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Need Some Advice on Making a New Solenoid for Bridgeport

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  • Need Some Advice on Making a New Solenoid for Bridgeport

    2 of the solenoids controlling the brake and speed on my BP CNC mill have gone open.
    I need to make a new bobbin and wind new ones if possible. The mechanical valves are good and are built on a heavy manifold.

    You can see the 2 solenoids I removed here, and the bottom one is the last good one, which I assume will be dying shortly....



    The windings are sealed in a molded plastic case:


    Smashing one open yields:


    The wire measures .007" dia after I burnt off the insulation, and about .0078" with the enamel.
    Resistance of the good one measures 69.5 ohms, which at 24 vdc yields about 345 mA of current which seems high for #33 wire, and has me wondering if that has something to do with 2 of these opening up. Maybe my flyback diode should be at the solenoids, and not at the power supply.

    Anyway, I ordered a roll of #33 wire and I would like to attempt to machine a bobbin and wind it.

    Here is a drawing I did showing what size I need the bobbin to be.


    So the question becomes, what type of plastic would be good to use for this bobbin? The thin .04" walls make me nervous in plastic. I have a piece of UHMW round on the shelf that would be perfect, but I know that UHMW is not the best turning material.

    How about ABS? Garolite?
    Last edited by polaraligned; 02-22-2021, 09:07 AM.

  • #2
    Garolite (G-10) should be excellent. The last shop I worked in did a lot of work for one of the major Garolite suppliers, it is very commonly used for electrical work and very tough stuff to boot.

    Comment


    • #3
      If these are air solenoid valves, they are available real cheap on ebay. If not, have you investigated the availability of a replacement coil for yours? A lot of those solenoids were real common items and replacement coils are available in various voltages. Versa is a common brand, complete valves or coils are not that hard to find. Attempting to wind a new coil would be a last resort. A failed attempt could take out the driving circuitry in the control.

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      • #4
        I make a point of never using AC solenoids, If they reach a point where the armature does not fully seat etc, they overheat and usually end up burning out.
        If converting from AC to DC, all you need to add is a small bridge rectifier.
        Never had a burn out on a DC version yet.
        If those are already DC, check the voltage, as that is about the only thing that does them in.
        Max.

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        • #5
          Originally posted by eKretz View Post
          Garolite (G-10) should be excellent. The last shop I worked in did a lot of work for one of the major Garolite suppliers, it is very commonly used for electrical work and very tough stuff to boot.
          Thank you. I have worked with Garolite before (milling only) and it does work decent.



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          • #6
            Originally posted by Sparky_NY View Post
            If these are air solenoid valves, they are available real cheap on ebay. If not, have you investigated the availability of a replacement coil for yours? A lot of those solenoids were real common items and replacement coils are available in various voltages. Versa is a common brand, complete valves or coils are not that hard to find. Attempting to wind a new coil would be a last resort. A failed attempt could take out the driving circuitry in the control.
            Sparky, I looked up the Versa part number and came up with nothing. Best I can tell the part is: versa ksg 4232 6k3tc
            I don't really know if I can just purchase a compatible coil only that would properly fit these valves. I would love to get new replacement complete valves as these are 40 years old and the seals inside must be near the end. I find a lot of similar valves but they are 120v, and I need 24v. I just know nothing about air valves and am at a loss.

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            • #7
              It is either a 3 way or 4 way valve.
              Why not replace the whole valve with something more common and readily available ?
              Winding a new coil for something that is so easy to replace with new makes no sense.
              But maybe the voices in your head are telling you to do it.

              -D
              DZER

              Comment


              • #8
                Originally posted by MaxHeadRoom View Post
                I make a point of never using AC solenoids, If they reach a point where the armature does not fully seat etc, they overheat and usually end up burning out.
                If converting from AC to DC, all you need to add is a small bridge rectifier.
                Never had a burn out on a DC version yet.
                If those are already DC, check the voltage, as that is about the only thing that does them in.
                Max.
                These are marked 24v, and I am using them with a commercial quality Meanwell 24vdc supply. The voltage is right on. I do find it odd that 2 of these are open, but I am at a loss to explain why. The current thru them is about 345 ma as stated earlier, which seems high for 33 AWG wire. All the mechanicals do work, the brake goes on when operated and the air motor spins forward and reverse when those were all operating. Thing is that these are never on for more than a short period of time, the ones that operate the air motor especially.

                Comment


                • #9
                  Originally posted by Doozer View Post
                  It is either a 3 way or 4 way valve.
                  Why not replace the whole valve with something more common and readily available ?
                  Winding a new coil for something that is so easy to replace with new makes no sense.
                  But maybe the voices in your head are telling you to do it.

                  -D
                  I would love to. Do these valves come in standard hole patterns? They fit on a manifold that the hoses go into so the holes would obviously line up. Or am I speaking out of my ass? As I stated, I know nothing about air solenoids. Can you offer advise in this regard?

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                  • #10
                    Maybe like D03 mount hydraulic valves ? ? ?

                    -D
                    Last edited by Doozer; 02-22-2021, 11:41 AM.
                    DZER

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                    • #11


                      Versa Valves KXX-4333-3TC-243-24VDC double solenoid 4-way 25-175 psi, 7W | eBay
                      DZER

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                      • #12
                        I may have thrown some of those valves away. I have a bridgeport boss3 cnc but the control is retrofitted to linuxcnc. I tossed the air motor speed control and use a VFD for that. The brake I changed back to a lever like the manual bridgeports have, got rid of the air cylinder. If you are still using the air motor, I assume you are also using the original Bridgeport control.

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                        • #13
                          Thanks Doozer. You are the best. I put an offer in on that solenoid and if the whole mechanical assembly doesn't work, hopefully the coils will.

                          Sparky, I am not using the original controls. I have a Centroid on it. While the Centroid will operate the motor speed and the brake solenoids, I don't have them hooked up, so I just use them via switches. I wouldn't mind getting a speed sensor on this so I can have CNC control over the speed for tapping, etc. It is just very hard to add a sensor to these Bridgeports.

                          I am either running full speed, 4200 RPM, in aluminum pretty much regardless of the cutter, or I am down to half that when in steel. I assume you are using the back gear when you need to slow down a lot? The torque drops way too far off to use a VFD alone.

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                          • #14
                            Originally posted by polaraligned View Post
                            Thanks Doozer. You are the best. I put an offer in on that solenoid and if the whole mechanical assembly doesn't work, hopefully the coils will.

                            Sparky, I am not using the original controls. I have a Centroid on it. While the Centroid will operate the motor speed and the brake solenoids, I don't have them hooked up, so I just use them via switches. I wouldn't mind getting a speed sensor on this so I can have CNC control over the speed for tapping, etc. It is just very hard to add a sensor to these Bridgeports.

                            I am either running full speed, 4200 RPM, in aluminum pretty much regardless of the cutter, or I am down to half that when in steel. I assume you are using the back gear when you need to slow down a lot? The torque drops way too far off to use a VFD alone.
                            Although the torque does reduce in theory with slow speeds I have not had any issues there. My original config was to leave the varispeed head set for approx 3600 rpm and vary the speed from there with the VFD. More recently, I ditched the varispeed pulleys and went with a fixed polyvee belt drive. I had the motor armature dynamically balanced locally. Now I can run at 6500rpm effortlessly which is great with aluminum and small carbide endmills. It is also very much quieter and smoother. I use the backgear for speeds below 1000 rpm. I have a encoder on the top of the head which is accurate for high range and just apply the mathematical gear ratio in software for low range. I do not use the encoder for rigid tapping or positioning, only for spindle speed feedback which gives me extremely accurate spindle speeds because my spindle is closed loop with PID control. The PID control also helps with any torque loss at lower speeds, it just pumps up the drive to the motor to maintain speed. I did mount a small muffin fan on the motor for better cooling at low speeds, it has never ran what even remotely would called hot.

                            I put a onscreen bargraph spindle load meter which also displays numeric values for spindle motor current. The VFD operates with a modbus interface and motor current is one of the available outputs from the VFD. I don't think I have ever had the motor reach anywhere near full current, the rigidity of the bridgeport is usually the limiting factor.

                            I have had a lot of fun retrofitting the old bridgeport cnc and its a real decent machine now. The most recent project was a 24K rpm auxiliary spindle which I am extremely pleased with. Running those 1/16 and under endmills is so much nicer now. 3D toolpaths with a 1/16 endmill at 30-40 ipm is a whole new experience.
                            Last edited by Sparky_NY; 02-23-2021, 06:14 AM.

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                            • #15
                              Sounds like a nice machine Sparky. I have seen a few machines that eliminated the varidrive- it seems like a good idea. Good thing nowadays is that you don't need to use slow RPM's. With modern coated carbide cutters you can happily cut with a surface speed of 450 SFM. I might do that once all my stock of HSS cutters is used up.... Heck, thinking about it, maybe getting rid of the back gear is ok too, unless you are tapping. You have a spindle encoder, is there a reason why you can't or don't do rigid tapping?

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