Y calibration

Y calibration

Postby bbrown64 » 2015-Jul-Mon-07-Jul

I went through the complete X_Y_Z_E calibration and changed the M92 line in the EEPROM settings. However, in real time printing the Y dimension is off by .5mm. My question is can I simply subtract .5mm from the Y measurement to correct the problem in the EEPROM?
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Y calibration

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Re: Y calibration

Postby Mooselake » 2015-Jul-Mon-08-Jul

No. X and Y calibration not includes the motors steps/mm, but also includes how much the extrusion width differs from it's calculated value - otherwise no matter how much you fiddle with axis calibration you'll only get it right for one size print. Use the calculated value (usually, but not always, 80 these days) and concentrate on proper extruder calibration. Use the calculated value for Z, and concentrate on your extruder.

Unless you have bottom of the barrel belts and pulleys any attempt to refine the calculated value will be lost in the stepper motor, belt stretch (aka backlash), thermal and humidity expansion, controller's microstep variations, etc. Slic3r's calibration directions are a good reference, even if you're using Cura.

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Re: Y calibration

Postby bbrown64 » 2015-Jul-Mon-15-Jul

Kirk, your answer baffled me. You you provide the formula that you are referring to, calculated value of 80. When I did the calibration for X_Y_Z_E I used the instruction I found at Instructable web site. http://www.instructables.com/id/Calibrating-your-3D-printer-using-minimal-filament/ I know I did the math correctly. Why would the Y_Z dimensions be off by .5mm?
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Re: Y calibration

Postby frankv » 2015-Jul-Mon-16-Jul

What Kirk is talking about is that if you print something and it's not the right size in the Y axis, that may be due to two different things. Firstly the Y axis calibration, and secondly the width of the outermost extruded layer (i.e. the E calibration).

Following your link, it says to calibrate the Y axis by sticking tape on the printer. I respectfully suggest that the 0.5mm discrepancy is in your measurements, not the printer. How accurately can you stick tape? I'm sure I'd struggle to get it within 0.5mm, especially with parallax issues. Are you measuring that distance strictly along the Y axis, or at some slight diagonal? With digital/vernier calipers, or with a ruler? You need to measure with calipers if you want to get sub-mm accuracy.

I suggest that the calibration instructions in the instructable are good to get a basic (within +/- 1mm) calibration of your printer. Once you've done that, print a cube and measure that to get a better calibration. I think that Kirk assumed this was what you were doing.

The X,Y,Z calibration of the printer that is being talked about in steps 2-4 are ratios... your 0.5mm error is meaningless without also giving the nominal length (70mm in the instructable). If the ratio was wrong in one dimension by a factor of 1.05, a nominally 50mm cube would print at 52.5mm in that dimension, whereas a 10mm cube would print at 10.5mm.

If your E calibration is wrong, you will get over or under extrusion, and each line deposited will be too wide or narrow (and too high or low). This also affects the size of the object, but *not* proportionally to the size of the object. If you're over-extruding to the extent of 0.5mm of width (which would be quite a lot, and I have no idea how erroneous the E ratio would have to be to get that), then (assuming the XYZ calibrations were correct) a nominally 50mm cube would print at 50.5mm in all dimensions, and a 10mm cube would print at 10.5mm. (This is somewhat over-simplified... there's probably other side-effects of over-extrusion).

Adjusting the XYZ calibration factors to compensate for an E calibration error would mean that you would only get accurate prints at one particular object size.

Hope this clarifies.

Frank
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Re: Y calibration

Postby Mooselake » 2015-Jul-Tue-12-Jul

What frankv said... I might have been a bit terse as this is a frequent issue and probably posting from my tablet.

I meant that you should calculate the x, y, and z calibration numbers from the microstepping settings and tooth count (screw pitch on z), not from printing and measuring objects. The procedure in the instructable is even worse and more prone to errors than print and measure, although it would be improved by using a dial gauge like I did back in the printed gear days. Notice his numbers were right around 80. Today the errors from measuring (ignoring an NIST quality lab at your disposal) are greater than using the calculated values. The firmware likely came set with the correct numbers, and if not somebody with the same model can give them to you. Plus if you managed to measure and correct the very small error, it would be insignificant compared to the other variables (temperature dimension changes, filament variations, etc.) and be different the next time you print something.

Use your time getting the extruder numbers as close as you need (or want). After you get some experience and can consistently get good quality prints then you can decide if you want to pursue it further.

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