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Keeping that darn bed level

Posted by crutonius 
Keeping that darn bed level
March 11, 2012 10:42PM
It seems like with nearly every other print, I have to make sure that the bed is perfectly level with barely a sheet's of paper thickness between the nozzle and the glass. It's like it drifts or something after every print.

Is this normal?

thanks
Re: Keeping that darn bed level
March 12, 2012 03:18AM
What is the y - carriage made from? I tried 6mm MDF and had exactly that problem. I switched to 3mm Dibond and the problem was solved.


[www.hydraraptor.blogspot.com]
Re: Keeping that darn bed level
March 12, 2012 05:36AM
nophead Wrote:
-------------------------------------------------------
> What is the y - carriage made from? I tried 6mm
> MDF and had exactly that problem. I switched to
> 3mm Dibond and the problem was solved.


Aluminum 3mm. I'm wondering if there's an easy way to make some kind of auto bed levelling feature. Maybe bring the extruder down on every corner and detect when it's hitting the bed and then backing up half a millimeter or so.
Re: Keeping that darn bed level
March 12, 2012 06:28AM
If it is aluminium it should stay level. What sort of bed are you using? Is the frame standing on a solid surface?

As for auto levelling, this is how I did it [hydraraptor.blogspot.com], but it requires interpreting the g-code on the host, rather than sending it to the firmware as I think 3D transformations would be a bit too much for the Arduino.

I only use it on HydraRaptor where the MDF frame sets the position of the nozzle relative to the bed. I don't need it on my Mendel, Prusa, or Mendel90. The first two are a pain to get level but they don't change much over time unless they are moved.

One problem I had with my Prusa, which nearly drove me mad was one side of the Z-axis would get lower over time. The amount it shifted was proportional the duration of the build. It turned out that one of the couplings would walk down the motor spindle very, very slowly, no matter how tight it was. I degreased the spindle with some meths and that fixed it.


[www.hydraraptor.blogspot.com]
Re: Keeping that darn bed level
March 12, 2012 08:57PM
I'm not sure what you mean by those questions exactly. Here's a picture of the bottom. I bought it off Ebay from Lulzbot(heresy, I know).

I'll take a look at that link. I saw another similar project too in another thread.

thanks for the info.
Attachments:
open | download - carriage.jpg (129.9 KB)
Re: Keeping that darn bed level
March 12, 2012 10:16PM
Okay so, today's lesson is don't build a chamber and poke a single hole on the top for the filament to feed through. It will drag on the bearings enough to wear them down pretty fast.

Hopefully that's the problem. My stupidity is much easier to deal with then design deficiencies.
Attachments:
open | download - don't make this.jpg (136.5 KB)
Re: Keeping that darn bed level
March 14, 2012 02:28PM
crutonius Wrote:
-------------------------------------------------------
> Okay so, today's lesson is don't build a chamber
> and poke a single hole on the top for the filament
> to feed through. It will drag on the bearings
> enough to wear them down pretty fast.
>
> Hopefully that's the problem. My stupidity is
> much easier to deal with then design deficiencies.

Was it drag or was it that they melted? Looked like PLA bearings. I've heard of enclosed build chambers but they generally warn that the printer parts should be ABS. Considering ABS friction, a bearing upgrade might be in order.

I have a similar set up, except with LM8UU holders, and there is some kind of drift on the leveling screws leading to it coming out of level. I see you have glass and another bed, but I can't tell if it's a heated bed. I've been chalking up the drift so far to heat expansion/contraction cycles, but a week or so ago I was printing cold on masking tape over the usual glass and I was having to level things often as well, so maybe vibrations? To be fair, I was also tearing up my tape while removing prints and lifting the glass to scrape it off and reapply.
Re: Keeping that darn bed level
March 15, 2012 03:45PM
Mazaw Wrote:
-------------------------------------------------------
> crutonius Wrote:
> --------------------------------------------------
> -----
> > Okay so, today's lesson is don't build a
> chamber
> > and poke a single hole on the top for the
> filament
> > to feed through. It will drag on the bearings
> > enough to wear them down pretty fast.
> >
> > Hopefully that's the problem. My stupidity is
> > much easier to deal with then design
> deficiencies.
>
> Was it drag or was it that they melted? Looked
> like PLA bearings. I've heard of enclosed build
> chambers but they generally warn that the printer
> parts should be ABS. Considering ABS friction, a
> bearing upgrade might be in order.
>
> I have a similar set up, except with LM8UU
> holders, and there is some kind of drift on the
> leveling screws leading to it coming out of level.
> I see you have glass and another bed, but I can't
> tell if it's a heated bed. I've been chalking up
> the drift so far to heat expansion/contraction
> cycles, but a week or so ago I was printing cold
> on masking tape over the usual glass and I was
> having to level things often as well, so maybe
> vibrations? To be fair, I was also tearing up my
> tape while removing prints and lifting the glass
> to scrape it off and reapply.

It was a drag mostly. Actually I think one of the bearings deformed from the heat and the strain.

That's a heated bed.

As far as I know it didn't actually make it unlevel. It just made it seem that way. The filament going through the hole would cause the extruder assembly to pull up a little when it was on either end of the x axis. So that would wear down the PLA bearings faster. With the bearings sufficiently worn down the filament would actually pull up the extruder so it didn't make good contact with the bed so it seemed like the bed was unlevel.

So for all I know the bed levelling might actually be behaving itself. I don't mind mushing the first layer against the bed to make better contact so I'm probably not as sensitive to a totally level bed as others might be. I still think it's one part of the Mendel design that needs some work though.
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