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  1. #13
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    Default Re: Selecting the right ball screw Size and system

    Hi,

    Non expert here but, aiming to build the same kind and size of machine, I've been searching, reading and learning from every web resources I could find.

    Like you, in the beginning, ballscrew seemed the best way to go. In the end, my machine will use so kind of R&P system.

    The complexity and requirements (and price) rocket when you consider BS for sizes over 1,5m with high acceleration and high speed. They do in a way that if the purpose of the build is to cut wood, it barely doesn't make sense any more.

    For my project, DamenCNC's straight rack and double pinion system, discovered through RoboCNC's excellent X2 build series on YT, made me make the switch to R&P !

    I'm also considering helical R&P for best of breed choice but these again, needing an high precision ground support, raise requirements for the structure. Also, creating an axial load on the motor/gear assembly, this has to be taken into account in the design. Thus, helical R&Ps can't be directly substituted in straight R&P machine designs we can find around :/

    Hope it'll help
    Jérémie

    Envoyé de mon A0001 en utilisant Tapatalk



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    Default Re: Selecting the right ball screw Size and system

    ger21, does that machine use a single ballscrew on the long axis under the table or does it have two?

    Would you say the performance is any better than the rack and pinion machines you have?

    Interesting that it is a rotating ballnut but it still needs a spring loaded support in the center.

    Here's a video on Youtube



    And he posted CAD files of the parts he had to make

    https://grabcad.com/library/rotative...t-isel-25x10-1

    I still think this is not the best idea for such a large machine compared with rack and pinion, but thought you might find that interesting. You might find a couple used rotating ballnuts on EBay. For an arm and a leg.

    Also looked at a couple videos of rotating nuts on YouTube that sounded awful.

    John,
    Can we at least agree that for a machine that long, a regular ball screw with a not rotating nut is a bad idea?



  3. #15
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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by silopolis View Post
    Hi,

    Non expert here but, aiming to build the same kind and size of machine, I've been searching, reading and learning from every web resources I could find.

    Like you, in the beginning, ballscrew seemed the best way to go. In the end, my machine will use so kind of R&P system.

    The complexity and requirements (and price) rocket when you consider BS for sizes over 1,5m with high acceleration and high speed. They do in a way that if the purpose of the build is to cut wood, it barely doesn't make sense any more.

    For my project, DamenCNC's straight rack and double pinion system, discovered through RoboCNC's excellent X2 build series on YT, made me make the switch to R&P !

    I'm also considering helical R&P for best of breed choice but these again, needing an high precision ground support, raise requirements for the structure. Also, creating an axial load on the motor/gear assembly, this has to be taken into account in the design. Thus, helical R&Ps can't be directly substituted in straight R&P machine designs we can find around :/

    Hope it'll help
    Jérémie

    Envoyé de mon A0001 en utilisant Tapatalk
    That's interesting. First time I've come across this double pinion. I just skimmed through a couple of videos on the Robo CNC website.

    I'm wondering, why he's using a 10:1worm reduction on a stepper motor for rack and pinion? What is the radius of the pinions, they look quite large? Do you know what the overall machine travel is per rotation of the motor? Any mention of backlash on the worm gear? Hmmm, you know, you could do the same thing, 2 pinions, with belt gearing instead of a worm gear on the other side (but not at 10:1, like 2:1 or 3:1)

    I couldn't find any videos of the thing actually running or what speeds and accels they are getting. Also, I didn't notice any spring loading but I may have missed it.

    I will reserve final judgement until I see the thing actually running around cutting, and hear some user reviews, but definitely interesting. Thanks for sharing.

    Perhaps John should just buy the parts from robo CNC and do a kit build, sourcing the rails and T slot from whoever is closest / least expensive for him.

    Of course, a single pinion for each motor works fine.



  4. #16
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    Default Re: Selecting the right ball screw Size and system

    ger21, does that machine use a single ballscrew on the long axis under the table or does it have two?
    Just one. It's a cantilevered gantry that's open on the front side of the machine. It's a 6ft gantry beam, about 18"x18", made of bent and welded 1/4" plate, to form a tube, with the ends capped.

    Interesting that it is a rotating ballnut but it still needs a spring loaded support in the center.
    Just to keep it from sagging when the machine is parked at the home position. It doesn't do a lot.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by NIC 77 View Post
    That's interesting. First time I've come across this double pinion. I just skimmed through a couple of videos on the Robo CNC website.
    For those interested:
    * RoboCNC X2 page: https://www.robocnc.nl/?page_id=5300
    * RoboCNC X2 build YT playlist: https://m.youtube.com/playlist?list=...yCkJLcRBChdojC
    * DamenCNC Worm Gearboxes: https://www.damencnc.com/products/me...404_w_75__GB_1
    * DamenCNC linear motion modules: https://www.damencnc.com/products/mo...404_w_72__GB_1
    * DamenCNC RTR kits: https://www.damencnc.com/products/ma...04_w_340__GB_1

    I'm wondering, why he's using a 10:1worm reduction on a stepper motor for rack and pinion?
    Seems to be the recommended ratio by DamenCNC for high loads, vs 5:1 for light loads

    What is the radius of the pinions, they look quite large? Do you know what the overall machine travel is per rotation of the motor?
    Can't remember, but pretty sure Marcel mentions all these infos in his detailed videos

    Any mention of backlash on the worm gear? Hmmm, you know, you could do the same thing, 2 pinions, with belt gearing instead of a worm gear on the other side (but not at 10:1, like 2:1 or 3:1)
    For the gearbox backlash, from the V30 i spec:
    * 8 arcmin or less on reduced backlash models (no load conditions)
    * 8 arcmin or more on normal backlash models

    I couldn't find any videos of the thing actually running or what speeds and accels they are getting. Also, I didn't notice any spring loading but I may have missed it.
    I know Marcel has been busy since his last video but came back lately to announce follow ups soon... Agreed I'd love DamenCNC to have demo videos, and will surely suggest them to make some in my next message. As they invited me to visit them to see a machine running, I may end up filming it myself...

    About spring loading, I have to watch Marcel's worm gear assembly and mount videos again...

    I will reserve final judgement until I see the thing actually running around cutting, and hear some user reviews, but definitely interesting. Thanks for sharing.
    You're welcome As told, ain't no guru here and so, all opinions, PoV and constructive criticisms are very welcome and looked for.

    Perhaps John should just buy the parts from robo CNC and do a kit build, sourcing the rails and T slot from whoever is closest / least expensive for him.
    Parts, modules and kits should be bought from DamenCNC.com. Don't hesitate to contact them for further informations and advices, they're very competent and willing to help Selecting the right ball screw Size and system

    Of course, a single pinion for each motor works fine.
    Of course, but in this case I'd love to find a solution to build a structure suited for helical R&Ps



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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by NIC 77 View Post
    ...
    I will reserve final judgement until I see the thing actually running around cutting,...
    Only video I could find is here

    And here is the link to the R&P anti-backlash assembly: https://www.damencnc.com/products/me..._w_74_554_GB_1

    There's no spring loading of the pinions on the rack, but you'll see slots for adjustment. Could be modified to add spring loading I think



    Envoyé de mon A0001 en utilisant Tapatalk



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    Default Re: Selecting the right ball screw Size and system

    I see, you can use either a 5:1 or 10:1 worm gear.

    https://www.damencnc.com/products/me...w_74_247_GB_1#

    Oh, I see, the 15T pinion has an effective diameter of 30mm.

    8 arcminutes of backlash is (8/60) = 0.133 degrees

    (2 x pie x 15mm) x (0.133 / 360) = 0.035 mm = 0.0014" backlash from the worm gear. So not too much, but more than a thousandth. Perhaps more on the non reduced backlash model.

    It seems to me like the 5:1 is a better choice. 10:1 is too much for a stepper.

    https://www.damencnc.com/userdata/fi..._Ghirri_MV.pdf

    So if we look at page 18, the efficiency of the 5:1 MV40 is 76% and for the 10:1 MV40 is 69%. Did I misread that somehow? That's really bad. A typical planetary gear is around 94% I believe.

    Also, I could not find the gear output inertia listed. That's needed for acceleration calculations. Do you know where to find it?

    So 160 Euros for the gear + 270 Euros for the two pinion system + VAT = 430 Euros + VAT = 514.22 USD + 103 USD VAT @20% (not sure if you have to pay this if you live in another country, instead, probably customs and import to your country.) That's pretty expensive.

    I would like to see the video of doing a 3d carving in wood at 500 IPM with 800 IPM rapids.

    The double pinion system might have merit, but at this point, I'm not convinced in this particular system.



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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by NIC 77 View Post
    I would like to see the video of doing a 3d carving in wood at 500 IPM with 800 IPM rapids.

    The double pinion system might have merit, but at this point, I'm not convinced in this particular system.
    If you want a machine to perform , then you have to have a good selection of components, the machine in these videos, was built for speed and high production, both where achieved, the cost was high for the machine build, the machine payed for it's self in less than a year, that was 5 years ago, it now has multiple tool change racks and 2 ATC Spindles

    This Home built machine here can run 2500 IPM Rapids and runs 3D easy at 600IPM cutting

    , it was running at 500 IPM in this Video cutting



    Mactec54


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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by mactec54 View Post
    If you want a machine to perform , then you have to have a good selection of components, the machine in these videos, was built for speed and high production, both where achieved, the cost was high for the machine build, the machine payed for it's self in less than a year, that was 5 years ago, it now has multiple tool change racks and 2 ATC Spindles

    This Home built machine here can run 2500 IPM Rapids and runs 3D easy at 600IPM cutting
    That's a nice machine. Is it your build?

    Is that a single pinion system using servos and gear reduction?

    I'd like to see the system from Damencnc using nema 34's do the 500 IPM 3D carving and 800 IPM rapids. That was my point, to validate the performance of that specific system. I believe comparable systems, for example, from CNCRP, are capable of that, but at the same time are certainly a step down from the all steel, servo driven machine that you have posted videos of.

    Although, your post is definitely relevant for the OP who is thinking of using ballscrews for a huge router.

    For a large wood working machine, I don't see a problem with a single pinion R&P system to give good performance. On a budget, perhaps he should spend his money on motor upgrades to servos and planetary gear reducers on a single pinion R&P system than to pursue a rotating nut design using stepper motors or even the expensive damencnc double pinion system? Tell us your thoughts.



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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by NIC 77 View Post
    That's a nice machine. Is it your build?

    Is that a single pinion system using servos and gear reduction?

    I'd like to see the system from Damencnc using nema 34's do the 500 IPM 3D carving and 800 IPM rapids. That was my point, to validate the performance of that specific system. I believe comparable systems, for example, from CNCRP, are capable of that, but at the same time are certainly a step down from the all steel, servo driven machine that you have posted videos of.

    Although, your post is definitely relevant for the OP who is thinking of using ballscrews for a huge router.

    For a large wood working machine, I don't see a problem with a single pinion R&P system to give good performance. On a budget, perhaps he should spend his money on motor upgrades to servos and planetary gear reducers on a single pinion R&P system than to pursue a rotating nut design using stepper motors or even the expensive damencnc double pinion system? Tell us your thoughts.
    It has a single pinion, Precision Ground Helical Rack 1Kw Ac servos 20Bit Encoders ( 1,048,576 ppr ) the machine Table is 12' X 6' of Travel

    Mactec54


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    Default Re: Selecting the right ball screw Size and system

    NIC 77

    Here is a photo of the Helical Pinion and lubricator, on that machine, this is what you need if you want / need accuracy and performance

    Attached Thumbnails Attached Thumbnails Selecting the right ball screw Size and system-pinion-jpg  
    Mactec54


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    Default Re: Selecting the right ball screw Size and system

    That is quite the pinion! Obviously those are flange mount planetary reducers?

    Is this system spring loaded or just carefully aligned?

    I've never seen something like that before with the lubrication. Thanks for sharing.



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Selecting the right ball screw Size and system
Selecting the right ball screw Size and system