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  • Machine Vibration

    I bought a new Jet GH1340W-1 lathe in December and set it up in my attached 3-car garage. When we built the garage, we poured the floor in three equal slabs due to the width of the building. The Jet's headstock base has two sets of two leveling bolts, and when we set it up, due to space constraints and not wanting to have to move a radial arm saw, I had the far left levelers on one slab, while the other two headstock & tailstock levelers are resting on the adjoining slab. I used 1/4" thick steel plates as shims between the steel leveling pads that came with the machine and the floor - it took three under the front corner and four under the rear corner of the left end of the headstock, while the other points only took one apiece. I leveled the lathe with a 6" Starrett machinist's level, and did have to adjust things a few times during the first month of operation, but since then, it's remained stable. It was cutting a .004" taper over a 9" length, but adjusting the tailstock reduced that to .0005" or less over 14".

    Now the problem - I stayed within the owner's manual recommended max. 650rpm for the first six hours of operation, and it runs smooth, giving a fine surface finish. But the first time I shifted up to the next highest speed - 910rpm - it shook like a Maytag on spin cycle with an unbalance load. The amplitude of the vibration decreased considerably at the next two higher speeds - 1280 & 1800rpm, but it was still there. Jet's warranty dept. arranged for a local machine shop to send a guy out to have a look at it, and he thought the set up on two different floor slabs could be contributing to the vibration, although he did agree that the OEM drive belts weren't the best, and had a new set sent out. I installed the new belts and checked the vibration at 910 with them running just tight enough not to slip, and a bit tighter. The belts did help, and it seems to run a bit smoother with them tighter rather than looser, but there's still an unacceptable amount of vibration. Being a novice, I'd have accepted the guy's opinion about the floor slabs causing the problem, but he diddled around with his own level on the ways, and when I checked his work, he had things more twisted & screwed around than the worst I'd seen with my level while setting the lathe up. I re-leveled it and checked for taper cut again, and all is well - except for the vibration at 910.

    This isn't a light bench lathe - it has cast iron bases weighs 2080lbs. It does have a single phase motor. I could get some help and move the radial arm saw, then move the lathe over so that all the leveling pads are sitting on one slab, but thought I'd ask for opinions before screwing with it.
    Regards,
    Dennis

  • #2
    The slabs shouldn't have any effect on the presence of vibration. The machine shouln't be vibrating in the first place. The different slabs could only be allowing the vibration to be more noticeable. (which I doubt) The slabs aren't CREATING the vibration. To test the point you could temporarily move the lathe over onto one slab, relevel it and I bet the vibration will still be there.

    Something in the drive train is at, or very near, it's resonant frequency at 910 rpm setting.

    What about one of those segmented belts? They advertise them as being able to reduce or eliminate vibrations. I know you shouln't have to be messing with this but it's an idea.

    Mike P
    Mike P
    1919 13" South Bend Lathe
    1942 Bridgeport M-head Mill

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    • #3
      Is the lathe just resting on the shims or is it bolted down? If the weight is not equily distributed then resonance vibration could be more apparent due to small movement of the lathe stand. I have an Emco V10P and the lathe bed is so stiff relative to the stand I found that I had to bolt the stand to the slab in order for shims to have an effect.

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      • #4
        take the chuck off and run the machine, if it runs smooth it is the chuck.

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        • #5
          There was a post recently about this lathe having the same problems at that speed, going to the link belt sounded like it helped.

          The slab can cause vibrations if the stiffness of each slab is different, but I doubt that is the cause from the description of your problem. From your description, it is also not unbalance, you would notice that at any speed and it would increase as the speed increases. This is most likely a belt resonance, the reduction in vibration as the belts are tightened is a good indication of this. I would recommend trying the Link Belts, they seem to work very well at reducing belt vibration.

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          • #6
            I run link-belts on most of my machines (mill, bandsaw, belt/disc sander, table saw) and they really help. Here's the link to Fenner who makes the belts: http://www.fennerindustrial.com/prod...twist_ind.html

            You can isolate the source of the vibration by removing all drive belts & starting the motor. Rest your hand on the motor housing. If there's much vibration, remove the motor pulley and recheck to see if vibration is less.

            It could be something as simple as an out of round pulley or a lumpy belt. Also check the bolts that connect the motor to the machine. There are only a few items that will cause this vibration. Once isolated, you can work on the solution.

            ------------------
            Barry Milton
            Barry Milton

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            • #7
              As I recall, the GH1340 is a gearhead lathe? If so, then the belt is going to have the same vibration at all speeds. Changing speeds is a gear change, not a belt change. You might be changing load on the belt, but not much.

              I would be wondering about the gear for that speed range. If it is slightly off center.

              I have the Grizzly equivalent lathe. I put mine on machine feet

              http://www.grizzly.com/products/item...mnumber=G7159&

              I haven't had vibration problems. Its also easy to adjust the level if needed.

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              • #8
                Flat,it may be worth checking the alignment of the pulleys.It's very easy for the motor to be misaligned on it's base,causing vibration and high belt wear.my$0.02

                ------------------
                Hans
                Hans

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                • #9
                  My Sharp lathe (16x60) had device on end of spindle for balancing. It was three weights with set screws. If not check the chuck first. If it is the chuck set up static balance between centers on lathe and drill back to remove weight. You might check movement on corners of base with indicator. Put indicator on stable base on floor push against lathe to see if you are moving. If not check pulleys. Worst case would be bend shaft on motor or spindle is bent. It could be any of the above mentioned items also.

                  CT

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                  • #10
                    Thanks for all the replies. I'll check pulley alignment, and then look into the linked belts. If that doesn't do it, I think it's best to turn it over to Jet and let them figure it out. After all, avoiding this sort of problem was the main reason for buying a new machine.
                    Regards,
                    Dennis

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                    • #11
                      After several phone conversations with Jet's warranty dept., we arranged for the nearest Jet dealer (165 miles from here) to bring his repairman out and examine my lathe. I was more than satisfied with his level of knowledge & competance. He determined that both chucks that came with the machine were out of balance, plus the 3-jaw wasn't fitting the camlock spindle taper worth a hoot. They took both chucks back with them, and the dealer told me he'd arranged to have Jet send out two new semi-steel chucks. This was on a Friday - the follwoing Tuesday afternoon, I found the two new chucks sitting at my back door where the UPS man had left them. I installed the camlock studs and wiped them both down to remove the oil/grease, then ran each one up to 910rpm - results were gratifying - very little vibration, certainly a huge improvement over the original chucks. I may try a set of Fenner drive belts to eliminate what little vibration is left, and when I can afford the vertical mill that's on my wish list, I now know a dealer who I can call. I know this probably sounds like an advertisement for Jet machines, but I've never been shy about voicing my displeasure when a purchase fails to live up to my expectations - I figure it's only fair to write about good service when I receive same. The dealer's name is Randy Puls; he & his wife Sue own & operate Hutchinson Industrial Supply in Hutchinson, Ks.
                      Regards,
                      Dennis

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