The perfect level height ?

[S Scherrer]

Hi

 

I have perhaps a stupid question, but not sure I got a clear answer from reading over web. Thought I would shoot it here... We read a lot on leveling and how to practically do it. Now the question : Is there an exact level height we should be aiming for when printing and if yes what would the theory say ? (this puts aside all practical aspect to achieve it in reality)  So if I print for a resolution Z of 0.2 mm, should I aim for the nozzle to be at 0.2, 0.25, 0.22 when extruding? And if I print with Z resolution of 0.1mm , should I aim for 0.1, 0.15 ?  I guess the filament width when extruded when into account.

 

I realize the leveling script is perhaps setting this height to a different value (I'll try gather this one actually) but whilst asking to fit a piece of paper is certainly easy to start, it just does not feel like defining an exact measure precisely and I'd like to figure out what is it.

 

I am really curious on your thoughts.

 

Thanks !

 

[Jay]

I 'was' using the magical business card then switched to feeler gauges which are much more accurate...but had problems and one of the "wise men" (think it was dnewman but I might be wrong) told me that the height needs to vary. I'll let the more experienced explain it the correct way but the jist he tried to give me is the bead is supposed to be HALF the height of the resolution so you get the correct 'squish'.

Makes sense...if your bead is .027 then you want the gap between nozzle and the next lowest horizontal to be .013-ish. that way you get the optimal spread. Someone else chimed in with an analogy about peanut butter and bread but it's been a couple of months.

[Damian Gto]

That only is true for the first layer.

After that you will have the right hight.

Many time I slice I will make the first layer 0.3mm. The reason is simple. It will remove some uneven stuff on the leveling. Also printing that layer with slow speed maker sure it will stick to the build plate. Its kind of a raft, but it will not make the object look bad.

But I will also trim my build plate like this. Over the screws its 0.15mm. In the middle its 0.1mm for the build plate is warped 0.05mm in the middle. I use to print at 0.15-0.20mm.

[Dan Newman]

On 20 Jun 2013 , at 10:36 AM, Jay wrote:

> I 'was' using the magical business card then switched to feeler gauges
> which are much more accurate...but had problems and one of the "wise men"
> (think it was dnewman but I might be wrong) told me that the height needs
> to vary. I'll let the more experienced explain it the correct way but the
> jist he tried to give me is the bead is supposed to be HALF the height of
> the resolution so you get the correct 'squish'.

First, there's at least three ways to tweak the height and at least one of
them can happen behind your back. (Actually two of them.)

1. Tramming / leveling the build plate. Here you set the gap between the
build plate and nozzle. For a Replicator 1, 2, or 2X this is the gap which
is present when the bot thinks it is at Z=0. You control this. However, it
goes out of whack over time which is why you want to check it from time to
time. (I check mine maybe once or twice a month?). Mechanical vibration,
warping, pushing/pulling on the build plate when removing prints will all
contribute to it getting off.

2. Z Home Offset which is a setting in your bot's EEPROM. When the bot
moves from the Z home position to Z=0 it's actually moving from the Z Home Offset
to Z=0. So if the Z Home Offset is 0, it doesn't move up or down at all in
Z. If the Z Home Offset is 0.02 then to move from the homed position to Z=0
it actually need to move the bed UP by 0.02 mm. You control this setting.
It defaults to 0 mm. It doesn't change behind your back.

3. The starting Z height of your sliced print. With RepG the "Bottom"
plugin adjusts this. It's typically

Z starting height = base altitude + 0.5 * layer height

And this is what Jay was referring to: depending upon the layer height the
slicer adjusts the initial gap between the print bed and nozzle. So, for
a 0.3 mm layer height, the Z starting height is typically 0.15 mm (that's
with base altitude = 0 mm). So, if the Z Home Offset is 0 mm and you
trammed the build plate with a gap of 0.1 mm then the actual gap will
be 0.25 mm. If after slicing that gap is too much (poor adhesion of the
first layer), you can increase the Z Home Offset to, say, 0.02 mm. Then
the initial gap will only be 0.23 mm. Huh? Well the bot thinks that
for the first layer it needs to move to Z=0.15 mm. If the Z Home Offset
is 0.02 mm then it thinks that after homine it's at Z=0.02 mm. It then
moves to Z=0.15 mm by only moving the build plate down by 0.13 mm instead
of 0.15 mm. Then add to that the 0.1 mm gap you trammed in and you now
have an initial gap of 0.23 mm for that print.

I tend to fine tune by playing with the Z Home Offset -- saves reslicing.
You can alternately play games with the already generated gcode.

Now some folks have warped build plates. And the X axis rods sag by a
measureable amount due to the load. The build plate warping tends to be
a crowning in the middle if it's a heated, metal build plate. Combine
that with the X axis rods sagging the most at their center. Net, net,
you can have a noticeable difference in the gap at the center of the build
plate vs. the edges. This presents an additional challenge when printing
models which span a significant part of the build plate.

Dan

[Jay]

That's it !!! That's the discussion I was talking about!!

Thanks Dan...much more technical than I could come up with at work...

Jay

[S Scherrer]

 

OK and THANKS for taking the time for these explanations. It;s not necessarily easy to get all so if you allow this is my understanding of your explanation :

 

 - Home offset, I get it. I'll assume for rest that it is 0, the default. (By the way on 7,3 firmware for 2x, I got replictaorG complinaing that offset were obsolete... could this be it or perhaps X Y too )

 - When we level, the noozle is set to Z=0= Z Home position.

 - The height we should aim for leveling is independant of the actual resolution we print as this is being adjusted at print time by the formula : Z start of print = Z Home+ 0.5 * print resolution (again assuming Home offset = 0 , otherwise we add / substract Z Home offset)... 

 - On next layer I guess it will do a Z = Z+ Resolution and then extrude ?

 

So, for

Z home = 0.2 at level

Print resolution  = 0.3

Z home offset = 0

 

First layer positioning is Z = 0.2 + 0.3/2 = 0.35 extruding a plastic

Second layer position would be Z+= 0.3 => Z =  0.35 + 0.3 = 0.65 ?

So essentially a resolution indeed of 0.3 between each layer, except for first layer that would be

 

>> So if I understood correct and extrapolated correctly on second layer... am I right to understand that when we level which is Z=0 we should aim to be AS CLOSE as possible to build bed without touching it like 0.100 or even less ?  Just check typical paper caliper range from 0.02 - 0.04inc  so that would translate like 0.08 mm ie 80 microns.

 

>> Sounds as well that the offset could be used to avoid to have to level at 0, but rather aim like a 50microns a Z home and then set an equivalent Z offset to basically set your starting at Z = 0 very precisely. Guess you could ruin your build plate with improper values ... if you do wrong so not sure you really  want to do that.. ?

 

Thanks again

 

Stephane

[Jetguy]

"replictaorG complinaing that offset were obsolete"

Sorry, don't confuse the 2 different offsets, they have totally different meanings and usage.

There is the homing offsets for X, Y and Z. Those are used to get the bot to the right coordinates using the homing switches.

This way, 0,0,0 (X, Y, Z) is center of the bed, nozzle at start layer height.

 

Then, for dual extruder bots only, there is the toolhead offset. That system has changes several times, that is what replicator-G is complaining or notifiying you about.

You are getting that warning because in Replicator-G preferences (under the file menu at the top left) there are some defaulted settings:

"Review GCode for potential toolhead problems before building" is checked.

 

Normally, I change the following defaults:

Uncheck all the following:

"Display Accelerated Speed Warnings"

"Automatically connect to machine at startup"

"Automatically regenerate gcode when buildign from model view."

 

That only leaves the following checked:

Monitor temperature druing builds

[MBuser]

Ah... a thicker first layer. Slower too. I guess this would indeed be a pseudo raft. 

[S Scherrer]

Thanks. This is clearer now. I'll try those settings next time in replicatorG... I need to read a bit more now on those software docs and settings... since initial days excitement of watching every slice building is fading ... I can now concentrate and read whilst I print anything I find :)

[Dan Newman]

On 21 Jun 2013 , at 6:34 AM, S Scherrer wrote:

>
> OK and THANKS for taking the time for these explanations. It;s not
> necessarily easy to get all so if you allow this is my understanding of
> your explanation :
>
> - Home offset, I get it. I'll assume for rest that it is 0, the default.
> (By the way on 7,3 firmware for 2x, I got replictaorG complinaing that
> offset were obsolete... could this be it or perhaps X Y too )

The defaults are

Z Home Offset = 0 mm
X Home Offset = horizontal (left/right) distance from the X endstop to the center of the build plate
Y Home Offset = vertical (front/back) distance from the Y endstop to the center of the build plate

> - When we level, the noozle is set to Z=0= Z Home position.

Yes. And a gap is created between the nozzle and build plate.

> - The height we should aim for leveling is independant of the actual
> resolution we print as this is being adjusted at print time by the formula

Correct.

> : Z start of print = Z Home+ 0.5 * print resolution (again assuming Home
> offset = 0 , otherwise we add / substract Z Home offset)...
> - On next layer I guess it will do a Z = Z+ Resolution and then extrude ?

Correct.

> So, for
> Z home = 0.2 at level
> Print resolution = 0.3
> Z home offset = 0
>
> First layer positioning is Z = 0.2 + 0.3/2 = 0.35 extruding a plastic
> Second layer position would be Z+= 0.3 => Z = 0.35 + 0.3 = 0.65 ?
> So essentially a resolution indeed of 0.3 between each layer, except for
> first layer that would be
>
>>> So if I understood correct and extrapolated correctly on second layer...
> am I right to understand that when we level which is Z=0 we should aim to
> be AS CLOSE as possible to build bed without touching it like 0.100 or even
> less ?

You're aiming for a consistent distance of about 0.1 mm. Some people
aim for more (e.g., 0.15 mm) and then maybe have their slicer configured
for a different initial starting height or they've altered their Z Home Offset
or some combination. This is less critical when you print with thicker
layers (e.g., 0.3 mm).

> Just check typical paper caliper range from 0.02 - 0.04inc so that
> would translate like 0.08 mm ie 80 microns.

1 inch = 25.4 mm. So 0.02 inch = 0.508 mm

>
>>> Sounds as well that the offset could be used to avoid to have to level
> at 0, but rather aim like a 50microns a Z home and then set an equivalent Z
> offset to basically set your starting at Z = 0 very precisely. Guess you
> could ruin your build plate with improper values ... if you do wrong so not
> sure you really want to do that.. ?

Correct, if you do wrong you can drive the nozzle into the build plate.

Dan