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  • chuck turning reistance

    Hello,

    Can anyone tell me how hard it should be to rotate an eight inch chuck by hand? Or, when disconnected from the belt drive, should it spin relatively easily, or stop immediately? I'm trying to figure out if there's an extra strain on the motor causing it to bog down. BTW, the motor's at the shop right now being tested electronically for bad windings. Thanks in advance.

  • #2
    The rule of thumb , used for years, is that you should be able to spin the chuck by hand by gripping it and rapidly whipping it downward ( called "rapping the chuck" ) and have it spin one full turn. This tells you the bearings are set properly. It also requires that no gears, or drive belts be engaged, and that the spindle is in a free mode. Obviously, with larger chucks it is harder to spin them and 8 to 10 inches is getting there.
    Once you have the motor installed, run it with out a load ( no cutting) and in the mid-range of speeds. Then feel the spindle bearings. If they luke warm after 5 minutes of running, you are OK. If they are hot, then you are too tight, OR have to much grease in them (roller/ball)

    Rich

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    • #3
      Thanks Rich. I gave it a spin and got almost 3/4 of a turn. What do you mean by "too tight?" The lathe is a 1984 Tida 1336 (WTTool/Chinese) that I bought a couple months ago. It sat for a year or so before I got it. I had to replace the start capacitors to get it running, but it worked fine after that for a month or so. The motor recently began to shut down under the slightest load. It will come back on if I cycle the forward/reverse lever, but cuts out again too easily. Should I be thinking about re-lubing or replacing the bearings?

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      • #4
        3/4 of a turn for a large chuck seems ok to me it wont revolve and revolve for a while it's too heavy for that .Others with more knowledge, will tell you better than me but I reckon it's about right. Alistair
        Please excuse my typing as I have a form of parkinsons disease

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        • #5
          Good to know, thank you. That means I'm probably in the market for a new motor.

          Comment


          • #6
            When you say you cycle the forward reverse lever to get it going again it makes me wonder if maybe you have an electrical supply problem.
            Is there some way you can check the voltage at the motor when it is running. That should tell you if there is an electrical problem upstream from the motor.
            Larry - west coast of Canada

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            • #7
              That's a good idea! I did check the current before I took the motor to the shop. Amperage was 13.2 without the belt on the pulley. I think the data plate says 22 full load amps. I don't remember enough about circuits to know if the 13.2 was a reasonable reading. Hopefully I'll get the motor back tomorrow with a good report, then I can start looking at other causes. Has anyone had luck finding a replacement motor for this size lathe (13x36?) The original one is 1.5 hp, but has 600 mfd worth of start capacitors. I don't know if this is relevant, but I tried a harbor freight 2 hp motor on the lathe and it worked for a while. Soon, though, it started cutting out like the original motor. I assumed the new motor wasn't set up for the heavy starting load.

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              • #8
                I've put my original motor back on the lathe. The motor technician said everything seems okay. If the pulley/belt arrangement is set to the lowest speed, it will keep running indefinitely. If I set it to a higher speed, the overload switch in the junction box trips after about ten seconds. Also, I don't think the motor is getting up to full speed, and the cord from the wall is getting warm. The overload switch is adjustable between 12 and 18 amps (I think, because of the markings,) maybe so the system can be either 110 or 220 volts. Would it help to change it to 220, so less amperage is going through the system? The overload switch might be going bad because of its age, but I don't think that explains the motor not getting up to speed. Any EE's out there?

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                • #9
                  If the cord is getting warm, you are drawing too much current. It's possible your machine was originally set up for 220V, if it has a dual voltage motor or the motor has been changed, this could be the cause of your problem. A 110V motor will draw twice the current of a 220V motor of the same HP. The overload trip has to be set accordingly. If the overload is tripping, check that the trip setting agrees with the motor full load current rating. Also check that the current is actually going to the motor and not shorting out. In an ideal world, a machine designed for dual voltage would be fitted with suitable guage wiring for safe operation with either voltage but that does not always happen. Check also for loose or corroded connections, signs of overheating of switches and contactors.
                  Dave

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                  • #10
                    Originally posted by ewood View Post
                    That's a good idea! I did check the current before I took the motor to the shop. Amperage was 13.2 without the belt on the pulley. I think the data plate says 22 full load amps. I don't remember enough about circuits to know if the 13.2 was a reasonable reading. Hopefully I'll get the motor back tomorrow with a good report, then I can start looking at other causes. Has anyone had luck finding a replacement motor for this size lathe (13x36?) The original one is 1.5 hp, but has 600 mfd worth of start capacitors. I don't know if this is relevant, but I tried a harbor freight 2 hp motor on the lathe and it worked for a while. Soon, though, it started cutting out like the original motor. I assumed the new motor wasn't set up for the heavy starting load.
                    13.2 amps at "idle" is not unreasonable reasonable for a 22AMP full load. I'd normally expect about 40-50%, but this is a Chinese motor so except some variability. If it's not getting to full speed then it will draw excessive current and trip the limit. Also.. don't assume the limiter is completely accurate.

                    "Warm cord" means voltage drop before it even gets to the motor. Put on a decent power cord - 12awg minimum. I'd convert it over to 240v, wind the limiter back to about 12 amps +/- and be done with it; obviously you aren't having a lot of luck with 120v. Actually, I'd probably dump the single phase and fit a 3 phase with vfd, but that's another thread
                    Last edited by lakeside53; 11-26-2013, 08:01 PM.

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                    • #11
                      If I were to check out your setup the first step is to start the lathe and listen for the start switch to cut out. Having to replace st. caps seems to say faulty starting sequence.
                      If the startup is draggy I would make sure the motor is set for the voltage to which it is connected.
                      If after a short run it dogged down or cut out, turn the chuck by hand first forward then reverse to track down any tight spots.
                      It is a puzzle since your spare motor seemed to act the same as the original.
                      I will be interested in hearing the outcome.
                      Jim

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                      • #12
                        Thanks Dave and Lakeside. I'm pretty sure the motor and voltage are original. The junction panel door has "110 volts" and a lighting bolt painted in red! I turned the dial on the overload breaker up to 18 amps, just to see if it kept it from cutting off, and got some new strange noises (clicking and such.) I turned it off as quickly as I could and am hoping I didn't do any damage. Lakeside, I measured current right at the motor when I got the 13 amps, and today measured voltage and got between 119 and 122 (with no load.) I'm not even sure the start caps are cutting off based on the rpm it seems to get to. I do plan to switch to 240 tomorrow, and hope it rights itself. Hopefully the lower current will do the trick. Next step might be going 3-phase. Is a VFD better than a static phase converter? Could I actually control speed with it? Thanks for the help, this site is a great resource.

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                        • #13
                          This is weird
                          I went over to a friends shop last night and he has the same problem almost on his 13 x 36 Chinese made lathe that is at least 10 years old.
                          he thought the chuck was to tight or something.
                          I rapped the chuck and got 3/4 of a turn, yet when he engages the drive in high the motor kicks out ( apparent overload )
                          The motor also has the cap relay /contacts, kicking in and out so it is really overloaded or there is a motor problem.
                          Didn't have a amp meter to check the amps and don't know if he is on 120 or 240 volts ?

                          When I say tight, I mean the bearings being adjusted too tightly

                          If yours is a greased headstock bearing, be very careful adding grease . More than 1/4 of the cavity filled with grease will cause the bearing to overheat, and actually increase the drag on the spindle . Temperature of a running spindle is most important
                          He has oil on his bearings and the spindle turns as it should , being cold in the shop (40-50 F)

                          Have to go back and help my friend next week ..only with a amp meter, as it looks mike a motor problem at present

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                          • #14
                            The problems you are having point to a problem with the electrical supply. Single phase motors draw a lot of current when starting, if they fail to come up to speed promptly, you could be trying to draw 2 to 4 times the maximum rated current. Something will give, a fuse, circuit breaker or possibly the wiring. A correctly proportioned supply will handle this, VERY BRIEFLY, but constant abuse (overload) will cause damage to the wiring, the connectors, plugs and outlets. Such damage will cause connections to loosen, increasing the electrical resistance, the connections will get HOT and the terminal voltage will drop because the power is being dissipated (as heat) throughout the wiring rather than being delivered to your machine. If your shop supply is taken from the house via a long cable, this cable has to be capable of carrying enough current to start your machine. All this may sound obvious but most of us never give it a thought. Before dismantling your machine, it may be worthwhile to check this.

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                            • #15
                              My 3hp 240v single phase compressor gave many years of reliable service before it started tripping the 16 amp breaker on first startup from cold. It rapidly got worse until it wouldn't start at all. Although the capacitor gave a sensible reading, I replaced it and normal service was restored.
                              Paul Compton
                              www.morini-mania.co.uk
                              http://www.youtube.com/user/EVguru

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