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Z axis rigidity

Discussion in 'CNC Mills/Routers' started by John Meikrantz, Apr 19, 2015.

  1. John Meikrantz

    John Meikrantz Veteran
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    As I have started using my Ox (Cebu) more, I've noticed some flex in the z axis. At first I thought it was the x axis beams, and was planning to bolt them together. However, it seems like the x axis beams are fairly stable, and the flex is coming from the z axis components themselves. The z axis extrusion with motor on top can move back a bit without moving the x axis beams. The carriage wheels on the z axis assembly are quite tight against the x axis.

    It looks like the flex is coming from the side wheels (three on each side) on the z axis? I only have eccentrics on one side, so the other has the original "loose" fittings with spacers on the opposite. Right now it's too much trouble to disassemble everything to put eccentrics on that side, and I'm not sure it will fix the problem. I wonder if the M5 bolts are bending slightly?

    Anyway, I don't mean that I am dissatisfied with the overall design. It works well, but I've had to change feeds/speeds a bit to avoid (minor) flexing in the z axis.

    Just wanted to start a thread on thoughts. Maybe the x axis beams are shifting slightly, and I just don't notice it?

    For those that have bolted together the x axis, did it make a big difference?

    Thanks,

    John
     
  2. Jonny Norris

    Jonny Norris Veteran
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    I have the same issue, I think it a combination of the bolts, bearings and wheels.

    The only solution I can think of is using a piece of channel with the v wheels in the channel and the channel bolted to the x assembly with v wheel bolts through the existing holes. So that the vwheel Botha are supported both ends.

    I bought my ox as a kit from robocutters so I reserve the right to be dissatisfied with his kit as it wasn't cheap. Definitely areas which should have been rectified by now.

    I too was told to bolt the x profiles, which I did aswell as epoxied, this helped initially but soon found that the flex here before was preventing further flex in the z wheels, so with less flex in x more strain went into the v wheels and Inturn the flex lost in the x was regained in the z. Though I think In a bid to rectify the issue the x will need bolting as well as a fix for the z.
     
    #2 Jonny Norris, Apr 19, 2015
    Last edited: Apr 19, 2015
  3. John Meikrantz

    John Meikrantz Veteran
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    Okay, I figured out a part of the problem. On the Y gantry plates, one of the eccentrics needed adjustment, as the bottom wheel was not making contact with the vslot! Not sure how that happened, in all the tweaking, moving about, wiring, etc.

    Was able to get that adjusted, and it took out most of the remaining flex.

    Unfortunately, the Cebu is now bolted to it's table, and pretty stuck by wiring, drag chain, etc. Tweaking the bottom eccentrics was quite an ordeal!

    -- John
     
    GrayUK likes this.
  4. danwood

    danwood Well-Known
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    I too bought a CNC kit from Robocutters.
    Turns out to be £2,300 worth of junk!!!
     
  5. Jonny Norris

    Jonny Norris Veteran
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    ouch. Yeah Colin's designs where he's doubling stuff up is not enough to sell the size kits he makes.

    Which kit did you get?

    was there missing parts?
     
  6. danwood

    danwood Well-Known
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    I was missing LOTS of parts. I lost count.
    I also can get a refund!!
    It is a very flimsy and weak machine. It needs much much more bracing. At my expense.
    Shame as I had lots of orders.
    Back to the hand tools!!;-)
     
  7. Jonny Norris

    Jonny Norris Veteran
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    That's typical of Colin, 6 month wait for me from him.

    Get the refund, or credit and use Colin to source the parts for something stronger like a h or I beam version .plenty of guys here that can cut the plates for you.

    £2300 could quite possibly build the strongest 1500x 1500 ox yet

    was it the rediculous 8x4 machine he's selling by any chance?
     
  8. danwood

    danwood Well-Known
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    You guessed it!!
    CNC was, is new to me and a great addition to my furniture business.
    Or so I thought!
    He won't refund me as he does not have my money.
    I'll use bits from what I have and re design it;-)
    I did build a 2x3 solid box section frame. Is the best bit there. 2mm out on corners and flat as a pancake'!;-)
    I may ask your advise when I start designing the new one. If that's ok?
     
  9. Jonny Norris

    Jonny Norris Veteran
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    That guy should loose his openbuild merchant license for the way he operates his business to be honest.

    No problem. Happy to advise.
     
  10. danwood

    danwood Well-Known
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    I agree. And thank you. It's good to know some one is on my side.
    I checked out your website. Pretty cool.
    And loads of joints!!!;-)
    Where did you get your CNC from?

    Cheers
     
  11. Jonny Norris

    Jonny Norris Veteran
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    Thanks. It's my own ever evolving design. All purpose built around the idea of keeping Cnc affordable with Low overheads.

    Though the 5hp atc that is the next upgrade may break the bank somewhat.
     
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  12. Jestah

    Jestah Veteran
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    I have been waiting for a small ATC spindle I got on kickstarter for well over two years.... It is finally on its way down to NZ and cant wait!!!
     
  13. Jonny Norris

    Jonny Norris Veteran
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    Is that the atc cartridge? There is already a couple of other atc attachments, even one for kress but £500 each. How much the kickstarter one going for?
     
  14. Jestah

    Jestah Veteran
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    it was a project that funded quite a long time ago, you can now get the same out of china for less as I would not recommend the guy I got mine off... I have found it rather painful but glad after a 2 year wait its finally being shipped!
     
  15. Jonny Norris

    Jonny Norris Veteran
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    yes but if it the cartridge type it means it compatible with any spindle that you can fit a pulley or coupling which is nice.. id say its more for vertical mills tho than routers as your now bolting the cartridge and spindle either side by side or direct drive, and adding a fair bit of weight doing so and having direct drive your spindle center of gravity is higher which isnt such a good thing. kind of tempted tho as it looks more robust than the chinese versions.

    id hope not to wait 2 years tho!
     
    #15 Jonny Norris, Sep 9, 2015
    Last edited: Sep 9, 2015
  16. Jonny Norris

    Jonny Norris Veteran
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    I see colin has withdrawn sales of his larger "stronger and better" ox design., cant recall what he called it, probably because it was pants.
     
  17. dddman

    dddman Master
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    I have an idea to strengthen the Z axis! I just have to test it and/or design a little something...
     
  18. Jonny Norris

    Jonny Norris Veteran
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    having the vwheel bolt supported at both ends would help massively.
     
  19. dddman

    dddman Master
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    Look at this! It will help a lot! Do it on both side :)

    20150912_092617[1].jpg 20150912_092645[1].jpg
     
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  20. John Meikrantz

    John Meikrantz Veteran
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    That is awesome! I've been thinking of a way to support the vertical beam from behind, but couldn't find a place to attach.

    -- John
     
  21. andrew Adsit

    andrew Adsit Well-Known
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  22. Jonny Norris

    Jonny Norris Veteran
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    Im thinking this would help as leaving those bolts unsupported really isn't good: Ignore the scale its all wrong.

    [​IMG]

    if any one wants a set of two of these i can mill from solid aluminium bar for £10 per set, scale and holes to match ox plates corrected or custom. can ship anywhere from the uk.
     
    #22 Jonny Norris, Sep 15, 2015
    Last edited: Sep 15, 2015
  23. Indieflow

    Indieflow Veteran
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    Nice cassette concept :thumbsup:

    Any pictures of a completed set? Have you installed them on your own OX?
     
  24. Jonny Norris

    Jonny Norris Veteran
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    Lol no it's on my never ending list of to do's and hadn't recieved much interest to mill any, but I have ascertained that it can be done simply by sandwiching a solid aluminum square bar between two rectangular bars. Can't quite recall the dimensions of each but holding a vernier up to your machine will tell you the thicknesses you need you just have to keep in mind the wheels require ideally two washers either side between bars. And some additional holes through the solid part of the sandwich would be required to bolt them all together.

    Failing that I would be happy to mill some up from a single bar for you, Wheel placement and wheel bolt holes the same as original.

    Think it's without doubt that a lot of the flex in the z is caused by spring in the unsupported wheel bolts, infact mine have begun to bend, so this would eradicate the possibility of this issue.
     
    #24 Jonny Norris, Nov 25, 2015
    Last edited: Nov 25, 2015
  25. Indieflow

    Indieflow Veteran
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    I know exactly what you mean regarding never ending list of improvements!

    To be honest I was thinking a solid block of aluminium with a pocket for each wheel and a taped hole for the LP screw would be by far the most solid way of combating the flex. The only part I'm struggling to picture would be the opposite side with eccentrics! Could even incorporate Danny's rear support wheels in the cassettes. These cassettes would nicely fix to the current X-axis plates as a modification for strength though!
     
  26. Jonny Norris

    Jonny Norris Veteran
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    Ahh yes the eccentrics, sorry forgot about those, I've actually designed a block that allows for the escentric spacers, it also has access holes for each spacer individually for adjustment and the outside holes (bolt tip holes) also have eccentrics.

    A neater option would be to have adjustment on the entire block instead of each wheel individually. I'll get the design up of the one with escentric and see if I can come up with a simple way of adjusting the entire block instead as soon as I can.
     

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