Noise and smell when bed was on the bottom

Bambu Lab X Series
1

This morning something strange happend :
Yesterday evening I printed in vase mode. I do remember that I moved the bed down a bit via the touchscreen to grab my print from the bed. A few minutes after that, I shutdown the printer.
This morning when I powered up the printer there was a loud noise coming from the bed, it was trying to go down but it was already at the bottom. Strange because after a normal powerup its not default behaviour that it moves the bed by my knowledge.It was trying for like 2 seconds, twice and then it stopped. No messages or what so ever, but a very bad smell ( as in electric smell of burned motor).
I started another print and couldn’t notice any problems or difference.

Still it makes me a bit anxious. That should not happen and maybe next time it will burn my Z engine.
Anyone else had this and or can explain what happend ?

2

I’m finding that the bed “bottoms out” whenever I start a new print after a previous tall print. It’s a bit ugly, yes. I hope BL can come up with a solution to this, especially since the software does detect blockage when raising the bed.

The “bad smell” is troublesome, though. The motors going out of step like that shouldn’t be an unusual case that it would cause burns. Perhaps BL can comment here? If it does end up causing a failure, I think BL are on the hook to deal with it.

3

i mentioned this to bambu support in the past, the response was to make sure you HOME your printer before you use it…also, It will lose track of home after like 30 minutes being idle.

4

How to home the printer when the power is off ?

5

So one could reproduce that by:

  1. Moving bed down to the max
  2. Shut down printer
  3. Start printer
  4. It will try to catch itself on fire?
6

exactly, I am not gone try again for now if you don’t mind :slight_smile:

7

Dont turn the printer off while it is bottomed out?

8

Yeah, I agree. Good idea. That’s under the heading of “take your fingers out of the door before closing”. But a good idea.

9

Well, you could always try to rotate each of the three Z axis screws by hand if it’s off. Turn them equal amounts.

A tiny bit of inaccuracy in doing it is no big deal as it’s handled when the printer is homed, but try to move as equally as possible. I’d do 180° on each in turn a couple times. 90° if you feel that’s too much or you feel it bind.

10

For me, the simple solution is to raise the bed as soon as i get the tall print out of the printer. Then i raise it 100mm. Next power up and home is good to go. I just use the touch screen or BLStudio to raise the bed. You have half an hour to do it.

11

Much more elegant. I was replying to his saying the printer was off with the bed at the bottom. But this is the ultimate habit to be in for sure!

12

#4 No… The printer wont catch on fire because the z-axis motor is cycling on it’s torque limit.

When the bed is at the bottom and you turn on the printer it will try to move the bed down but since its already at the bottom it becomes physically stopped by the end plates. Since the printer doesn’t know where home is it tries to continue its startup code by moving the bed down. When it reaches the end plates you will hear it making a terrible sound. It’s the z-axis motor stopping and starting rapidly due to reaching its designed torque limit or its the belt slipping if the belt is loose. They are limited by torque output so they wont break anything if bound up.

13

“Dont turn the printer off while it is bottomed out?”
“For me, the simple solution is to raise the bed as soon as i get the tall print out of the printer.”
“Yeah, I agree. Good idea. That’s under the heading of “take your fingers out of the door before closing”. But a good idea.”

It’s a machine… how on earth should should this be something one has to actively look out for?

Stupid question: Why and when does the printer lower its bed on powerup in the first place?
For me, the bed does not move when powering up while not being bottomed out.

14

Commen sense dude? :thinking::thinking:

15

For something to be common sense, a rational and logical explanation is paramount.
What is your logical justification for “a 3d printer must not be turned off when its bed is on the floor”?

16

The smell may be from the z-axis belt drive sprocket slipping while trying to turn an unmovable belt.

17

First part - Because it’s an obviously known problem that has yet to be addressed. People here are sharing ideas to help until BL gets a change introduced to fix it.

Machines don’t “just work”. There is extremely sophisticated software telling this machine how to be a machine. The behavior was programmed this way, it didn’t “just happen”.

BL can’t “just fix it”, they have to carefully find why it happens, when it doesn’t, what it affects if they change it, and what other problem(s) they may introduce as a result. This isn’t magic, my Friend, it’s complex engineering, and they aren’t “idiots” for designing it this way, they had a reason.

“Stupid question” part - Well I maintain there aren’t stupid questions, the stupid people are the ones that don’t ask and aren’t willing to learn. You asked so you don’t fall into that camp! :grin:

As for why it moves the bed down - we don’t know. I know that some printers are programmed to “present the print” by lowering the bed to make for easy removal. Why it moves down at start? Not sure.

They could have placed an ‘end stop’ switch, which some printers have, but perhaps decided the cost of the switch, wiring, added assembly time, added point of failure (I have replaced numerous failed microswitches over the years, high failure point), and adds another sensor, which the CPU may not have another port available to support.

Hall effect switches are another answer and more reliable, but cost a lot more and require a magnet as well.
Lets see - $3 for the sensor, $.25 for the magnet, $3 in wiring, a couple hundred at least for the engineering to design it and wire routing, $2 in clips to hold the wires, perhaps $2 for rubber grommets where it goes through a metal wall, $.25 in screws, $2 for someone’s time to install and route the wires during assembly, $10 for adding data to the assembly plans & drawings, $5 for storage of parts and additional fees to keeping the parts in stock. Times 10K printers so far - $155K in parts (not counting the one time fees mentioned like design), with an ongoing amount for each new printer.

So - why didn’t they they “just add a switch?!?” People have no bloody idea how complex and such a statement actually is, and that was just off the top of my head, reality might be even more.

They did it for reasons, not because they’re stupid.

Lots of reasons for them to not put a sensor there, especially since it’s rare for the bed to be down there in normal use.

18

Thanks all, for now I will check when I turn off the printer what the location of the bed is.

Happy printing !