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Bridgeport fuse problem

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  • Bridgeport fuse problem

    My Bridgeport Series I CNC mill has a problem that keeps recurring. This must be a common problem because I was warned about this very same fuse holder by a Bridgeport technician who had never seen my mill, and when I openned my electronics cabinet I found that someone had drawn an arrow to this fuse holder and marked it "Z-FU14." Sure enough my Z-axis will stop working and I'll find that the solder has melted out of the 10 amp fuse. Often the solder glob will make removing the fuse a problem. I'm getting tired of this, and I'm wondering why only the Z-axis fuse holder? The Z-axis doesn't even get the workout that the other axis's do. Should I be looking for a problem in the spindle?

    The bank of fuse holders is made by Weidmuller and is called "Saks 6" and it is mounted on a rail called "TS32"

    Boy, they want $21 just for a spare screw-in fuse cap. Anyway, I've cleaned it up and I'll try to find a high-temperature 10amp fuse but I don't know why this is a problem fuse holder. I'd like to replace it with a breaker.

  • #2
    Clean teh fuseholder and make sure it has good tension to keep down contact resistance.

    Contact resistance is a fuse killer, because it heats the fuse directly.

    Fuses are thermal devices, and the current rating takes a nosedive if the fuse gets very hot. If it gets hot due to contact resistance, it really blows fast.

    Keep eye on ball.
    Hashim Khan


    • #3
      $21 they would take a flying leap.Got to be a cheaper cartridge fuse out there some place.
      I don't like breakers for motor protection,how about a resetable heater like on a motor starter?

      I just need one more tool,just one!


      • #4
        I've researched the fuse that the designer specified and I found it was a FNM 10 amp 250v fuse. Maybe this fuse is delayed reaction fuse. It is special because it is designed to allow surge currents to exceed the rating. This fuse is a 1.25"x .25" fuse. I'm having trouble finding a source. Is there an equivalent fuse? Should I replace this fuse with a slow-blow of a higher rating? I have no indication of any problems in my machine. The Z-stepper is not heating up at all. the oiling system is working perfectly. No noise or any vibration is evident.


        • #5
          Mr. Jorgensen-

          FNM is a Bussman fuse designation. The dimensions are shown in the catalog as 13/32" x 1-1/2" and it is a time delay fuse. By design a time delay fuse will allow the current to exceed the rating by a fixed amount based on time, the greater the overcurrent the less the time. There's nothing particularly unusual about this fuse and it's availabilty should be pretty good. The Bussman FNM crosses over to a Ferraz-Shawmut TRM or a Littelfuse FLM. Hope this helps.

          Take care

          [This message has been edited by bernie l (edited 06-22-2005).]

          [This message has been edited by bernie l (edited 06-22-2005).]


          • #6
            Mr. Jorgensen-
            After responding this morning I looked and I've got some FNM10 fuses, if you want to contact me in private and give me your address I'll send you a couple. I suspect the problem isn't really the fuse though. More likely the fuse holder, or an actually overcurrent situation exist. Would it be possible to get an amp meter on that lead to monitor current. Alternatly sometime after you've been running the machine for awhile, stop it, power down and touch the fuse holder to see if it seems unordinately hot. With regards to using a circuit breaker for the motor, it's actually done quite a bit, you'd want to find a breaker with a trip curve that approximates the fuse, you probably wouldn't have much luck finding one for $21 though.

            take care


            • #7
              Thanks Bernie,

              I'll try to find a local source for those first. I'm not sure that a 13/32" fuse would fit this holder so I'm a little confused by that. I'm sure that this is a common problem with that particular fuseholder. I'm pretty motivated to put three amp meters on my mill.

              Thanks again,



              • #8
                I couldn't find fuse holders I wanted when I redid mine. I mounted a small 220 panel on the outside of the machine and fed the inverter, xfrmer and other items directly off the breakers.

                The panel, breakers were 1/3rd the cost of the fuseholders. Not to mention the fuses.

                Do you have 3phase hooked to the machine? How? Didn't you move it home?



                • #9
                  No Dave,

                  I was pretty distressed when my freind closed his shop and I needed to move my mill, because I live in an apartment and I don't have much space. However I fell into such an excellent group of people as you would ever hope to meet (of course just like all those gentlemen here included!) My friend's shop has 3 phase and we have three milling machines. One machine is being converted to CNC and will use BobCam. These guys are mostly involved in antique motorcycles and high performance antique cars. Some new stuff too. A 2003 Mini Cooper project is underway, and one of the men showed off a five speed 2006 Mustang that everyone was pretty impressed with.

                  These guys all outclass me by a longshot, but I'll do my best to pull my weight.

                  What do you think about adding three amp meters for the steppers? I don't know why the Z axis would load over 10 amps when the X and Y axis are doing a lot more action and they never blow. It deserves some looking into, but since I know others have faced this issue I was hoping to gain from their experience. I'd better talk to George T. Wroclawski. This guy has a lot of background on these machines as a service technician. He first mentioned it and it has proved exactly true.


                  • #10
                    I may have 3 amp meters.. I'll have to look.

                    Usually a ampmeter is only a 0/50 mv movement and you use a shunt to get the proper current/mv ratio. OR, you have a 5 amp current transformer (Doughnut) to run the ac power through and it reads it direct to the meter.

                    For a 50 amp doughnut? running a 25 amp device? You run two coils through it. For a 50 amp with a 10 amp load? run 5 wraps.. it is just a transformer and you can alter the ratio by altering the turns input.

                    I am off for the next 3 days, got my daughter thou.. I'll try and look around.


                    • #11
                      I've been thinking that I would like three bar-graph LED amp-meter indicators for my X, Y, Z axis. and maybe one that could indicate any load on the spindle motor. That one might need to be calibrated sensitively in order to indicate dull blades or loading of aluminum. That would be pretty cool.

                      Would you have any idea how to construct something like this? I would want a 15 amp DC range.

                      Thanks Dave,