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Thread: Home made machine vibration

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    Exclamation Home made machine vibration

    Hi guys, I made a machine sometime ago (http://www.cnczone.com/forums/diy-cn...530-180mm.html) had made some changes over the time (DMM Servos, C5 TBI ballscrews, Aluminum table, etc) and I love the machine, there are a couple of thing I would do diferent right now but that's normal I guess... always learning... Anyway, I mainly cut aluminum on this machine and I'm very pleased with the results, better than I expected before I tested the machine... Lately I'm having a problem, If I'm machining a straight part, along Y, if I'm outside cutting when, and only when the machine is cutting the left side (so it's cutting with the right side of the tool) it makes a vibration, it's not the tool shattering it's the machine itself vibrating, if I'm cutting from the inside it's the other way (cutting the right wall with the right side of the tool). If I'm cutting an inside circle it makes the vibration when in the 3 to 2 o'clock if is cutting an outside circle profile it will do on the 9 to 10 o'clock... don't know if you understand me... I may do some drawings or even a video if necessary... I checked the backlash and I'm getting close to none, like if I use an indicator I tell the machine to move 0.01mm on any direction and then move back the dial indicator moves 0.01mm and get right back to 0... Spinble bearings were replaced by NSK 7005 high precision bearings sometime ago (those on golden boxes and very expensive XD), I check for runout and was really low like 0.001-2mm.... I checked for any loose screws and found any... I'm a bit out of my league here so I'm calling for help...

    I'm tempted to order a new X ballscrew since I made a noob mistake when ordered this one, like initially when I made this machine I used some steppers on it so I bought some chinese 10mm pitch ballscrews, later I changed for DMM 400W servos and later upgraded the ballscrews but keep the 10mm pitch... big mistake I think, I think I should have gone for the 5mm ones to increase RPM on servos since unlike steppers the servos have more torque at higher RPM... I think the problem might the the servo struggling to keep the spindle in position and a 5mm pitch ballscrew would help it ALOT instead of the 10mm... Or this can be a very stupid idea since the problem only occurs when forces from right to left are applied at the spindle....

    anyway I don't know what to think anymore, what you guys say to me?

    thanks in advance

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  2. #2
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    Default Re: Home made machine vibration

    vakeiros,
    Sounds like you are experiencing the difference between climb cutting and standard cutting. You can look on google and they will explain the difference. Your machine should be able to do both, but climb cutting requires the machine to be much stiffer. Servos have more power and torque at higher RPMs like you said, I had that issue myself, and ended up adding Harmonic Drives which are really precision reduction gears which allow the servo to spins faster to get their best torque and the reduction also adds more torque to the machine. The issue with any gear reduction is they often introduce backlash which is a nasty word in the world of CNC. Some people use pulleys and belts to create this reduction and if you select the right ones you can address the issue. A machine is 5mm pitch ballscrews is pretty fine but depending on what you are doing can be fine. The 10mm if more common but my guess is you are dealing with the lack of stiffness in your machine.
    Russ



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    Default Re: Home made machine vibration

    I understand that Russ, but it's a new symptom, started about yesterday... and I always do climb cuting.... that what's bugging me... if it were always like that I undertood but started only yesterday and I kept my feeds and speeds as always...

    thanks for your input



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    Default Re: Home made machine vibration

    vakeiros,
    Your test for backlash is probably not a good enough test. Move the axis say 200mm and then back to where you started and see if it really is a zero. The backlash probably would not cause the vibration. Have you disconnected your motors and moved the machine around manually to ensure you do not have a damaged ballscrew or linear bears. Either one of these that has been damaged could also cause your issue. You need to start running various experiments and keep a log of the experiment and the results and you will start to isolate your given problem. You can always adjust your feeds and speeds and depth of cut or even do an air cut and see if you get any vibrations. If the machine is really smooth cutting air then you are mostly likely dealing with feeds,speeds, depth of cut type issues. What kind of material are you attempting to machine?
    Russ



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    Default Re: Home made machine vibration

    sorry for the delay, I've been out. I'm machining aluminum as I always do but it will do the same when I machine polyethylene as I also usually do... the machines works all good since it makes the finish passes perfect, on the more aggressive paths it vibrates only on those places, like I said it worked great before with same cutting conditions, I use to make adaptive clearing 7mm depth of cut, 1.5mm optimal load on a 8mm end mill all day without a single vibration, now even if I do a 0.8mm optimal load and 5mm depth of cut it makes a vibration on the X axis, like i said,m only when forces are from right to left on the tool and that's the weird thing for me... if it was on all sides and since the beginning I knew it was a lack of stiffness but the fact that the machine use to work fine and now it as the problem that's what's killing me...

    one thing I just remembered to check is the coupler on the X axis... don't know it its related but it's one thing I haven't check yet...



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    Default Re: Home made machine vibration

    I notice in your build log that you are using those crappy flexible couplers which are not very suitable for a CNC and in my opinion should not even be used for 3D printers. I made the same rookie mistake... but replaced them eventually and after that my machine became smoother and quieter with less vibration. Swap those out to something better, like lovejoy or oldham type. That's definitely worth to do in such machine, and even if it may not solve all your problems, you will notice a positive effect and a difference in smoothness. Of course, screw and motor axis alignment is more critical with those couplers, so be prepared for some extra alignment work but it will be well invested time and effort.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: Home made machine vibration

    Quote Originally Posted by A_Camera View Post
    I notice in your build log that you are using those crappy flexible couplers which are not very suitable for a CNC and in my opinion should not even be used for 3D printers. I made the same rookie mistake... but replaced them eventually and after that my machine became smoother and quieter with less vibration. Swap those out to something better, like lovejoy or oldham type. That's definitely worth to do in such machine, and even if it may not solve all your problems, you will notice a positive effect and a difference in smoothness. Of course, screw and motor axis alignment is more critical with those couplers, so be prepared for some extra alignment work but it will be well invested time and effort.
    yeah I know that and that's something I made sometime ago, when one of the Y axis broke I replaced them all by anothers much better ones but still on the small side but made a big difference, a while ago I replaced the ones on Y again by some stronger ones and again much better motion but I didn't replace the one on X (I have to enlarge the hole on the gantry and I was just too lazy) but I guess it's time to do so I can cross another test out XD

    anyway can you guys recommend me some good couplers?

    I bought some of these from flebay, 30mm diameter 42mm length and I'm happy with them:
    Home made machine vibration-s-l1600-jpg



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    Default Re: Home made machine vibration

    This looks like the ones I am using.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: Home made machine vibration

    vakeiros,
    Those new couplers are much better, I have that style on my machines. On your vibration since you machine worked prior to the vibrations cutting the same materials, you should examine your ballscrews carefully. During heavy cuts you could have put enough force on the ballnut to allow a bearing to escape. Disconnect the motor and then even the axis and see if the ballnut feels nice and smooth and has no wobble, also examine the retaining clips and dust shields to see if they are all still in place. Sometimes you can even get metal cutting inside the nut and that can cause issues. I had that happen to one of my ballscrews. The aluminum gets crushed and it hard to remove from the ballnut it gets pushed into the bearing raceways.
    Russ



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    Default Re: Home made machine vibration

    Maybe spindle is not trammed well, so the load on the cutter is not evenly distributed, taking bigger cut at the bottom on the problematic side?



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    Default Re: Home made machine vibration

    Quote Originally Posted by CNCMAN172 View Post
    vakeiros,
    Those new couplers are much better, I have that style on my machines. On your vibration since you machine worked prior to the vibrations cutting the same materials, you should examine your ballscrews carefully. During heavy cuts you could have put enough force on the ballnut to allow a bearing to escape. Disconnect the motor and then even the axis and see if the ballnut feels nice and smooth and has no wobble, also examine the retaining clips and dust shields to see if they are all still in place. Sometimes you can even get metal cutting inside the nut and that can cause issues. I had that happen to one of my ballscrews. The aluminum gets crushed and it hard to remove from the ballnut it gets pushed into the bearing raceways.
    Russ
    yeah I'll take the complete X axis apart (motor and ballscrew) and check it out... it as to be something... I'll remove the nut and clean all good and smooth and re-assemble it... I've some experience on that... I'll swap the coupler and take a good look at everyting.... I'll get back to you in a couple of day to see if I discovered anything...

    Zekyx I'll talke a look on that to but I don't think so... but I'll check just to be sure.


    thanks for all the inputs



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    Default Re: Home made machine vibration

    well guys, I disassembled the whole X axis of the machine, including the ballscrew and nut. replaced the coupler for a bigger better one and found out a critical design error in the axis... yeah after about 2 years I'd found out something that was bad since the very beginning.... where the nut attaches to the Z plate, when I tight the nut to the nut mount it was forcing the nut out, making the ballscrew to bend away... on the midle of the axis it wasn't that bad but near the BF/BK blocks it was... I don't know how it didn't damaged the ballscew, I guess it was due to the high quality of those TBI (before I damaged some chinese cheap ones but I thought it was due to the poor quality... guess I was wrong), anyway the problem was due to a spacer on the nut mount that was a bit bigger than the mount and the nut was hitting that spacer, I solved the problem making a spacer to put between the nut and the mount this way the nut won't hit that spacer and now everything it's perfectly aligned and smooth as silk form beginning to the end of travel.
    I ordered a new ballscrew anyway to replace that one, more than 1 year running that bad I know that this one it's not at 100% so why take the change? A new ballscrew and nut this size isn't that expensive anyway....
    I just tested the machine and it runs great again... I intend to get some tweaking on the motor drivers also since I never got to deep in that since it was my first time with servos.
    I'm not really sure what the problem was since I made lot's of stuff at once, the spindle also was just a little bit out of tram but nothing serious, now it's perfect.

    anyway thanks for all the input...



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