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Attached is a picture of a first layer currently being printed. Note the inconsistent extrusion "thickness" (?).
This seems to come in waves somehow. The extruder does not obviously seem to be slipping. I've reduced the motor current just to be sure.

Any idea what might cause this?

Specs:
- ORION, stock extruder, stock hot-end
- 1.75mm ABS
- 220C/90C first layer, 230C/100C the rest

First layer speed was very slow (30% of normal, which is around 50mm/s).

I've been seeing this a lot more lately... why are you printing the first layer cooler and then bumping it up?

Is that the info in the manual now? Also, 10C is a huge jump in temp. If you can get good first layers at 220, there should be no need to go to 230 unless your speed is significantly increased.

A lower first layer temp (both bed and hotend), IME, doesn't stick as well as a hotter first layer.

The "ORIONABS.ini" file provided by SeeMeCNC does the first layer/rest temps:
http://download.seemecnc.com/orion/quickstart/#/23

I have seen this before. I don't think it has anything to do with the extrusion being inconsistent, but rather a combination of bed leveling and how the plastic adheres to the platform in those areas. It looks as though your first layer is squished a bit more than it needs to be, starting maybe 0.05 or 0.1 mm higher may net you better results.

Rule #1 of 3D printing:

Don't assume anyone else's pre-made settings are the correct ones for you.

Have you measured the filament?

You could very easily see a big change in extrusion width with a 10C change in print temp, have you tried keeping temp at 225 throughout?

Is your bed level?
The areas where it's thin could be because the print area isn't level.

Lochemage wrote:I have seen this before. I don't think it has anything to do with the extrusion being inconsistent, but rather a combination of bed leveling and how the plastic adheres to the platform in those areas. It looks as though your first layer is squished a bit more than it needs to be, starting maybe 0.05 or 0.1 mm higher may net you better results.

Bed is level as best as I can tell.

This picture is the best way of showing the problem, but i'm pretty sure it exists at any level height, anywhere on the bed. Note that the transition from "light" to "thick" is matching the pattern exactly. If it was bed level/adhesion, I don't think you'd see a crisp transition like this.