There are many many many ways to zero your machine. It all comes down to your preference.
It took me a while to get my head around it too. What is the correct way? How do others do this? What is the law? Turns out, there is none.
Frankley, I focussed purely on the machine but that is not the complete picture. XY0 is a handshake between CAD and CAM. It is the most important agreement between design and manufacteri g. Get that one thing wrong and everything will be.
Your design software focusses on the material you will machine the design into. It doesn’t care what machine you have. When you set a XY zero it will generate code coordinated around that point. Everything left of that point will be -x, everything below that point will be -y. If you put the XY0 at the bottom left, your design will be in the upper right quadrant and (prolly) wont generate negative coordinates.
Where you set your design XY0, you set your machine XY0. So you designed bottom left zero, you zero XY at the material botom left.
After you include the cad software into the picture, it all should fall into place. It all depends on what you need.
For example You have a setup with a (removable) fence that is on a fixed position on your machine bed. You can snuck square material against that fence having it clamped down at the same spot on the machine bed.
You could say, I home my machine and use that as my XY0, for the material will be always at the same spot. You can, but the offset needs to be accounted for in your design.
You could zero off the fence. Then again the offset from the fence to the material needs to be accounted for in your design.
You can zero on the material and have a clean design.
Another option is (when you have limit switches for homing.) To use workspaces.
Essential creating positions on your machine space that have their own XY0 points.
I mostly design dead centre my material, because it works for every material shape and keeps my designs consistant - leaving me less proun to have my XY0 wrong and is easier to use between different cad softwares (vectric - lightburn)
Another perk is that you don’t need exact material dimensions to get your design alligned with the material. The offset will be equal in every direction.
Ofcourse, the downside to zeroing centre is that a auto zero block is utterly useless. For XY0.
So, what I’m trying to say is, there are many ways to zeroing your machine. It all comes down to your preference on how to get your cad files allign with your material.
Not to take away from @Spamming_Eddie 's observations, but before getting into details, it would be good to know if your machine has limit/homing switches? What corner do you intend to home to? Any other details about your machine would be helpful.
A Homing cycle is done after connecting the machine to Gsender but only if there’s limit switches installed. It only really needs to be ran again if you disconnect the machine from Gsender or if something happens and the machine loses position.
As @Spamming_Eddie mentioned there’s a few different ways to setup and probe. I’ll explain what I’ve found works well for me, keep in mind I have limit switches installed and I run a Homing cycle.
Machine, Table and Software Setup
I have two probes connected to the machine, an AutoZero Touch Plate for X, Y and Z probing and a smaller touch plate that I made out of an aluminum heat sink fixed with foil tape to the lower left corner of the spoil board (my machine home position) for Z probing.
Having macros for moving the machine to certain positions and automating tasks makes things a lot faster and easier.
A macro is needed to probe with the second plate so I wrote one that moves the machine to a tool change position and then probes Z on my fixed touch plate after I change the tool.
For a fence, I used the machine to pocket out a few 1/4” peg holes in the spoil board that make a squared fence when dowels are inserted. (If you plan on doing this make sure you leave room for clamps between the edges of the spoil board and the workspace)
Workspace Setup – Probing X, Y workspace coordinates.
To Zero the X, Y coordinates I insert the dowels and align a 16”x24” Carpenter Square to them, then align the AutoZero Touch Plate on the square and probe for X, Y, this only needs to be done once for the workspace.
Work Piece Setup – Probing Z workspace coordinate.
How I Zero the Z coordinate will depend on the job. Most of my jobs consist of profile cutting, so I prefer to probe off the bed using my fixed touch plate, I don’t like cutting into my spoil board when the work piece is thinner than it’s supposed to be.
I only use the AutoZero Touch Plate for probing Z if I’m probing off the top of the work piece,
which is only if I’m surfacing, engraving, or doing a shallow carving.
There are some things that are first setup in the CAM software, like the Z zero position(bed, or top of work piece), work piece dimensions, X, Y home position, keep out zones, job sheet, etc.
The basics of my workflow for the first job of the day consists of…
open Gsender, connect to the machine and run a homing cycle.
use a macro to move the machine out of the way.
insert dowels for the fence.
place the work piece against the fence, open job sheet and clamp.
remove dowels.
use a macro to move machine to tool change position and probe for Z on my fixed touch plate.
load the tool path file while machine is probing and then start the job.
if necessary repeat step 6 and 7 until the job is finished.
Thanks all, I will definitely have limit switches, I have purchased proximity switches but I haven’t decided on exact placement, it’s a pretty large DIY CNC so I have space to play with. I’m very open to setting it up the way gSender or grbl works best with. As previously mentioned I’m going to use a T41U5XBB.
Update 1: Also I should add I have Cut2D and I’m sniffing around FreeCAD, I’m not 100% on the FreeCAD CAM (Workbench) situation, is it a feasible replacement for a CAM that you pay for?
Update 2: I just ordered the AutoZero and then thought to myself…can it be used on a metal cutting CNC, maybe I’ll need some adhesive plastic film on the bottom of the AutoZero?
