A couple of questions about homing the XL

Hi everyone! I’m new to CNC, so please pardon the ignorance.

I just finished setting up my Shapeoko 3 XL and ran the Hello World test with no issues. Now, I am just trying to get to know the machine. I imagine this will be the first in a long line of questions.

I have entered my table size in Carbide Motion settings: X=850, Y=430. I also sent the $130=850 and $131=430 using MDI.

When I use homing, the machine stops a bit more than 4mm from the where the limit switches make. It looks like there is about 3 or 4 more more mm past that before the actual limit of travel. Is that right?

After homing, when I use rapid position to move to the front-left corner, the machine hits on the X-travel but only the first time. If I rapid position back to rear-right then front-left it stops perfectly.

I thought initially that it might be a deceleration issue, so I jogged the carriage to very close to front-left and the used rapid position and it still hit even though it only moved a few mms.

The hit isn’t very hard and hasn’t left a mark in the powder coat but if it is an issue I want to fix it.

What exactly is the purpose of homing? I still always need to set the zero position of the carriage before each job anyway right?

Another quick question, in Carbide Motion, the MDI screen says to “To send directly to GRBL, begin line with /” when would I do that?

Thanks in advance!


Yes, the machine backs off a configurable (default is 5mm) distance off the switches after homing and sets that as the machine origin.

Homing allows one to have “work coordinate systems” and known offsets of position — once you get homing set up, you can use the nifty “rapid position” feature to get to the center of the work area (I had to tweak my table size a bit to get that positioned dead center over my center-line T-track).

Then, you can have fixtures which are matched to specific work coordinate systems (except for G54 — it’s reserved by Carbide Motion last I checked) and can spend more time cutting and less time manually setting the origin for a cut.

This tutorial goes over things nicely: http://carbide3d.com/docs/tutorials/tool-change/

The community has some notes at: http://www.shapeoko.com/wiki/index.php/G-Code#Using_the_Work_Coordinate_Systems


I’ve never used homing switches before, but now I don’t know how I lived without them.
You’ll love it for tool changes, or tweaks to a program on the same part.
I had to shorten my travel a few mm to avoid hitting.


Thank you Will, I’ll look them over. Lot’s of new stuff to learn, very exciting!


Thanks Jerry, I believe I will do the same.


Also I like to re home after I change tools, in case I’ve tweaked anything a little, tightening the collet.
So, I’ll run a tool/gcode, then after, rapid position to front/center, change tool, then re home (from the rapid positioning screen) BEFORE I touch and zero Z.

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The tutorial and wiki article were very useful. Thanks again Will!