Unanswered Base layer problems....

I can't talk about Cura, but make sure that the startup gcode block has the autoleveling setup correctly (if you are still using it) or that it is removed from the startup gcode if you are using manual leveling.

Refer to this post in the FAQ: http://community.robo3d.com/index.php?threads/faq-r1-r1-series-printers.19735/#post-119212

Normally with manual leveling there is NOTHING to save because the print carriage is manually leveled. So you would want to make sure that all traces of autoleveling are removed from the slicer and that it is not trying to enforce a Z offset (because you have manually/mechanically set that).

My startup GCode for manually leveled printers is a G28 and not a lot more...

 

It is likely that the slicer is not using the Z offset for the brim.
The actual model ... yes.
For it to dive down after the brim your Z offset is too low (or positive -- should be negative)

If you are manually leveling then the G29 needs to be removed and not used and the Z offset (M565) is not used.

If you want to continue to use it I would experiment with a larger negative number for the Z offset.
More negative => further from the bed
Less negative => closer to the bed

If you do a raft most slicers will NOT use the Z offset as part of the raft, they will once it start to print the model ON the raft.

The priming lines used by the C2/R2 are NOT using the Z offset -- it uses an absolute position to do the priming line.

 

Again that is all slicer specific (and I have not used Cura in a loooong time). So if you are happy with it working that way -- good.
Brim/Raft most slicers don't use the autoleveling offset for that at all.

 

Simplify3D for about the past 6 years

The Z sensor on the R1/R1+ is the nozzle. It uses that to find "the bed" and regardless of what you added on top of the bed, the "probe" will drive down until it "senses" whatever is there. That is your Z home. Are both of your Z home switches positioned correctly? It is easy for one of them to get out of position and if that happens it will simply not work correctly. Review the autoleveling video here if you are unclear on what I mean: http://community.robo3d.com/index.php?threads/helpful-videos-novice-expert.7478/

With no autoleveling being used it will not do the 9-step probing and Z home is the spot where one or both of the Z home switches trip when it drives the extruder down.

 

The Z offset was designed to help account for the inherent small amounts of mechanical slop that occur with the carriage and the switches. They are not high precision and there will be variance from one machine to another in the exact positions the switches trip. With manual leveling you would physically adjust the switches up against the crossbar until the nozzle is positioned where you want it for the first layer. You probably are familiar with the sheet of paper approach -- that gets you close and then you tweak from there until it is perfect. Without autoleveling -- that is the end of the story until you have to replace the nozzle or work on the extruder. After that you redo the manual leveling.

 

The original idea was the autoleveling was easier than manual leveling and that it would help account for beds that were bowed or warped. However the BiLinear algorithm used by default in Marlin 1.0 doesn't do well for warped beds. The newer Marlin versions used by the R2/C2 CAN do better if you use MESH or UBL (Unified bed leveling) rather than the BiLinear.

 

Heh, whatever makes your first layer look like this:

https://www.printedsolid.com/blogs/news/37035715-get-your-prints-to-stick-check-your-skirt

Seriously due to the fine differences it will almost never be the exact same offset for any two printers. I have 4 Robos and they are all different. Obviously the other non-Robo machines are different too...

There is a version of the R1 firmware using Marlin 1.1.x that is linked in the forums here and includes configuration files for the R1 and R1+ : http://community.robo3d.com/index.php?threads/marlin-1-1-9-release-for-robo-r1.22329/

 

It is a community supported version and not the same as the stock firmware. Not wildly different, but it does have the Marlin 1.1.x functionality

 

Actually getting manual leveling to work can mean lifting the bed and shimming the bed base mounts on each side or shimming the build plate (where the magnets hold it in place).

 

OK, that is not an unusual thing (sadly) but you can fix this in an easy way ...
Go to your local hardware store and get a sheet of float glass cut (that is what they make window panes out of) sized to fit over the printable area of the bed (or the entire bed -- your call). Put it over the printable area (you can use binder clips to hold it in place).

That is it... this works because window glass is invariably very flat. Not warped. If it were you would notice the visual effects
Does it have to be Borosilicate (Pyrex) to account for the heat? Nope, the bed does not get hot enough or change temperature fast enough for that to matter.

P.S. that pane of custom cut glass will be cheap....

 

Now if it is too close to the bed everywhere then you need to adjust the switches mechanically on the rods either up slightly (the mounts they are in have locking screws you can loosen to move them). This will cause the Z to trigger sooner (which will make the default offset higher). Mechanically the switches are jammed against the crossbar and will trigger (open) when the crossbar is lifted off of them and by lowering them fractionally you make that happen sooner. Worst case you can set a default axis offset that lifts the Z a fraction (not the M565 -- that is for autoleveling)

https://all3dp.com/2/z-offset-3d-printing-how-to-adjust-it/

So even if the switches can't be adjusted to suit you can force the Z to be lifted a bit before the printer starts.

 

Maybe. Take a look at this video and see if that offers any insight ... you want the Z switches to operate as close together as possible.