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IndustryArena Forum > Mechanical Engineering > T-Slot CNC building > How do you true the surface you bold linear guides to ?
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  1. #1
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    How do you true the surface you bolt linear guides to ?

    I need to build a large CNC router. I need a working area of 6 x 16 feet. I can buy 25 or 30mm linear guides in lengths up to 2 meters.

    I plan to use a welded table for my router.

    Question: how do I true up the surface that I bolt the linear guides to ?
    Last edited by CNCAddict99; 02-08-2020 at 07:02 AM.

  2. #2
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    Re: How do you true the surface you bold linear guides to ?

    This is a problem lots of large builds have to deal with. One solution is to make some dams on top of the horizontal members, and fill them with self-leveling epoxy. If you do it right, you end up with two co-planar surfaces that are flat and level, through which you can bolt your rails. Here's a thread from someone who tried it - he struggled, but maybe you can learn from his mistakes: https://www.cnczone.com/forums/cnc-w...gineering.html
    Andrew Werby
    Website

  3. #3
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    Re: How do you true the surface you bold linear guides to ?

    Hi,
    a very clever yet conceptually simple tool is the auto-collimator.

    Essentially it looks like a short telescope that you lay down flat on one end of the surface you are trying to measure and then there is a mirror on a small bed mount that slides along the surface.
    Observing the pattern in the eyepeice of the auto-collimator is an illuminated line that goes up or down as the angle of the mirror departs from vertical. It is possible to calculate and generate a plot
    of the surface accurate to within um. For instance an auto-collimator is used to measure and characterise granite surface plates, such is their accuracy and versatility.

    Regrettably auto-collimators are not cheap even second hand. Hilger Watts is a very good English brand which despite their antique look still do the business exceptionally well.

    https://www.ebay.com/itm/Hilger-Watt...wAAOSwyytdQeiZ

    Such a device would allow you to plot the bed onto which yo want to put your rails, it does not automatically machine them also!!!

    Craig

  4. #4
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    Interesting thread, Awerby.

    If I read that thread correctly, he hand scraped the Y axis rails to get them flat. He checked them with a machinist's level. Which essentially does the same thing as an auto collimator.

    Thanks, Craig.
    Last edited by CNCAddict99; 02-08-2020 at 07:01 AM.

  5. #5
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    Re: How do you true the surface you bold linear guides to ?

    Hi,

    Which essentially does the same thing as an auto collimator.
    An autocollimator is at least one, maybe two orders of magnitude more accurate.

    Craig

  6. #6
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    Re: How do you true the surface you bold linear guides to ?

    Quote Originally Posted by CNCAddict99 View Post
    I need to build a large CNC router. I need a working area of 6 x 16 feet. I can buy 25 or 30mm linear guides in lengths up to 2 meters.

    I plan to use a welded table for my router.

    Question: how do I true up the surface that I bolt the linear guides to ?
    You can have it machined as a complete frame or just have the rail mounting frame members machined and have them as a bolt to the main Frame where the rail mounts are mounted they would have to be machined as well or carefully fabricated to be true to the mounting surface
    Mactec54

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