Inventables Community Forum

Machine position reading negative?

I was watching some videos of the x-carve, and noticed that users are having their machine position displaying 0,0,0 for all three axis. When I look at my machines postion, it reads -789, -789. -1 when I have it homed.

Do I have some wires crossed somewhere that would be making this thing read backwards?

It’s just a traditional setting. (and the default setting for Inventables.)

It’s easy to change that by rebuilding grbl with a configuration change.

To be clear, by default, the top right corner (looking down) is the natural for the machine zero? And when it goes to my starting position (lower left), it is reading negative from that natural zero?

I would definitely like to change this. Is there a walkthrough on how to do the grbl rebuild?

To the best of my knowledge it was the way original CNCs were set up. They place the work space in the negative quadrant.

Which version of grbl are you running?

I am not running any version of it yet. I am still VERY new to all of this.

What version do you recommend?

If you don’t plan to use a laser then I would recommend 1.1f/g

If you do plan to run a laser, then I would recommend my 1.0c version, not 1.1f/g

No laser plans.

I will run the 1.1f/g version.

As I google for this, I am seeing mentions of an Arduino board. Is this needed for me to use grbl with the xcarve?

Can CNCjs do the same things as the grbl? (sorry if silly question)

The X-controller is an Arduino clone with stepper motor drivers on-board.

Here is a version of 1.1f that uses the positive quadrant.

grbl_1_1f_20170417_positive.hex (84.5 KB)

You can use Xloader to load it into the Arduino/X-controller.Instructions

Thank you for that. I appreciate the help. Will mess with this for a bit and reply with results and questions if any more arise.

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A CNC machine is by nature a remover of material. Remove => subtract => working in the negative domain :slight_smile:
As long as work zero and design is aligned all is good.

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Uploaded with no problems. I now have 0 for my machine position instead of the negative.

In the midst of all of this, I did notice my left belt had just a bit more play than the right one. So, I decided to tighten it up a bit. Didn’t even get to the same play as the right one before it snapped… so… looks like I’ll be down for a few days…zzzzz

Hi Larry. I run a Jtech laser on my x-carve with Grbl 1.1f, with no problems at all. Why should we be using 1.0c instead ?

It’s not should or shouldn’t. I have tried to be careful in using the correct wording. If I have ever said that you should or should not use 1.1f/g that would be a mistake.

What I do say is that I do not recommend using 1.1f/g for laser work.

Modifications to make the laser work were extended to try and make laser work safer, but have instead created scenarios where serious injury could occur.

I’m not saying that my version is safe, by any means, but my version does not change the way G-code works and therefore is not as dangerous as 1.1f/g which causes the user to change the way they use G-code to get 1.1f/g to control a laser.

An easy example:

In my 1.0c version with $32=1, M3 S255 will turn the laser on.

In version 1.1f/g with $32-1, M3 S255 will not turn the laser on unless other operations have occurred prior to issuing the M3 command. And then at a later time you issue a movement command the laser will come full on. Like a G1 command.

With my version a G1 command will never turn the laser on.

The specifications that grbl is built on do not specify turning on the laser or spindle is a function of the G1 command.

And there are many other examples.

I have had one report that when running 1.1f/g the laser came on at full power when the operator was not expecting it.

You can read more details here.

Larry - Just added a J-Tech 2.8 so taking this all in. Do you lose the Speed Override feature with 1.0c?

Yes.

I don’t really recommend 1.1f/g for laser work, because of some of the internal changes made there. It’s mostly a safety issue.

With my version of grbl you gain speed, but you do lose the feed rate and rpm over rides.

Thanks Larry, but I’m still confused. I use Lightburn for all my laser jobs. What difference would I see if I used both versions of Grbl?

Then use 1.1f’/g

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Thanks mate