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  • Rubber Mounted Lathe?

    My new to me lathe is a Logan benchtop Model 940-2 but it's not sitting on a Logan cabinet like I usually see. It's on a homemade table consisting of a 1/4 steel plate top with some angle iron legs that seems sturdy enough. But here's the crazy thing, it's got large sheets of neoprene under both ends.

    For the past several months I've been digging into all things machine and I've yet to see anything like it. Time and time again I've read the 3 most important things about setting a lathe are level, level, and level. I suppose you could adjust the bolts against the rubber to get level, but that ain't seeming like the right way to go to me. Could change over time etc.

    The other thing is the Logan cabinets invariably have an under drive in the cabinet. This table does have a hole torched in it where a belt used to go under the table, but the motor's mounted above the table now. WITH a piece of rubber stuck under one corner!

    The whole set up looks bogus to me.

    When I get it home I'll be mounting it on an existing 2x16 bench I put up along one wall of my garage. It's built out of 1.5 sq 1/8th wall tubing, legs every 4 feet, with a 3/4 plywood top. The plywood is sheeted with 20 ga galvanized that's bent for a backsplash up the wall the full length.

    The lathe weighs between 6-800 lbs depending on options and where I found the information. I'm thinking about chopping the legs out from under where the lathes going and replacing the 1/8 wall legs with 1/4, but haven't decided yet.

    I will weld some feet on and bolt the legs to the concrete floor. Right now it's only mounted to the wall thru the backsplash and I'll be needing to better than that. Brackets across the back just under table height so I can lag bolt into the studs oughta make that section part of the building.

    As always, any ideas, opinions, and advice are welcome.

    SP

  • #2
    He wanted it to be quiet. Those are noise / vibration dampening arrangements.

    Little is such bliss as quiet machines. There is nothing like it. Often the greater part of benchtop machine noise is resonance in the bench, stand or cabinet.

    The previous owner seems to have put some thought into it. Proper noise and vibration dampening is not so easy.

    I had a similar arrangement on one of my lathes. It was bliss.

    Regarding level-ness, it isn't so much level-ness as flatness which is important. And it could be that his was flatter than yours.

    .

    Comment


    • #3
      SP

      I do not see any problem with the previous owners set up. It may be different but not nessacarily bad. Yes sounds like he used rubber to dampen vibration. I have seen south bends set up with the motor under the bench as well as mounted in the rear. the main thing is not twisting the bed when you mount it and have a reasonably solid bench that does not rock. The easies way to insure the bed is not twisted is to use a precision level.Worry about the basics the details are a matter of preference. Re mount the lathe on a different bench if you want but I do not see a "need". As for the level changing over time because of the rubber it should be fine as long as you do not see signs of deterioration such as cracking or pieces crubling off.
      Tin
      Ad maiorem dei gloriam - Ad vitam paramus

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      • #4
        What type of machining are you going to be doing? are you going to be working on small stuff all the time that isnt taxing the lathe bed, then maybe you can get by with all the dampening, it will make it nice and quiet and can actually improve accuracy on very small parts because it cuts down on vibrations even when the machine is free running, you can still get everything level -------- however - if your going to be taxing it and using it for larger stuff then you want to utilise the table as support for all kinds of reasons but mainly because lathes go through a torsional twisting of the bed when put under load, this throws tool bit and part way off kilter and also promotes chatter, a table stablizes this, going to be doing a little of both? you might consider using UHMW between the two surfaces and then buckling it down with UHMW washers between the nut and bolt head, this will isolate your table from the lathe and give it a more refined feel yet still give you much of the needed ridgidity...

        Comment


        • #5
          Well that shows how much I know!

          There are some small parts involved. Bushings that are approx 3/8 in dia and maybe a 1/2 long with a shoulder and threads in aluminum. The largest part is a steel ring that's roughly 7" on the OD.

          I will need to switch benches because I don't have room for the current table, but I'm not against the idea of isolating it with UHMW. It's amazing. Yesterday I didn't what UHMW was and now I've already got a use for some!

          SP

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          • #6
            I think "level" is overrated. It's only a means to an end, which is alignment of the spindle axis with the lathe bed. As long as the lathe turns parallel you're fine, whether the lathe is level or standing on end.
            ----------
            Try to make a living, not a killing. -- Utah Phillips
            Don't believe everything you know. -- Bumper sticker
            Everybody is ignorant, only on different subjects. -- Will Rogers
            There are lots of people who mistake their imagination for their memory. - Josh Billings
            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
            Don't own anything you have to feed or paint. - Hood River Blackie

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            • #7
              Originally posted by pntrbl
              Time and time again I've read the 3 most important things about setting a lathe are level, level, and level.
              If level was important, all those shipboard lathes would be in trouble.
              Todd

              Comment


              • #8
                It appears to me the previous owner had problems with motor vibration and all that rubber represents his heroic attempts to reduce it.

                A belt driven lathe should ideally run noiselessly with maybe a whisper from the belt. A gear driven machine should run with the constant soft musical whir of the meshing gears. A single phase motor with its hum and vibration can make an otherwise quiet machine sound like a whole store full of bad flourescent fixtures.

                The hum is merely an annoyance. If the vibration affects the finish by "recording" itself into the work surface then it becomes a matter of some importance. Besides vibration can cause settings to drift, affects tool life, promotes chatter in marginal conditions all of which affects the work quality. And again 60 Hz motor vibration is damn annoying.

                There are a number of options to consider when confronted with a machine tool subject to single phase motor vibration. All motors are not equal. The simplest but most expensive solution is to replace the motor with one having lower vibration particularly with a type of motor noted for its smoothness of operation - I refer to DC motors and three phase motors.

                Another solution is to de-couple the motor from the lathe to the extent practical. Apparently the previous owner tried that using the shotgun method (blaze away at the problem until you hit a solution). The vibration a single phase motor transmits to the load is primarily tortional. The motor's armature is gripped by powerful magnetic fields. At idle the armature is jerked into sync ovesrhoots and is jerked back and repeat - irregularly. This produces torque pulses in the delivered power via the shaft and from the stator which is bolted to the machine.

                Many single phase motors are "cradle mounted" in rubber to mitigate the stator's tortional vibration from being transmitted into the driven equipment's structure. There is no need to surpress tortional vibration in motors driving air compressors, hydraulic pumps etc but there is for AC and refrigeration equipment where the consequent noise is a bother to people who have to live with it.

                Level is important only as an aid to ensue alignment of the spindle axis to the bed ways and to ensure the bedways as a reference plane. The machine builder uses a level to establish the reference plane of the machine during construction and assembly. The installer uses a level to ensure the machine is set-up to its original assembly alignments.

                Getting back to the rubber. If you can level the machine and the motor poses no vibration problem nothing is broke so don't fix it. If you cannot level (align) the machine because of the rubber then you have to fix it some way and if that means the removal of the rubber, then that's what you have to do.

                If removing the rubber exposes a motor vibration problem then life gets more complicated. Your either have to isolate the motor from the machine to prevent the vibration from being transmoitted to it or replace the motor with one that does not vibrate.

                Here is where I usually reccomend a three phase motor and a variable frequency drive (VFD) or a phase converter to change single phase power to three phase. These motors and drives are as smooth as DC and very reliable. A good alternative is a DC motor and a DC drive. Intalling of either should pose no problem of a shop shop machinist providing he seeks good electrical counsel.

                Low HP three phase motors can be scrounged from HVAC shops from junk air handlers - sometimes for free. A VFD may be obtained from internet auction sites or one of the many internet supply houses. Shop carefully and you can save a lot of money.

                DC motors and drives are available from the internet auction sites and catalog supply houses. DC motors are difficult to find compared to their three phase cousins but a good scounger will prevail. Owner of small lathes report they get good service from DC motors and drives they loot from old exercise equipment.
                Last edited by Forrest Addy; 11-18-2006, 02:43 PM.

                Comment


                • #9
                  You asked for opinions, so here is mine.

                  I can see no reason for the sheets of rubber. I don't think I've ever seen it done that way.

                  I think the guy had some kind of rattle going on with the bench and was trying to silence it by isolating the machine from the bench.

                  I would not get hung up in his solution. Whatever the reason.
                  Gene

                  Comment


                  • #10
                    Logan 940-2 originally came on legs, not a cabinet. 945 series lathes were on a cabinet, 935 series were on a pedestal (an odd Logan term for something much like a cabinet).

                    Rubber between the lathe and legs may or may not be a good idea, it's hard to tell a priori. Rubber under the motor usually wouldn't be a problem.

                    Comment


                    • #11
                      Now there's a lot to think about! Thanx to everyone for the replies.

                      Once I get the bench firmed up it will essentially be part of the building, so I think I'll go ahead and hard mount the lathe and see how much it can resonate that! I'll hang onto the neoprene just in case.

                      FWIW, it currently has a 3 phase motor and the more I learn about VFD's the more I like them.

                      SP

                      Comment


                      • #12
                        What?

                        Now Forrest, some people do not need to do what you say. The rubber is for dampening and sound. Isolation on any rotating device can also be cheap. Nothing complicated about it. There is no mystery...nor any reason to make it overly technical. Put the damn rubber down if you want...you're paying for it, no need to do the physics. Any machine tool will transmit vibrations in the Earth. Keep it simple and quit scaring people away from machining, such as Mr. Williams does. Evidently you will never admit why he does all the scientific references as backup. Scare people away....and they will never have Pretty pictures...which proves...Nothing.

                        Comment


                        • #13
                          Wrong

                          [[Your either have to isolate the motor from the machine to prevent the vibration from being transmoitted to it or replace the motor with one that does not vibrate.{{

                          Why would you tell someone to replace a motor, without ever seeing the machine tool run? There are NO experts in machining..and you suggest motor replacement over the internet? You may fool Most...but not all..thank God most guys will not run out and spend Megabucks for a new motor to fix a simple problem. Vibration is inherent in ANY rotating device...if you're smart, you will find the simple fix...Simple as that.

                          Comment


                          • #14
                            Millman, read and understand the posting before you sound off.

                            You missed a crutial pair of sentances: "If you can level the machine and the motor poses no vibration problem nothing is broke so don't fix it. If you cannot level (align) the machine because of the rubber then you have to fix it some way and if that means the removal of the rubber, then that's what you have to do."

                            In the balance of the post I discussed trouble shooting and possible solutions. I made no reccommendation for changing out the motor for no reason but I did post a discussion of the causes and means of vibration mitigation and suggested practical remedies.

                            Comment


                            • #15
                              OK

                              [[ I did post a discussion of the causes and means of vibration mitigation and suggested practical remedies.}} NOW,, explain that in detail, for the ones that do not have this trade as an occupation. You have never seen that machine in operation, so tell me WHO is Sounding Off.

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