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    Paul Kelly

    It’s not the absolute height that matters, rather the leverage the cutting edge of the tool has on the long axis bearings…



    Ok understood…



    It moves 🙂

    I went to make the stepper mounts and realised I needed to cut a 40mm hole for the front to sit in. I’m thinking of taking the easy option and just getting them all laser cut. In fact I’m thinking about getting something laser cut for the whole Z-axis carriage in order to save a bit of time.



    Paul Kelly

    Keep an eye on those Oldham couplers. While the rubber is new then they’re pretty tight, after a while they develop a bit of backlash and you start breaking tools.
    Get some of these http://www.ebay.com.au/itm/5-x-5mm-CNC-Motor-Jaw-Shaft-Coupler-5mm-To-5mm-Flexible-Coupling-07-/330960664981?pt=AU_Hardware&hash=item4d0ecaf995

    For a z axis, pretty much everyone uses these:
    They really are the ducks nuts in terms of rigidity.

    If you want a laser cut, built up Z axis then you can have one I first made for my router before I saw the light, I’ll bring it to work.



    Hmmm, didn’t realise you could buy it fully assembled like that. Done…

    That was always going to be the most complex part of the build, and well, it was reduced to a few mouse clicks 🙂

    I’ve got some of those couplers on the way to, 6.35x10mm.

    BTW with the screws mounted but without the motors, you can turn one screw while holding the other and the only thing that flexes is those damn round bearings! They are by a long way the weakest link.



    Paul Kelly, post: 1358, member: 25 wrote: 🙂 you’re going to regret using those round rails. Expect lots of tool chatter and broken bits.

    What do you see as the problems with the round rails, Paul? And what do you recommend in terms of long axis rails?


    Paul Kelly
    • The rails themselves aren’t very stiff.
    • Very few have the actual rail bolted directly to the machine.
    • The bearings only have one point of contact with the rail and block, so torsional loads open them up and create play.
    • They are only lightly preloaded.
    • I’ve never seen one that used idler bearings (every second ball is a poofteenth smaller) to smooth them out.

    A proper linear bearing

    • Has rigid mounting
    • High preload
    • Idler bearings
    • and is rated for hundreds of kg of load in all directions.

    They really aren’t that expensive.




    I can add that they even feel like a toy. There’s about 150kg of steel in my build, and those rails weigh a couple of hundred grams at best. As soon as you hold them you realise they’re never going to take much load. You can see those bearings PK linked have steel bodies, the round chaps are thinish ally.

    You’re welcome to come have a look at mine any time you want (albeit I live in the middle of no-where, Stoneville.)

    Paul Kelly, post: 1381, member: 25 wrote: They really aren’t that expensive.

    To put it in perspective, when I added it all up getting proper linear rails and bearings for all three axis on my build it was going to add ~$1k AUD. 4 bearings + two rails per axis. Those round bearings were effectively free as the cost of buying the individual ballscrews and pillow blocks came to the same price as buying the kit with everything in it (~$500).

    So given I was in no real hurry to get the machine to a fully functional state, I decided to go with what was in the kit. It’s pretty clear though they’ll need replacing at some point.



    Thanks for that feedback. I have a few sets of round rails lying around the workshop and have used one pair to make a hand-driven router(trimmer) guide and another to make an adjuster on a piece of equipment. They work OK in those applications, but I have been looking at the other rails and wondering if I should go that way for the machine that I am in the process of continuously upgrading at the moment.

    And thanks for the invite Derryn. You are welcome to visit as well. If you think Stoneville is in the middle of nowhere, try Pemberton 🙂

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