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  1. #1
    ok this will most likely be the most stupidest question to most of you guys on here, but for the love of trying i cant seem to find the answer.

    when i look for ballscrews i see 2 types, really cheap ones with no end machining and then really expensive ones that are machined..

    my question is do you buy machined ones for certain applications or do you always need to machine them?

  2. #2
    hi Wilfy

    The only stupid questions are the ones you don't ask! :-)

    You might be confusing precision ground ballscrews with end machining? The really expensive ones are likely to be precision ground eg very accurate, 830 nanometers per centimeter or less (or more). End machining is the sizing of the ends of the ballscrew to allow the fitment of bearings, pulleys or connector to some type of motor to get it to turn. You can and probably have to machine the ends of both types, depending on the application and how its used.
    Last edited by mocha; 19-07-2012 at 11:58 AM.

  3. #3
    Quote Originally Posted by wilfy View Post
    my question is do you buy machined ones for certain applications or do you always need to machine them?
    Pretty much every application needs them end machining.

    Plenty of people here, myself included, have bought ballscrews with end machining on eBay from linearmotionbearings2008. He will cut them to whatever length you require and can do custom end machining if required. He charges hardly anything for end-machining, so they are very cheap:
    http://www.ebay.co.uk/sch/linearmoti...ngs2008/m.html

    All the ballscrews he sells are C7 grade, which is 0.05mm per 300mm (not simply cumilative), or if for some reason you want nanometers per cm that's 1667. Howerer very few 'hobby cnc' applications require better although it's nice if you can get a higher grade cheaply.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #4
    ok it is in fact a silly question then as i had it in my head you could put a coupling straight on to a ball screw and attach it straight to the stepper.

    so with the mind set that i want to go for a straight motor to ballscrew i presume something like this is the kind of kit that would do everything including support one axis?? http://www.ebay.co.uk/itm/1antibackl...#ht_616wt_1163

    the above length is 547mm would this be the complete work length of that axis or do i need to take more out of that? i have nothing set in stone yet i am just trying to get an idea what i can work with and cost before i decide on the size of machine i need.

  5. #5
    Quote Originally Posted by wilfy View Post
    ok it is in fact a silly question then as i had it in my head you could put a coupling straight on to a ball screw and attach it straight to the stepper.
    One reason you can't do that is some bearings are required to resist the axial (parallel to the axis of the screw) and radial (to a lesser extent) forces on the ballscrew. The bearings in the stepper motor are very small and not the right type. The bearings in the BK/BF blocks you lined to are angular contact bearings which are used because they resist axial loads.

    Quote Originally Posted by wilfy View Post
    so with the mind set that i want to go for a straight motor to ballscrew i presume something like this is the kind of kit that would do everything
    Yes and no - the bearing blocks are generally fine, but sometimes they need a bit of TLC to get running smoothly. However the coupling is a flexible type, which has relatively poor torsional stiffness and are not particularly strong. I know of at least one member on this forum who has had problems with that type of coupling snapping. You either want to get solid couplings (if the motor can be aligned accurately) or oldham couplings, since these are the types that will not introduce backlash.
    You would be better of using a timing belt drive with two pulleys. This gives you the option to change the drive ratio between motor and ballscrew, to maximise either feedrate or resolution. In addition the timing belt has a damping effect which can help suppress resonant vibration, which ultimately leads to a smoother more stable system. Generally the most suitable belts and pulleys are 5M HTD (5mm pitch). Don't go below 15T for either pulley, ideally stick with more to prevent stressing the belt. Currently bearingstation is the cheapest place to buy belts and pulleys.

    Quote Originally Posted by wilfy View Post
    the above length is 547mm would this be the complete work length of that axis or do i need to take more out of that?
    547mm is the overall length of the ballscrew including end-machining. So since the ballnut is 42mm long and the end machining is 44+12mm, that leaves 449mm travel. Realistically a little less due to the seals and stuff getting in the way. Here's the end machining drawing to help work things out:

    Click image for larger version. 

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    Also, if you do decide to get pulleys I advise getting dimension F increased from 15mm to 25mm to make it easier to fit and align the pulleys.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. The Following User Says Thank You to Jonathan For This Useful Post:


  7. #6
    i was looking for a direct connection due to eliminating something extra to line up, this being my first machine. but if using a pulley system has it's advantages then i'll have to look at this route. i'm not bothered about the speed at which the router will complete a piece so making things better for speed do not interest me.

    thank you for the drawing that really helps me picture a few things, i've got alot mroe reading up to do but this certainly helps me start thinking about size and cost of the machine.

    thank you very much for your help guys

  8. #7
    I've also realised the reason i thought there was such a big difference in price between machined or not is due to me comparing a pre cut length machined piece vs price per 100mm :/

  9. #8
    Quote Originally Posted by wilfy View Post
    i was looking for a direct connection due to eliminating something extra to line up, this being my first machine.
    You've got less to align with the pulleys - just need to make sure the shafts are not skewed which isn't hard ... make sure you can adjust the centre distance so the belt can be tensioned. Easiest way generally is to put slots in the motor mount so the motor can be slid then bolted down.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  10. #9
    again thanks very much for your input as a new member it is very much appreciated

  11. I have just got my custom machined 1605 Ballscrew from Chai (linearmotionbearings2008), very happy with it and his servce, it took less then two weeks from me placing the order, and e-mailing him the drawings to when it turned up at my door.
    "If first you don't succeed, redefine success"

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