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    Question pads under feet of Bridgeport

    In the process of acquiring a used Bridgeport, have never installed anything as heavy, about 2,200 lbs, I think. Does one install a resilient pad underneath the mill? Or vibration isolation feet? Or just set it on bare concrete, and surround the thing with floor mats?

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    Shim if necessary to prevent rocking. Nothing else is needed.

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    The thing you have to do is level the machine on a possible uneven floor. The table should be level using a bubble level or something better.

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    Quote Originally Posted by rons View Post
    The thing you have to do is level the machine on a possible uneven floor. The table should be level using a bubble level or something better.
    Why does it have to be level? Level to within what tolerance?

    I think we put feet under them so we can slip a pallet jack under them to move them. A leveling foot that is 3” in diameter results in under 100psi, which is peanuts for a concrete floor.

    I’d have to think about whether introducing an elastomer under a machine dampens vibrations, or increases them. My knee jerk is the latter is true. If you want a stiffer machine, you should probably bolt it to the concrete floor, not put rubber under it.

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    Having the table level would be convenient when setting work at an angle using a protractor with a bubble. Otherwise it does not matter.

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    My floor is pitched & uneven so I put scrap steel blocks under the corners, shimmed so the machine doesn't rock. Via carpenters level I set it to pitch slightly backwards so coolant drains better out the table holes.

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    I read a lot of the past threads here on how to level a mill, and it always seems to boil down to personal preference on some of the details. ForrestAddy used to say you could practically bolt a mill vertically to wall and it would work fine. Seems the only reason to have them level is convenience of using a machinist level for work set up, as mentioned above. Obviously you want all four corners on the floor so it doesn't rock.

    There's also a debate as to whether pads reduce vibration or make it worse, as AdamC mentions. I've not seen anyone post any tests on it. Some softer materials seem to magnify vibration (like a wooden basketball court vs. concrete floor). On the other hand, vehicle engine mounts typically ride on rubber type grommets to reduce vibration.

    I leveled my mill using steel shims with a single layer of inner tube rubber underneath.

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    Quote Originally Posted by Randalthor View Post
    I read a lot of the past threads here on how to level a mill, and it always seems to boil down to personal preference on some of the details. ForrestAddy used to say you could practically bolt a mill vertically to wall and it would work fine. Seems the only reason to have them level is convenience of using a machinist level for work set up, as mentioned above. Obviously you want all four corners on the floor so it doesn't rock.

    There's also a debate as to whether pads reduce vibration or make it worse, as AdamC mentions. I've not seen anyone post any tests on it. Some softer materials seem to magnify vibration (like a wooden basketball court vs. concrete floor). On the other hand, vehicle engine mounts typically ride on rubber type grommets to reduce vibration.

    I leveled my mill using steel shims with a single layer of inner tube rubber underneath.
    Vibration remediation has several different methods, isolation, absorption, and damping.

    The motor mounts in an automobile application are mainly used to isolate the vibrations of the engine from the body.

    The purpose of bolting a machine to the concrete floor is to allow the vibration energy to be transferred into the concrete which has excellent damping characteristics.

    Rubber pads can be used for isolation and or absorption depending on the application specifics. There are no hard fast rules that always apply. The possible remediation is more of choosing the right tool to accomplish the job.

    You just need to do what works and try something else if it does not. Biggest issue is to remediate resonance problems as this will have a huge effect on finish and tool life.

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    Quote Originally Posted by Ziggy2 View Post
    Vibration remediation has several different methods, isolation, absorption, and damping.

    The motor mounts in an automobile application are mainly used to isolate the vibrations of the engine from the body.

    The purpose of bolting a machine to the concrete floor is to allow the vibration energy to be transferred into the concrete which has excellent damping characteristics.
    Makes sense. Do you know if there has been any actual testing one whether or not rubber machine pads actually increase or decrease resonance at the tool/work contact point?

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    Quote Originally Posted by Randalthor View Post
    Makes sense. Do you know if there has been any actual testing one whether or not rubber machine pads actually increase or decrease resonance at the tool/work contact point?
    That would be a function of the particular tool, tool speed, material hardness, the particular machine and how it is configured, floor construction and resonance characteristics of the floor.

    Then there is the issue of the durometer of the pads used and their construction.

    It would be extremely difficult to do testing that would give any specific recommendations that could be used in a general environment.

    A lot of this is just an educated guess and then tune from there.

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    Quote Originally Posted by Randalthor View Post
    Makes sense. Do you know if there has been any actual testing one whether or not rubber machine pads actually increase or decrease resonance at the tool/work contact point?
    Resonance happens when the frequency of the excitation (tool) matches the natural frequency of the item/structure of interest (mill).

    So, if the speed and feed of a cutter sets up some sort of buzz like 50hz say, and the natural frequency of the mill on hard concrete is 50hz, the amplitude of the vibration will be magnified as the mill joins the tools vibration and resonance is achieved. In that case, either making the mill's natural frequency higher (by bolting it to the floor) or lower (by putting it on rubber feet), will stop the harmonic. (I hope I got that right).

    Typically, I think motors and things exhibit frequency sweeps that are bottom up, not top down, so I suspect adding stiffness is typically better than adding rubber if the goal is to prevent a harmonic response. But I'm guessing we don't worry about it because big cast iron machines have super high natural frequencies and if you think you are about to hit a harmonic and the mill starts shaking, you stop.

    So (again hoping I got this right), I think adding leveling feet can be a good idea if you want to move your mill with a pallet jack (I know I do). Having them elastomeric is probably a good idea because the rubber will compress to ensure all 4 feet are contacting the ground, leaving no chance of the mill rattling. I don't think adding rubber feet or leveling feet makes the mill less prone to vibrating. I think the opposite. The feet soften the mill and reduce its natural frequency relative to the floor. But cast iron is an excellent damper and machines are super heavy so the feet probably cause no problem for most users.

    Does that help any?

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    Quote Originally Posted by Randalthor View Post
    I read a lot of the past threads here on how to level a mill, and it always seems to boil down to personal preference on some of the details. ForrestAddy used to say you could practically bolt a mill vertically to wall and it would work fine. Seems the only reason to have them level is convenience of using a machinist level for work set up, as mentioned above. Obviously you want all four corners on the floor so it doesn't rock.

    There's also a debate as to whether pads reduce vibration or make it worse, as AdamC mentions. I've not seen anyone post any tests on it. Some softer materials seem to magnify vibration (like a wooden basketball court vs. concrete floor). On the other hand, vehicle engine mounts typically ride on rubber type grommets to reduce vibration.

    I leveled my mill using steel shims with a single layer of inner tube rubber underneath.
    I wasn't trying to be a smart @ss about the level tolerance. I suspect bolting a mill to a wall is a bad idea. I'm thinking about how the wear surfaces are oiled, how the oil runs over surfaces etc. I like the idea about coolant. I hadn't thought of that. I also thought about how a mill on a sloping floor would wear the screws unevenly as you might be always pulling your table up hill. I think it would be best to have the table pretty level, but probably not better than a carpenters level could get you.

    When I think about my use of my machinist level, I'm not so interested in leveling machines with it as I am about detecting wind or twist of a lathe bed for example.

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    Quote Originally Posted by cobnashine View Post
    In the process of acquiring a used Bridgeport, have never installed anything as heavy, about 2,200 lbs, I think. Does one install a resilient pad underneath the mill? Or vibration isolation feet? Or just set it on bare concrete, and surround the thing with floor mats?
    It was before I started working at my company but all the machines in the workshop are on a kind of damping material instead of being bolted to the floor, I asked why, apparently the machines had bad resonance problems, I think it might be that the floor is made from slabs instead of solid concrete? Anyway, the solution they found was something called "Tico pads" a material designed to damp machinery and apparently it solved the problem, I've been machining in this workshop for over a year and have no problems with vibration

    James Walker Tp031042 Tico Pads 75Mmx1.2Mx12.5Mm Thick | eBay

    The materials expensive so you could see how it is, if you need it add it later

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    Transmission of vibration from machine to floor (and the rest of the building) can get difficult to predict. Milling could conceivably "excite" supporting floor at more than one frequency since cutting speeds, motor rpm's, etc. are different for each job setup. Didn't mean to open a can of worms, just doing a quick survey so I wouldn't wreck the shop or the machine.

    Thanks for all the input.

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    I have seen what happens if you leave the wrench on top and turn the "Mighty Comet" on. It will walk around. Pretty funny when the guy "engineer" was on his hands and knees crawling to the outlet to unplug it.


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