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Mechanical (re)calibration my way.

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Mechanical (re)calibration my way.

Postby ads » Sun Mar 15, 2015 8:43 am

Proper calibration and adjustment of the mechanical parts is a major part in getting good print results.
The printers i got delivered were very bad calibrated and not giving good print results in the beginning.
Over time a method to get good results evolved that worked for me.
Not claiming that this method is the holy grail for calibration.
It is the method i use and giving me satisfactory results.

As a start i searched for a reference point and used the top plate for this.
The four standing extrusions on the four corners are exactly the same length making the lower side of the top plate a good reference point.
(checked the length on both printers and the all 8 are the same length)

Checking the levelling of the y-axis rods against the top plate found variations of 1mm in the distance.
Not a real good starting point for getting everything level.
First tried to adjust with a good quality calliper (not an el cheapo from ebay or supermarket) tried to get the four plates holding the the rods in position but realized this was not the best way.
Made a adjustment rig from aluminium strip and the only drawback is that you have to remove the two stepper motors and idler wheels in the front to get access to the bolts.
For me the correct distance between the top plate and the rod was 42mm.
(This distance varys from machine to machine and could be up to 50mm. If you set the distance to small the Y-axis home switch will never touch the aluminium bearing block and Y homing will fail.)

The next thing to check are the nuts on the vertical spindles.
Again took the top plate as a reference and with a piece of aluminium strip placed the right front spindle at a reference point.
(Difficult to change the position of this one because off the plate holding the idler obstructing access to the grub screws.)
Make the distance on the left-front and rear spindle equal to the right front one by loosening the grub screws in the pulley.
Hold the pulley in position and carefully rotate the lead screw to the desired position.
After adjustment tighten the grub screws and proceed to the next spindle.
When everything is tightened again recheck the positions to make sure all three nuts are at the same distance from the top plate.

As a result you have the carrier for the heated bed level and that is a good starting point to get the heated bed level.
The distance you use is not important because it is relative and the final adjustment on the Z-axis sensor makes it absolute.

Now the motors and idlers for the y-axis can be put back in their place.
Position them correctly so the belts are straight in every way and properly tensioned.

Now that there is good starting point the heated bed can be levelled.
It can be done relative to the nozzle with or without a fixed distance piece at the four corners of the bed.
I made a dummy plate for x-axis that replaces the motors and nozzles with a dial gauge.
Maybe this is over the top and also got good results with a fixed distance piece under the nozzles.

When the bed is level the only thing remaining is adjusting the z-axis sensor for the proper homing point.

With this procedure i never felt the need to implement the auto bed levelling in the firmware.

(Later will add the files and some pictures)

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