Selecting the right ball screw Size and system


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    Default Selecting the right ball screw Size and system

    Hi there

    I am trying to build a new system, and I have a question on selecting the linear drive system. question is as follow;

    this is for a 2 meter * 4 meter wood cutting Router.
    I know if I use a Rack and pinion system because of the nature of the pinion, I gain speed but I lose power.

    what I was thinking is to use a Ball screw system rather than Rack and pinion, But In order to compensate for the speed that I lose,

    I want to use Screw with Pitch distance of a bout 2 or 3 Cm.

    Do you recommend such system? What would be the right crew Diameter for the Y axis of about 4 meter?
    And if you know the proper brand name that has such screws please let me know. Finally do you recommend the Double Nut or ball on it?

    regards
    johnansaro

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    Default Re: Selecting the right ball screw Size and system

    Neither rack and pinion or ballscrews is more powerful. It just depends on your gearing. You're entire drive system needs to be matched together to work the best. You should take into account what motors you plan on using when you make your selection?
    Personally, I think rack and pinion is a much better choice for a 4m axis.
    For a ballscrew that long, I'd use something 32mm-50mm in diameter, with a 32mmpitch, and a fixed screw with spinning nut.

    Gerry

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    Default Re: Selecting the right ball screw Size and system

    4 meters is over 13 feet long.

    Please use rack and pinion with an appropriate spring loaded gear reduction system. For servos, a low backlash planetary gearbox or belt reduction system 4:1 to 10:1 depending on pinion size. For steppers, a belt and pulley gear reduction system 2:1 or 3:1. Use at least Nema 34 if using steppers.

    If you are stuck on using ballscrews, then consider a rotating nut where the ballscrew does not spin.

    If you persist in using ballscrews that spin, a minimum of 25mm lead, perhaps 40mm lead. I'd really need to do the math considering a number of factors like the torque vs speed graph of the motors and the weights of the parts to give you a better answer. Also if the screw diameter is too large, you will need larger motors to accelerate and decelerate such a large screw. A number of factors come into play here, with how big, how heavy, how fast you want the top speed and acceleration.

    I assume that this is because of your last build where you had problems with missing steps and rack and pinion? Use gear reduction and a properly spring loaded pinion and you will have less problems. Best idea.

    2nd Best idea. Use a rotating nut.

    3rd Best idea. minimum of 25mm lead, maximum of 40mm lead. Not sure what the shipping cost would be on a 13 foot long ballscrew though. Probably 25mm diameter, no larger. That's my best guess without doing any math and not knowing all the factors.



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    Default Re: Selecting the right ball screw Size and system

    Hi There

    Thanks so much for your most valuable reply.
    But correct me if I am wrong, that a properly sized and designed Ball and screw system is better than a Properly sized and designed Rack and pinion system.

    For the simple fact of that pinion is only partially in contact with Rack compare to Total Contact of Ball and screw.

    The only draw back that I can see for Ball screw system is the size of my Table, which makes it hard to find and install a 4 meter Long Screw.
    (keeping it straight, and avoiding it to bend, I think is the challenge)

    From what I know the only advantage of Rack and Pinion, (besides that fact that they come in Length of 2 meter) is the Speed that they can get,
    and this can be Achieved by increasing the Length of Pitch Lead in Ball and screw systems.

    Therefore at it's best scenario a R&P Spring loaded System with 3:1 gear reduction. is a equivalent of a 32 mm Lead pitch.

    Also thanks for your recommendation of the Fixed screw and Rotating Nut System(some thing that I did not know about it),
    which makes a lot of sense, since I do not need to spin the 4 meter Long Screw, and All I have to spin is the Nut,
    but the draw back is that I need to move the motor just like the R&P System.

    Can you provide any link or Info's on all the types of Fixed screw and Rotating nut Systems?

    Regards
    johnansaro

    Last edited by johnansaro; 09-09-2017 at 11:12 PM.


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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by johnansaro View Post
    But correct me if I am wrong, that a properly sized and designed Ball and screw system is better than a Properly sized and designed Rack and pinion system.
    At the size of machine you're talking about, I don't think so. Also, you are building a wood working machine. Not a VMC. Have a look at all of the very successful commercial wood working machines of comparable size. I'm talking about Biesse, something like that. Very high end top of the line machines. Coincidentally, those kind of machines also cut aluminum well. So find a large, high quality, top end commercial machine, of the same size you want to build that uses a ballscrew. How many are there that do that? Rack and pinion is the better choice IMO, for a machine that large.

    Quote Originally Posted by johnansaro View Post
    From what I know the only advantage of Rack and Pinion, (besides that fact that they come in Length of 2 meter) is the Speed that they can get, and this can be Compensated by increasing the Length
    I assume you mean increasing the lead of the ballscrew? You'd also have to use more powerful motors to account for the inertia of the long ballscrews.

    Quote Originally Posted by johnansaro View Post

    Therefore at it's best scenario a R&P Spring loaded System with 3:1 gear reduction. is a equivalent of a 32 mm Lead pitch.
    It is in that ball park, but it's not a best scenario, it depends on the radius of pinion that you use, and there are different sizes you can choose from.

    I am not an expert on rotating nuts, perhaps someone else can help you there, or you will have to search online. I only know that for a machine that large, the only way I would consider a ballscrew is if it had a rotating nut. But that's just my opinion. It would be more costly to do it that way compared to rack and pinion. How easy it would be, I don't know.

    Your best bet is to copy a design that is easy to build and has worked well for other people, and meets your requirements for top speed, acceleration, and depth of cut. Those are of course parameters that you must balance cost and time against performance.



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    Default Re: Selecting the right ball screw Size and system

    Hi John,
    Have you seen nexen if you want to overcome limitation on using traditional gear and rack... but maybe very expensive ...

    http://www.nexengroup.com/



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    Default Re: Selecting the right ball screw Size and system

    Hi there
    My particular thanks to NIC 77 , and asuratman for your reply.

    The nexen product that asuratman has mentioned seem very interesting and promising,
    I have to check to see that, if I can find them in my neck of the wood.

    Have any one had some experience with them? Please let me know.

    But NIC 77 , I know that possibly most of the most Professional wood cutting machines
    that have been made use R&P Systems, off course as you know that

    They mostly use Servo Motor with some kind of Gearing system, which is expensive.
    Not that I do not want to go that path, But i am just curious,
    that If one does not want to spend that much. Can one put together a Descent enough Machine
    using step motors? and knowing the limitation of step Motors in higher speed,
    I came up with Idea of using Long pitch Lead Screw.

    I just want to make it as simple as possible, Basically the system that I am thinking
    has only Step motors mounted directly on the Screw,
    OR for the case of fixed screw through a pulley system.

    I am just concerned on using that 4 meter long possibly with 25 mm or 30 mm diameter Screw,

    Has any one had such a experience? Is it physically possible to use such a
    Long screw with out being bent,/ curved, and causing some kind of malfunction on it's behavior?

    regards
    johnansaro



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    Default Re: Selecting the right ball screw Size and system

    Quote Originally Posted by johnansaro View Post
    But NIC 77 , I know that possibly most of the most Professional wood cutting machines
    that have been made use R&P Systems, off course as you know that
    Of course I know that. I'm just trying to get you to do some searching at what other people have made to be successful. Also, I'm not an expert on the subject, so perhaps you will find something I haven't.

    Quote Originally Posted by johnansaro View Post
    They mostly use Servo Motor with some kind of Gearing system, which is expensive.
    Not that I do not want to go that path, But i am just curious,
    that If one does not want to spend that much. Can one put together a Descent enough Machine
    using step motors? and knowing the limitation of step Motors in higher speed,
    I came up with Idea of using Long pitch Lead Screw.
    If you're looking at using Nema 34 steppers, yes, I believe that you can make a decent enough machine for a rack and pinion system. For a ballscrew of that length, I don't think so. For rotating nut ballscrew design, quite possibly.

    If you want really fast accelerations and top speeds of 1000 IPM, then no. But a decent enough machine, yes.

    Quote Originally Posted by johnansaro View Post
    Has any one had such a experience? Is it physically possible to use such a
    Long screw with out being bent,/ curved, and causing some kind of malfunction on it's behavior?
    Whether or not you can buy such a long screw from China without it being bent, I don't know. To buy it from somewhere else, really expensive.

    I have seen a video of someone using a long screw but they had to make a contraption to prevent whip and support the screw in the middle then move out of the way as the ballsnut passed by. It seemed very precarious to me, I'm not sure it's the best idea.

    I've got a .pdf file from THK for rolled ballscrews, it gives the ballscrew root diameter for their different rolled ballscrew sizes. I assume all rolled ballscrews will be fairly similar from different manufacturers, so I just use this file for calculations.

    If we look at the Nook Industries Critical speed calculator (which can be over conservative depending on how straight the screw is, but it is what they recommend)

    Metric Critical Speed Calculator | Nook Industries

    Using a bearing to bearing distance of 4000mm and an end fixity of "B"

    25mm ballscrew, about 22mm root diameter gives a critical speed of 166 RPM

    32mm ballscrew, about 28mm root diameter gives a critical speed of 212 RPM

    so for a 40mm lead, 212 RPM x 40mm per rev = 8480 mm / min = 333 IPM

    And a 32mm ballscrew, 4 meters long, will need a larger motor than rack and pinion or rotating nut. If you go with larger than 32mm then the cost will be much larger as well, and the size of the motor needed will go up, and the relationship isn't linear.

    Of course, the Nook calculator can be a bit over conservative, and perhaps the 4 meters was overall length and not length of travel.

    I have found some videos of fast moving ballscrew driven machines from China on YouTube, but they don't tell you if it's rotating nut, or what the lead is, or what the motor size is. It could be a 2" diameter high lead screw driven by a 1kw servo with belt reduction for all I know. Lots of $$$ to do that.

    So for a 40mm ballscrew, about 35mm root diameter, you are looking at a critical speed (according to Nook) of 264 IPM

    and for a 50mm diameter ballscrew, about 44mm root diameter, 332 RPM

    So for a 4080, 264 RPM x 80mm = 21120 mm / min = 831 IPM, but you're not going to get away with Nema 34s on that. Perhaps Nema 42 or a large servo with belt reduction, I'd have to do the math, sufficeive to say, it's a high budget option.

    For rotating nut, perhaps someone else can help you, I've never tried to design a rotating nut machine, or have even looked into it very much.

    Good luck.



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    Default Re: Selecting the right ball screw Size and system

    Keep in mind that the bigger the motor, the slower it's going to spin.
    A rack and pinion system with CNC Router Parts carriages is going to be the least expensive by far, and the best performing. Imo, there's no way to get good performance from a 4m screw and steppers. Remember, with steppers, as you increase speed, you lose resolution, because steppers have a fixed resolution, and more speed usually means spinning them slower.
    A spinning nut will work, but you'll need a good design for one, and the ability to fabricate the components.

    I use a 4m long machine with a ballscrew every day. It uses a large AC servo, and spinning nut. And it still requires a support in the middle of the screw, to prevent sagging. The support moves out of the way when the carriage passes it.
    It's a $150,000 machine.

    Gerry

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    Default Re: Selecting the right ball screw Size and system

    Hi ger21 , and NIC 77

    Thanks a lot for your reply.

    Could you please provide a picture or a video link of that Moving support, that you mentioned.

    Is this moving support a must to have or is it a good optional Item?

    otherwise if I do not have it, am i going to have a sagged screw?

    reagards
    johnansaro

    Last edited by johnansaro; 09-11-2017 at 04:29 PM.


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    Default Re: Selecting the right ball screw Size and system

    Hi ger21

    Also about your machine's screw, could you tell me, what is the Length of your pitch Lead?

    and what is it's Diameter?

    and do you use any gearbox with your servo motors, and if not, and you use only a pulley System,

    is it a simple pulley (1:1 ratio) or is it a speed reduction of some sort(like 3:1 ratio)

    Regards
    Johnansaro



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    Default Re: Selecting the right ball screw Size and system

    I won't be able to check for a few days.
    It's between 30-50mm pitch, and the screw is about 32-40mm.
    It uses a roughly 3:1 belt reduction on the spinning nut.

    The support is just a spring loaded support in the center, that gets pushed aside as the machine passes. Yes, the sscrew would sag a lot without the support.
    Also, the screw is under tension. It's installed with a dial indicator, and tightened until it moves about .03". It's a LOT of tension.

    Gerry

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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

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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?



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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.



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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

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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



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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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