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## Junction Deviation Explained and Visualized

Wow that singular diagram of what Junction Deviation is makes the whole thing make so much more sense. Great work. If I can give some constructive feedback, you probably shouldn't call jerk a velocity. Calling it a velocity isn't really right, its a bound on how quickly you can change acceleration not how quickly you can accelerate. Post a Comment. Computing Junction Deviation for Marlin Firmware. October 11, As part of developing my own 3D printer firmware, I also keep an eye on what is happening in other firmware. One feature that is causing confusion in the Marlin community is the junction deviation setting. Up until recently, Marlin used the jerk method hence forth referred to as "archaic jerk" it inherited from Grbl for computing corning speed junction velocity. With the option now in Marlin to use junction deviation instead of jerk, there are many people who want to know what are good settings for junction deviation to insure they get reasonable movement while printing. In this post I will give an equation for converting the jerk values into junction deviation and my derivation of this equation. Plugging these numbers into the above equation goes like this:. So for this example the junction deviation would be set to 0. The smaller the junction deviation number, the more the machine will slow down when encountering corners. Making this number too small may slow down the print speed and cause over extrusion in the corners. Making the number larger will increase the speed at which the machine traverses corners. Setting this number too high may cause vibrations in the mechanism that produce ringing in the print surface or in extreme cases a stepper motor to loose position. If you only came here for the basic equation, you do not need to read any further. For those who would like to learn where the above equation came from, keep on reading. To setup this problem, we are going to imagine a situation where the printer traverses two moves that are at right angles to each other:. This is a convenient situation as it is the case where one axis suddenly stops moving, and the other axis suddenly starts moving. When using the archaic jerk functionality the first axis will decelerate down to the the jerk velocity in the corner and then instantly stop, at the same moment the second axis will suddenly jump up to the jerk velocity in its direction and accelerate back up to printing speed. To simplify this, we can say that with a 90 degree corner, the junction velocity is the same as the jerk setting. Next we can take that same corner move and add the virtual arc that junction deviation uses to compute the junction velocity:.

## Grbl v1.1 Configuration

Grbl should respond with:. These either immediately change Grbl's running behavior or immediately print a report of the important realtime data like current position aka DRO. Grbl should respond with a list of the current system settings, as shown in the example below. All of these settings are persistent and kept in EEPROM, so if you power down, these will be loaded back up the next time you power up your Arduino. In prior versions of Grbl, each setting had a description next to it in parentheses, but Grbl v1. This was done to free up precious flash memory to add the new features available in v1. However, most good GUIs will help out by attaching descriptions for you, so you know what you are looking at. To manually change e. If everything went well, Grbl will respond with an 'ok' and this setting is stored in EEPROM and will be retained forever or until you change them. Everything else is the same. Stepper drivers are rated for a certain minimum step pulse length. Check the data sheet or just try some numbers. You want the shortest pulses the stepper drivers can reliably recognize. If the pulses are too long, you might run into trouble when running the system at very high feed and pulse rates, because the step pulses can begin to overlap each other. We recommend something around 10 microseconds, which is the default value. Every time your steppers complete a motion and come to a stop, Grbl will delay disabling the steppers by this value. ORyou can always keep your axes enabled powered so as to hold position by setting this value to the maximum milliseconds. The stepper idle lock time is the time length Grbl will keep the steppers locked before disabling. Depending on the system, you can set this to zero and disable it. On others, you may need milliseconds to make sure your axes come to a complete stop before disabling. This is to help account for machine motors that do not like to be left on for long periods of time without doing something. Also, keep in mind that some stepper drivers don't remember which micro step they stopped on, so when you re-enable, you may witness some 'lost' steps due to this. This setting inverts the step pulse signal. By default, a step signal starts at normal-low and goes high upon a step pulse event. When inverted, the step pulse behavior switches from normal-high, to low during the pulse, and back to high. Most users will not need to use this setting, but this can be useful for certain CNC-stepper drivers that have peculiar requirements.