Aluminium extrusion tolerance


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Thread: Aluminium extrusion tolerance

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    Default Aluminium extrusion tolerance

    Hi there,

    I'm building my first moving table cnc machine. I'm going to use kanya PVS extrusions. While working on a design, I faced a question do such profiles have enough surface tolerance to mount hiwin rails on it? Product manager gave me an answer that they can give some extra work on surface so it will have 0.25mm surface tolerance on the length of 1200mm, but in general DIN EN 12020 says it to be 1.3mm on the length from 1000 to 2000mm, So my question is for those who've built their routers using extrusions - have you done extra surface machining before mounting rails to the extrusion or you've just compensated flexures (if it is suitable word here) of frame by making proper tuning of your software?

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    Registered LeeWay2's Avatar
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    Default

    In the machines I built, I used CRS flat bar to mount onto the extrusions first and then the rails mounted to this bar. It gave more rigidity and mass and also provided a nice place to add shims should they be needed.
    The two builds I mention was a mill and lathe.
    This extra height also provided extra clearance for the ball screws.

    I did mill down the first machines extrusions to be flat, but this was really not needed.



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    Default Re: Aluminium extrusion tolerance

    I'm curious what thickness of cold rolled steel bar you would recommend for this? I was thinking of doing the same, and using another length of flat bar in the t-slot channel drilled and tapped for the rails rather than individual nuts.



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    Gold Member LeeWay's Avatar
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    Default Re: Aluminium extrusion tolerance

    I think it was 1/2" on one and maybe 5/8" on the other.

    The Tnut bar sounds good. Nice and solid.

    Lee


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    Default Re: Aluminium extrusion tolerance

    Using cold rolled 1018 is good for the rail support, but still needs to be machined for the rails to be mounted on, both the extrusion and cold rolled don't have very good flatness tolerance, depending on what precision grade and preload,your linear rails are, will determine, how flat the rail mounting surface has to be, check the manufacturer's rail mounting/flatness spec to see what you need

    Even Ground 1018 bar you can buy, is still not in tolerance for mounting linear rails on

    There are a lot of Hobby builds that mount there rails direct to an unmachined surfaces, but they do not have any precision, in there build by doing this, and face the possibility of early failure

    Mactec54


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Aluminium extrusion tolerance

Aluminium extrusion tolerance