bCNC.. Am I missing something very basic?

Where is all the documentation for bCNC? (I know about this one:

Long version:
Hi, I’m two days into my first cnc experience after rebuilding an old 3D-printer to something that is going to become a pcb-mill. My current setup is grbl on a makerbase board and I’ve installed bCNC on my Mac. I’ve semi-successfully drawn a circle with a pen, so the setup is pretty much working. My big problem so far has been the intense lack of documentation. So much so that I really think that I have been searching for the wrong things or just plainly suck at googling. I cannot find any documentation for the majority of buttons and functions, and it’s giving me a diagnosis. One example is the probe tab which is attached below. WHAT DOES IT ALL MEAN? (read dramatically). I have studied this page ( like an overly conscientious munk, but to no avail. My last hope is therefore seeking the knowledge that lies deep within the forums of the legendary Makers.

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Doubt you are going to find about magic documentation that hasn’t been added to the official wiki… :stuck_out_tongue:

If you ask specific questions here about what things mean, though, you might get answers to your specific questions and be in a position to help improve the bCNC wiki!

Ok, so at least I’ve not missed anything very obvious… Here are a number of questions from the tab I mentioned. I’m both interested in the answers themselves as well as where to find the information. If I find a good source, I will definitely do some suggestions to the wiki!

1: Whats the difference between “fast probe feed” and “probe feed” and when are they used?
2: What is TLO?
3: What does the different alternatives in the “probe command” drop down do?
4: What does everything in the “record” section do/mean?
5:How does the “probe” section work? What is a probe cycle?
6: How does “center” work? I’m guessing it’s about finding the center of a hole, but what happens when you press the center button? I don’t want to risk breaking anything by blindly experimenting…
7:What does everything in the “orient” section mean/do?

I could probably ask the same questions for the other tabs as well, but this is what I am working on at the moment. Again, I am serious about contributing to the wiki, and being a total noob, I think I can help make it more accessible for beginners.

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Just to be clear, as far as I know no bCNC maintainer is here on MakerForums. So we can talk about it here, but it’s not necessarily truth… I’ve never used bCNC myself, and doing a search for bCNC on MakerForums doesn’t show a lot of posts since early 2019 when we imported history from Google+; all the older history is from Google+.

TLO is “tool length offset” and this is at on the wiki you linked to.

Typically fast probe is a first pass to get an approximate measurement quickly, then pull back and probe again more slowly for greater accuracy.


I’ve used bCNC quiet a lot, but I cant answer all of your questions.

I can tell you this though. I use the probe function, and all I do is connect the probe to the spindle, and put a value in the third “pos” box in the probe group. If you hover the mouse over, it will tell you that is the Z axis.

The value you enter is the max you want z to try before giving up.

I usually drop my Z so its about 10mm from the probe and put a value of -10.

Click probe, and it should gently work its way down.

If its the first time you are doing it, touch your probe base plate to the bit , and see if you stop.


Thank you:) Could you have a look at the other answers as well? I will implement everything in the wiki!

The reason I cant answer all of your questions is because the probe functionality I described is all I know about it.