David A's New 2x3 Bench Top CNC - Page 30


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Thread: David A's New 2x3 Bench Top CNC

  1. #349
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    Default Re: David A's New 2x3 Bench Top CNC

    SIDE TO SIDE:

    Place something straight on
    the table.Here, a 1515 will do:
    David A's New 2x3 Bench Top CNC-3-img_7732-jpg

    Place one dial on one end of the
    straight and note the reading. Start
    sliding the dial towards the other end:
    David A's New 2x3 Bench Top CNC-4-img_7733-jpg

    Compare with the reading at the other end:
    David A's New 2x3 Bench Top CNC-5-img_7734-jpg

    Last edited by davida1234; 03-15-2019 at 05:32 PM.


  2. #350
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    Default Re: David A's New 2x3 Bench Top CNC

    Adjust the straight with paper underneath
    so that both ends read the same on the dial:
    David A's New 2x3 Bench Top CNC-6-img_7735-jpg

    Place both dials on the straight and see if the axis is
    off. Side to side was right on the money in this case:
    David A's New 2x3 Bench Top CNC-7-img_7739-jpg



  3. #351
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    Default Re: David A's New 2x3 Bench Top CNC

    FRONT TO BACK:

    Do the same with the straight
    in the other direction. This time
    the Z-axis was off as the weight
    of the slide has skewed the axis
    during installation:
    David A's New 2x3 Bench Top CNC-8-img_7740-jpg

    By pulling the plates towards/away from linear blocks:
    David A's New 2x3 Bench Top CNC-9-img_7742-jpg

    David A's New 2x3 Bench Top CNC-10-img_7743-jpg

    Tram can be adjusted quite accurately:
    David A's New 2x3 Bench Top CNC-11-img_7741-jpg



  4. #352
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    Default Re: David A's New 2x3 Bench Top CNC

    Do you relly only on friction to keep tram or you have some kind of exentric shoulder screw?



  5. #353
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    Default Re: David A's New 2x3 Bench Top CNC

    Excentric shoulder screw where?

    Just at the front portion of the X-carriage,
    where the Z-axis is bolted to, are 48 bolts
    to keep tram. And another 16 at the back.

    It's really not something you do often like
    a belt tensioner.



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    Default Re: David A's New 2x3 Bench Top CNC

    Not complaining at all, just asking, this buld is fantastic, i guess that 64 bolts will be more than enough to prevent any slippage!



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    Default Re: David A's New 2x3 Bench Top CNC

    No problem, just keep asking.

    Personally don't know of any
    excentrics for tram on a DIY.



  8. #356
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    Default Re: David A's New 2x3 Bench Top CNC

    .
    X-AXIS POWER NUT DRIVE:

    X-axis power nut is installed.
    Break-in for about 10 min.
    Starting with one inch per minute.

    Very slight jerkiness, probably
    due to too short of a break-in.

    More videos tomorrow:


    Last edited by davida1234; 03-16-2019 at 10:45 AM.


  9. #357
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    Default Re: David A's New 2x3 Bench Top CNC

    Ok, more random thoughts from my 150 mile drive home tonight...

    First, now that I see the belt size, I retract my questions about stretch or adjustment. I guess I didn't have a good perspective from your pics before and thought you were only using one of those 1/4 inch belts.

    Second, unless I missed it before, have you already accounted for any twist that could be present in your ways on the X and Y axes?



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    Default Re: David A's New 2x3 Bench Top CNC

    Outlawtaz, where do you think twist could
    occur as I don't have any traditional ways per se?

    The only place I could imagine it occurring would
    be the ball screw itself. And I don't think that is
    going to happen at loads we have when cutting.



  11. #359
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    Default Re: David A's New 2x3 Bench Top CNC

    Let me start by saying that I typically WAY over engineer my stuff, so take it with a grain of salt...

    Twist would be along the linear rails from one end to the other in both X and Y. And not along one rail but the surface of the pair of rails in relation to each other. It only occurred to me when you trammed in the spindle and you used a piece of paper to level your straight edge. Typically, paper is 0.004-0.005" thick (I always used 0.005 as a reference and a "round" number). It appears that the piece of 1515 was around a foot long so this could possibly induce a difference of 0.015" over the length of your machine. Even if you skimmed your base plate, it would just make a curved surface that would come out if you made parts that filled the entire machine. I hope this is making sense... It makes sense in my head but I can't always type my thoughts exactly...

    What I was always taught was to level the table / base first and remove any twist. Then, if I was concerned about X and Y being perpendicular, I would throw a granite angle on it to adjust one or the other. Next, came verifying Z to the table / base (if needed) again using the granite. Tramming the spindle would be the last step.

    Again, this is probably overkill. Also, I just happen to have all the precision tooling for this since I averaged doing this a couple times a month over 6 years when I was a field tech.

    I'm just impressed with your design and I think with a little playing around, you could have fairly precise machine with good repeatability.



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    Default Re: David A's New 2x3 Bench Top CNC

    Break-in for about 10 min.
    Starting with one inch per minute.
    We need more speed
    In particular to see the effect of the rotating mass. I think inertia increases by something like the square of diameter increase ?
    I don't know the exact formula and as they say the proof is in the pudding.
    This design is as light as possible with 2 flanged ball nuts, I hope this works as good as it looks.

    Anyone who says "It only goes together one way" has no imagination.


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