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Mill motor problems--again!

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  • Mill motor problems--again!

    I posted on loosenut's thread a couple weeks back w/ a picture of how I mounted a c-face motor on my rf45 clone mill. It worked great at first! The motor was nice and smooth, good power--all that.

    I've been working on a couple of little projects here in the shop. I noticed that the mill head was "chattering" when I started it up. So, I'd shut 'er down quick and shift gears and most times it would go away right away. At first I thought maybe I had it between gears or something and that I was getting some gear grinding. I'd shift and it would seem to go away. . . . It seemed consistent.

    I thought I might have to tear the mill head apart and look for something that was getting stuck in the gears. So, I googled "rf45 good bad" and a bunch of other similar stuff "rf45 teardown", etc. I found a thread on Chaski back 2009 wear a guy tore his rf45 clone apart because "it sounded like a cement mixer". He went through the effort of replacing gears, seals, bearings, redoing keyways, etc. Basically it scared the hell out of me. The guy was just about to get it all back together after 9 months of posting and then he never followed up!

    So, I was out in the shop yesterday working on another small project. The mill worked fine for several hours. Then it started making the noise again. I decided that it really didn't sound like a grinding noise. It seemed to be more of a harmonic thing. I was thinking loose keyways, bad bearings, etc. after reading that post on Chaskis. Anyway, I tried shifting to make it go away, but no joy. Finally it popped the breaker.

    I pulled the motor off the mill and tested it without it being connected to the mill. It turned freely, so no bearing problems, but it wouldn't run smoothly. It blew the breaker again without being hooked up to the mill head. I pulled the capacitors off, and "tested" them. They both seemed OK from what I've read on the internet on testing capacitors. The start capacitor was warm, not hot. The run capacitor seemed more like room temperature.

    If you've gotten this far--I know that was pretty long--what now? Just replace the capacitors anyway? Any other ideas? I'm not sure what to do. I don't have a motor shop to take it to. The place I took the old motor would charge basically replacement cost to fix the old motor, so I'm not too eager to go back there.

    thanks,

    Jim

  • #2
    What kind of motor did you use as a replacement - Baldor, US Motor, Chicom

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    • #3
      I bought an Emerson off Ebay for cheap. It was made in Mexico.

      http://www.ebay.com/itm/400253012446...84.m1439.l2649

      Jim

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      • #4
        Maybe some part of the centrifugal mechanism is hung up.Need to take the motor apart to look.

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        • #5
          I pulled the motor apart to check out the centrifugal switch. The contacts were stuck together. I pushed them apart with a screwdriver, and then reassembled everything. It starts and runs fine now. . . . I guess the sound I heard was the motor running on the start capacitor.

          Is there anything I can do to prevent this from happening again? The motor is like new. It has probably 10 hours of run time at the most right now. Should I just clean the contacts with brake cleaner? Thoughts?

          thanks,

          Jim

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          • #6
            Is it a horiz. motor mounted vert. maybe the centrifugal switch doesn't have enough oompf to open correctly and the points just arc together. Just my WAG.

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            • #7
              If you think it's the motor and it's 'internals' , burnish the contacts on the centrifugal switch and see if that doesn't clean things up. . . Otherwise. . . Hummm.

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              • #8
                That's what I suspected- the start switch. Check to make sure all the springs are there if it has springs. The open and close action should be crisp. I'd sand the contacts using something like 400 grit, and I'd run the sandpaper across some copper pipe, back and forth a few times to break off any loose grit and even out what's left before using it on the contacts. Then I'd burnish the contacts, using if possible another scrap contact that has been sanded and cleaned. The whole idea is to get all the carbon and crap off, then flatten out the hills and valleys left from the sanding process, without leaving a foreign material behind. You could use a point file if you can find one instead of the sandpaper. With luck there will be enough silver alloy on the contacts that you won't go through it to the base metal, which isn't going to be as good of a contact material. Sometimes the contacts have only a plating of contact metal.

                Is there crud building up inside the motor that could be affecting things? If so, you might try to arrange a shield to minimize this.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  No, there's nothing at all inside the motor. It's totally enclosed and brand new--and it looks like it too!

                  I don't know how this motor is supposed to be mounted, but I don't know as I'd want to mount it horizontally as it is a c-face motor w/o any other way of mounting. It sure seems like the vertical orientation would be proper.

                  I've got some 600 grit here. I'll take it easy and clean up the points good when I'm done. Hopefully that will take care of it.

                  Jim

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                  • #10
                    Originally posted by Jim2
                    I pulled the motor apart to check out the centrifugal switch. The contacts were stuck together. I pushed them apart with a screwdriver, and then reassembled everything. It starts and runs fine now. . . . I guess the sound I heard was the motor running on the start capacitor.

                    Is there anything I can do to prevent this from happening again? The motor is like new. It has probably 10 hours of run time at the most right now. Should I just clean the contacts with brake cleaner? Thoughts?

                    thanks,

                    Jim
                    You are probably right about the sound you heard, ie the centrifugal switch is not operating reliably, making funny things happen inside the motor. In my experience if its happened once it will keep happening.

                    Assuming the switch is of the thin spring steel variety it is possible to adjust (bend) it a little. If you can mount the rotor and switch assembly in your lathe you will be able to spin it up and down to check the switch operation.

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                    • #11
                      Replacement starting switches are available from companies that specialize in electric motor parts. It is also possible to replace the switch with a current or potential relay but it would take a little work to properly select and connect one. It is generally possible to clean and adjust the old switch.
                      Don Young

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                      • #12
                        If the switch was just "dirty", clean it. If it was arcing and was pitted, you might want to go to the effort of finding a replacement. In either case, in addition to refinishing the contacts, do what you need to to make sure it operates freely.
                        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                        • #13
                          Did the start cap have a bleeder resistor soldered on across the terminals?If it didn't you might want to add one,they help save contacts.

                          1/4 watt 25,000 ohm is the size I use most often.
                          I just need one more tool,just one!

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                          • #14
                            Grainger sells bleeder resistors.P/N 12N986 $3.60 ea.They are 15,000 ohm 2 watt.

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                            • #15
                              I had a Dayton fan motor that wouldn't start right. The plate that held the starter contacts had actually slipped forward on the shaft where they would never open. It was not hard to move and lock in to place.


                              be

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