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Print height problem

Posted by Ramclear 
Print height problem
June 23, 2014 10:25AM
Hi everyone,
Just finished building my first Prusa i3 rework and I'm having what I'm pretty sure is a newbie problem.
When I print the 20mm calibration test cube all sides are exactly at 20mm but the height is only about 2mm high
Otherwise the print looks fine.
I believe the issue may be with the steps x mm for the z axis but not sure how to proceed.
The motors are minibea nema17
I'm using 1.75 PLA filament and a 4mm extruder.
Any help will be extremely appreciated smiling smiley
Re: Print height problem
June 23, 2014 04:29PM
you have same pic?
how that print can look good is 10 times smaller in heigh?wher that filament go

Edited 2 time(s). Last edit at 06/23/2014 04:34PM by premek.
Re: Print height problem
July 04, 2014 07:13PM
Beats me!
I fiddle with the settings in marlin and got it to print a cube now 20mmx20mm by 8mm high (first 2 pics)
Also when I tried to do the 50mm tower adjustment, I get a print that's 10x10 x32mm high (other 2)
I'm not sure what the width of the tower should be, but I do know it should be 50mm high for sure smiling smiley
My problem seems to be only with the Z axis, I'm using minibea nema 17 motors with a direct drive to an M5 rod.
Any help with this will be GREATLY appreciated... it's driving me nuts! lol
open | download - IMG_0275.JPG (88.3 KB)
open | download - IMG_0276.JPG (72.6 KB)
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open | download - IMG_0278.JPG (75.7 KB)
Re: Print height problem
July 04, 2014 11:38PM
What is your layer height set to? Try printing the "0.5mm-thin-wall" test piece as well. There's something in the gcode telling the printer to make the print at those heights. If the z-axis just wasn't advancing fast enough you should have a large amount of excess plastic and very messy prints.

Edited 1 time(s). Last edit at 07/04/2014 11:39PM by MaFraL.
Re: Print height problem
July 05, 2014 02:03PM
Your Z steps depending on your stepper set at mines standard setting at 1/16 if using M5 thread should be set at 4000 that should not change not like configuring your belts on x and y but you may have your steppers set at 1/8 and your firmare z steps set for 1/16 as pictures shows the top layer is near on peRfect

Check my rubbish blog for my prusa i3

up and running
Re: Print height problem
July 05, 2014 04:50PM
Chris33, wouldn't being set to 1/8 make the z motor act weird? When I set the steps to 4000 the z axis goes up fine but on the way down, moves a bit then stops and makes noise. I know it's not binding because it doesn't do it at 1000. Do you think that could be a voltage problem to the motors and may need to adj the drivers?.

MaFral, yes, the prints look very good except for the height. I printed those tests at a layer height of .07.
I will print what you suggested and post the results
Re: Print height problem
July 05, 2014 06:31PM
The layer height has nothing at all to do with it - its all about the z steps per millimeter. Tell me this - without even printing, just by using the manual controls, or by entering g code directly, if you tell the carriage to move up by 10 millimeters, how far up does it go? It should be exactly 10 millimeters - every time. How did you calibrate your z steps, and what are the physical characteristics of your z axis? Are you using micro stepping, and did you take that into account when you calibrated?
Re: Print height problem
July 05, 2014 08:00PM
My axis is an M5 rod with a coupler to the motor shaft (2 1.8 deg nema 17 minibeas)
I used the prusa calculator which told me to set marlin to 4000 , another problem I'm having is that,
If I set it to 4000 it will go up fine but on the way down, moves for a few mm then stops and makes noise. This doesn't happen when I use a lower number ( strange behaviour)
Newbie question: to make the carriage move by 10mm , is that the meaning of the 10 that I see
on the pronterface interface for the Z axis?
I'm away from the machine right now but will try or test and post tomorrow.
Thanks for all the help
Re: Print height problem
July 06, 2014 01:09AM
The 4000 value is the steps per millimeter of movement. On the z axis, it is an exact mathematical computation based on the characteristics. It us not an estimation, and it is not a value to be experimented with. Insert the value and change other things if it doesn't work, but don't change the steps per millimeter unless you discover you calculated it wrong. If the motors do not go as far as you indicate, perhaps there is binding on the axis. Can you decouple the screws from the motors and see if you can move up and down freely? If there is any binding, the motor will stall and emit nasty sounds.

One thing you didn't tell me was whether or not you are using microstepping (actually a steps/mm value of 4000 is a pretty good indication that you are). On the ramps, this is controlled by jumpers that are installed beneath the driver boards. I don't know what electronics you are using.

In pronterface when you control the axis manually, you control the distance - usually in millimeters - and the speed - usually in mm/minute.
Re: Print height problem
July 06, 2014 03:05PM
Hi Jbernardis,
I am microstepping (3 jumpers installed).
I reset my config.h to 4000 and the noise on the way down returned but I noticed one thing, the motor was alot faster going down
So...I went to M203 on Pronterface and set Z to 1 (was at 10) to test and now the axis is moving 10mm and no noises or stops on the way down.
What is a good setting for the speed of Z ? obviously 10 is too much for my setup ... or should I fly by the seat of my pants and keep going up until
the motors start acting up?
I'm printing the 20mm cube again, will post pics of the results.
Re: Print height problem
July 06, 2014 03:50PM
That speed setting means nothing when you are printing - it only controls Z speed when sending interactive commands. The slicer embeds the Z speed that is used during printing directly into the G Code. Inside your G code, you'll see lines like: "G1 Znnnn.nnnn Fnnnn.nnnn" where the number after the Z is the new Z height (or the difference from the current height if you are operating in relative mode) and the number after the F is the speed - in millimeters/minute. Divide this by 60 to get milllimeters/second.

To be honest, I'm not sure how the slicer computes Z speed, because there is generally not a setting for just Z, but you can limit it in your firmware with the M203 command. I think the firmware value is actual what limits the Z speed in most cases.

Having said all of this, I still think it would be good for you to diagnose the Z axis. There can be issues if the two rods and not EXACTLY parallel. One way to see is to do what I said earlier. Disconnect the couplers from the motors, and move the axis up and down with your hands. You should be able to lift and lower with just a single finger, and further, you should be able to do this not only from the middle, but from either end - and there should be no deflection in the axis. If you see and binding or looseness, the axis needs some work.
Re: Print height problem
July 06, 2014 04:53PM
I did as u said, disconnected the rods, couplers and also run each motor separately.
The only time I had the noise and binding was when I set the z speed to 4000 in pronterface and only when the motors moved the axis down.
Everytime even without load ... I have no idea why, didn't matter if I run one motor or both.
It's like when it was going down the motors were spinning too fast.
Now that I changed that setting in pronterface, my Z axis started to behave.
I'm really confused now, if that setting does nothing while printing, why is it that my tower is now the right height? (no idea here)
Could it be something else on my config.h causing all these things?
Re: Print height problem
July 06, 2014 05:47PM
Maybe all of this manual adjusting worked out the kinks???
Re: Print height problem
July 06, 2014 05:54PM
I'm a noob...lol.. I have no idea why this happened.
I do appreciate you getting me on the right track, I understand this machines a little better now.
Let's see what happens next,,,
To be continued, I'm sure you haven't seen te last of me!! smiling smiley
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