Z Backlash on TOM squishes bottom layers
cptnAWESOME
Whosawhatsis
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Attachments:- Calibration Test.jpg
Greg Thorstad
Thorstad Computer/Thor3d.ca/Canadian Makerbot Distributor
Box 268
Outlook, SK
S0L 2N0
306 867-9596
cptnAWESOME
On Dec 11, 10:28 am, "Greg Thorstad" <g...@thorstad.ca> wrote:
> I agree. If you take your Z motor out- the Z Platform should always just slide to the bottom- it should move very free. Oil the bushings lots- especially the bottom ones. I think this issue is just showing up lots since the MK7 got released because it is so light and there is not a lot of weight pulling down on the Z.
>
> Greg Thorstad, B. Comm.
> Thorstad Computer/Thor3d.ca/Canadian Makerbot Distributor
> Box 268
> Outlook, SK
> S0L 2N0306 867-9596
>
>
>
>
>
>
>
> ----- Original Message -----
> From: Whosawhatsis
> To: make...@googlegroups.com
> Sent: Sunday, December 11, 2011 9:03 AM
> Subject: Re: [MakerBot] Z Backlash on TOM squishes bottom layers
>
> Try oiling your Z rods and checking the alignment of the bushings. Gravity negate any backlash in the Z axis unless it has WAY too much resistance.
>
> On Sunday, December 11, 2011 at 6:14 AM, cptnAWESOME wrote:
>
> Okay, So I have printed out way too many calibration cubes trying to figure out what was going on.
>
> As you can see in the orange block, the bottom is flared out. When you watch these layers print there is a lot of globing, that told me the flow rate was too high. So I tried chasing down how to limit flow on the bottom layers, nothing seemed to have an affect. When I printed on a raft the flare disappeared.
>
> Was my Heated Build Platform too hot? No.
> Was the hot end not at the right height for the first layer? When I printed the first layer I would stop the print and measure the thickness and it was .15 ~ish so that was fine. However the entire part was .5mm shorter than what it should have been.
>
> Then it dawned on me that the Acme nut holding the Z Table had a lot of backlash. Here is what I did that fixed the problem.
>
> At the end of the homing section G-Code I added...
> G1 Z-2
> G1 Z0
>
> I bring the hot end down below the build platform and then back up. You need to ensure that the hot end does not crash into the build platform. This is not a problem on my TOM.
>
> The Lash add-in has X and Y settings but not one for Z.
>
> You can see that the green cube has much straighter side walls.
>
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Mark Cohen
stage left and right to align the bearings
Sent from my iPhone
Steve K
cube are wider and essentially "squished'.
I tried adding in gcode that made the z axis move below the print bed
then back up to the starting position to eliminate the backlash but it
seems to only reduce it.
Did you do anything different cptnAWESOME to compensate for the
backlash? Also, is "hold z axis" enabled or disabled?
I think the z axis may be moving down to a different starting
location, essentially negating the gcode I added, so I have to check
the gcode to see what it is doing when i actually start to print the
outline.
> Calibration Test.jpg
> 6KViewDownload
cptnAWESOME
of the messages that there may have been a bug where the checkbox does
the inverse. But you can make sure that the Z Stepper is holding its
position by trying to manually turn the Z shaft in mid print. If it
turns then its not really holding position.
The Z position on my machine needed to be re calibrated once I added
this code.
I had to adjust the machine settings for the Z offset in replicator
G.
Steve K
I added the code cptnAWESOME was talking about, and also altered some
other gcode. I added the following:
G0 Z-3 (move down 3 just to be sure, make sure you have clearance to
move this far)
G0 Z1.0
Where the second line is my starting Z height in respect to my zero
position. I added those two lines of code after the homing stage which
brought the z axis down below the bed then back up to the starting
height. After those two lines of code I have the bot wait to reach
temps on the extruder and bed. Then I have it move the Y axis FIRST
(this is so the nozzle doesn't hit the HBP plastic clip / wires) then
move the X axis to the starting position to start printing the
outline. After that the bot follows the rest of the un-altered gcode.
Also in the skeinforge profile you have to change the bottom altitude
value to the same number as that second z height value above, in my
case i changed it to 1.0 (default is 0.3 so make sure you change
this). This is so the z-axis stays in that position and does not try
to move down after it sets it self up in the outline starting
position. The exact gcode I use it as follows:
(**** end homing ****)
G0 Z-3
G0 Z1.0
M6 T0 (wait for toolhead parts, nozzle, HBP, etc., to reach
temperature)
G0 Y-57 (Position Nozzle)
G0 X25 (Position Nozzle)
M108 R4.0 (Set Extruder Speed)
M101 (Start Extruder)
G4 P1500 (Create Anchor)
(**** end pre-wipe commands ****)
*NOTE* Y and X outline start position gcode must be on separate lines
so the Y moves first then the X, don't want them to move at the same
time. When I get home I will edit and put the exact code I used for
reference purposes since everyone's z-calibration is different.
Here is a quick picture I took showing the difference between the
backlash print (LEFT) vs. the backlash negated print (RIGHT):
The calibration cube on the right is spot on 20x20x10 mm while the one
on the left is 20x20x9 mm. So after adding this code AND making sure
the bottom altitude height in the skeinforge settings was set to the
same starting position my backlash was totally negated and I've been
getting great prinst now. BTW those cubes are printed with 0.36mm
layer height.
As far as the "hold Z axis" setting, no matter what I select I cannot
move the z axis threaded rod by hand during a print so I'm guessing
its always on? Hope this info helped anyone with this issue.
Jamesarm97
unchecked and checked the Z-hold option. Do I need to do that every
time I turn off / on the makerbot? If I manually adjust the Z axis
with the control panel I always see a light of some sort on the Z axis
controller which would indicate it is staying engaged and only turns
off when I disable the steppers. While the tom is printing I don't see
the lights on the Z driver unless it is adjusting the height, which I
would think there would be a light on all the time (2 red, 2 green) as
long as there has been a step command issued and it is holding. Can
anyone verify that there are lights on (besides the power indicator)
if the z axis is currently being held during printing?
Dan Newman
On 19 Jan 2012 , at 8:28 PM, Jamesarm97 wrote:
> I'm having the same intermittent problem with squished layers. I have
> unchecked and checked the Z-hold option. Do I need to do that every
> time I turn off / on the makerbot?
No. The issue is with a new motherboard/arduino nvram. There's
random bits in the location of relevance and the firmware doesn't
see it as being set on even if it is non-zero. RepG, on the otherhand,
sees it as non-zero and thus as set to on. So, initially RepG
reports it as being set (if the random value is non-zero). So, you
need to set it to a known value. Since the RepG interface only
lets you toggle it from on to off or vice versa, you're stuck with
turning it off, saving it to NVRAM, and then setting it on, and
saving it to NVRAM. And, if RepG shows it as off, then all you need
to do is set it to on. Once you go through this procedure, you don't
have to do it again.
Also, make sure you are using the latest version, ReplicatorG 29 rev2.
> If I manually adjust the Z axis
> with the control panel I always see a light of some sort on the Z axis
> controller which would indicate it is staying engaged and only turns
> off when I disable the steppers. While the tom is printing I don't see
> the lights on the Z driver unless it is adjusting the height, which I
> would think there would be a light on all the time (2 red, 2 green) as
> long as there has been a step command issued and it is holding. Can
> anyone verify that there are lights on (besides the power indicator)
> if the z axis is currently being held during printing?
On my ToM with Z-Hold enabled, lights other than the power LED remain on
all the time on the Z-axis' stepper driver. I can also confirm that the
stepper driver is holding it's position as I cannot rotate the lead screw
with my hand -- it's firmly holding it's position.
Dan
jeff oconnell
>> unchecked and checked the Z-hold option. Do I need to do that every
>> time I turn off / on the makerbot?
>
> No.
i know this is supposed to be the case, but i've had cases where i've
had to reset the z-hold after turning my ToM back on.
i haven't been able to narrow down how/when it gets unset, but to save
myself from the potential of a crappy first print, i've made unsetting
and re-setting part of my startup procedure.
a couple more times doing so and i'm sure i'm going to brush up on
some RepG coding and write a script to do it for me with one click!
Mark Cohen
the z hold. Far has told us that the z issue will be fixed in the next
firmware release. I have proven this on my own Tom. Or you can go get
Jettys firmware release. I have seen that this appears to work
correctly.
Sent from my iPhone
Jamesarm97
makerbot), so this must be my problem. I am checking the Z Hold option
(actually unchecking, save / reset, then checking / save / reset
again). So what I am reading is the checkbox is inverted and should be
left unchecked? I also do not see my Z stepper driver lights on
indicating it is holding like Dan mentioned, so this must be my
problem. My layers would print right for about .1 ", then flair out,
then repeat, kind of like an accordion. The first test print I ever
did of the 20x20 box was almost perfect, so it must have been after I
made sure the Z hold was checked that it started happening. I also
noticed that when using the controller and moving the Z I hear a hum
because the stepper stays on until I disable the steppers. I am
definitely not hearing that while printing.
Does everyone's X axis move a freely as the Y? I am concerned mine is
binding too much. I have tried to adjust it a few times but it sill
takes about 3-4 times more force to move as the Y although the prints
are not too bad. Trying to track down a irregular circular patter. I
may have to sand out the left rod holes above the stepper. I think the
problem is the rods spread out ever so slightly from the right to the
left. I measured (going by memory) something like 58.5mm across the
two rods on the right and about 59mm on the left side.
Dan Newman
On 20 Jan 2012 , at 7:56 AM, Jamesarm97 wrote:
> I am running 29.2 and firmware 3.1 (updated the day I got my
> makerbot), so this must be my problem.
And, FWIW, I've been running Jetty's firmware and as such my results
were with those fixes.
Dan
Jamesarm97
last lube and tightening of the belts made the biggest difference in
the world. Everything is practically perfect.
Mark Cohen
in the git and since he rebuilt from the latest then it worked its way
in. Since he labeled his 3.1 also then there will be a little
confusion.
Sent from my iPhone