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Limits to Automatic Bed compensation?

Posted by auser 
Limits to Automatic Bed compensation?
March 04, 2014 02:11PM
are there limits to "how far" the automatic bed correction can work?
just measured and had one corner roughly 2mm above Z-home!
I fear the bed definitely needs replacing.
what I don't like most: I could print fine with auto-bed leveling just a few days ago... still wondering what I might have done to incure the warth of the 3d-printing gods :-(
Re: Limits to Automatic Bed compensation?
March 12, 2014 04:42PM
I've just started to try the auto setbed with no success. (yet)
Having fitted white electrical tape on the corners and removed the Kapon tape I was expecting the compensation to work.
The nozzle senses each white pad but seems not to register the data.
When I run square.g the nozzle touches the glass in places as it circumnavigates the bed.
I'm hoping the new DC42 no. 5 may sort this.
Unless I'm doing something very wrong, which is highly likely!
Sorry not to be of much help. Just offering my experience so far.
I'm going to re read the instructions again in case I missed something.
Re: Limits to Automatic Bed compensation?
March 12, 2014 04:47PM
As well as setting the 4 compensation points to place the sensor head in the middle of the white tapes, I strongly recommend you edit homex.g and homey.g homez.g and homeall.g to change the Z homing point to be the same as the first bed compensation point.

Edited 1 time(s). Last edit at 03/13/2014 10:28AM by dc42.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Limits to Automatic Bed compensation?
March 12, 2014 05:11PM
Thanks I'll do exactly that.
Just found the old forum posts on bed levelling to go through.
Jon
Re: Limits to Automatic Bed compensation?
March 13, 2014 04:34AM
Quote
dc42
edit homex.g and homey.g
not homez.g and homeall.g?
Re: Limits to Automatic Bed compensation?
March 13, 2014 04:45AM
Quote
Jon Steward
Thanks I'll do exactly that.
Just found the old forum posts on bed levelling to go through.
Jon

If Your setbed.g is twisted but You know your glass is flat:

Quote

Run the nozzle out to the outer corners of the bed, any difference in these corners (while moving the nozzle in the plus minus y-direction) is caused by the outer y-rod, this misalignment if any, is mirrored in the outer bed corners

Use nozzle measurements to adjust the y-axis-end-plates so the rods are at the same hight in both ends
[forums.reprap.org]

Erik
Re: Limits to Automatic Bed compensation?
March 13, 2014 07:05AM
Quote
ormerod168

Use nozzle measurements to adjust the y-axis-end-plates so the rods are at the same hight in both ends


Can say a vernier caliper be used to align the two rods to the table surface first?
Just trying to find a way of parallelling them without continuously running the bed up and down.


Another RS Ormerod Mk1 meets the world smiling smiley

Retired now but I used to make....
CNC Machined Mk1 aluminium bed support plates for the Ormerod
CNC machined X-plates and ribs for Mk1 & Mk2 Ormerods
CNC machined bed support arms for the Mk2 Ormerod.
Dual Hot-End heatsink blocks.
Re: Limits to Automatic Bed compensation?
March 13, 2014 08:10AM
Quote
Davek0974
Quote
ormerod168

Use nozzle measurements to adjust the y-axis-end-plates so the rods are at the same hight in both ends


Can say a vernier caliper be used to align the two rods to the table surface first?
Just trying to find a way of parallelling them without continuously running the bed up and down.

The bed is 200mm and distance between center of rods 81mm, so to get the bed within 0.1mm at the corners we are talking measurement of 0.0405 so there's no easy way I'm afraid, its a trail and error thing

Erik
Re: Limits to Automatic Bed compensation?
March 13, 2014 10:29AM
Quote
auser
Quote
dc42
edit homex.g and homey.g
not homez.g and homeall.g?

Quite right, it's homez.g and homeall.g.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Limits to Automatic Bed compensation?
March 13, 2014 01:28PM
Quote
ormerod168
... so there's no easy way I'm afraid, its a trail and error thing

Erik

...but If the y-axis end plates were made of a sufficiently broad material as to guide the (had to be 40mm longer) rods, eg. 20x40mm aluminium extrusion, and the holes for the rods were drilled with a close fit in the same machine setup, there would be no need for adjusting the Y rods at all as they would be perfectly aligned

...and mill/slice a thin trail through the center line of the holes in each extrusion as to fix both rods with through-going bolts in the middle, that would make the Y axis assembly rock solid and a perfect foundation for the rest of the build

Erik
KP
Re: Limits to Automatic Bed compensation?
March 13, 2014 04:24PM
Just thinking aloud, but:

  1. Remove the bed.
  2. Slide the bearings to either end of the ground rods.
  3. Lay the glass bed on the ground rods.
  4. Twist as required to get the glass to lay flat.

You would need to do this on the edge of a table as the rods are not at the same height. The glass could be held on the rod nearest the extrusion by an elastic band or similar.


Kev.
Re: Limits to Automatic Bed compensation?
March 13, 2014 04:46PM
I need to address this, I have had the bed level on three corners and 1.5mm low on the last!

When I fit the new bed plate, I'll go over it all.


Another RS Ormerod Mk1 meets the world smiling smiley

Retired now but I used to make....
CNC Machined Mk1 aluminium bed support plates for the Ormerod
CNC machined X-plates and ribs for Mk1 & Mk2 Ormerods
CNC machined bed support arms for the Mk2 Ormerod.
Dual Hot-End heatsink blocks.
Re: Limits to Automatic Bed compensation?
March 14, 2014 03:43AM
Quote
KP
Twist as required to get the glass to lay flat.
Kev.

Good thinking! - yes that might work with sufficient accuracy, if you got fingerspitzgef├╝hl you should be able to feel when the glass is true to the rods

Erik
Re: Limits to Automatic Bed compensation?
March 15, 2014 03:46AM
I've rearranged the bed as described and am now at the point of adjusting the Y rod as my bottom right hand corner drops just over a mm, the three other corners are good as far as my eye can judge.
It's not too obvious to me but I've tried to slacken the black acrylic Y bracket to adjust but it's quite solid, not much adjustment.
Am I in the right area to adjust?
Re: Limits to Automatic Bed compensation?
March 15, 2014 04:11AM
Quote
Jon Steward
...It's not too obvious to me but I've tried to slacken the black acrylic Y bracket to adjust but it's quite solid, not much adjustment.
Am I in the right area to adjust?

Yes but you may have to loosen the screws and adjust the printed parts (y-idler-bracket or y-motor-bracket) as well as the acrylic part do not have much slack, they are fix quite close up against the aluminium extrusion

You can force and fix either printed part up with a spacer between printed part an extrusion



Erik
Re: Limits to Automatic Bed compensation?
March 15, 2014 04:39AM
Thanks that's the one to adjust. Now the bed is visually flat when running square.g
Do you have any tips on fine tuning?
Also, does running setbed.g do anything at this stage? Can't say that I've noticed any difference after running that file.
Re: Limits to Automatic Bed compensation?
March 15, 2014 05:08AM
Quote
Jon Steward
Thanks that's the one to adjust. Now the bed is visually flat when running square.g
Do you have any tips on fine tuning?

Fine tuning yes, if you, (as of the picture posted) in the end of the aluminium extrusion loosen the lower 6mm countersink screw then you can the use the upper 6mm screw as a hinge to fine adjust the end plates with the hex screw at the arrow if you as a spacer use a small slice of rubber or some other springy material, and when you get it just right, tighten the two 6mm countersunk screws in the aluminium extrusion

Quote

Also, does running setbed.g do anything at this stage? Can't say that I've noticed any difference after running that file.

No, you setbed.g was to compensate for twisted y-rods, if you run your old setbed.g the glas will again seem twisted as seen from the nozzle
If you got it just right and make a new setbed.g it should look like mine and be of no influence to the printing and there fore no need to run and your treaded z-rod will only be moving between layers, not while you are printing the layers

G30 P0 X60 Y20 Z0.0
G30 P1 X60 Y180 Z0.0
G30 P2 X180 Y180 Z0.0
G30 P3 X180 Y20 Z0.0 S

Erik
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