There seems to be a possibility to completely natively control the CNC using just the LCD screen, ie using uploading through a SD card native G-code and start it from there. Is this correct ?
Yes, that is correct. I have a Primo, not a Lowrider, but I run all my jobs off the SD card. I don’t like having my good laptop at risk in the shop. The only downside is that the interface for moving the axes for electronically positioning the router is clunky. There are ways to address the issue (joystick, pendent, manual movement).
If you do decide to run your jobs from an SD card, and if you use a touch plate for setting your Z height, modifying the Z homing in the V1 custom menu to take into account the touch plate thickness will make your job easier. It is a simple change to the firmware, but it does require you to learn how to compile your firmware using PlatformIO.
Is there any advantage/disadvantage (except workflow) to control the CNC using a PC connected to the Rambo, and if so what is the recommended freeware PC based control SW
There are a variety of things you can do with most g-code senders that are clunky with the screen and a SD card. For example, manually sending g-code commands, or programming option buttons to send sets of g-code commands for common tasks. Historically Repetier-Host has been the recommended g-code sender, and there are some setup instructions here. Note there is a bug in the latest version where arcs (G2, G3 g-code commands), are not displayed correctly in the Windows interface, though they do mill correctly on the CNC. You can 1) ignore the display, 2) turn off arc commands in your CAM, or 3) run an earlier version of Repetier-Host.
using Fusion 360 with LR2
For running Fusion 360 with a Primo or a Lowrider, you need a postprocessor. You will find the recommended one here. In terms of learning the CAM, I list some of my learning sources in this post, though these materials are a bit dated.
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That leaves the question of LR2 cases. I’ve seen more than one used including this one.
Anyone who is, or has been, a LR2 owner: do have a specific case recommendation?