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C-Beams, Ball Screws, and MGN Rails

Discussion in 'General Talk' started by Philip UD, Oct 28, 2016.

  1. Philip UD

    Philip UD Well-Known
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    Latest project on hold for parts (AWP :() so I thought I’d post some pics of my C-Beam experiment.

    C-Beam with Relatively inexpensive stainless steel MGN12 linear rails and 1204 ball screws.
    01 Show Z back on table.jpg
    MGN12 Rails
    Pros: They fit, are relatively inexpensive, and available in stainless steel.
    Cons: Tiny 3mm mounting screws, smaller blocks and rails are hard to align so the screw hole spacing needs to be absolutely accurate and the surface need to be flat and level. The screw length and torque also needs to be correct.
    Tricks: Surface the mounting plate, my aluminum stock looked flat but wasn’t truly level.
    Wish: Surface milled 100x50 C-Beams for MGN-15 linear rails.

    1204 Ball Screws
    Pros: They fit, a very smooth 500 steps per millimeter with my gecko drivers.
    Cons: A hair small for longer lengths, i.e. the 750mm X axis gantry of the router I’m building. Also the 30.25 x 40.5 mm ball nut flanges need to be modified.

    DIY vs FK10 Ball Screw Mount
    FK10 mounts fit and are just what I needed for the belt driven dual Y axis screws on the router I’m building however by making a simple DIY internal mount I don’t need motor standoffs on the Z and X.

    Made some temporary mounts and attached the Z stage to my Ox for testing.
    02 Z on Ox.jpg
    Maybe not perfect but works for me.
    Cheers
     
    #1 Philip UD, Oct 28, 2016
    Last edited: Oct 29, 2016
    Kyo and GrayUK like this.
  2. GrayUK

    GrayUK Master
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    Hi Philip. Thanks for sharing your build so far. Got some questions for you, if you don't mind? :rolleyes:
    May I ask where you are based, from a postage and carrier cost point of view. Who supplied your Rails and Ball Screws, are we talking China? I seem to have this built in concern about sending money to China and not getting anything back! But many seem to to do so with no problem. :)
    I'm beginning to feel that the small extra cost for this stuff can simplify and offset the potential problems of wheels etc.
    However, I would be looking in the 1000mm area for my CNC. What size and diameter screws are you using?
    What I can see so far, your CNC looks quite substantial :thumbsup:
    Would be great if you could supply some more pictures of the set-up.
    Cheers
    Gray
     
  3. Philip UD

    Philip UD Well-Known
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    Hi Gray,

    US, small island NW corner of Washington State.

    China ball screws and rails. The rails were ordered cut to size with extra carriages from RobotDigg, not listed as is on their website, Ball screws eBay seller.

    Ordering from China…not possible to cover in 1000 words or less… short version of what works for me:
    • Use a payment method with buyer protection, i.e. PayPal, eBay etc. if the item doesn’t show you eventually get your money back.
    • Free shipping is not your friend, you want… no need tracking.
    • Test order small first, find a supplier you trust.
    • Know what you are ordering and where it should be shipping from, example: Hiwin makes some fairly nice linear rails at a reasonable price, they are made in Taiwan not mainland China so green and red rails and carriages shipped from China, big red flag, are probably not actually Hiwin rails regardless of the description. However that doesn’t necessarily make them bad, I intestinally ordered a pair of Chinese look-a-likes for a table saw jig project that are a whole lot nicer than I expected for the price, what they aren’t is stainless steel, and I had to remove some pretty heavy packing/preservative grease and re-lubricate before use, which you should do anyway.
    • And finally expect a lemon now and then, lower price usually means no QA regardless of where it’s made.

    Once it’s a little farther along I plan on posting detailed build in the router section, that is if it works ;) and maybe even if it doesn’t.
     
    #3 Philip UD, Oct 29, 2016
    Last edited: Oct 29, 2016
  4. GrayUK

    GrayUK Master
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    Thanks Philip.
    What do you mean as to "Free shipping is not your friend"?
    And you've had no problems, so far?
    Thanks again
    Gray
     
  5. Ronald van Arkel

    Staff Member Resident Builder Builder

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    @GrayUK Most free shipping has no tracking number, comes with regular post and they leave the tracking out to save 1.50USD or so. Takes also a darn long time to get your things if they ever arive.

    To tell you the truth, I don't even use Mexico postal service as they are government owned and don't give a rats behind so to say ;), and it's the same in the USA, might be like that in England. I remember that the OpenBuilds partstore send me a few 15mm screws (think 100pcs it was) with USPS to Mexpost, and then it never came in but was signed by "Ronal".

    Any way, this might be too far off-topic ;).

    @Philip UD,

    Looks like a sturdy Z axis. Reversing the C-Beam so the reals would get closer to the gantry was teh best thing to do indeed. Still I wondering if the V-Slots and just 8 wheels can handle the load on the gantry.

    -Ronald
     
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  6. Philip UD

    Philip UD Well-Known
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    Polite but Convoluted
    Typically, when we see ball screws for example we are tempted to assume the one that cost more is of higher quality, and with free shipping we are just getting a good deal right? But from China that is usually not the case, from my experience true shipping rates are usually a better indication of quality, I think it might be a cultural thing like being proud of an item so you don’t jack-up the price and want it shipped/handled right or something. Additionally, free shipping is almost always the cheapest and therefore slowest method possible with more opportunity for damage and no usable tracking, literally “the slow boat from China” especially with large packages.

    Or Cynical
    You take the factory second ball screw, double the price to $64 and sell it the Gweilo with free shipping so the DF thinks he’s getting a good deal, as an added benefit 30 days of abuse on the slow boat lets you honorably blame any defects on shipping damage.
    Verses selling your best ball screw to regrettably a westerner but at least a not so greedy one for $36 + $30 shipping (total $68) so that when DHL knocks on his door 10 days later at least the pride of your ball screw stock will arrive in reasonably good condition.

    Seriously from my experiences free economy shipping from China is great for small items like drill bits and end mills but for long and easily bent ball screws, rails, and the like suppliers that uses DHL, FedEx, or UPS are the better choice, and more often than not the total price will not be all that much more, sometimes even less for a higher quality item.

    Ball Screw Size
    The 1204’s (12mm diameter, 4mm pitch) I used with the C-Beams are ok for shorter distances great at 300mm, ok up to 500mm, 750mm max and that is really pushing their limit even at a hobby level, definitely not 1000mm. For 1000mm you would want at the very least 1605’s (16mm, 5mm pitch) or better yet 2005’s for heavier cutting of larger items, over a meter is a long way for a ball screw like twisting a steel rubber band they bow and flex under load (whip) introducing significant error in far end cuts.

    Problems? With the router build a few dificulties, not real problems. Ordering from China, very few in the last 15 years or so.
     
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  7. Philip UD

    Philip UD Well-Known
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    Exactly what I wanted to see by temporarily putting the it on the Ox. Its final home will be on a reinforced C-Beam gantry again with the small mgn12 rails.

    What I’ve noticed so far is that it works but yes a little heavy, most of the flex I’m seeing in not from the bolts and wheels but the beam itself, and my major complaint about the wheels on a gantry since I can't see how to stiffen the beam in width other than making it larger requiring longer bolts, which then would most likely start to be an issue. I do eventually want to try an 80mm beam on the Ox along with a few other modifications I've seen.

    As for the :D on topic C-Beam with mgn12 rails all good so far, meaning that the 3mm screws haven’t broken or pulled out, the internal ball screw mount is holding under load, and the bearing blocks are operating smoothly under load with no signs of grinding, or sliding bearings.
     
    #7 Philip UD, Oct 29, 2016
    Last edited: Oct 29, 2016
  8. Adam Filipowicz

    Adam Filipowicz Veteran
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    with Double gantry, are you not worried about the two steppers getting out of sync and binding?
    thought about running a short belt loop between them?
     
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  9. GrayUK

    GrayUK Master
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    In theory...... The very nature and principle of a Stepper motor, is that you set the steps, which are exact movements designated by yourself.
    Therefore, if both stepper motors are exactly the same, and they are set up, exactly the same, in theory, they should always be in sync with each other.
    The Ox CNC has worked on this principle for a long time now, with two stepper motors with Belt drives attached, in the Y axis, and there has been very little in the way of problems of syncing.
    There are of course other factors which could cause loss of sync, possibly electrical or mechanical, but it is not likely to be anything to do with a pair of well set-up steppers.
    Gray
     
  10. Adam Filipowicz

    Adam Filipowicz Veteran
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    having dual Z steppers on i3 3d printers has been a pain, they dont seem to stay in sync over the long term.
     
  11. Ronald van Arkel

    Staff Member Resident Builder Builder

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    They use 2 cheap drivers, if they would use one good driver it would be better, and if possible a digital one.

    -Ronald
     
  12. Philip UD

    Philip UD Well-Known
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    Ronald
    I like the gantry, was thinking you should try a single motor and belt to drive both screws.

    Something like this:
     
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  13. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Hello @Philip UD,

    Cost of the belt, pulleys and tension hardware is more expensive than adding an extra motor and using a good driver, however, if a reduction is added it's indeed better to use one motor. And if we go that way, the belt will be placed on both the X and Y axis.

    There are pro´s when working with a belt, for example the machine can be more compact in footprint, 2:1 reduction. I don't see a problem using 2 motors on the same driver, as I said before, the motors have a margin of error that is pretty small, and a cheap or badly adjusted driver will be a problem like on an "i3 printer" build.

    A double Acme screw might be overkill on the design I made so when the machine goes in production we'll test a single Acme screw setup first and let you know how it worked out ;). The design is maxed out in upgrades so it's easier for me to design the plates.

    -Ronald
     

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