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Thread: Is this normal?

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  1. #1
    I bought a 4th rotary axis, which I am not sure if I should be happy about on a "you get what you pay for" basis or should have received something better. Are my expectations too high from these 300$ things? This is what I bought (Option 2):

    https://www.aliexpress.com/item/1005...47104c4dI8LQr7

    Everything looks nice, but...



    So the question is, if you think this is "normal" or not. I did complain to the seller, he asked to make a video to show the problems, so I made one today. I am still waiting for his reaction, but basically what I asked for is:

    1. A new large gear or a chuck or both, because I thing that's the biggest issue.
    2. A new MT2 live center., or at least a new pin for my MT2 taper.

    Unfortunately, I don't know how to replace the pin or the large gear, so I also asked for instructions in that case. I don't know if the center pin is glues or not, but it sits so tight in the bearing that I can't remove it. I removed the three screws at the back of the large gear, but then there is nothing else to remove, and the gear still is firmly attached to the axis, so even there I need instructions because I don't know what to do. The chuck is more straight forward, I din'd try to remove it, but probably held only by three screws.

    What do you think? I have zero experience with rotational axis, but dry running seems fun and works well with UCCNC.

    I am also making a new 48V 7A supply just for this purpose, and also made a "Lathe mode" box, which basically is giving pulses and direction signal so that I will be able to run as a "lathe". I know, I know, don't laugh... it's not a lathe, but I will play with it and it may work for soft material. Anyway, if not good enough but I like the idea then I'll change the 1.8Nm motor to something considerably stronger, or a servo. Anyway, this device is based on an Arduino Uno and it will give pulses matching a set rpm, which can be set (as it is designed) between 0-350 chuck rpm. Of course, it has a display and it will accelerate/decelerate as well.

    As usual, if there is an interest for this box then I will share the Arduino code, but will first make a box and everything before I will show it. It's a simple thing, but will be fun to try.

  2. #2
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 17 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,745. Received thanks 331 times, giving thanks to others 8 times.
    Woohoo, I can finally reply.

    I wouldn't be too worried about any of that.
    The pulley runout isn't ideal, but as long as the belt isn't going tight at any point, I wouldn't worry.

    Runout on three jaw chucks is perfectly normal, as chuck scrolls are not a precision item.
    If you need better tolerances, then you either need to use custom bored soft jaws, a collet chuck, or a 4 jaw chuck.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  3. #3
    Now that replies are possible :-

    m_c The chuck as far as I can tell is a 4 jaw and hopefully independant jaws.(edit K12-100 4 jaw is self-centreing - meh).



    My comment (sent as a PM) is that you should remove the chuck and measure run-out on the face and periphery of the back plate. If this is within limits then you should be able to set up the workpiece in a 4jaw chuck using a dti (plenty of vids on Youtube).

    Run-out on the driving pulley unless massive is inconsequential.

    Hope this helps,

    Rob

  4. #4
    As per the above comments, runout of the pulley shouldn't be an issue, the 0,1 runouts of the chuck could be down to the chuck centering but also shouldn't be much of an issue on a router. I think the most important thing will be the backlash in the chuck axis (C axis?)
    I tried to reply to this on Friday but it wouldn't let me!

    Sent from my M2003J15SC using Tapatalk

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  6. #5
    I'd say that for both ends to move a bit. The alignment (balance) of the internals - bearings, shaft, etc, to the body. Are just slightly off from straight.
    Machined parts will likely come out looking fine.

  7. #6
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 18 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 8,412. Received thanks 1,442 times, giving thanks to others 108 times. Referred 1 members to the community.
    You have to remember these are rotary axis, not lathe's so the runout will hardly be noticeable for the majority of work and if you require higher precision then you either use 4 jaw chuck or use soft jaws and bore them as MC suggested. The pulley runout is of no concern whatsoever in this application.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  8. #7
    Now I am back. I was a bit busy so I could not answer. Anyway, I don't know what happened, why replying was not possible earlier.

    I didn't want to pull it apart before I was through the discussions with the seller, but now we made an agreement so I am good to go on. Basically, the seller admitted that the MT2 live center is not normal and we agreed on my proposal refund which basically covers the purchase of a new live center. He could not ship one from EU, and I did not want him to ship from China, which is why we agreed on refund so I can buy from someone else. For the chuck play, he basically said that that's normal, "you get what you pay for", which I understand very well also, even though I was hoping for something better and it is actually outside his own specifications.Anyway, with the refund I paid 250 USD for the 4-jaw 100mm 4-th axis and the MT2 tailstock with the damaged center pin, which I think is still usable, unless I really need the very sharp pinpoint edge. I think that's a good price.

    What I did so far to improve the situation is that I removed the chuck and the pulley and cleaned up everything. I reassembled the pulley and also moved the stepper pulley out a bit. After this it's a bit better, there is not as much play in the pulley as before, but of course, the chuck is the important part.

    Before reassembling the chuck, I made some measurements on the chuck plate, and that shows no real problem as far as I can judge, so that's good. The thing I noticed was that it was very hard to remove the chuck, and the reason for that is because the chuck plate inner flange (I don't know if that's the proper name of it) is I think a bit too large in diameter, so the chuck is VERY tightly fitted on that flange, I think it is too tight because there is ZERO possibility to adjust the chuck. I will see if I will try to do something about that later, but for now I don't have time, so I just reassembled the chuck after cleaning the surfaces and made some new measurements. To my surprise, the play is now half of what it was before, so it is definitely within the specifications, which means that I am satisfied for now.

    So for now, I am OK with this as it is, I will test it ot for some real work also before I try to fix anything more. Perhaps one thing I will do is that I remove the chuck once again and try to clean that flange with some very fine sand paper, maybe some grit or something else will be removed by doing this which might improve it even more. I feel that before staring to grind anything I will need to learn some more about using the 4-th axis. I don't want to destroy it or make it worse, after all, a slow start with a less then perfect chuck is better than a destroyed and useless one.

  9. #8
    Quote Originally Posted by m_c View Post
    If you need better tolerances, then you either need to use custom bored soft jaws, a collet chuck, or a 4 jaw chuck.
    You are right, the pulley play does not matter that much, unless the play is transferred to the chuck.

    This is a 4-jaw chuck, it is a self centring type, I don't know if that's good or bad, I think in some situations it is good, in some it is bad.

  10. #9
    Quote Originally Posted by cropwell View Post

    My comment (sent as a PM) is that you should remove the chuck and measure run-out on the face and periphery of the back plate. If this is within limits then you should be able to set up the workpiece in a 4jaw chuck using a dti (plenty of vids on Youtube).
    Thank you for the comment and the PM. I was too busy so I had no time to answer earlier. Don't know what happened to this post or the forum, why replying was not working before. Anyway, yes, the is a self centring 4-jaw 100mm chuck. Maybe it's a bit too large for my tiny CNC, but I thought it's better to buy a bigger one than a too small one, and also got it what I regarded a good price, 280USD including EU taxes and three days shipping from Spain. Now with some refund the price I paid was only 250USD, so that's even better.

    Anyway, I did what you suggested (after I agreed with the seller) and the chuck plate seems fime apart from what I mentioned before about the flange, which I think is a bit too large. I will see if I will continue improving it, though grinding is not my favourite first choice, since I don't have anything which is good and reliable enough for this sort of precision grinding. The Dremel seems very rude and inaccurate, but maybe that doesn't matter. Anyway, I will see later on if I will continue or not, and in which order.

    One thing I discovered was that the jaws for the ID clamping (not the ones which are in the video) are definitely something wrong with because one of the jaw is not closing completely, but maybe that's normal, maybe you not supposed to clamp in it like if it was OD jaw. I will need to check how well it grips on a pipe before I conclude that there is something wrong with it, but in any case those jaws are not as important as these OD ones for me.

  11. #10
    Quote Originally Posted by CharlieRam View Post
    I think the most important thing will be the backlash in the chuck axis (C axis?)
    Backlash is good, as far as I can measure, but will make some real tests later on through milling a piece of material.

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