# Need help with G-code parameters

#### spinnaker

Joined Oct 29, 2009
7,835
I am finally going to attempt my first milling job to cut some circles and need some help. With parameters. My machine is one of those cheap Chinese engravers, so it can't be worked too hard.

First attempt is just to mill a few large circles in some soft plywood. The sheet I have is 5.5 mm thick.

Here are the parameters I need to set in the dxftogcode software that I have.

What is the Z Retraction and Safety margin setting and how should I set it?
What would be a safe infeed depth for my cheap machine for plywood? For lexan?
What would be a safe feed xy rate for plywood? For lexan?

What spindle speed should I use? Slow or fast? (I don't have my tachometer working yet so I have to deal with slow or fast ). I can take the spindle from 0-8000 rpm.

Joined Jul 18, 2013
23,109
Where did you get these parameters?
The Z is zeroed to the top of the work piece.
Retract to .5906"
Set workpiece top to 0.0".
You have the parameters in inches but the material is in mm. IOW -5.5" will take you into the table with 5.5mm material!
You need high rpm for both materials.
Also tool dia/offset has to be entered/allowed for.
Are you using any CAM program?
Max.

#### spinnaker

Joined Oct 29, 2009
7,835
Where did you get these parameters?
The Z is zeroed to the top of the work piece.
Retract to .5906"
Set workpiece top to 0.0".
You have the parameters in inches but the material is in mm. IOW -5.5" will take you into the table with 5.5mm material!
You need high rpm for both materials.
Also tool dia/offset has to be entered/allowed for.
Are you using any CAM program?
Max.

They were in there by default. What is Z Retraction Area???

What do you mean "Retract to .5906"?

What is IOW??

good call on the inches think. I did not see the little [in]. Software options are set to mm so I assumed the measurements where in mm.

Joined Jul 18, 2013
23,109
Where did the default positions come from?
I assume retraction maximum retract in the Z, and safety margin is the retract between machine operations?
Without knowing the actual maching area it is just a guess at this point..
IOW = In Other Words.
Max.

#### spinnaker

Joined Oct 29, 2009
7,835
Where did the default positions come from?
I don't know. They were defaults. I assume the programmer?

I assume retraction maximum retract in the Z, and safety margin is the retract between machine operations?

Without knowing the actual maching area it is just a guess at this point..

Max.

Let me ask it this way. What is the definition of Z Retraction area and Safety margins?

If I know that I might be able to figure out how to set it.

Joined Jul 18, 2013
23,109
Not sure what they mean in that context, but you normally have a home position with the Z full up when zeroed, so any move down is in the minus Z, so if you (re)set the Z zero to the top of the work piece, any move down from there is in the -ve, and above that will now be in the Z +ve.
When performing certain operations such as peck drilling etc, you normally set a retract point above the table in order to move to another XY position to clear the tool.
There are different was of setting what is called a work coordinate system where you set the program XY reference to say the corner of the part and the Z to top surface.
In code it is a G53 to G59 for up to 6 different work coordinates.
Max.

#### spinnaker

Joined Oct 29, 2009
7,835
OK so maybe retract is tool change position?
Just for a test I entered 1,2,3,4,5,6,7. I found out they do have a mailing list. If I can't find a tutorial I might try the list.

Here is what it produced

(Generated with: DXF2GCODE, Version: Py3.6.2 PyQt5.9, Date: $Date: Mon Sep 25 13:57:11 2017 +0200$)
(Created from file: E:/dxf3gcode/AnalogClock.dxf)
(Output format description: G-CODE for LinuxCNC)
(Time: Mon Oct 30 13:34:49 2017)
G20 (Units in inches)
G90 (Absolute programming)
G64 (Default cutting) G17 (XY plane) G40 (Cancel radius comp.) G49 (Cancel length comp.)
G0 Z 0.591

(*** LAYER: Contour ***)
T1 M6
S6000

(* SHAPE Nr: 0 *)
G0 X 0.393 Y 1.035
M3 M8
G0 Z 5.000
F7
G1 Z 5.000
F6
G2 X 1.660 Y 2.302 I 0.633 J 0.633
G2 X 0.393 Y 1.035 I -0.633 J -0.633
F7
G1 Z 5.000
G0 Z 1.000
M9 M5

(* SHAPE Nr: 1 *)
G0 X 2.385 Y 1.093
M3 M8
G0 Z 2.000
F5
G1 Z -0.059
F15
G2 X 3.638 Y 2.345 I 0.626 J 0.626
G2 X 2.385 Y 1.093 I -0.626 J -0.626
F5
G1 Z -0.118
F15
G2 X 3.638 Y 2.345 I 0.626 J 0.626
G2 X 2.385 Y 1.093 I -0.626 J -0.626
F5
G1 Z 2.000
G0 Z 1.000
M9 M5

(* SHAPE Nr: 2 *)
G0 X 4.386 Y 1.046
M3 M8
G0 Z 2.000
G1 Z -0.059
F15
G2 X 5.653 Y 2.313 I 0.633 J 0.633
G2 X 4.386 Y 1.046 I -0.633 J -0.633
F5
G1 Z -0.118
F15
G2 X 5.653 Y 2.313 I 0.633 J 0.633
G2 X 4.386 Y 1.046 I -0.633 J -0.633
F5
G1 Z 2.000
G0 Z 1.000
M9 M5
G0 X 0.000 Y 0.000
M2 (Program end)

Joined Jul 18, 2013
23,109
Do you have a dry run, you can remove the tool and see how it runs, traditionally dry-run does not turn the spindle on and runs through faster.
Also I generally use the M30 instead of M02 for program end, it rewinds to the top of the PGM instead of just halting.
Max.

#### spinnaker

Joined Oct 29, 2009
7,835
Is there even a feed rate setting in that code?

What should I use for my cheap machine?

Joined Jul 18, 2013
23,109
Doesn't appear to be a F value?
I haven't machined those materials, you probably would find some help on the web, also usually for those materials 8krpm is the min spindle. So Feed rate will correspond to the 8krpm.
And No of tool flutes/dia etc.
Max.

#### spinnaker

Joined Oct 29, 2009
7,835
Doesn't appear to be a F value?
What does this mean? Remember this is a CNC for dummies thread.

I haven't machined those materials, you probably would find some help on the web, also usually for those materials 8krpm is the min spindle. So Feed rate will correspond to the 8krpm.
And No of tool flutes/dia etc.
Max.
Is there some rule of thumb for setting based on rpm?

Joined Jul 18, 2013
23,109