Issue with too much first layer adhesion

Hi there,

I'm currently using a printrboard, sli3er 9.7, pronterface and a prusa mendel from makerfarm, nozzle diameter 0.35mm.

Recently, I accidentally sent a few too many commands for the z-axis to go down... it ended up pushing the heat bed. I noticed the limit switch was out of place so i fixed that, then i noticed the bed wasn't level (probably bent the linear bar on the y-axis a tiny bit) so i leveled that off.

Now, when I print the first layer, adhesion is so 'good' that it is squished down onto the heated plate. Prior to this incident, I was printing parts that weren't adhering to the surface enough but just enough to get some pretty decent prints. So now I'm assuming the nozzle was never close enough to the heat bed.

Because the first layer is so squished, it causes the filament to kinda squish outwards then moves upwards, therefore creating a very rough first layer with filament sticking out. The bottom layer looks like this from slic3r is nicer.

What i'm trying to achieve is this again... from slic3r is nicer.

I have played with the extrusion width and the z offset. I also have my first layer height set at 0.35.

I might be playing with these variables incorrectly, corrections are gladly welcomed.

Edited 2 time(s). Last edit at 12/13/2012 04:39PM by RonSkian.

Have you tried repositioning the bed, or the endstop? When my Z is too low consistently, I try to correct it through mechanical adjustments rather than through slicing parameters.

My strategy is to have the print head actually touching the bed at z=0. I achieve this by homing Z and if it is too low, I use my host software to raise it by 0.1mm increments, counting them, until the head lifts off of the bed. Then I adjust my endstop. My endstop is adjustable with an M3 screw. I know the thread pitch of the screw, and I know how far I need to go, so I calculate how many turns I need to make - it's usually pretty close (of course this all starts with leveling the bed).

As far as the slicer goes, I use both skeinforge and clis3r. In skeinforge, I use the bottom plugin and have analtitude of 0 and a height over layer thickness of .9. Thus my first layer using 0.3mm layer height, prints out at .27mm. In slic3r, I have the bottom layer factor set at 90% to achieve the same thing. I very seldom change these numbers.

jbernardis Wrote:
-------------------------------------------------------
> Have you tried repositioning the bed, or the
> endstop? When my Z is too low consistently, I try
> to correct it through mechanical adjustments
> rather than through slicing parameters.
>
> My strategy is to have the print head actually
> touching the bed at z=0. I achieve this by homing
> Z and if it is too low, I use my host software to
> these numbers.

What do your first layers look like?

Mine look like this [imgur.com]

I have to admit that I've had some variation in first layer adhesion, but since I've rebuilt my z axis, it's been spot-on. Of course now that I have it working fine, it's time to move on to another printer build - but that's another story.

Incidentally, when I rebuilt the z axis, I discovered that the X ends I was using - which I purchased on ebay - were not the proper distance between the smooth and threaded bars. Off by a fraction, but enough to cause lateral stress on the axis. This was exacerbated by Z constraints I was using top and bottom. When the X ends approached either the top or bottom, the lateral stress increased. I think this was the reason for my inconsistency. When I rebuilt the axis, I totally removed the constraints and I'm extremely happy. In my mind, the stability of the Z axis is provided by the smooth bars, not the threaded bars. We put these couplers between the threaded bar and the motors to allow for any off-axis issues, and then we constrain the threaded bars. Based on what I had and on what I have, I won't use Z constraints any more.

Rather than adjusting the end stop, which is tricky to get right, a better way is to index in z using code in your start gcode file and then resetting that point as your new 0,0,0. Now when you print, all your positions are offset up by the z amount you placed in the first line of code. You can have a look at your print, and then on your next run, you can adjust it in code rather than moving your stops.

Your problem isn't first layer adhesion, it's that your stop is not adjusted to 'z'.

You can compensate with the settings (software) but then you'll have to keep fiddling with it with each setting and remember that it's there.

If you fix your hardware you don't have to do this and it's not difficult.

Here's what I do if I haven't used the printer in a while or if it's messing up the first layer.

1. Level the print bed all around.
2. home all axes.
3. press reset button on Ramps board (or whatever board you're using), this will make it so the printer has to zero out all of the home locations based on the endstops.
4. Home Z and take a measurement. If it's too high adjust the switch a little lower, if it's too low do the reverse
5. Go back to step 3 and repeat until Z is spot on.
6. For good measure just double check that the bed is still level at all extreme edges and the middle
7. ... and Bob's your uncle.

Edited 1 time(s). Last edit at 12/18/2012 09:22AM by a_shorething.

Sorry about the super late reply... haven't had the printer for a while (I share the machine with my pal)

Looks like you guys were right, it did have something to do with the z-offset. But it wasn't just that parameter. I did some googling and I found this website which pointed me towards proper prints.

[solidoodletips.wordpress.com]
and
[solidoodletips.wordpress.com]

Now I have the following settings (just a few that mattered):

Layer Height = 0.25
First layer height = 100%
Default extrusion width = 0.25*1.4 (width to height ratio) = 0.35
First layer extrusion width = 100%
Z-offset = 0.18 (this WILL vary with your setup)

Hope this is helpful to anybody who reads this.

Thanks for the help all!