# Speeding up X and Z axis velocity in LinuxCNC



## 4DThinker (Feb 16, 2014)

I noticed when using the LinuxCNC configurator app provided by probotix.com, that my Z axis jog and max cut speed had slowed down quite a bit. 24ipm in fact. 

Digging into the probotix.ini file I noticed the MAX_VELOCITY value for X(0) and Y(1) axes was 3.34, while that same value for the Z(2) axis was .4. Knowing my X and Y axes are limited to 200ipm on my Meteor, a little math (200/3.34=60ish) reveals these small numbers must be inches per second. I changed the MAX_VELOCITY for my Z axis to 1.0, saved the file, then ran LinuxCNC again. My Z axis now jogs and can feed up to 60ipm.

By extension, this MAX_VELOCITY value can also be changed to alter the max jog/feed speed your Probotix CNC can move in X and Y directions. Knowing the 200ipm value was chosen by Probotix to minimize thrashing of the feed rod while traveling in the Y direction, I'd keep the Y value at 3.34 (200ipm). The X feed rod is half the Y length, so I suspect faster velocities should be fine for that axis. 

I've changed my Z max velocity, but haven't yet tried changing it for X. I know Probotix sets X and Y at 300ipm(5.0) for their small V90 MK2 CNC. It has 20 inches of X travel. For a Meteor or Comet with 25" of X travel 286ipm (4.77) should be just as safe. For the Nebula and Asteroid with a 37" X axis the math says 250ipm (4.17) should be fine in that direction. The Y value for the Asteroid should be safe at 286ipm. 

We do a lot of fluting cuts to make tapered tenons for furniture projects. The constant up and down Z motion is where a great deal of cut time can be saved by speeding up Z velocity. I'll be changing the X velocity of the college Meteor and Nebula to these new values to potentially speed up all cuts from now on while keeping the Y value at a safe 200ipm. 

4D


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## 4DThinker (Feb 16, 2014)

I've been playing with values for my X axis this morning, and 286ipm sounds just a bit too fast to keep the machine happy in that direction. I've settled down to using 260ipm (4.34) in the X direction for the 25" travel range of my Meteor. 

4D


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## rrrun (Jun 17, 2014)

4DThinker said:


> I've been playing with values for my X axis this morning, and 286ipm sounds just a bit too fast to keep the machine happy in that direction. I've settled down to using 260ipm (4.34) in the X direction for the 25" travel range of my Meteor.
> 
> 4D


Fascinating post.

My Nebula's X jog works great ... until it starts to make a screech when jogging at speed. My latest theory is this happens when the rails get warm: the machine seems quiet in the morning, but after 4 hours of use, any quick jog on the X results in a loud screech. No amount of oil seems to help at that point.

Any theories?


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## honesttjohn (Feb 17, 2015)

I use oil on the tubes and a little lithium grease on the screws.


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## 4DThinker (Feb 16, 2014)

Just a theory, but the lead screw may be heating up the plastic nut it goes through after hours of back and forth X travel. A hot nut may shrink a bit? I'm not sure if they are delrin or some other concoction, but some sylicon/whatever spray on the lead screw may quiet your X squeals.

I've heard the Z axis on our college Meteor start to squeal after doing a few hours of tapered pins with repeated Z up and down motion. Of course when I've stopped the machine and gone to find some lubricant it has cooled down and won't squeal when I get back. 

4D


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## 4DThinker (Feb 16, 2014)

45%: The percentage of cut time a tapered tenon array joint sample took to cut using 60ipm for Z axis plunge speed vs 24ipm and the same tool paths.

Faster Z speed should speed up 3D cuts as well. Some experimenting might be worth it to figure out just how fast Z plunge speed can be set to speed up all cuts. Profiles and pockets might need a ramped entry point for end mills that don't plunge efficiently. A slower speed can always be set when creating a tool path, but HAVING a higher potential speed to use when you can seems like a win-win to me. The short vertical distance most cuts require will self-limit the maximum plunge speed as the bit accelerates then decelerates quickly. 

4D


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