The first, and most basic, way to set the distance between the hot end and the bed is a long screw that hangs down from the extruder assembly. Each time we select the bed height option on the console, the printer homes the machine so that this bolt can activate a switch and then the printer uses that position to move to the center of the bed and lower the hot end to the position called for the bolt's length.
The manual calls for adjusting the hot end so that it barely touches the bed. "Barely" is the operative term. I'd like something a little more measurable. To get the most precise setting, I decided to use a mechanic's tappet gauge. So, I started with the 0.102mm leaf on the mechanic's gauge to get the hot end as close as I am able to measure. But, through trial and error, I found that my particular printer responded best (laying down an undistorted raft) at 0.254 for PLA.
Here are the steps I use.
- Press the Z-Height Selection
- Make sure the Z-Height Offset is 0
- Try the 0.254 leaf of the gauge under the hot end.
- If there is a lot of clearance, tighten the adjustment bolt.
- If there is no clearance, loosen the adjustment bolt.
- Exit Z-Height adjustment
Repeat the above steps until the gauge just slips under the hot end. Do NOT make changes to the Z-Height offset. You are setting the base point and will use the offset to further fine tune for different situations or special cases.
I understand the critical nature of getting the hot end (Z-Axis) height right for the raft. But, it's still unclear to me that it makes much of a difference in subsequent layers as the Z-Axis increments should take care of itself in spite of the starting height as long as the height was sufficient to create a starting raft.
And, the optimal height for any given printer with any given material might be a bit different. That is because the setting you end up using is the setting that is able to lay down a nice raft without tearing it or distorting it.
The point is that we can get more precise in by using tools, like a mechanic's tappet gauge, we are better able to control our printing environment on a repeatable basis.