Grinding noise/vibration from linear rails

Hi,

I have a self built D-bot with a good few modifications including linear rails.
I'm having great difficulty in identifying and solving a serious vibration/noise seemingly coming from the X-axis. See attached video.
The vibration is very easy to feel when touching the area around the hot end, but not when feeling the rail itself. It doesn't appear to have an impact on print quality.

[youtu.be]

The rails are Chinese equivalents, sorced from the reccomended Voron BOM vendor. I stripped, cleaned, replaced bearings and regreased the rails/carriages prior to using them and they ran smoothly.
Having previosly deciding it must be the bearing iteself, i purchased another from a different supplier, but it still exhibits the same problem.

Things i have done/tried so far:
- strip, clean and regrease rails. check consistent bearing size, greased with superlube.
- Swap the the x and a y rail + cariage
- check all fasteners
- Cold run of the printer with no hot end/fans etc.
- alter print speeds.

I'm running a Duet 2 Wifi with (i think) average jerk and accelerration settings (800mm/min, 2000mm/s^2).
I believe it's a mechanical issue rather than settings.

Does anyone have further suggestions or experince? Or am I out of luck using these Chinese rails?

Thanks

Most probably these linear rails were made out of recycled Lychees cans. Therefore this is totally normal.
The ones running smoothly are made with recycled Soviet era nuclear submarines. They are better just a bit radioactive.
So you are lucky.
Note they can be recycled as Lychees cans.

How much for your Duet ?

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Which noise are you referring to? I hear normal motor noise when it's printing the curves but some horrendous stuff when the Y axis moves from the back to the front of the machine.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The horrendous stuff. And the metal sounding vibration at points in the curve.

It sounds like a Y axis problem, not an X axis problem,. It doesn't look like the X axis is moving when it makes the noise,

Check the motor current- should be around 80% of rated current or less.

Move everything around manually with and without belts and see if you can get it to make that noise.

I'd probably start looking for some new, high quality linear guides. Here's something to keep in mind when you're shopping: forget what some idiot posted on reddit. If you have to take it apart and replace the balls before you use it, it isn't a quality linear guide. If you're lucky enough to get it to work at all, it isn't likely to work for long..
Look for NSK, IKO, THK, NB guides. If you are patient you will find a good deal on used or new-old-stock guides for little more than the cost of the crappy HiWin knockoffs (they have part numbers that start with "MGN and MGH"). The main spec you need to be worried about is the length of the rail and number of bearing blocks that the guide comes with. You can cut the rail to the length needed with a cutoff wheel on a grinder. Don't attempt to buy rails and bearing blocks separately.

Here's a deal: [www.ebay.com]
and here's the manual with specs: [www.ikont.com]

Search for terms like " Linear guide THK -MGN -MGH"

Edited 3 time(s). Last edit at 04/20/2020 08:44AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I have chinese made ball bearings where the races were SOFT steel ! I am pretty sure that in addition to loose tolerances, these junk linear bearings are not properly heat treated and grounded !

I have seen these guys on youtube who replace the undersized balls with better one. Just that they degrease everything, assemble then show how well the parts move freely ! These are JERKS who have NO clue in mechanic ! You NEVER do that, ALWAYS lubricate BEFORE.

Better spend your time learning from professional documents than from these youtube engineers.

Edited 1 time(s). Last edit at 04/20/2020 08:17AM by MKSA.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

I have tried moving by hand, and everything feels quite smooth. I'll dive into it again with more focus on the Y axis this time.

Motors are at 1200mA ~80%.

I have been considering better rails, but being in the UK makes it a bit more difficult. Do you have experince with Misumi products? Hard to get here but have read they're good value/quality.
As I understand the rails and blocks are made for one another, so no i haven't considered them seperately.

I've seen other settups that run quite quietly on the Chinese rails. I understand they're generally poor quality, but i hoped there was somthing I was missing to solve the annoyance.

I haven't come across anyone who thinks they can get away with no lube. I like to think i know better than that anyway.

I have had similar issues in my home cnc converted mill. It sounded as it had dirt in the bearings and I was deeply concerned how it happened. It turned out that I was pushing the stepper motors to the limit of their capacity. On a mill, there is a certain mass to move, but the similarity is that steppers make noise when too close to their limits. It can go from crushing noise to downright painful howling.
The fact that your bearings sound and feel fine when you operate them by hand suggests that it is a stepper issue.