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  1. #181
    Quote Originally Posted by teamloks View Post
    HI JAZZ thanks for your insight regarding my question just talk with my ball screw supplier he suggest me to use 4040 for 3.2meter axis and 3232 for 2 meter axis..and i might follow their suggestion regarding that if budget is not constraint..anyway maybe i opt for 3232 all axis 4040 is really expensive
    Do they know you are rotating the nut and tensioning the screw.? Makes big difference.
    This is the first 10x5 machine using rotating ball-nut I've built, I've built plenty of 8x4 and the difference between them really surprised me.

    The secret is keeping the nut rotation speed down and getting a good tension on the screw with nice straight pull.

    Good luck

  2. #182
    Kitwn's Avatar
    Lives in Exmouth, Australia. Last Activity: 11 Hours Ago Has been a member for 1-2 years. Has a total post count of 180. Received thanks 27 times, giving thanks to others 3 times.
    Quote Originally Posted by JAZZCNC View Post
    Yes, 32mm pitch with 2:1 ratio will give the same linear torque as 16mm pitch 1:1 so torque is canceled by pitch difference like you say.
    However, when I say Torque is doubled so the smaller motor can be used, what I'm referring to is that if 1:1 the 32mm pitch would require a larger motor to give the same linear force as 16mm pitch. So the ratio doubles the torque and allows the smaller motor to have the same linear force as 16mm pitch.
    Aha! The point I had missed is that your 'smaller motor' required to drive a 32mm pitch screw with 2:1 pulleys is NOT smaller than the motor required to directly drive the 16mm pitch screw. In fact it may well be the same motor, which is at the heart of what I was trying to say. Thanks for clearing that up.

    Is there a case for using the direct driven screw with a bigger motor? You are saving the cost and complexity of the 2:1 drive and halving the speed required from the motor, so running it in it's higher torque region anyway?

    Kit
    Engineering is the art of doing for ten shillings what any fool can do for a pound.
    Wellington.

  3. #183
    Quote Originally Posted by JAZZCNC View Post
    Do they know you are rotating the nut and tensioning the screw.? Makes big difference.
    This is the first 10x5 machine using rotating ball-nut I've built, I've built plenty of 8x4 and the difference between them really surprised me.

    The secret is keeping the nut rotation speed down and getting a good tension on the screw with nice straight pull.

    Good luck
    do you use BK/Fix unit on both end side?

  4. #184
    Quote Originally Posted by teamloks View Post
    do you use BK/Fix unit on both end side?
    Don't need end bearings because not spinning the screw. The ends need to be either externally threaded or internally-threaded so you can tension the screws. I've used both methods on different machines and prefer externally threaded as can get more torque.
    The force required to take Sag out over 10ft is considerable so make sure the brackets holding the ends are substantial and adjustable so can align screw in two planes.

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  6. #185
    Quote Originally Posted by Kitwn View Post
    Is there a case for using the direct driven screw with a bigger motor? You are saving the cost and complexity of the 2:1 drive and halving the speed required from the motor, so running it in it's higher torque region anyway?

    Kit
    Can do either but using a larger motor usually doesn't cost less because requires larger drive and often more volts so larger PSU.
    However, on long machines rotating nut wins hands down and requires a belt connection, so the ratio is no extra cost. Rotating the screw on the long machine means much larger ballscrew is required and this really starts to ramp up the costs because everything scales up with it, Bearings, couplers, motors, drives, PSU
    Even then a rotating the screw system cannot achieve the feeds a rotating nut can.

  7. #186
    Reading this thread with interest (as I may need to go this route on my "big" machine soon), I noticed the concerns over rotation speed of ballnuts. This made me recall some stuff I read in the TBI catalogue some months back about different types of ballnut (differing mostly in the configuration of the return paths) and their relative speed capabilities, worth a read and maybe doing the sums they outline there.

  8. #187
    Quote Originally Posted by Voicecoil View Post
    Reading this thread with interest (as I may need to go this route on my "big" machine soon), I noticed the concerns over rotation speed of ballnuts. This made me recall some stuff I read in the TBI catalogue some months back about different types of ballnut (differing mostly in the configuration of the return paths) and their relative speed capabilities, worth a read and maybe doing the sums they outline there.
    Certainly worth a read but what helps with rotating nut is to get shortest length Nut possible.
    It's also critical that the Shaft as a Flange which is machined perfectly concentric to the Nut otherwise concentricity to the screw is misaligned so causes big vibrations.

  9. #188
    Quote Originally Posted by JAZZCNC View Post
    Certainly worth a read but what helps with rotating nut is to get shortest length Nut possible.
    It's also critical that the Shaft as a Flange which is machined perfectly concentric to the Nut otherwise concentricity to the screw is misaligned so causes big vibrations.
    What's the thinking behind the shortest possible nut please?

    The concentricity is an obvious thing and might rule out some of the cheaper offerings if my experience on the machine I've just completed is anything to go by. Having set everything up and got it working smoothly I thought I'd spin one ballnut through 180deg to get better access to the lube nipple. Major fail, that side of the axis got really stiff, it turned out that the casing/flange of the ballnut was something like 1 or 2 degrees out of alignment with the axis of the screw.

  10. #189
    Quote Originally Posted by Voicecoil View Post
    What's the thinking behind the shortest possible nut please?
    access/interference and balance/inertia mostly, it's no big deal and depends on the design to some degree but shorter is better in my experience.

    Quote Originally Posted by Voicecoil View Post
    The concentricity is an obvious thing and might rule out some of the cheaper offerings if my experience on the machine I've just completed is anything to go by. Having set everything up and got it working smoothly I thought I'd spin one ball-nut through 180deg to get better access to the lube nipple. Major fail, that side of the axis got really stiff, it turned out that the casing/flange of the ball-nut was something like 1 or 2 degrees out of alignment with the axis of the screw.
    It's not always the case obvious to everyone that's why I mentioned it. However most ball-nuts, even the cheap ones, have a machined reference surface on the outer body which you can chuck upon and skim flange if needed. Thou I've not had any issues if honest.

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