too much weather got into it. So I am making an adaptor plate for a 1 1/2 three phase motor.
    My question: Is a vfd a nessecity or a luxury?
    I already have a rpc that will work. What milling applications would be better with a vfd?

  • #2
    IF you already have an RPC, I'd run that. I went with an RPC over a VFD because I am running two pieces of equipment off of it, it was easier to wire, cheaper (because of the two pieces of equipment), and I don't regret it a bit. My mill has a two speed motor so I have high and low there plus high and low range on the head. Takes me all of 20 sec to switch. I don't think I've even messed with changing pulleys yet.


    • #3
      Originally posted by 1-800miner
      What milling applications would be better with a vfd?
      As long as you can change speeds on your Bridgeport, you don't need VFD. Just use the RPC you already have.


      • #4
        A VFD isn't quite a necessity but it's definitely not a luxury.

        You can fine tune the spindle RPM to get the best usage from the milling cutter, slow it a trifle as it wears, etc to maximize the life and stock removal for the tool.

        A deft hand on the speed control cycling it rapidly up and down over a 20% range makes milling into inside corners squawk free.

        A three phase motor on a VFD develops full rated HP. On an RPC about 80% (weak leg) and is not a serious loss. On a static phase converter the motor devewlops about 40% of name plate ratings is the best I could determine via informal tests.

        Being able to dial the RPM down to zero when tapping out of a drill chuck makes depth control and reversal very much simplified. Add a little logic and a foot switch and you can switch from mill to tap mode at will.

        Light duty milling where little power is demanded from the motor means you can forget about belt changing. When you need more motor power you can set the belt and back gear in the range you want and dial in the speed with the VFD going at the most productive cutter speed.

        A VFD gives you a painless way to increase the top spindle RPM should you need to for very small scale milling and drilling.

        A VFD is quiet and efficient, compact, and if you don't mind disconnecting one motor plug and connecting another you can run more than one machine with it but one at a time.

        I have several VFD's: for the drill press, the turret mill, a grinder, table saw, and the lathe. I wouldn't have an RPC in the shop unless I had a multi-motor machine tool that was a PITA to alter.

        VFD's are not for people with little imagination to see their advantages. VFD's require some study before connection to the machine. A new control panel may be a good idea depending on the machine to be connected and what functions you wish to employ.

        There is no doubt that an RPC may be simpler to implement and requires fewer mods to the machine electrical system. VFD's bring in complexities of their own that should be studied and considered before selecting an upgrade path.

        It would pay for one unfamiliar with VFD's to run a machine equipped with one, study the literature, learn the common lies and exaggerations surrounding three phase motors and how best to power them from single phase, and study VFD's as a path to greater home shop versatility and enjoyment.
        Last edited by Forrest Addy; 06-06-2011, 05:52 AM.


        • #5
          I bought my 15" YMZ late with it's built-in two speed motor, complex set of 5 contactors, ganged switches, etc. non-functional; using a VFD properly wired and programmed I was able to replace all the dubious electrical gear with a VFD.

          Much simpler, and overall, cheaper I believe.

          - Bart
          Bart Smaalders


          • #6
            From what I've heard the static phase converters work quite well on bridgeports, you might consider that.

            I put a VFD on my variable speed bridgeport for flexibility and I have to admit that I've never used the speed adjust. I did program a decelleration cycle to "brake" the motor, but had to back off of that because something rattled and kicked out the VFD when I did that. I hope its not my milling head going south, but it keeps on working.

            I just bought a hardinge lathe and I am building a rotary phase converter (RPC) for that since the spindle and coolant pump are three phase. there are also mechanical levers with linkage rods going to the reverse and High/low speed selector levers. I suppose if I ever get sick of hearing the RPC running or something expensive breaks on the controls side of things that a VFD will find its way into the control cabinet and a whole mess of contactors and crap will fly out the door. There is also a motorized speed change control that may or may not be three phase (I'd have to check the schematic). I just mentioned this as an example of where a RPC might make sense.



            • #7
              Miner, I built a RPC for my lathe a Clausing 6900 a few years ago, and I do not regret that decision. I now have three 3ط machines that can be run off the RPC. Since you have the RPC, it is s simple matter to wire the new mill to it, I have a 3ط breaker in my RPC's control panel that protects the outlet that my lathe plugs into right now and use that outlet and an extension cord to power both mills right now.
              Eventually when I have the machine room constructed I will have a 3ط panel that all my machines will be wired to.
              If in the future you want to add a VFD to the mill, you still can.


              • #8

                I just joined the VFD club a couple weeks ago after picking-up a Brown & Sharpe surface grinder and couldn't be happier. Got the VFD from "Automation Direct" on a recommendation from a trusted friend... After 20 minutes of reviewing the manual, it was configured and running in 10 minutes. Having the ability to tweak the RPMs downward is very helpful to find the sweet-spot for a particular wheel. Certainly the same would apply for a mill or lathe. I have a PM 45 mill and would convert it to 3 phase in a heartbeat... and when a lathe upgrade comes along, my preference will be a 3 phase which will be driven with a VFD.

                A feature of VFD's that I feel is worthwhile, is to utilize the ramp-up and ramp-down modes. You can specify the number of seconds to reach full speed or come to a stop. Can't help but to think that will save your equipment's gears and bearings from getting pounded on.

                If you're low on funds, you could always wire the output side to an appropriate female socket and move it among your equipment as needed.

                I thought about going with a RPC but, in my (ageing eyes) view of the world they're just another very heavy piece of machinery that needs servicing. -Heck with that... if/when my 2.5 pound, $170 VFD dies, out in the trash it goes.


                • #9
                  if yuor willing to learn a VFD,s functions,go for it. a buddy was considering a VFD for a lathe but after finding out there was a considerable amount of "new" stuff to learn and that he would have to by-pass the lathes original controls, he decided on an RPC. the lathe works as designed and hes happy so all is good.