Strong vibrations in ball screw linear actuator - is it normal

[mbridge87]

Hi,

Happy new year,

I've got a linear actuator which I'm using for motion control video, not cnc. I've noticed that at slow speeds there can be a huge amount of vibration going through the machine, so much so that I can feel it standing a few feet away. Is this normal?

This is what I have - https://www.fuyumotion.com/heavy-duty-compact-ball-screw-linear-axis-robot-arm.html

It's 1000mm long.

Would love to hear thoughts.

Thanks,

Max

[Neale]

If it is stepper motor driven, then it could be that it is not using micro-stepping. The positioning accuracy given suggests this - you might expect higher resolution with micro-stepping. However, more to the point, stepper motors driven without micro-stepping, whether you need the resolution or not, can sound and feel like marbles in a cement mixer. Depending on the mechanical setup, this might be worse st slow speeds where there is little flywheel effect.

Only guessing - difficult to tell without hearing/seeing!

[m_c]

Is it stepper or servo driven?
That webpage mentions both.
And what kind of drive is powering the motor?

I suspect it's suffering from some kind of resonance.

[mbridge87]

Thanks for the replies. It's driven with a stepper motor and a dm542t stepper driver from stepper online.

The micro stepping is set to 3200.

I can record a video tomorrow and add a link here if that would help?

[mbridge87]

Hey everyone. So here's a video which shows the vibration issue:

https://drive.google.com/file/d/16sIi4UlYmZTug9_Qod8Tfq2Q0ZSU5NFL/view?usp=sharing

As I mention in the video there seems to be a sweet spot in terms of movement speed where the vibrations are really bad. If moving faster or slower than this sweet spot it seems to be ok. I experimented with different micro step settings a week ago and this didn't seem to make a difference, although this was before I realised there was this sweet spot and so I may test again.

The motor is hooked up to this driver, it's a 3DM2283T.

https://www.omc-stepperonline.com/digital-stepper-driver-2-1-11-7a-176-253vac-for-3-phase-nema-34-42-stepper-motor.html

Would love to hear your thoughts.

Thanks,

Max

[JAZZCNC]

I don't think that's anything to do with the stepper motor. It sounds like a mechanical resonance, to me something is loose or badly misaligned. Bent ball screw perhaps.?

[mbridge87]

Oh no. That's gonna be tough to go back to the supplier with. I bought this from a Chinese company in July (ish) but have been building the whole machine from then until now so I've not used it much....perhaps it was broken on arrival?

It's quite an expensive part to replace on my own right?

[Doddy]

As always - isolate the problem - looks a fairly heavy set-up(?) but could you lift it from the wooden stands to verify that the noise is local to the slide table? (and not resonance from the stands)... I think unlikely - but a cheap test.

What's interesting with the video - from 02:40, the noise appears co-incident with the rotational position - would like the OP to verify this - from the short clip - seems to be the same bit of the motor coupler visible when the noise is at it's loudest - so is this a bent screw?, some mechanical foul along the motor/screw axis?

Does the problem remain with the (weight of the) camera mount removed? If not, does the problem remain with the bed fully supported? (can it be dropped onto the ground, or lifted onto a table?)

Next thing for me would be to remove the panels from the bed. Or to decouple the motor from the screw and to manually assess the freedom of rotation of the screw (decouple from the motor-side, and thumb/forefinger rotate the coupler)

[JAZZCNC]

Oh no. That's gonna be tough to go back to the supplier with. I bought this from a Chinese company in July (ish) but have been building the whole machine from then until now so I've not used it much....perhaps it was broken on arrival?

It's quite an expensive part to replace on my own right?

I wouldn't be rushing it back just yet based on my quick observation, identify the problem first.:hysterical:

My main point was I'm quite sure it's not resonance affecting the motor for the following reasons.
#1 It's not spinning fast enough
#2 It's a 3 phase motor on a digital drive so it's highly unlikely
#3 It's fastend firmly with a good strong mounting.

Eliminating the motor/drive and from the sounds it's making everything points to alignment, binding or bent ballscrew or rails even.?

I don't know what's under those covers in terms of rails or ballscrews but if it's using precision linear rails then any twist or misalignment could cause binding that will result in vibrations and because of the size of the motor it won't stall but rather just power past it increasing the vibrations. Also, the wooden frame it's sat on looks a little "heath robinson" so could easily be putting the stage into twist.?

This is the problem with precision equipment, if the rest of the setup doesn't match it's pointless. I would set the whole stage down on a flat surface and make sure it's fastened securely.

[m_c]

I'd like to know the inner workings of that actuator.

Given the lack of detailed information about it, I'm going to guess it's probably not using that good a quality linear slide which has some play in it rather than being preloaded, which is then being amplified by resonance probably triggered by some runout in the ball screw.
Your setup will be adding resonance due to it's centre of gravity away from the slide, so any play in the slide will be amplified.

What happens if you press down, and put a load on the slide as it moves?

[mbridge87]

Hey everyone,

Thanks so much for the help so far. I’ve contacted the company I purchased this from to see what their opinion is. In the meantime, here are answers to all your questions:

1) The noise still persists when taken off the table. The table is extremely strong and sturdy and the slider was held down with G clamps but it was worth a try.
2) The noise does seem to coincide with the rotational position – see video below – I also notice that the noise seems to be worse when travelling away from the motor in the centre of the slider. In addition, there seems to be a noise like sand/metal inside almost like it’s grinding. You may be able to hear this on the video.

https://drive.google.com/file/d/16y3z97yhr_iiryqXfqD58o3Fea8ChFcx/view?usp=sharing

3) Problem does remain with camera mount removed. Problem also remains when on the floor
4) Taking everything apart will be my next step
5) The table is something I use for photography / videography. It’s rock solid, weighted down, and the slider is held in place with G clamps. It’s only temporary but I’d be surprised if it was causing any issue. I have put it on the ground and the issue persists.
6) Pressing down on the slider as it moves has very little effect. It does decrease the vibrations a little but the main nasty noise is still there.

I think that answers all the questions. Here’s another video which shows the slider moving back and forth a couple times. The noise seems to be worst in the centre of the slider when it’s moving back from the motor side.

https://drive.google.com/file/d/170VcaRtqw0l7tg13-To1kdHgSWu4JAG4/view?usp=sharing

Apologies I seem to have filmed that video upside down...new phone.

I think the next step is clearly to take it apart and see what’s going on. I’ll wait to hear what the manufacturer says first though.

Side note – Where is the best place to purchase something like this from? If my budget were say £700 for something similar, where would you guys go? I know £700 is not a huge amount for a ball screw slider like this.

Thanks again

[Doddy]

I also notice that the noise seems to be worse when travelling away from the motor

I think the next step is clearly to take it apart and see what’s going on. I’ll wait to hear what the manufacturer says first though.
Thanks again

Agreed with dismantling... a bit at a time. And appreciate you wanting to sanction this with the supplier first.

Interesting observation on moving the platform away from the motor (screw between bed and bearing block (or motor) in compression). My random logic would be to check on the tightness of the nut on the bearing block behind the motor coupler... or for mechanical interference in this area (or between coupler and motor - explains the rotary position association), or even if the bearing blocks are bolted tightly down. Pure speculation of course.

Of interest (and what would make me cautious with running ahead with disassembly) is how motion is achieved with the dust-proof guard in place - does that move (conveyor-like) with the table? If not (and I've read a couple of sites that intimate that a stainless steel band is fed into the carriage - around a couple of rollers... and these would require lubrication... but that would all be explained in the product literature). Again, pure speculation.

Okay, out of ideas... but watching this thread with interest.

[JAZZCNC]

Sounds like you have a few things going off here.

I'd definatley say this is something to do with the linear rails or ballscrew alignment, or bent, etc, as it doesn't take much to cause binding. Possible end bearing supports are lose or poorly fit bearings.

I'd also say because of the grinding noise, which is common with cheap Chinese ballscrews, the ballnut needs stripping and cleaning.
It's common for Chinese ballscrews to not be cleaned properly at the factory so grinding dust etc is left in the ballnut. That said I wouldn't recommend you go stripping the ballnut down without knowing a little about how they work and being prepared and setup to do it, other wise you'll have dozens of little balls all over the floor.!!




Side note – Where is the best place to purchase something like this from? If my budget were say £700 for something similar, where would you guys go? I know £700 is not a huge amount for a ball screw slider like this.

What length do you need.? I could make you something like this easy enough. PM me if you want to discuss it and I'll give you my details.

[mbridge87]

Yes, I am a little concerned about stripping this all down. I've heard people say that all the ball bearings can fall out if you're not careful.

I posted this same question in a Facebook group which is all about motion control, it's full of people with lots of experience building motion control video rigs. It's called DIY motion control for those interested. Anyway, the consensus there seems to be that this is quite common at particular speeds when using ball screws for motion control and is a resonance thing.

Now, I don't know if they're correct and I'll still be investigating this but it's interesting that they all seem to think this is normal. I wonder if using this for motion control video has an impact. For example, in that use case I think, and correct me if I'm wrong, that it would be more likely to use a ball screw at this slow speed and at more speeds in general; fast, slow etc. Whereas cnc users would generally be going a bit quicker?

I'll pop you a separate message Jazz. Would love to chat

[JAZZCNC]

I see no reason why it should judder at this speed, I can tell you without question that any decent CNC machine would easily move at this speed and slower without juddering. It wouldn't be much use if it didn't as those vibrations your feeling through your feet would show in the cut quality.

To me I can't see why if it was setup correctly without binding or anything being bent, etc, and securely fastened down why this linear stage should vibrate.

[mbridge87]

Thanks Jazz. It's great to hear from someone knowledgeable in this area.

It did surprise me that the guys in the motion control Facebook group seemed to think it was normal. I'll continue investigating things with the manufacturer and see what they say.

Given they're in China, if they suggest stripping it down is that a difficult thing to do? I imagine it would be relatively simple, the only part I'm not sure about is the ball screw part with the bearings (not sure of the name). Fingers crossed they also honour the warranty.

[mbridge87]

Hey everyone. Quick question. I double checked my current settings as I was told that this could cause some of the problem. I reduced the current and the issue improved, it didn't go away but was definitely better. The downside is that performance, in terms of speed, drastically reduced.

At the original current setting, with 32x micro stepping, I could move the slider very fast, I'm afraid I can't quantify that as I'm not sure how to measure it but with no payload I couldn't really get it to stall. At least, I got to a point where it was far faster then I'd ever need and stopped. With the slightly lower current setting it stalls very easily. Again, this is hard to quantify but not very fast.

This video shows how fast it could move at the higher current setting - https://drive.google.com/file/d/17A-GPd9nO_-bZDj3YBuk-stxbiaTGfip/view?usp=sharing

I'd estimate that at the lower current setting it can move at maybe 1/6th of this speed.

This is the info for the stepper motor - https://drive.google.com/file/d/1rhcfEZHkzQRQuPfQTMp-_XazJji5bfHY/view?usp=sharing - if that link ever breaks the model is FM86128SJT03 - it's rated at 3 amps.

I originally had it set to 3.2A (RMS) and 4.5A (peak) on the driver. I tested it quite a lot at this setting and the motor barley got warm so I thought this was ok. The next setting down is 2.2A (RMS) and 3.1A (peak). That lower setting is where the performance drops off.

Did I have the current set too high?

[Clive S]

No. It won't harm the motor, it can run hot well in excess of 50C.

Ie. re the drive what voltage can it handle. if it is 50V then use about 10% less 45V. it is the volts that matter.

What voltage are you using and what amps can the power supply give?

[m_c]

I think you might need a few things clarified.

The microstepping setting simply controls how many steps the drive takes on the input, compared to what it outputs. A more accurate description would be step-multiplier/ratio.
I'd guess the drive output will never go above 16 or 32 microsteps, as above that resolution, it makes no difference to motor smoothness, and it certainly does nothing for accuracy, as microstepping is by nature inaccurate. Due to the very nature of microstepping, what it's essentially doing is holding the motors rotor between two electromagnetic springs, so position cannot be guaranteed other than to the nearest step.
Personally, I would never run above 32 microsteps, as there is no real benefit.

In terms of current. In electric motors, current = torque. Reduce current, you reduce torque. Less torque means you can't accelerate as fast. It also likely means you'll hit the stepper motor/driver bad resonance point and stall at a lower speed.
Too high a current could cause failure due to overheating, but I'm sure you would have noticed if the motor had heated up.
As Clive says, stepper motors can run hot. 80degC after running for a long time is acceptable, but if they get that hot in a matter of minutes, then you've got a problem.


One thing you could try, is unbolt the motor, and separate it from the screw (that style of coupler will simply pull apart)
Try spinning the screw by hand, to see if it feels smooth
And run the motor with no load.


Having watched the video again, it could just be the fact it's using a big stepper motor.
It does sound like the stepper motor vibrating, and being amplified through the relatively light weight rig. There does seem to be a variation in sound level per revolution, but probably nothing you'd need to worry about.

A solution would be either a small servo, or possibly a smaller stepper motor with some gearing.
Although given you don't need high precision, I wonder if the existing motor could be mounted using some kind of anti-vibration mounts to isolate the motor vibration from the rig.

[mbridge87]

No. It won't harm the motor, it can run hot well in excess of 50C.

Ie. re the drive what voltage can it handle. if it is 50V then use about 10% less 45V. it is the volts that matter.

What voltage are you using and what amps can the power supply give?

This particular driver (linked below) connects directly to AC so it's 240vAC. It has the PSU built in unlike the DM 542T drivers I have which utilize a separate PSU that supplies 42.5 volts. I double checked and there is nowhere you can select the voltage, the manual suggests this is set automatically by the driver. Do let me know if I've done something stupid there.

https://www.omc-stepperonline.com/digital-stepper-driver-2-1-11-7a-176-253vac-for-3-phase-nema-34-42-stepper-motor.html

In terms of Amps, this screen grab shows you all the different options.

29338

[mbridge87]

I think you might need a few things clarified.

The microstepping setting simply controls how many steps the drive takes on the input, compared to what it outputs. A more accurate description would be step-multiplier/ratio.
I'd guess the drive output will never go above 16 or 32 microsteps, as above that resolution, it makes no difference to motor smoothness, and it certainly does nothing for accuracy, as microstepping is by nature inaccurate. Due to the very nature of microstepping, what it's essentially doing is holding the motors rotor between two electromagnetic springs, so position cannot be guaranteed other than to the nearest step.
Personally, I would never run above 32 microsteps, as there is no real benefit.

In terms of current. In electric motors, current = torque. Reduce current, you reduce torque. Less torque means you can't accelerate as fast. It also likely means you'll hit the stepper motor/driver bad resonance point and stall at a lower speed.
Too high a current could cause failure due to overheating, but I'm sure you would have noticed if the motor had heated up.
As Clive says, stepper motors can run hot. 80degC after running for a long time is acceptable, but if they get that hot in a matter of minutes, then you've got a problem.


One thing you could try, is unbolt the motor, and separate it from the screw (that style of coupler will simply pull apart)
Try spinning the screw by hand, to see if it feels smooth
And run the motor with no load.


Having watched the video again, it could just be the fact it's using a big stepper motor.
It does sound like the stepper motor vibrating, and being amplified through the relatively light weight rig. There does seem to be a variation in sound level per revolution, but probably nothing you'd need to worry about.

A solution would be either a small servo, or possibly a smaller stepper motor with some gearing.
Although given you don't need high precision, I wonder if the existing motor could be mounted using some kind of anti-vibration mounts to isolate the motor vibration from the rig.

Thanks for the comment and explanation on Microstepping. I knew some of that already but just provided the info as I know some people may ask for it.

I knew that voltage had an impact on torque but didn't realise current also does. Thanks for explaining that. With what you said in mind, is it odd that I noticed a reduction in vibrations when I reduced the current? From what you said the vibrations should have increased?

Precision is a big factor for me. When you shoot at 1:1 macro levels, in other words very very close to things, I think accuracy will be a big factor. Think filming a watch face or panning over a diamond. Mistakes at that level would be really obvious.

I'm hearing mixed things from people, some are certain it's an issue and some not so sure. I think for now, I'll wait to hear what the manufacturer says, then perhaps take it apart and investigate further...If all else fails then perhaps a geared motor as you say could be a good approach.

[m_c]

The other part of the motor equation is voltage. Voltage is what gives you speed.

As a motor spins faster, the back emf (electro motive force - essentially voltage that fights back against the applied voltage) increases, so in order to maintain current (which is what give you the torque), you need to apply an ever higher voltage.
The driver handles all this, so all you need to do is set the current.


As for why the motor seems smoother at lower current, I wonder if there is a fault somewhere. Without having a motor or drive to substitute, there isn't really that much testing you could do. Measuring the resistance through the coils of the motor would test for any obvious electrical faults with the motor, but they probably wouldn't be that conclusive.


My comment about precision was although Macro photography needs accuracy, it's more a case of needing repeatability, rather than pure precision. You don't really need the position to be highly accurate, you just need it to be repeatable.

[mbridge87]

The other part of the motor equation is voltage. Voltage is what gives you speed.

As a motor spins faster, the back emf (electro motive force - essentially voltage that fights back against the applied voltage) increases, so in order to maintain current (which is what give you the torque), you need to apply an ever higher voltage.
The driver handles all this, so all you need to do is set the current.


As for why the motor seems smoother at lower current, I wonder if there is a fault somewhere. Without having a motor or drive to substitute, there isn't really that much testing you could do. Measuring the resistance through the coils of the motor would test for any obvious electrical faults with the motor, but they probably wouldn't be that conclusive.


My comment about precision was although Macro photography needs accuracy, it's more a case of needing repeatability, rather than pure precision. You don't really need the position to be highly accurate, you just need it to be repeatable.

Oh good, glad to hear I'm not wrong about the driver setting the voltage automatically. OK, so I can safely increase the current back to where it was and eliminate that as a cause for this issue. That's another thing down, moving in the right direction!

Hopefully the manufacturer can shed some light but if not I'll see if there's anything obviously wrong when, or if, I take it apart. If it came to replacing the motor is there any motor you'd recommend?

[Clive S]

This particular driver (linked below) connects directly to AC so it's 240vAC. It has the PSU built in unlike the DM 542T drivers I have which utilize a separate PSU that supplies 42.5 volts.

Just to be clear that you are using the 3 phase driver that is supplied by 230v ac. I so that is fine.

As a lot of steppers are two phase. I take it your stepper is actually 3 phase.

What controller are you using to drive it ?

[mbridge87]

Just to be clear that you are using the 3 phase driver that is supplied by 230v ac. I so that is fine.

As a lot of steppers are two phase. I take it your stepper is actually 3 phase.

What controller are you using to drive it ?

Yes, it is a 3 phase stepper.

The controller is a piece of software called Mantis which is designed for motion control video - https://www.bfg-motion.com/index.php?p=1_4

[m_c]

I'm currently wondering, if a single coil in a 3 phase stepper had failed, would it run but with vibrations?
If you've got a multimeter, disconnect the motor wires at the driver, and compare the resistance between all the wires.
The datasheet lists resistance as 2.48ohm per phase, but I don't know if that will with coils connected (i.e. give an actual reading of 2.48ohm) or for each coil individually (which would give a reading of about 1.66ohm ).

I'd also unbolt the motor and try running it. It's only the 4 bolts that hold it in place. As long as there's no marker paint on the bolts and you don't damage anything, the supplier will be none the wiser you've had it off.
If the motor runs rough disconnected from the slider, then you know that's the main problem.


For a replacement, I'd probably go for a 200W servo, and combine it with a planetary reducer box to give more control (3000rpm is a bit much for something with this short a travel directly coupled to a 10mm pitch ballscrew!)
Have a look a http://servo.xlichuan.com/ for ideas. Servo motor size would be 60 frame, and you'd need a new adapter for fitting the motor, but that's nothing major.
You can buy Lichuan servos via Aliexpress - https://www.aliexpress.com/store/1907567
Although I think all their gearboxes are built to order. The last one I ordered added a couple weeks delay to the order, as they had to build the gearbox.

[JAZZCNC]

Ok well, this convinces me even more that it's something wrong with the linear stage rather than the motor.

I fit these types of motors all the time, by type I mean 3 phase Motor with 220V mains powered drives and I can tell you without a doubt that at this size just reducing the current shouldn't make it stall on an unloaded linear stage that using ball-screws.! . . . Unless the stage as gots excessive friction from misalignment or something being bent.

This also fits with the noise because the power in these motors will easily overcome any friction, other than outright sticking, this would cause vibrations as it powers thru any sticktion.
For instance, a 7.5Nm Nema 34 motor with 220V drives connected to a ball-screw will easily lift a fully grown man off the ground and not bat an eyelid.
When working on a CNC machine it will happily accelerate a 50kg mass holding the spindle in excess of 2G to a velocity of 20mtr/min and bring it back to a dead stop in fractions of seconds and then push that same mass with a 12.5mm tool thru a solid piece of Oak at 8mtr/min.!!

So hopefully you're getting some idea of what I mean when I say an unloaded linear stage that uses a ball screw shouldn't be making it stall just because the current is set a little low.

I'm sticking with my first suggestion that the linear stage is binding or bent or twisted.!

[Doddy]

I'm currently wondering, if a single coil in a 3 phase stepper had failed, would it run but with vibrations?


I like your thinking. Not sure if that's what would happen, but interesting and simple test. Of course, it could also be the drive.

[mbridge87]

Thanks again everyone.

Once I have the OK from the manufacturer I'll take the drive off and run some tests to exclude it as an option.

JazzCNC - What you're saying makes total sense. It seemed so odd to me that the drive would stall that easily when the current was lowered and there was no load. Makes total sense that something else is causing friction. Couple quick things:

1) Is there anything I could have done which could have caused this? The slider has hit the end a few times while I was getting used to the software but nothing major.
2) Would this be obvious when I take it apart or could it be a subtle bend?
3) How would you test for it?

I'm just thinking about what the manufacturer will ask and what I'll need to come back with. Sadly, my experience with Chinese companies on sires like AliExpress is that they don't like to take responsibility when there's a problem. Hopefully this will be different.

Finally, if you're correct in your assumption, is it easy to fix?

[JAZZCNC]

Thanks again everyone.

Once I have the OK from the manufacturer I'll take the drive off and run some tests to exclude it as an option.

JazzCNC - What you're saying makes total sense. It seemed so odd to me that the drive would stall that easily when the current was lowered and there was no load. Makes total sense that something else is causing friction. Couple quick things:

1) Is there anything I could have done which could have caused this? The slider has hit the end a few times while I was getting used to the software but nothing major.
2) Would this be obvious when I take it apart or could it be a subtle bend?
3) How would you test for it?

I'm just thinking about what the manufacturer will ask and what I'll need to come back with. Sadly, my experience with Chinese companies on sires like AliExpress is that they don't like to take responsibility when there's a problem. Hopefully this will be different.

Finally, if you're correct in your assumption, is it easy to fix?

#1 Only if you hit very hard and fast would I expect big damage.
#2 It should be quite obvious if it's sticking to the point it stalls the motor.
#3 I've never used one of the stages so I have no idea what's under those covers so I can't advise on how easy to test or difficult to fix, if indeed I am correct.

Just for a laughs n giggles, and to point out the power of steppers, here's a single 4Nm 2 phase Closed loop stepper running on just 60Vac being stress tested at 10mtr/min.
I'd estimate you have more than twice that power and much smoother action with 3 phase motor.


https://www.youtube.com/watch?v=u5HuW9AqwpU

[mbridge87]

Ha ha ha! That's some pretty good stress testing!

Good to hear that I wouldn't have caused the damage. In my initial test when I was setting current etc. for the first time I remember the marked performance increase when going to the higher current so clearly it's been like this since day 1.

One other very quick question, I have a job next week which I want to use this on. It won't be very taxing, slow moves, nothing crazy, and it still works fine just makes noise at that speed. Do you guys think it's still ok to use this? I'm not going to cause further damage? Hard to say I know.

[JAZZCNC]

One other very quick question, I have a job next week which I want to use this on. It won't be very taxing, slow moves, nothing crazy, and it still works fine just makes noise at that speed. Do you guys think it's still ok to use this? I'm not going to cause further damage? Hard to say I know.

I can't imagine it will do much damage provided it's not working for a long period, but like you say it's hard to know. Please if it's anything that is bent then the damage is done already.

[mbridge87]

Thanks Jazz. It would be working for two days but on a video shoot so nothing like being used for CNC. Most of the time it won't be doing anything. Cheers for giving your opinion.

I've just had a reply from the manufacturer and I'm waiting to see if it's ok for me to take it apart. Fingers crossed I hear from them tonight and then I can investigate this tomorrow.

[mbridge87]

Hey everyone,

So I've started investigating things today. I need to read through the thread again and see all the suggested things to test but so far I have:

1) Taken off the motor and tested it on it's own. It was fine. This was the loudest it got:

https://drive.google.com/file/d/18nGmwp3BDawML3MMJPoA45ImcWcO3yTl/view?usp=sharing

2) Removed the top and tried moving it by hand and visually inspecting. Moving it by hand seems to suggest to me that there is a problem. I recorded another video to show you all:

https://drive.google.com/file/d/18mvohNPeSqOQz42Wfz6nxp74HmIX_xtS/view?usp=sharing

What do you all think?

[m_c]

There's definitely something wrong with that. Sounds like some contamination.

How does the ballscrew feel when you turn it by hand through the sticky section?
If the ballscrew feels notchy/gritty when turned by hand, it's likely to be something ballscrew related, but if the ballscrew just goes a bit tight, it's more likely to be something to do with the linear guides.

What are the coloured sections on the ballscrew? Grease?

Any chance of a couple photos showing the carriage assembly?

[JAZZCNC]

There's only one word for that noise.!!. .Grrrrrrrrriiiitttttyyyyyy bad. It should be more Swissssssshhhhhhh than growwwwllllllll.

It's not unusual to feel resistance in the movement because that's the preload in the linear bearings and ball-nut, however, the sound should be more of a Swish than a growl.
So absolutely got something going in there and I'd tip it's the ball nut doing most of the growling.

I would remove the bolts that attach the carriage to the ball-nut and move the linear guides on their own. This will identify the bad guy.

I can't quite see on the video but do the rails have bolts holding them down in every hole.? If not then you could also have an alignment issue which is compounding the issue. Linear guides are great when set up correctly but unfortunately because they are precision components they don't accept sloppy fastening or poor alignment very well and will binding and can growl if the alignment or parallelism is out.

Time to move onto the next phase and take those bolts out of the ball-nut. It should soon become clear where the problem lies.

[mbridge87]

What are the coloured sections on the ballscrew? Grease? - Yes they are

Any chance of a couple photos showing the carriage assembly? - I've taken a few photos this morning, lots of the ball screw in the area where it gets stuck. Hopefully these will be helpful:

https://drive.google.com/drive/folders/18u8XCdY1c1Vt5_VLLeng18PMAEoaA7AM?usp=sharing

I just started to remove the bolts then realised I need to take the whole thing apart (the metal surround/case). Sadly, I've got way too much prep to do for this job next week so I've not got the time right now. I'll have to come back to this after the job is complete.

Thanks everyone. I'll post more once I have time again

[mbridge87]

Strange development. Having put it back together, it's now running even worse. I say strange as I barely did anything. All I did was decouple the motor, remove the top part of the carriage and then begin to remove a few other screws until I realised it was going to take too long. Then I put it all back together...

I've tried coupling the motor again a few times but it's not helping. I also took the carriage off and am running it like that but the problem is still there...I'm not really sure how this is happening but it's definitely struggling in that same place. The place it gets stuck

[mbridge87]

Hey everyone.

So I've finally finished my shoot, it was a very busy ten day shoot but glad to be working given how things have been this year.

Now I've got time to investigate a bit further, I removed the ballnut from the carriage and moved each component individually. The carriage moved perfectly on the linear rails, no sticking, juddering etc. Moving the ballnut by hand it did feel as though it was oscillating a little rather than moving perfectly on axis but it's hard to say if what I felt is normal given I have so little experience with these machines.

When I put the ballnut and carriage back together the problem returned. This suggests to me that the issue resides with the ballnut + ballscrew but I'd love to hear opinions. As usual I recorded a couple videos so you guys can see what's going on.

https://drive.google.com/file/d/1EfNzlqDed7jFEGEmei2Pa72jx0MvSseN/view?usp=sharing

https://drive.google.com/file/d/1EleFjww35gNk5mBl_mCXZSehsCdHPRja/view?usp=sharing

In the meantime, the Chinese company have asked me to locate the issue and then they will send replacement parts. As such I'd really love to hear what you all think. Am I right in thinking the cause is the ball screw? If so, is it difficult to replace this part?

Thanks!

[Gary]

As Dean pointed out, this sounds like a bent screw.
if you can remove the screw and the stage moves freely, this will be a good indication where the trouble lies.

[Gary]

Move the stage to the end, and remove the four bolts holding the ball nut in place, then slide the stage back, and the nut should come away from the stage.
you can then see if the issue is the screw and nut.
I think the issue is more than just a dirty nut, this really points to a screw that is bent in a number of places.

[mbridge87]

Hi Gary,

Thanks for the reply,

Dean thought it may either be the linear rails or the screw. It seems obvious to me, given the quick investigation shown in the videos, that it's the screw. I just wanted to confirm that before I ask the company to send a replacement screw. As they're in China I'd hate to have them send the wrong part.

Would you agree then? Based on the videos in my post earlier that it definitely seems to be the screw?

[JAZZCNC]

I'd say it's the screw for sure, Like Gary I think it's got several issues with being bent and it also sounds gritty but that could just be the camera making it sound worse than it really is. I get this all the time on videos, the mic seems to applify the slightest noises and makes them sound much worse than reality.

If they are prepared to send you another I would take it without hesitation. But it could easily arrive in exactly the same state because Chinese ballscrews are ok for hobby routers etc, but not the best for precision stuff like this which you need to be super smooth.

[mbridge87]

Audio quality on phones is not the best but it definitely does sound gritty.

Like you said, I may as well get them to send me another but in the meantime it seems sensible to explore other options. This machine was a bit of a headache on the shoot. It was really good, software worked well, the camera moves I was able to accomplish were great but the vibrations ruined shots. Everything would look fine until I got into the edit and noticed these violent vibrations which would cause the lettering on the pen we were shooting to almost buzz for a moment.

In other words, still really interested in what you can put together Dean.

Shall I ask them to send another ball screw and ball nut? From what I understand it's hard to put those two elements together so I'd be a little concerned if I needed to put the new ball screw on the old ball nut.

[Gary]

Personally, i would get them to send both. especially if the ballscrew and nut are Chinese, Replacing a nut was always an issue, because the Chinese buy the reject screws from the big factories like TBI in Taiwan and then make their own nuts to suit the screw. But they get rejected for a number of issues like the root diameter is not within specification.
So you end up getting a replacement nut and it does not fit correctly on the screw and is either too loose or too tight.
Get them to match the nut to the screw and test its straightness prior to sending.

[mbridge87]

Thanks Gary. I've asked for both now so hopefully they'll send it all over and it'll be easy to fix...here's hoping :)