From 56f33d261c91457b0838fdd2dd06f9c5795b17b1 Mon Sep 17 00:00:00 2001 From: lawgicau Date: Mon, 31 Aug 2020 08:30:07 +1000 Subject: [PATCH] Add glass/shim method of compensating for a warped bed. --- calibration.html | 1 + 1 file changed, 1 insertion(+) diff --git a/calibration.html b/calibration.html index 2fafb93..a2b0737 100644 --- a/calibration.html +++ b/calibration.html @@ -154,6 +154,7 @@

During printing, the firmware will reference the mesh and compensate for an angled and/or warped bed by raising and lowering the nozzle using Z axis movement. This means the nozzle can travel up and down to match the contours of the bed, ensuring a good first layer.

In the printer's bed is perfectly flat, it is reasonable to claim ABL is not needed. Some users may still prefer it for the added convenience. In the event that the bed is warped (very common), it can be impossible to get a good first layer without ABL or manual mesh bed levelling. An example of this situation is shown in the video above.

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It's worth noting that you can compensate for a warped bed in other ways, such as shimming the lower portions with a thin and flexible material. You can also use a glass/mirror plate over the top, which are typically quite flat. The downside of this is a longer time required to reach printing tempratures and additional load on the Y stepper (on an i3/'bed slinger' style printer) that may require lower print speed/acceleration.

The bed can be probed at the start of the print with a G29 command, with the resulting mesh immediately used to compensate as the initial layers are produced. Alternatively, the bed can also be probed some other time (while not printing), the mesh stored in the EEPROM and then restored with M420 S1 at the start of a print. In this case the print will start sooner, since we do not need to wait for a new mesh to be probed, although it may not be as accurate if anything has changed since probing. Either of these gcode commands should come after the G28 home command in the start gcode.

Although ABL can compensate for a crooked/non-levelled bed, it is still better to attempt to level manually first and get everything in the ballpark.

Probing the bed and building a mesh only accounts for an uneven or warped bed. Like manual levelling, we still need to set the distance between the nozzle and bed to get a good first layer. This is where the Z offset comes in, which is simply the vertical distance between where the probe triggers vs the nozzle tip. Here are some examples: