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  1. #1
    Join Date
    Aug 2013
    Posts
    980

    Weight on the table

    I have a contract job I will be doing for three weeks and will not be using my tormach.
    Do folks think it safe to leave the heavy 8" tilting rotary table (269 pounds) and vise mounted on the table or should I just pull them off and remount them when I get back to the machine?
    I am worrying about possible table warpage and staining that may occurre under the fixtures.
    Thanks
    Nathan

  2. #2
    Join Date
    Jul 2004
    Posts
    1424

    Re: Weight on the table

    I would pull it off to avoid any issues with rusting.
    Tim
    Tormach 1100-3, Grizzly G0709 lathe, Clausing 8520 mill, SolidWorks, HSMWorks.

  3. #3
    Join Date
    Aug 2013
    Posts
    980
    Thanks tmarks
    I bad being lazy
    I pulled everything off.
    Even though I use kool mist at the recommended percentage,
    I have had some staining in the past.

    Quote Originally Posted by tmarks11 View Post
    I would pull it off to avoid any issues with rusting.

  4. #4
    Join Date
    Mar 2008
    Posts
    216

    Re: Weight on the table

    Quote Originally Posted by CadRhino View Post
    I am worrying about possible table warpage and staining that may occurre under the fixtures.
    Table warpage - NO, table staining - Yes. The PCNC 1100 table is rated for 500 pound loads, and it isn't going to "warp" even with that much on it.

  5. #5
    Join Date
    Aug 2013
    Posts
    980
    I guess I am a little paranoid. I even lowered the head so it wasn't at the highest z (less cantilever force in my mind).



    Quote Originally Posted by Zetopan View Post
    Table warpage - NO, table staining - Yes. The PCNC 1100 table is rated for 500 pound loads, and it isn't going to "warp" even with that much on it.

  6. #6
    Join Date
    Nov 2007
    Posts
    2151

    Re: Weight on the table

    Hi Nathan,
    Don't forget to lube that bad boy on shut down and first thing on startup! I would if I was expecting to not use the tool for a few weeks. Also there is no shortage of old bed sheets stored in closets around here and they work great for machine covers. My shop has pesky grime and dust if I use it or not.
    Something to consider!

  7. #7
    Join Date
    Aug 2004
    Posts
    780

    Re: Weight on the table

    In practice, with these puny loads, there is no issue re:twist, break, or bend.

    Steel and cast iron are very springy,
    They bend very easily, and spring back good as new.
    The movements are very small, and most non-machinists think the them as "rigid". No such thing.

    To really bend or twist, permanently, the table or damage the components, you would need about 10x or more, the mass.
    Machine tools are, technically, lightly loaded components, with heavy walls.
    The loads are typically about 1-2% of carrying capacity of structure !

    Ie a machine tool is designed for 10-50 N/um kgf bend.
    A lathe of 12x size can carry about 100 metric tons before breaking.

    We are concerned with rigidity, not strength, in design.
    The impact loads on bearings, spindle, linear guides, etc. from machining are about 10-50x mass loads from weight.

    A tiny 7x minilathe can carry 1200 kg on spindle.
    My small VMC can carry 32 000 kg on the linear bearing blocks, theoretically, for 2 million metres of travel (in spec).

  8. #8
    Join Date
    Aug 2009
    Posts
    610

    Re: Weight on the table

    The only thing that I would be worried about is the staining. If you are using a water resistant grease, high molybdenum lubricant or graphite on your vise, table and/or fixtures you will be fine. The next worry would be the type of lubricant that you are using in the oiler. Not all lubricants bind well (cling), possess rust inhibitors and/or provide boundary lubrication to protect surfaces in contact with one another. These guys provide a pretty light overview of the forms of corrosion that we can run into in the real world. I always try to bound my thought processes around which one of these I am potentially going to have to deal with.

    Eight forms of corrosion

  9. #9
    Join Date
    Feb 2007
    Posts
    1538

    Re: Weight on the table

    Hi Nathan. I agree with above. You will get a little flex but permanent distortion or breakage needs much more load that that.

    What is worth considering though with heavy weights on the table is that the castings will flex, and that may cause issues with optimum slideway/gibs adjustment and local wear at certain pressure points especially when the weights are overhanging as in when at extended travel off centre on the X. If you load the table when off centre and measure the flex with an indicator it is surprising how much movement occurs - and this must affect fits, friction, and wear.

    Cheers, Keen

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