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Bridgeport motor

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  • Bridgeport motor

    I bought a Bridgeport series 1 with the 1 horse 3ph "J" head. After looking at phase converters, the cost & the room they take up I started wondering if there might be a 1 horse 220 single phase motor that will bolt up to it & work??? Any help on the problem would be appreciated.

  • #2
    The bridgeport motor has an oddball mounting flange,not like common motors.
    I just went through the same problem.
    I made an adapter plate from 1/8 plate steel.
    It took some accurate measuring,but not a major project.
    When it was done I had to slide the drive pulley down the shaft 1/8 inch to line up the belt.


    • #3
      Install a VFD.


      • #4
        If you change to 220V you lose your instant reverse capability.

        I use this for tapping all the time and can't imagine being without it.

        I just run an idler motor. (A three phase motor which has an momentary button and a capacitor on the third leg to start it. This then runs on 220 while generating the third leg of three phase.) The "generated" third leg only runs at about 80% power, but never has been a problem.

        I'm sure the VFD solution others will talk about is more versatile and better, but often old 220 motors are easy to find if not free, if cost is an issue.

        PS. You have to use an idler motor larger than the largest one you are running.
        VitŮŽria, Brazil


        • #5
          Originally posted by macona
          Install a VFD.
          That is the best route for sure, and it gives variable speed as well without messing with the belts.


          • #6
            The adapter plate is entirely doable, and while you may not have "instant" reversing with a 1ph. 220 motor you will still have reverse - you just have to let things come to a full stop before starting up in reverse.

            edit: For the cost of a new 1ph motor you might think about just getting a static ph converter, not the best solution, but it'll get you by for a while (several yrs) for much less money and won't take up the space a rotary will, you will lose some hp on the mill motor though.
            Last edited by Scottike; 08-21-2011, 10:20 AM.
            I cut it twice, and it's still too short!


            • #7

              but you loose instant reverse capability with a vfd also it says "You must be able to connect directly to the motor bypassing any existing switches and contactors." there is a little switch on the top of my mill that reverses it & I would loose my E-stop to.


              • #8
                Originally posted by mich_88_13
                " there is a little switch on the top of my mill that reverses it & I would loose my E-stop to.
                This would go into the FWD/REV input on the VFD, and the contactor would be moved to the VFD supply input for E-Stop function.


                • #9
                  So what you are saying is that IF I get a vfd I need to make sure that IT has instant reverse???


                  • #10
                    ANY VFD will give you instant reverse having regard for motor accel and decel times. I tap with mine and I'd almost swear the time from FWD to REV is about 1/10 second running the motor at about 15 Hz (1/4 rated RPM) in low belt direct.

                    My BP clone turret mill coasts to zero from 2750 RPM in about eight seconds. Under VFD brake it takes two. Don't use the E-stop for general motor stop on a FVD because you lose the electronic braking. Just hit the regular motor stop and the electronic brake will stop the motor in its programmed decel time.

                    Anyway, take a little time and study up on VFD's; there's a lot to them. Learn what they can and can't do.

                    A 1 HP VFD is about the size of Machinery's Handbook and has:

                    -variable speed,
                    -programmed accel and decel,
                    -hook up for the mechine's existing control station pushbuttons,
                    -jog and other control options if you monkey a litte with the programming.
                    -quieter and electrically more efficient
                    -adding Fwd/Rev tapping via a foot switch is an easy mod.
                    -develops full rated HP whereas your motor will run about 85% on an RPC.

                    All are all either difficult or impossible to do running from an RPC.

                    VFD's do not lay golden eggs or improve the weather.

                    A VFD's single disadvantage is it will run only one motor at a time.

                    Here's a link to only one of a dozen on-line VFD sellers


                    Scroll down about half way to get to the 1 HP units. These run a 1 HP 230 V 3 phase motor from a 115 volt wall outlet. No de-rating. A 1 HP unit will run a 1 HP motor to full ratings. No re-wiring your shop for 230 V if you don't have it. They also have 230 single phase models.

                    If your budget will stretch to $99 to $140 a VFD might be a good choice for you. Trust me. I have 4 machines equipped with VFD's: my mill, lathe, drill press, and table saw. If you can avoid an RPC by installing a VFD on your three phase equipment you will be glad you did.
                    Last edited by Forrest Addy; 08-21-2011, 11:35 AM.


                    • #11
                      My understanding is that the better VFD's have both a built-in reverse and E-Stop. And they're still under $350, which is cheaper than a rotary phase converter setup. It's also quieter, and delivers more power than a Phase-O-Matic static phase converter.

                      I ran a 1HP 3-phase Bridgeport off of a Phase-O-Matic static for about 2 years before I got a RPC setup. It was like half-power. I couldn't use any decent-sized face mills, bigger drills needed multiple pilot drills, and forget about power tapping.

                      My dad had got a 15HP 3-phase motor to use as an idler, free. The place he worked had 10 and 20 ton rooftop A/C units and the power company offered replacement "energy efficient" motors to them as part of a conservation program. He asked if he could have one of the old motors, they told him to "take 'em all". He didn't, but did take the nearly-new one he had recently replaced. I went to American Rotary Power for the "box only" deal on a RPC drive, and for about the price of one VFD, we got enough power to run all three 3-phase machines at once if we want.

                      The downsides are the noise and that it stays running even when spindles aren't making chips. I'm probably going to move it over to an outside shed, and just have an indicator light to remind me it's on.

                      If you only have the one machine, a VFD is the way to go. If you have multiple 3-phase machines, don't need variable speeds, and can find a decent idler motor for cheap, go RPC. I don't want a VFD on the surface grinder, and worry about affected lifespan of the Taiwanese 5HP motor on the lathe or OE 1961 motor on the BP if I were to use 3 VFD's. What you don't want is single-phase on a machine tool if you can have 3-phase.


                      • #12
                        Since I'm using an RPC for all my machines, I always wondered how people manage belts/pulleys or speed gears on their VFD-driven machines. Do you still switch the speeds using the belts/gears and allow the VFD to regulate speed within each range?
                        Last edited by MichaelP; 08-21-2011, 11:34 AM.
                        WI/IL border, USA


                        • #13
                          On my step belt, 99.9% of the I just leave the belt in the second to top position, and vary with the VFD. If I need torque at low speed, I use the back gear.

                          I put a 2hp motor on my step head - helps with low speed power. I turned down the shaft from a Varispeed head, and had the motor dynamically balanced. Lots of messed up varispeed motors out there -the shafts get worn beyond repair.

                          I've found on numerous BP's, particularly on the 2hp motors that you really need a VFD with more than the motor rated power. The 2 hp motor on later models was rerated to 3hp for max 30 minutes. On acceleration the 2hp motor easily exceeds the current of a 2hp vfd, and does so for more than the allowed overload period. Yes, you can use a 2hp vfd on the 2hp motor (and I currently do), but if you want rapid acceleration / deceleration, it's a delicate balance of parameters to stop vfd trips.


                          • #14
                            I wonder about that too.

                            Do you set the gearing of a lathe to maximum speed and run the motor very slow, or set the gearing at low and overspeed the motor? What about the torque curves? I know that with a fixed rpm motor I always have the same Kw rating available, and depend upon gearing to make the best use if it. How does this change with an VFD?

                            It seems to me that both situations are something the motors weren't designed to do, hence my fears of affecting the life of the motors.


                            • #15
                              listen to Forrest ! I read his posts a few years back, and now have 3 vfd machines ; drill press,lathe,and mill. super neat way to control the machines !!