Hi everyone, hoping for some guidance.

General CNC CNC Routers
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Hi everyone, hoping for some guidance. I’m a few months into building my first CNC machine. Learning a lot. and having fun. Basic build is:

  • 8020 extrusion gantry style frame
  • 20mm linear rails and 1605 ballscrews
  • Arduino with GRBL and TB6600 drives
  • 1.5kw chinese spindle (ordered yesterday)

I have the basic build together and smooth motion in all direction, using manual commands from Universal Gcode Sender. Getting close! I mounted a marker to the z-axis and can manually draw on paper.

I have couple questions around getting homing setup…

Which direction is standard for positive axis movement vs negative? I.e. which corner is standard to home to,… and when I move out from that corner which axis are moving into a positive space vs a negative space? (Currently, when Z is raised fully and X and Y are back left, then everything is moving into positive space as I plunge and move towards the center.)

My limit switches are installed and connected to the proper Arduino pins for GRBL. But homing, hard limits, and soft limits are not yet enabled and configured. Does anyone know of a simple reference for initial/basic GRBL settings for these capabilities? I am familiar with the GRBL wiki, which is a great reference, but would be nice to have a solid starting point configuration.

Thanks for your thoughts on helping me get past these points and onto cutting some air!

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You can setup your coordinate system anyway you like, but many people have home set at the front left.

Have a look at chap 4 on coodinate systems here:

3

I have my mill set up so 0,0,0 is at the left, front, lowest point of the workspace volume, so all absolute positions are positive numbers. You may choose differently, but a lot of people expect that. You can always offset your workpiece, and traditionally many people bolt a vise onto the mill table and then change the relative 0,0,0 to be a point on the fixed jaw of the vise.

4

There’s no rules. I home to the middle of my work envelope.

5

Another consideration is z0 as the highest point. I don’t remember the exact logic.

6

One obvious reason to have Z0 as the highest point is so you don’t forget and tell the mill to go to x0 y0 z0 and crash the hell out of it as it attempts to shove a milling bit into the left side of your table. A lot of CAM packages assume Z0 is at the top of your part and all depths are negative numbers.

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@Kyle_Kerr I home Z in the middle of its travel too. With tool touch off I don’t see that it matters much.

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Great, thanks everyone for the help! That pdf on the fundamentals of CNC is helpful. Makes a lot of sense regarding the home location. I do like the idea of homing Z to the highest point and plunging into negative space and will home X-Y to the front left and move into positive space as I move towards the center of the table.

Now I need to get my GRBL parameters setup. Are any of you using GRBL?