Problems with the leveling

Hi guys,

I built my SmartRap a few months back and have been really pleased with it so far. Got some help from my friend Cliff to get everything up and running and it has been working fine until I started to try and print larger objects. The problem I have is that close to the frame the print gets smeared onto the glass and on the far end of the glass it barely sticks to the glass.

I noticed early that the glass was flexing when performing autoleveling and printed a support for the glass. I use a ballhead hex screw to be able to adjust the height easy as can be seen in the pictures.



I have executed the autoleveling according to Serge's instruction several time and although I think it works properly it does not make the printer print evenly.

Any tips anyone ?

/Pontus

#define Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_X 0.5 // smartrap: special quantic error mesurement from porte a faux design (see marlin.cpp)

This will add or subtract z height as the machine moves front to back to compensate for the glass flex.

Excellent, will try that out.

/Pontus

Yeah, that sort of worked.
I managed to get it to print evenly on one end of the glass (Y) but then on the other end the same thing happened.
I am playing around with a Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_Y option to see if I can get everything to print evenly.

HI Guys,
Regarding the thread above.
Should I replace the red X 0.5 with the X value from the G29 probes?
#define Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_X 0.5
Thanks
Mike

No.. You have to play around with it. It compensates for the glass, rods flex when probing.

I never managed to get it perfect so i decided to add set screws that allows me to adjust the height of the glass on three points.
I'll try to remember to take some snaps of it when I get home.

Much easier to do it with a set screw and it is now perfectly levelled.

/Pontus

It is not as easy as it should be for now.

BUT... I just finished testing with inductive sensor and small aluminium foil under the glass ..and it works perfectly. I will integrate this solution right away ( even on the actual shipping kits). I found this really good and we don't need Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_X anymore because we never touch the bed anymore .

the sensor is : [www.aliexpress.com] ans it is used in place of the Z endstop.

However I'm interested by your solution with screws sweet peas ? I've never found a good one and i find good to have this option with the Smartrap.

thank you

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Using this method is so easy and very accurate too.
Just one variable to change in the firmware and then the rest is done automatically.
1. Home the Z.
2. Lower nozzle to bed position. Use paper to get the correct bed space.
3. Send M114 from Pronterface to read the position.
4. The reading shown on the screen will be the exact value to put in the firmware for the offset.
5. Program the board as usual.
Takes just a couple of minutes beginning to end and can be checked at anytime and changed if anything moves out of kilter So Easy.

// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR -1

#define min_software_endstops false // If true, axis won't move to coordinates less than HOME_POS.
#define max_software_endstops true // If true, axis won't move to coordinates greater than the defined lengths below.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

Serge, you stated that
"I just finished testing with inductive sensor and small aluminium foil under the glass ..and it works perfectly."
If it sees the foil under the glass, will blue tape, PVA glue or kapton tape confuse the proximity sensor?
I mean if the probe probes the bed in 3 places, then those 3 points would have to be absolutely clear from tape, plastic or PVA right?

Another thought, maybe the machine could put down the first layer at a layer as measured by the sensor in real time. Without probing at all. So the machine constantly measures the gap and compensates for the height while working.
Regards
Mike

Edited 1 time(s). Last edit at 09/13/2014 09:36AM by mikefiatx19.

that would be great indeed. You need a full metal bed and the right height of the sensor so you don't need any offset ( when it triggers, the head would be at the right height) . That's possible as the sensor has a screw to adjust height.

maybe i will try that ? . Can be nice with not so plane metal beds

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Hello all, Im back on the forum again

Metal beds seems to be a nice tought. If it would work, then why not to try use it as the heated bed in the same time. Only the mounting should be somehow heat resistant, and the bed shrinking from the changed temp. can be a bit problematic.

Annyway, Mikefiatx19 idea with measuring the gap in real time while printing sounds grate!

Edited 2 time(s). Last edit at 09/13/2014 04:16PM by verteez.

Thank you verteeez ,

I'm testing aluminium heated bed for production , as people say that PLA can stick well on an alu bed at 60 and stop sticking at lower temp. I've never tried it before .

About the sensor mike, I use a 18mm ith 8mm detection, so it works with anything on the bed, tape, glue, whatever, it will work the same.

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Hi Guys,
just wanted to pass a comment on Mr Reg Pye's last post in this chain....because I too have had a sore head trying to understand how to calculate off-set, possibly due to zero experience at printing.

Many thanks to the detailed response by Reg this is clear for a single point setting on the bed – but what I am having a tough time trying to understand is how to take into consideration if the glass is at an angle or not perfectly flat (unlikely). .
So I was looking at the GCodes and I would have thought we need to use a G32 with M557 using a 4 point reference points to ensure against any twists.

Am I over thinking all of this?

The G29 in the slicer code takes care of any angle in the plane of the glass. The 3 point level reads the height of the bed at 3 points and records the angle to use as a reference for the gcode commands. If you watch a print after the 3 point level has happened you should see the Z screw constantly turning to compensate for the uneven bed.
The only time I can think of when this would not work correctly is if the glass was somehow bent and like you said i think thats unlikely to happen.

Edited 1 time(s). Last edit at 09/15/2014 07:47PM by mikefiatx19.

Quote
mikefiatx19
The G29 in the slicer code takes care of any angle in the plane of the glass. The 3 point level reads the height of the bed at 3 points and records the angle to use as a reference for the gcode commands. If you watch a print after the 3 point level has happened you should see the Z screw constantly turning to compensate for the uneven bed.
The only time I can think of when this would not work correctly is if the glass was somehow bent and like you said i think thats unlikely to happen.

One thing I will pass on to you guys about this particular subject.
Glass is slightly flexible and will bend.
If the bed that the glass sits on is bent and you use four spring clamps or paper clips, it will bend the glass to the shape of the bed underneath.
In this case it is best to use only two clamps so that the glass plate is held in the centre (Australian spelling) of the front and back edges only. That way the glass will not bend and will stay flat.

If using wooden rails as some of us are doing, the four glass clips can be used because there is nothing in the centre to make the glass bend.

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[regpye.com.au]
"Experience is the mother of all knowledge." --Leonardo da Vinci

Excellent thank you guys ....I had not realised that G29 calculated the plane of the bed... The reference I was using did not include that part it just said it probed.

Will the Z offset compensate for the x axis flex, too? I printed my smartrap out of ABS (cheap ABS at that) and the X axis has boatloads of flex. But like Serge says it only flexes when it is probing.

I don't really think I get that much flexing during the probes. How far away from the home position are you probing?
I suppose the further from X0 you go to take the probe point the more flex you will have in the X axis. Try probing closer to the start position. So, if you are currently probing X180, Y0 try changing it to X100, Y0 and see if it still flexes.

hi shootquinn,

for the flex, i've setup a hack in marlin on our github. It's in configuration.h at line 412 :

#define Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_X 0

you can enter a value here , like 0.2 to ..whatever you feel is good

this will add an offset to the last Z probe to recover from the extra Z coming from the flexing . It gave very good result until now ( logically ) .

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I did the same thing but for the Y axis since my printer was crooked somewhere and now it prints like a dream.....

#define Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_Y 0.4 // smartrap: This is my own addition to tweak my slightly crooked printer.

and added the following to the set_bed_level_equation_3pts function

// My own mod:
z_at_pt_2 += Z_PROBE_OFFSET_FROM_EXTRUDER_DELTA_Y;

haha. cool
the funny thing is : i did the same at home but didn't put it online .. i had one bad printer i couldn't manage to know why it wasn't straight on Y .

and it works, right ?

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