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  1. #1
    Hi everybody
    Yesterday i receive from Chai the above things

    2X anti backlash ballscrews RM 2010 C7 end machined -1603mm Overall length
    2 ballnuts for 2010 ballscrews
    1X anti backlash ballscrews RM 2010 C7 end machined -1153mm Overall length
    1X anti backlash ballscrews RM1605 C7 end machined -501mm Overall length
    1 ballnut for 1605 ballscrew
    3 Set of BK/BF15
    1 Set of BK/BF12
    1x Ball Nut Mount/Bracket Flange For 1605
    3XBall Nut Mount/Bracket Flange For 2010
    -------------------------------------------------------------------------------------------------------------------------------------

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    I open the box to see if everything is ok
    I attach the bf/bk at the ballscrews, and i realize that the screws seems to be bended
    I give them motion with a wireless drill and they are "dancing" like crazy especially one of the 2010 1603mm long ballscrew. It seems to move 4-5mm out of the center axis. Also the other three are whipping(1-2mm).

    Here are the videos that i capture
    The worst one is at video #1 bended ballscrew 1603mm long - YouTube
    At the following videos 0-4 the ballscrew is rotating with the help of a cordless drill and the bf/bk fixed on a C shape beam
    At the Videos 5-7 i rotate the ballscrew with my hand.

    0 bended ballscrew 1101mm long - YouTube
    1 bended ballscrew 1603mm long - YouTube
    http://youtu.be/TWbHcTfAPws
    3 bended ballscrew 1101mm long - YouTube
    4 bended ballscrew 500 mm long - YouTube
    5 bended ballscrew 1101mm long - YouTube
    6 bended ballscrew 1603mm long - YouTube
    7 bended ballscrew 1603mm long - YouTube



    My questions are
    1. Is this bend so bad that make the ballscrews useless
    2. Is there any way to correct the bend
    3. What should i expect from Chai?
    a.To refund me the money?
    b. send other ballscrews with no cost?
    c. Something else?
    4. If i put that screw to my machine should i have resonanse or bearing ware problems?
    5. Did anybody had such problem with Chai? if yes what Chai did ?


    Thanks
    Vagelis
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by ba99297; 04-06-2014 at 08:13 AM.
    The creative adult, is the child who survived

  2. #2
    Wal's Avatar
    Lives in Stockport, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 5-6 years. Has a total post count of 278. Received thanks 24 times, giving thanks to others 6 times.
    Hey Vagelis,

    I'm fairly sure that my (considerably shorter) z-screw isn't 100% straight - they could really do with packing 'em in a rigid box as opposed to cardboard/bubble-wrap, but who knows - it could as easily be a factory issue..! I guess it's a bit of a 'get what you pay for' scenario - having said that, it hasn't really caused me a problem. I think your screws look a lot worse than they perhaps are because the bearing blocks don't appear to be fastened down hard and everything's moving around, which is exacerbating the whip.

    This is a vid I made when I first got my steppers running:



    It looks REALLY bad, but when everything's bolted down it's actually okay. You could really do with having a look at this with the hardware fixed in place, as opposed to bouncing around on a couple of planks... That'll give you a better idea of how bad (or good) things are.

    Chai seems like a decent guy. Always been very helpful on the few occasions I've had to contact him for advice.

    Wal.

  3. #3
    I have told you this in an email but obviously you don't believe me.? . . . . Your cordless drill is exagerating the Wobble greatly and when on the machine and fastened down and aligned correctly it will most likely not be a problem. I have seen worse being used without problems.!!

  4. #4
    The runout on my cordless drill is huge, so if yours is the same that will make things appear worse.

    I recieved a noisy ballscrew which had about 0.5mm run out (measured with it bolted properly to the machine and driven by a stepper motor through a coupling).

    I considered returning it but they are packed in carboard boxes so chances are it would be no better if they sent another one.

    So I sent it off to a UK company and they straightened it to a claimed <0.05mm run out. Cost 45. After that it ran very smoothly and quietly.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #5
    Wal thanks for your answer.
    Dean of course I believe you
    The main reason I upload the videos and the photos is because I want to get a general idea from other members that had the same problem, and get some advices about what to do with Chai.

    1. Ask him to replace the ballscrews
    2. Ask for a refund.
    3. Do nothing because this bend isn’t enough.

    Is this bend enough to make such a claim?

    Also should I try to straighten the ballscrews?
    It is more than possible that if I bolt everything down the problem will be reduced but my main concern is the forces that will be applied to the ballnut and the carriages are enough to ware linear rails and ballscrews.

    Generally I want your opinion-advice about what to do with Chai

    Routercnc mine ballscrews have a runout 2mm one 1603mm long, and 1mm the other three. You can see that at videos 5,6,7 when i turn the nut with my hand and not with the cordless drill.



    Thanks for your time.

    Vagelis
    Last edited by ba99297; 04-06-2014 at 11:53 AM.
    The creative adult, is the child who survived

  6. #6
    Wal's Avatar
    Lives in Stockport, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 5-6 years. Has a total post count of 278. Received thanks 24 times, giving thanks to others 6 times.
    I'm a novice builder, but for what it's worth here's what I'd do:

    1. Fit your screws and make an assessment based on the the hardware being fastened down correctly.
    2. If it's still bad (and it may prove to be just fine...) then get a quote from someone local to you about getting 'em straightened. The screws probably won't seem like such a bargain by that point, but hey - chalk it up to experience. It'll be less hassle than sending back/waiting on new screws etc.
    3. If it's burning you up and you feel strongly that you've got the raw end of the deal* - then write him a calm email explaining your issue.

    *Chai is not in the business of selling rubbish - he gets plenty of recommendations and repeat business for a reason, sometimes things don't work out but I'm sure he'll try to help you as best he can.

    4. Fit your screws and make an assessment based on the the hardware being fastened down correctly.

    Wal.

  7. #7
    I ordered a set of ball screws and linear bearings from Chai. When they arrived the box was badly damaged at one end. I took photos of the damage before opening. The ends of two rails were bent. I mailed Chai and he said that the cost of shipping was prohibitive for replacement. If I placed another order for whatever I didn't need, he'd happily slip in a replacement. I cleaned the ends up on my mill and ground the linear bearing ends so they are now nice and pretty (previously it looked like they were cut off with a chop saw).

    Roll on several months and I build my z-axis. Installed the ball screw etc. and when rotated the re-circulating bearing oscillates up and down. I initially suspected that the screw was bent, but after much fiddling I concluded that the screw was not turned centrally when the shoulder was machined for the fixed bearing mounts. This is because even with the ball re-circulator at the fixed bearing end, it still oscillated by the same amount as when it was in the centre. If the screw was bent I would expect the movement to diminish as the bearing reached the extremes of travel (think plucked guitar string).

    As this was discovered six months after delivery, rather than get into a discussion (argument?) with Chai, I priced up a replacement (~19 delivered). I have fastened the ball screw down with as near as damn it half the error to try and minimise the forces placed on the screw (this makes it have stiff-spots when rotating). It is not brilliant, but I will try it on the machine and then decide to throw more money in Chai's direction. I am a couple of months away from having power on the z-axis so this decision is deferred.

    Even with the less-than-brilliant experience as described above, the price is a small fraction of parts sourced in the UK (Moore International etc). I wanted to buy British, but it just doesn't make sense as I would have spent ~1500 more on the basic drive parts.

    Neil.

  8. #8
    I ordered 4x ballscrews for my 4x4 machine off chai. All are good apart from the y axis one which seems to be bent towards the motor end. This results in the driver stall detect coming into play when the z moves into that area. Was thinking about trying to straighten it myself, but not too sure...
    i would e-mail him your concerns, get them bolted in place and run them off the steppers and see how they look then. If you are still concerned e-mail chai to see if he will replace them.
    Dan

  9. #9
    I contact with Chai i ask him to see the videos and he told me
    -----------------------------------------------------------------------
    Dear Vagelis,
    Can you adjust it as this linked instruction:

    Screw Shaft Straightness

    AS you know, the ballscrews have to be checked and adusted Before they are mounting to the machine.

    Thank you very much for your consideration and cooperation!

    Chai

    "

    Has anybody followed the above procedure for ballscrew straightening?
    I am not sure for the result.
    The creative adult, is the child who survived

  10. #10
    Quote Originally Posted by ba99297 View Post
    Has anybody followed the above procedure for ballscrew straightening?
    I am not sure for the result.
    Yes it's standard way to straighten any shaft not just ballscrews. . . . BUT . . Trust me on this Vagelis chances are they will be OK when on the machine and setup. If any is bent enough to cause a problem then it's not difficult to straighten them like is shown in the link above and often this can be done in a standard vice with pair of V blocks. It doesn't take much effort to straighten screws just a little patience.!

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