101 lines
3.5 KiB
Markdown
101 lines
3.5 KiB
Markdown
# Skew correction
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Software based skew correction can help resolve dimensional inaccuracies
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resulting from a printer assembly that is not perfectly square. Note
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that if your printer is significantly skewed it is strongly recommended to
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first use mechanical means to get your printer as square as possible prior
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to applying software based correction.
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## Print a Calibration Object
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The first step in correcting skew is to print a
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[calibration object](https://www.thingiverse.com/thing:2563185/files)
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along the plane you want to correct. There is also a
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[calibration object](https://www.thingiverse.com/thing:2972743)
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that includes all planes in one model. You want the object oriented
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so that corner A is toward the origin of the plane.
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Make sure that no skew correction is applied during this print. You may
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do this by either removing the `[skew_correction]` module from printer.cfg
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or by issuing a `SET_SKEW CLEAR=1` gcode.
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## Take your measurements
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The `[skew_correction]` module requires 3 measurements for each plane you want
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to correct; the length from Corner A to Corner C, the length from Corner B
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to Corner D, and the length from Corner A to Corner D. When measuring length
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AD do not include the flats on the corners that some test objects provide.
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## Configure your skew
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Make sure `[skew_correction]` is in printer.cfg. You may now use the `SET_SKEW`
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gcode to configure skew_correcton. For example, if your measured lengths
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along XY are as follows:
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```
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Length AC = 140.4
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Length BD = 142.8
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Length AD = 99.8
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```
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`SET_SKEW` can be used to configure skew correction for the XY plane.
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```
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SET_SKEW XY=140.4,142.8,99.8
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```
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You may also add measurements for XZ and YZ to the gcode:
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```
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SET_SKEW XY=140.4,142.8,99.8 XZ=141.6,141.4,99.8 YZ=142.4,140.5,99.5
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```
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The `[skew_correction]` module also supports profile management in a manner
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similar to `[bed_mesh]`. After setting skew using the `SET_SKEW` gcode,
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you may use the `SKEW_PROFILE` gcode to save it:
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```
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SKEW_PROFILE SAVE=my_skew_profile
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```
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After this command you will be prompted to issue a `SAVE_CONFIG` gcode to
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save the profile to persistent storage. If no profile is named
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`my_skew_profile` then a new profile will be created. If the named profile
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exists it will be overwritten.
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Once you have a saved profile, you may load it:
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```
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SKEW_PROFILE LOAD=my_skew_profile
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```
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It is also possible to remove an old or out of date profile:
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```
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SKEW_PROFILE REMOVE=my_skew_profile
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```
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After removing a profile you will be prompted to issue a `SAVE_CONFIG` to
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make this change persist.
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## Verifying your correction
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After skew_correction has been configured you may reprint the calibration
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part with correction enabled. Use the following gcode to check your
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skew on each plane. The results should be lower than those reported via
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`GET_CURRENT_SKEW`.
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```
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CALC_MEASURED_SKEW AC=<ac_length> BD=<bd_length> AD=<ad_length>
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```
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## Caveats
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Due to the nature of skew correction it is recommended to configure skew
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in your start gcode, after homing and any kind of movement that travels
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near the edge of the print area such as a purge or nozzle wipe. You may
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use use the `SET_SKEW` or `SKEW_PROFILE` gcodes to accomplish this. It is
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also recommended to issue a `SET_SKEW CLEAR=1` in your end gcode.
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Keep in mind that it is possible for `[skew_correction]` to generate a correction
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that moves the tool beyond the printer's boundaries on the X and/or Y axes. It
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is recommended to arrange parts away from the edges when using
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`[skew_correction]`.
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