Mechanical Resonance?

Hi guys,

For days I was using this DIY Prusa i3 3D printer without calibration, it beared no physical problem apart from bad printing quality.
However, when I then began to calibrate the printer, problems started to appear, and one of the most signifant (annoying, actually) is this mechanical resonance.

Before I calibrated it, the belt is quite loose that it have significant backlash. The current is also quite excessive it sounded like sophisticated machine in sci-fi movie.
The Y-axis motor resonance is just producing little tremor on the bed. It might affect the quality, but rather overshadowed by the one caused by X-axis motor.

If the Z position is at 0, the extruder vibrate rigorously near 40mm/s, and substantially dampened 30 and 50mm/s. At high Z position, like in 100mm above bed level, the resonance band seems widened. The vibration is still significant, around half the peak amplitude, even at 80mm/s.
If I loosen the belt again (thus allowing backlash), the resonance dissapears, but not completely. at Z=0 and speed=40mm/s, if the X position is at the middle, the vibration is negligible. But, near the end of the X axis, the vibration grows higher.

I am not sure whether this is caused by the motor resonance (yes, the motor alone is actually vibrating quite strong), or is it because of the anything else.

Any insight or solution to dampen the vibration is highly appreciated.

Thanks

Check motor current- set too high can increase vibration. What size motor?

What micro-step setting are you using?

I'm sorry, but I'm really new to 3D printing and haven't know really much about it.

Quote
the_digital_dentist
Check motor current- set too high can increase vibration. What size motor?

I've experimented with the motor current, but the vibration cannot be minimized by that.
Well, not sure what size this is for I have no comparison. 17, maybe? I've attached the picture of it instead. The filament is 3mm.

Quote
JamesK
What micro-step setting are you using?

My printer kit came preprogrammed and I've never had a hands on on 3D printing firmware nor I can reprogram it. How to know the current firmware settings? How to set it?

Thank you.

The details depend on what electronics board you are using. If it's a mega 2560/ramps combo, then the microsteps are set by jumpers that go on the pins under each stepper driver module. If there aren't any jumpers on the pins then you get full steps and lots of vibration. Your firmware has to be configured to match the micro-steps setting on the board. There is lots of configuration in the firmware that you will probably want to experiment with to get the most out of your printer, so it's well worth learning how to edit and upload new firmware. There's lots of information on the wiki, you just have to know which board you are using

Sorry, forgot to mention my thingies~

This is a Prusa i3 model (most likely, i don't recognize other models, hehe). The controller is of Melzi and by default is embedded with Marlin firmware.
Also, I am in no possession of any AVR downloader right now, so I can't change the firmware.

Ah, looks like the Melzi has the micro-step signals wired up by default, so it's less likely that your problem is anything to do with that.

Quote
JamesK
Ah, looks like the Melzi has the micro-step signals wired up by default, so it's less likely that your problem is anything to do with that.

I've tried exchanging the X motor with the Y motor, so the motor that usually drives the bed now drives the extruder.
Trying to move the extruder with several different speeds bears vibration that is far softer than using the previous motor, although there still is vibration. However, it is tolerable and it only vibrates noticeably in the middle of the rail.
From this experiment, is the source of the problem really the physics of the motor itself? If yes, how can that happen when I only tightened the belt?

So the only thing you changed was to swap over the motors? If so, and that changed the amount of vibration, then yes it must be the motor that is the source of the problem. I don't know enough about stepper motors to know why that might be. As far as tightening the belt goes, I would think that with the belt loose it was absorbing some of the vibration, and when you tightened it up it transmitted the vibration more faithfully to the carriage, making it more obvious.

Ok, I'll throw in some curve balls.

My Y axis rods were not the same diameter end to end. This was causing my bearings to grab tightly at one end and make the loud sounds that I thought were the motor, belt, current as well.

I replaced my rods with some scrap rods from inkjet printers that i bought off craigslist and the problem went away.

So, from this experience, I determined a couple of important facts.

Linear bearings from ebay are 50/50 crap.

Cheap rods are....cheap.

X and Y smooth rods really need to be case hardened and polished. Not drill rod (typical ebay quality) or "stainless" stainless <> case hardened. The difference is the ball bearings are hardened and will eat soft rods for lunch. You can get these for about $10 each or you can hunt around. Just do some measuring first on your rods, and check the bearings.

Inspect your Y axis rods and bearings. Do they travel smoothly? Do they make noise? Does all this happen with the entire bed disassembled or only when you put it all back together... Could be getting some lateral binding between the rods and causing them to not be parallel.