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  1. #11
    It's relatively easy if both shaft sizes are the same,use the straight end of a steel rule lay it against the two shafts(piece of white paper behind) and you will see daylight on one of the shafts if there is misalignment, will be tricky though as you will have limited access below your table. If one shaft is bigger than the other put the straight edge on that one and just try to guestimate the run out.
    Good luck

  2. Oldham type are great for this as their design allows for misalignment in the hubs, I would still do as Mike suggests though because something isn't right, the original couplings are rubbish though to be honest (no offence) unless everything is perfect, even then you can't really push them to hard, the forces can be to great really for such thin ali, they are designed for light weight machines really, 3D printers, engraving, machines like that.

    For the price they pay for them I don't know why they even bother using this type on a machine.


  3. #13
    Hi Kevin,

    I used to use a short length of stiff rubber tubing (similar to the reinforced sort used on cars for flexible brake hoses) which was a tight friction fit on both shafts. This worked a treat giving a bit of vibration isolation and alignment, and it never slipped or broke. These were fitted to both X motors and the Y motor. Z is belt driven.

    Click image for larger version. 

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    After many, many hours of use I decided it would look more professional fitting a coupling so went for the spiral aluminium type. One of them broke eventually, and the problem with them is that it is not obvious that they have broken as they can still transmit drive to the ballscrew most of the time.

    I then fitted a larger diameter one, and this has been running for some time although the other day I was looking at them wondering how long they would last.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #14
    Hi guys, I got the Flexible Couplings recommended by Mekanik. They do the job but the outer diameter (18mm) on these is quite a bit thinner than the original (25mm).

    Also, within a week, a second of the original FC's sheared of in the same way!

    I had a bit of trouble getting these new FC's to fit so I sanded the inside with 600 until it fit nicely. Well it is now making a nasty creaking sound when I run it so I expect it to break fairly soon.

    So, In preparation for this I am on the market for some high quality Flexible Couplings, preferably Oldham as these seem to be the type that would take most abuse.

    I'd imagine steel to be less likely to break than the Aluminium ones I am currently using.

    I have found these (very expensive) Oldham FC's on eBay but there must be something less pricey in the UK!

    Another issue I keep running into is that they seem to come without the Polyacetal Spacer thingy in the middle!

    Am I missing something or why would one ever want these without the spacer?! Madness! Lol.

    If someone could suggest a place to buy these in the UK I would be very grateful!

    Cheers guys Kevin.

  5. #15
    Hi Kevin
    Try this link
    Looks like you will have to give them a ring for price.
    This one probably cheaper
    Last edited by mekanik; 10-10-2015 at 09:46 AM.

  6. #16
    I like the idea of the rubber tubing couplings, though I would clamp it to the shaft with hose clips.
    I had a coupler break and I replaced it with a similar one, but I wish I had thought of the rubber tube, it is a bodge, but in keeping with the standard of my MD machine.


  7. #17
    Mike to the rescue again!

    You are a a legend mate! This is exactly what I'm after!

    I like the look of CNC4YOU. I'll have a good wee nosey at this now shortly!


    I've never heard of this particular bodge. I like it!

    Sounds like it could pull one out of a hole in an emergency.

    Can you elaborate please? What kind of tubing etc?

    Cheers mate!


  8. #18
    Hi Kevin,

    I'm just echoing the posting from routercnc further back in this thread. All I am saying is that I would use hose clips to make sure the little fecker didn't slip. I would probably use a bit of gas hose as that is flexible and braided.

    I haven't actually done it, but I would probably do it in preference to fitting the ones like yours that broke, even though I have a couple of them spare in a drawer.

    I had a lot of trouble with the clamp type slipping and eventually drilled them out and bonded a slitted tube in as a shim to get the internal diameter right for the stepper shaft.



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