504,416 active members
4,785 visitors online
IndustryArena Forum > Hobby Projects > Hobby Discussion > A circle, a simple circle. How hard can it be?

# Thread: A circle, a simple circle. How hard can it be?

1. ## A circle, a simple circle. How hard can it be?

I'm new to CNC having built a 2-axis plotter driven by Arduino, CNC-Shield and GRBL 1.1.

I can draw a square.

I now want to draw a circle and have failed miserably for days.

I have googled on and off for about a week now and looked at dozens of examples. Not one of them does a circle. Not on my machine nor in any of about 5 different simulators I've tried. At best a limp arc, at worst straight lines or nothing.

Come on.

A circle.

Could someone post the GCode to do say a circle centered at X=0,Y=0 with radius 5cm?

Since I now believe it is impossible. Please check your work here:
GCode Simulator
or here:
https://nraynaud.github.io/webgcode/

2. ## Re: A circle, a simple circle. How hard can it be?

G0 X0 Y5
G2 X0 Y5 I0 J-5

Doesn't work in the first simulator you linked, but works in the second one.

3. ## Re: A circle, a simple circle. How hard can it be?

Hi, if you took the time to learn G code all will be revealed, but you gotta be in it to win it.
Ian.

4. ## Re: A circle, a simple circle. How hard can it be?

Originally Posted by ger21
G0 X0 Y5
G2 X0 Y5 I0 J-5

Doesn't work in the first simulator you linked, but works in the second one.
Yeah... doesn't work on my machine (running GRBL).

The first command works but the circle doesn't and I get:
error 33 for G2 X0 Y5 I0 J-5

5. ## Re: A circle, a simple circle. How hard can it be?

OK, the circle code works in UniversalGCodeSender but not in GrblController 3.6.1

I thought these programs just send GCodes to the machine so how can they get different results??

6. ## Re: A circle, a simple circle. How hard can it be?

I think that GRBl doesn't allow full circles, only partial arcs.

7. ## Re: A circle, a simple circle. How hard can it be?

But GRBL is on my Arduino - I'm just switching between different PC software which both send "G2 X0 Y2 I0 J-2"

8. ## Re: A circle, a simple circle. How hard can it be?

I think that Universal G Code Sender breaks the circle up, and sends multiple arcs to GRBL.

9. ## Re: A circle, a simple circle. How hard can it be?

I think I see what's happening. If you're in relative mode (G91) you can't draw circles.

FAIL:
>>> G91
>>> F100
>>> G0 X0 Y2
>>> G2 X0 Y2 I0 J-2
ok
ok
ok
error:33

SUCCESS
>>> F100
>>> G0 X0 Y2
>>> G2 X0 Y2 I0 J-2
ok

Is there any way to just draw a circle centered from wherever you are?

10. ## Re: A circle, a simple circle. How hard can it be?

I think I see what's happening. If you're in relative mode (G91) you can't draw circles.
You can, but the code is different.

G91
G0 X0 Y2
G2 X0 Y0 I0 J-2

11. it's really hard for me

12. Different controls read g-codes differently.
I think that GRBl doesn't allow full circles, only partial arcs. It sounds very hard buy have you tried looking for it in the Internet& There are a lot of tutoriels there.