GRBL Settings Pocket Guide Rev B

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DIY Machining - GRBL Settings - Pocket Guide
The following settings are specific to GRBL v0.9 - For more information visit www.DiyMachining.com/GRBL
Definition
Explanation
Command
View Settings

$$
$0=10

Step Pulse Length (µsec)

$1=25

Step Idle Delay (msec)

$2=0

Step Pulse Configuration

Axis
Config.
Table
$3=6
$4=0

$5=0

$6=0

$10=3

$11=0.020

$12=0.002
$13=0
$20=0
$21=0
$22=0
$23=1

Setting Value Reverse X
0
NO
1
YES
2
NO
3
YES
Axis Direction
Step Enable Invert

Displays current GRBL settings stored in EEPROM (memory) of the Arduino
This sets the length of the step pulse delivered to the stepper motors. The goal is to have
the shortest step pulse your motors can reliably recognize. The data is available on some
stepper motor data sheets otherwise 10 is a good default.
Sets the time delay in milliseconds that GRBL will power the stepper motors after a
motion command is complete. A setting of 255 tells the motors to stay powered on to
hold position.
Defines the step signal sent to the stepper motor drivers. By default the step signal starts
low and goes high to denote a step pulse event. See Axis Config. Table below.
Reverse Z
Reverse Y
Reverse Z Setting Value Reverse X
Reverse Y
YES
NO
NO
4
NO
NO
YES
NO
NO
5
YES
NO
YES
YES
NO
6
NO
YES
YES
YES
NO
7
YES
YES
Changes axis motion direction without changing wiring. See Axis Config. Table above.
Controls the signal sent to the enable pin of your stepper drivers. $4=1 sets the enable
pin to high. (Invert)

Limit Pins Invert

This refers to the limit switch pins which by default are set to high using the Arduino's
internal pull up resistors. Grounding the pin tells GRBL the limit switch is tripped. For the
opposite behavior use the setting $5=1 which tells the system that a high is the limit
switch trigger. You must also install external pull down resistor with the $5=1 setting.

Probe Pin Invert

This refers to the probe pins which by default are set to high using the Arduino's internal
pull up resistors. Grounding the pin tells GRBL the probe is tripped. For the opposite
behavior use the setting $6=1 which tells the system that a high is the probe trigger. You
must also install external pull down resistor with the $6=1 setting.
Defines the real time data sent to the user. By default
GRBL reports running state which cannot be turned off,
machine position & work position. The table to the right
details the settings. Note to send a combination of status
reports, simply add the values of the desired report types
and send this value to GRBL. For Example, say I want Work
Position (2) & Limits (16), I would send $10=18.

Report Type

Value

Machine Position
1
Work Position
2
Planner Buffer
4
RX Buffer
8
Limit Pins
16
Think of this as cornering speed. A high values allows for fast motion around corners but
increases the risk of missed steps resulting in decreased accuracy. Conversely, lower
Junction Deviation (mm)
values reduce the speed around a corner decreasing the risk of missing steps while
potentially improving accuracy.
GRBL treats curves as a collection of small straight lines. This setting defines how smooth
Arc Tolerance (mm)
the curves will be. The default is .002mm and will not likely need to be changed as this
value is below the accuracy of most machines.
Feedback Units
Sets position feedback units from mm to inches. $13=1 for inches or $13=0 for mm
Requires "Homing" be enabled and checks to see if gCode commands will exceed the
Soft Limits (Enable/Disable)
travel limits of the machine. $20=1 Enable $20=0 Disable
Requires limit switches be installed and looks for one of the limit switches to be
Hard Limits (Enable/Disable) activated which triggers "Alarm" mode. In this mode, all machine motion, the spindle
and coolant are shutdown.
Homing Cycle
Requires limit switches be installed. Enabling this will lock out all gCode commands until
(Enable/Disable)
a "Homing" cycle is run.
Allows the user to change the direction of the homing cycle us the values from the Axis
Homing Cycle Direction
Config. Table on page 1.
Status Report

For more information visit www.DIYMachining.com/GRBL

Command
$24=50.000
$25=635.000
$26=250
$27=1.000
$100=314.961

Definition

Explanation

Feed rate used in the "Homing" cycle once the limit switches are located. The lower the
Homing Feed (mm/min)
value the more repeatable the zero position.
Feed rate used in the "Homing" cycle to locate the limit switches. Set this to the highest
Homing Seek (mm/min)
value that does not cause the machine to crash into the limit switches.
Length of the software delay in milliseconds that minimizes switch noise. A value
Homing Debounce (msec)
between 5 an 25 is typical.
Tells the machine how far to move away from the limit switches after finding the "Home"
Homing Pull-off (mm)
position so as not to trigger the hard limits.
Tells GRBL how many steps are required to move the machine a given distance.
X (steps/mm)
Steps/mm = (Steps per Revolution)*(Microsteps) / (mm per Revolution)

$101=314.961

Y (steps/mm)

$102=314.961

Z (steps/mm)

$110=635.000

X - Max Rate (mm/min)

$111=635.000

Y - Max Rate (mm/min)

$112=635.000

Z - Max Rate (mm/min)

$120=50.000

X - Max Acceleration
(mm/sec2)

$121=50.000

Y - Max Acceleration
(mm/sec2)

$122=50.000
$130=225.000
$131=125.000
$132=170.000

1) Steps per Revolution = 200 Typical - This is the number of steps required
for your stepper motor to make 1 complete revolution.
2) Microsteps - 1,2,4,8,16 - Is a setting on your stepper motor driver. A higher
value means lower torque but higher accuracy.
3) mm per Revolution - Determined by your machine setup. (lead screw pitch)

Z - Max Acceleration
(mm/sec2)
X - Max Travel (mm)
Y - Max Travel (mm)
Z - Max Travel (mm)

$#

View gCode Parameter

$G

View Parser State

$I
$N
$N0=line
$N1=line

View Build Info
View Startup Blocks

$x=value

Save GRBL Setting

$C

Check gCode Mode

$X
$H

Kill Alarm Lock
Run Homing Cycle

~
!
?
ctrl-x

Save Startup Block

Cycle Start
Feed Hold
Current Status
Reset GRBL

Defines the maximum speed for a given axis. This is found experimentally for each axis by
incrementally increasing the value and then sending a test gCode command to move the
axis. Be sure the command allows the axis to move enough to reach the maximum rate.
You will know the maximum speed when the stepper motors stalls. Reduce the value by
10-20% These values may be different for each axis.
Defines the maximum acceleration for a given axis. This is found experimentally for each
axis by incrementally increasing the value and then sending a test gCode command to
move the axis. Be sure the command allows the axis to move enough to reach constant
motion. If you decide to use a jog command make sure the jog increment is several
inches. You will know the maximum value when the stepper motors stalls. Reduce the
value by 10-20% These values may be different for each axis.
Used when soft limits are enable to tell GRBL the maximum travel for each axis. This also
requires the use of a homing cycle.
GRBL Commands
Lists work coordinate offsets (G54-G59), Predefined positions (G28 & G30), Coordinate
offset (G92), Tool Length Offset (TLO) & Probing cycle (PRB).
Displays the active gCode modes in the GRBL parser.
Example - [G0 G54 G17 G21 G90 G94 M0 M5 M9 T0 S0.0 F500.0]
Shows the GRBL version and source code build date.
Displays the startup blocks run each time GRBL is powered on or reset.
Command used to save startup blocks. Substitute valid gCode commands for the "line"
portion and these will executed each time GRBL is powered on or reset.
Command used to save a GRBL setting. Replace the "X" with a number from the list
above and the "value" with the corresponding setting.
Processes all incoming gCode commands but does not move the axis, spindle or coolant
so the user can check a gCode program.
Overrides the alarm lock to allow for axis movement.
Executes the homing cycle.
Real Time GRBL Commands
Starts buffered gCode commands. Used to resume cutting after a "Feed Hold."
Stops active cycle by controlled deceleration preventing position lose from missed steps.
Returns the active GRBL state & current machine & work positions.
Soft reset command retains machine position without powering down the Arduino.

For more information visit www.DIYMachining.com/GRBL



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