I have found a bit of a workaround for my own inquiry. You can use the "Variable Settings Wizard" to use three different processes on the same part. I have been playing with it and have greatly improved the first layer above the raft. I am still working on perfecting it, but here is what I have found works okay on a machine with a heated glass bed, direct drive extruder, and 1.75mm PLA material.
Process 1: This is the raft and only the first layer of the part (start @ 0.0mm/ stop @ 0.2mm)- The key here is to crank up the Extrusion Multiplier to something near 1.5, Infill Outline Overlap to 99% (as high as it can go), use only two perimeters, and use a higher temperature than normal printing and increase your retraction settings. I am using the following settings for other parameters:
First Layer Settings:
Width: 125% (could probably drop this)
Speed: 25% (could probably bump this up)
Top Layers: 2
Base Layers: 1
Separation Distance: 0.24mm (pretty well bonded to the raft here)
Top Infill: 78% (ends up nearly 100% with increased flow)
Above Raft Speed: 25%
This jams a lot more plastic in the first layer. The 99% outline overlap drags a lot of the inner perimeter material around to fill in the gaps and serves as a sacrificial pass. The perimeters still don't bond well so using more than two of them is counterproductive. Tip- The more you increase the Extrusion Multiplier on your machine the more you will need to increase the Raft Offset.
Process 2: This is the 2nd and 3rd layer of the part (start @ 0.2mm/ stop @ 0.6mm)- For some reason, even though the above process gets a pretty nice surface on the first layer, you still need to flow more material than normal on the next layer or two to print normal on. Lower the temp to normal, drop the Outline Overlap to something like 50-60% and increase the number of perimeters to what ever you want the rest of the part to have. You can probably get this done in just one intermediate layer but I am still tweaking on it.
Process 3: This is how the rest of the part will print (start @ 0.6mm)- Just use your normal settings for printing from here on out.
The attached image is of the top of the raft (left) and the bottom of the part (right) on a little squircle calibration model I am using to dial this in. You should be able to greatly improve your part quality using this general approach with some simple trial and error for your particular printer.
- Improved raft-to-part results