My Site

Distance From the Nozzle

When you are printing before each layer the nozzle moves up. This leaves a fixed distance from the nozzle to what is below it. The only time this does not nappen is for the first layer. You usually have to handle this yourself.

When you power on a printer it has no idea where the head is. As part of the startup it figures out where 0, 0, 0 is. X and Y are usually switches that something hits when it is all the way over. On an Ender the head moves all the way to the left where it hits a switch, to mark X0. Then the bed moves back until it hits a switch, to mark Y 0. Then It splits. Without ABL it moves down til it hits a switch and that is Z0. With ABL it moves down until a sensor sees the bed and that is Z0.

X0 and Y0 just have to be close, since it does not matter if the print you are about to do is 1mm off in some direction since all of it is relative. The Z0, on the other hand, has to be exact, since for the first layer you will use that to set the height. Some ABL methods measure the distance from a probe to the bed and the important thing is the nozzle, not the probe. There is an offset for the Z distance. You quite often have to set this yourself, even with ABL you have to set this by hand.

So, now you know where the bed is and where the nozzle is, let’s do the first layer. Move the head above the bed by the first layer height, set in the slicer. Draw the first layer. If you have a mesh, probably created by ABL, and the gcode to use the mesh is in the print file, the mesh is used. As the head moves around for the first layer it moves up/down to keep a constant distance from the bed. If there is a high spot on the bed the head will move up whenever it prints in that area and it will move down for a low spot.

This movement is cut down for each layer and by the time you are a few layers up each layer will be flat.

When each layer is printed it is flat. The head moves up the layer height, from the slicer, and does the next layer. At the start of a layer the head is layer height above the last layer and it will not hit it. If your first layer comes unstuck the print will bend up and the head will not be layer height above the part that came unstuck. You can get curves where the corner of a print turns up cause it came unstuck and the layer height is short there. In a bad case the print can move up enough for the nozzle to hit the print as it moves around.

Another problem can occur when the head passes over a line for the level that has already been printed. You can not stop/start the extrusion of plastic in the .4mm that is the width of a line do you spit out plastic and let the nozzle flatten it. As the head crosses the already existing line it is real close. It should not hit, but it is a physical thing and stuff can happen.

This is often a problem in infill. Some infills cross more often and can be a problem more often.