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  1. #41
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    wooooooooooooooo

    very nice information , nice work

    cheers



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    I am sure I missed this somewhere,but does a ballscrew have a gear ratio?eg
    20mmdia pitch05mm
    Thanks
    Larry



  3. #43
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    Hi there,

    nice sumup swede!!

    may i bother you to ask if the ground acme leadscrew has "zero"backlash

    must be fun grinding a nut though.
    Should i imagine like 5' abrasive acme leadscrew wich the nut are driven from one end to another until the abrasive screw stops wearing ?

    THX alot



  4. #44
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    Ground Acme screws have backlash (plenty of backlash), but also have a higher potential for linear accuracy than ballscrews do. High quality Acme screws can undergo further correction and finishing, whereas additional finishing on ballscrews upsets the thread form.

    You can buy a hydrostatic leadscrew, which provides the positioning accuracy of an Acme screw with spit and polish, and the zero-backlash of a high quality ballscrew.

    However, hydrostatic leadscrews are ridiculously expensive. Direct, uncorrected positioning to a couple millionths of an inch doesn't come cheap.



  5. #45
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    were is a good place to purcase ball screws



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    any one know the difference between rolled ball screw and a precision one .



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    Difference 'tween rolled and precision are found in PRICE and ACCURACY, specifilally in how they spedify lead and repeatability..

    The supplier of/for the screw has specs regarding both - they vary from maker to maker and accuracy class to class.

    HIWIN is a good place to go for information on prrecision ground as opposed to rolled screws.



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    Default Precision for Rolled Ballscrews

    Your question, use of terminology is incorrect as you are trying to compare a product that has an association with a factor of itself.

    Precision is dependant upon a standard measurement, we call this class
    Unfortunately there a various standards through out the world.

    As a rule: Precision Ballscrews are equal to or better than Class 5, Rolled ballscrews fall into this standard when they can be assembled as preloaded.
    Due to the process of manufactuing a rolled Ballscrew spindle only a few spindles in each batch fall into this class.

    Lead is also a factor due to the plastic deformation process and heat treatment used when producing rolled spindles. Only certain leads are available as rolled.



  9. #49
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    i foud some ball screws with the accuracy of c5 (.018/300mm) are these okay .they also have a double cut ballnut all greek to me .seems to be a good price any feed back would be welcome thanks so much to everyone for the help.

    Last edited by woffler; 12-11-2007 at 08:11 PM. Reason: forgot somethig


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    Question NEED HELP WITH ABC's OF SCREWS

    Looking for the basics of what I need to know before I jump in and buy screws for my cnc router project. I just assume that ball screws are better??? What diameter??? What pitch???




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    Default Ballscrew Terminology

    Double cut refers to a ballnut which has flats machined on the locating flange as opposed to a fully round locatng flange, example see our Hiwin Ballnut: http://www.worldofcnc.com/main.asp?category=Ballscrews In Europe this style has a standard: DIN 69051, the flange drilling is at 30degrees to the centre line.

    Class 5: for home use this is as good as it gets!!!!

    Quote Originally Posted by woffler View Post
    i foud some ball screws with the accuracy of c5 (.018/300mm) are these okay .they also have a double cut ballnut all greek to me .seems to be a good price any feed back would be welcome thanks so much to everyone for the help.




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    Default Screws for a CNC router

    Confused, having read many ballscrew posts we understand your confusion, too many posts, someone in a professional manufacturing capacity must moderate!!!!

    Don't jump in, your application may be more suitable for trapezoidal spindles.

    To help....we require more information as our advice for machining steel is completely diffent to soft materials!

    What material do you intend to machine, 80% of the time?
    Spindle lengths: How long are the unsupported lengths? (from the fixed / motor drive end to the floating end?)
    Can you supply a drawing?


    Quote Originally Posted by 44propmaker View Post
    Looking for the basics of what I need to know before I jump in and buy screws for my cnc router project. I just assume that ball screws are better??? What diameter??? What pitch???




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    Quote Originally Posted by marchantdice View Post
    Confused, having read many ballscrew posts we understand your confusion, too many posts, someone in a professional manufacturing capacity must moderate!!!!

    Don't jump in, your application may be more suitable for trapezoidal spindles.

    To help....we require more information as our advice for machining steel is completely diffent to soft materials!

    What material do you intend to machine, 80% of the time?
    Spindle lengths: How long are the unsupported lengths? (from the fixed / motor drive end to the floating end?)
    Can you supply a drawing?
    I think I will be machining .125 acrylics, up to 1" balsa wood and thin aluminum up to .060".
    What do you think? Am I asking too much? As far as unsupported lengths... I'm not sure exactly what your referring to. Is it the amount of stock that would extend outside the cutting parameters?
    I don't have any specific drawings of anything yet, This is just going to be a tool to add to my collection.




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    Default can you take the nuts off the screws?

    Ok, I'm going to ask a really dumb question that I haven't seen discussed:

    If I get a ballscrew and ballnut of whatever precision, can I take the nut off (I assume the nuts come assembled on the screw)? Do all the bearings just fall out? Can I get them back in or do I take pains to not let the nut get unscrewed all the way in the first place? Can I set the backlash myself or is it set at the factory by the size balls, etc?

    Thanks. I am starting a build and I am deciding between ACME and ballscrews for wood routing.



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    Can you take the nut off? Yes Would you want to? Hardly.

    The replacement of the balls can be an exercise in futility as it is a PIA to do. Granted, it can be done and once you do it, the next time is easier. BUT the process is time consuming and not one that works well with SWAG or helter skelter processes. There are better and more productive things to do with your time.

    The raceways that the balls travel thru are not simply curved radii like a gutter at a bowling alley. Rather they are a form of a gothic arch. This causes the balls to make 4 point contact - 2 points in the nut, two in the screw. Essentially, the balls make contact at points roughtly 45 degs off of vertical up and down on the nut and screw.

    To adjust backlash, simply put in larger or smaller balls. BUT you only should change balls in 0.0001" increments. Hence, it is often a hit miss process of fitting severa size balls to get what you want for backlash. SInce you are working in tenths changes in ball diameter, the trick is to find a source of various diameter balls this accurate when/if you sit down to reset backlash in a ball screw/ball nut.

    I used to source balls of this accuracy from Winstead Precision ball. Whether or not they have what you need or will still sell in small quantities is the problem. And, you have to buy HUNDREDS if not thousands of balls at a time - the Graingers and M-C's of the world dont' typically specialize in balls of this quantity, size differential and/or accuracy. Regarding accuracy, you want to get Grade 5 balls - there is a noticable difference 'tween 5's and anything less accurate.

    Explanation: picture a go cart running on 4 different sized tires. It is easy to see how the tires would be unequally loaded. Same deal when you use Grade 5's versus 10's, 25's or even 100's to try to roll evenly and smoothly thru the ball path where you are essentially operating with metal to metal contact and ZERO radial/axial clearance. All of a sudden if larger or smaller balls come into play, things get noticeably harder or easier to turn.

    Resettnig clearance in ball screws is NOT a hit or miss deal. Throwing a half thou SWAG change in ball size could result in locking the nut onto the screw and, worse yet, brinnelling the pall path. Once you brinnel the ball path, the screw is junk as you'll always have brinnell dents at that point and the screw will ALWAYS turn rough and sloppy at the damaged point.

    Find a ball screw repair house and have them do it. It is not that expensive. In my case I know how to do it, know where to get EVERYTHING yet I still pay to have it done. That should say something about the process.



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    (Ballnut, spindle and a few balls on the floor - what can go wrong?)
    Ballnuts can be removed by the end use however as a ballscrew manufacturer we would not reccomend this as rebuilding can cause issues......

    So remove the ballnut from the spindle and most of the balls will fall out.

    Replacing the original balls, this is easily done using a mandrel (a tube machined to the same diameter as the spindle root diameter) insert the tube into the bottom of the ballnut, fill the first circuit advancing the mandrel as you go. 2nd, 3rd circuit etc etc.
    Next place the spindle horizontal in a machine vice (use 2 peices of wood to protect the spindle) placing the start of the spindle thread in the 12 o'clock position. Carefully look in side the ballnut for the start of the first circuit and mark the position on the out side of the ballnut.
    Slide the mandrel and ballnut over the end machining with the ballnut in the 12 o'clock position rotate the ballnut in a clockwise direction and the nut will advance down the spindle (like a nut and bolt) If the ballnut sticks, lightly tap the nut body.

    You only learn by making a mistake......

    Preloading, leave this to the manufacturers or a rebuild service.



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    Default Go for a ground ballscrew of lower accuracy

    This is all true with one exception - accuracy class of ground ballscrews! I worked for a ball screw manufacturer some years ago and this is my advice:
    buy lower accuracy ground ballscrews because practically all classes of ground ballscrews have more or less the same high accuracy. This is due to the fact that ballscrews are ground on high precision CNC grinders. Such CNC grinder is not programmed differently for a lower accuracy class than for higher accuracy screw! Therefore, if a ballscrew manufacturer gets an order for e.g. 10 lower accuracy ballscrews he (they) will always use the same program and machine setup to make only 10 pieces - the same as if he had an order for 10 highest accuracy screws. Ror this reason I would never order anything higher than C5.



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    Offcourse jazek, the manufacturer will use the same g-codes.
    Though i'm sure that there will be a difference in the machining proces in regards of how many times the grindingstone will be dressed and how many cycles he will run it.Cycles meaning a tolerance check and regrinding when necessary.
    I also can't see what would stop a manufacturer to put the 10 by "accidentally" C1 grade screws on stock and getting to charge some one that orders c1 much more for the same screws whilst just manufacturing you 10 different c5 screws.

    I'ld like to hear what nccam has to say about this subject.

    Finally CHIPS you can have as much as you can without the doc. complainting about your cholesterol.


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    Jwezy is right, that ball screw plant is pretty much geared to make one product accuracy grade. Hence, you can PROBABLY get away with the lowest accuracy part although you'll PROBABLY be getting high accuracy. SOMETIMES, the ONLY difference is the certification papers.

    I know of an instance where the highpoint of eccentricity markings on a bearing were essendially phony. The bearings had NO perciptible or even measureable eccentricity BUT the market was so accustumed to seeing high point, markings, they put them on even though there was none.

    Ditto that for this particular plant's ABEC ratings. The bearings were all ABEC 7 (ISO P4) or better, yet the bearings were packaged and priced to the order requirements that were made. Yes, ABEC 7's were packaged as 7's, 5's and even 3's, and priced pursuant to the market price for the corresponding grade of bearing.

    Caveat: not all bearing companies do that sort of deal so you you CAN'T take this as a blanket claim.

    Regardless of the application, the more accuracy you scrimp and save for and build into your machine, the better it will run/finish. In other words, buy the best you can't afford and you woun't be disappointed. Nobody I know of was ever disappointed from buying something better than they needed.



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    that being said ,i must have completely misunderstood the manufacturing process of these beautiful tools referred to as ballscrews.I'll study more.

    I guess one should keep track of wich manufacturer was the las tto upgrade their production machinery since they'll pro bably have most high-grade overstock.

    my earlier response was stooled on the idea that flat and especially form/thread grinding requires frequent tolerance checks and adjustment for the wear of the grindingstone.
    So i assumed a manufacturer will put more effort into the checking and adjusting of the higher then the lower grade screws.
    '
    The last i would like to state is that i think the "lower grade"precision ballscrews are way-deluxe for a hobbyist so you almost can't miss when acquiring screws that are in good condition.

    Finally CHIPS you can have as much as you can without the doc. complainting about your cholesterol.


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