X axis linear rails

Hello everyone.

So a few weeks ago I made a post about my machine not traveling the expected distance. After many hours of troubleshooting I have decided to take the whole machine apart and check my assembly. I have also ordered new spindle gears.

While waiting for parts I was still trying to see if I could get my machine to travel the expected distance and decided to take my steppers off the racks and reset them incase I had the springs set to tight.

My question is. My Y axis I can move it with 1 finger when the steppers are not touching the racks. But the X axis is a different story. It takes a fair bit of force to manually move it from one side of the gantry to the next.
Way more then for the other axis.

Could my linear rails be pinching the guide blocks or is this a standard thing? I would have expected the movement to be very easy as it’s carrying less weight then the y axis do and that was super easy to move.

If this is an issue does anyone have a better way to line them up parallel then what the manual says to do?


You can over torque the bearing mount screws and make a complete mess of the X axis. Same with the Y but you will notice it less.

Even the jig can’t overcome over torqued bearing screws.

When assembling mine I noticed the X-axis was harder to push than the Y exactly like you’re describing. I assumed it was because of the dual rails and 4 bearing blocks in close proximity. I didn’t think much of it. Been a while and nothing to report, seems fine.


I had the same issue with a tight y-axis. Sometimes the movement stops and the stepper squalls/stall (losing steps). I loosened all the lower rail screws, then worked my way down tightening, moving the carriage as I went. I have had to re-visit the issue, but my machine is subjected to some pretty wide temperature swings.


Set your top rail using the setup block, then with the lower rail loose move the spindle to within 2 of the bolts to the left side of the machine, then as you move the spindle tighten each screw as you move to the right so on and so on until you reach the other side. You should now be able to easily move the X from side to side with ease without the motor engaged.

JRG’s advice is right on. I could hardly move the carriage along the X axis when I first assembled my machine. I had to put all my weight into it to get it to move. It was shockingly bad and disappointing compared to a machine I had designed / built using linear rails. So, I followed a similar procedure to JRG and the carriage moves way easier. I can give it a good push and it moves a foot to 18 inches. I would REALLY like to hear from everyone as to how easily their carriage moves along the X axis for comparison and piece of mind. I still think mine is not as smooth as it should be.

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Hey guys. So here’s what my plan is.

I have designed a jig to 3d print that will hold a dial indicator. Since the top rail has a setting guide, which i used when I built my machine. I will assume that linear rail is set properly.

I will install my jig onto one of the bearing blocks on the lower rail and install the dial indicator. From there I can run the bearing block along the length of the gantry and check parallelism between the 2 linear rails. I really doubt it will be bang on. But it would be nice to see how much variation there is and may be able to adjust a bit.

I did follow the install instructions when I built my machine. But it’s weird how quickly I wore out the drive spindle. So I’m thinking the rails are causing extra friction resulting in premature wear.

@JRG gets the “Read the F-ing Manual” award :laughing:

I think the manual is the best way to make it work, period.

Again, once you start tightening the screws you had better use a “torquing pattern” and you should not over torque the screws. Those small screws are all “hand tight.” Which is either at or slightly less than 25 nm.

If I were to complain about AvidCNC instructions it would be that they do not list torque values or stress torque patterns.

Post photos of your dial gauge setup when you get it done! I first tried using a dial gauge to see if the rails were out of parallel when my Z carriage would hardly move but it didn’t work out. Also, Avid replaced my drive gears after I was getting iron filings shedding from them. They said the original gears were defective so replaced them.

How easy did your carriage move along the X axis after you first assembled the machine using Avid’s instructions for installing the rails along the beam???

The motion was smooth but owing to the fact precision bearings are preloaded, there was resistance.

It is a common mistake to believe that bearing based systems are easy to move. Nothing can be further from the truth.

So smooth but if pushed really hard by hand the system should come to a complete stop mere inches from where the force terminated.

My only issue (being the first assembly of the newly redesigned PRO60120 back in 2019) was the sensor flags and the dern software.

That all said, it is highly unusual to design a parallel linear motion system with both sides hard mounted. I myself would not have implemented the X axis in that fashion.

But that said, that will only introduce oscillation / vibration at high speed and wear the bearings prematurely. The rack is also driving the mass off center which isn’t a good choice again but so long as the speed never gets high enough, it will be the motors working harder and sustaining greater power draw.

If you are not mistaking preload or over torquing then you have parts that are bent. Which wouldn’t be surprising considering how crappy shipping is within the states these days.

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I think you all are experiencing a high preloaded precision bearing system for the first time.

In you minds the carriages for the X and the Y should move freely the entire distance of the axis when pushed, kind of like a skateboard. Being that the Y axis has more mass you would naturally wonder if something is wrong with the X axis.

The high preload in these bearings is to eliminate the radial play. Thus the bearings will require more lubrication and have a shorter life. But the goal is accuracy over freedom of motion. So we are taking a hit in the friction department to gain precision in motion.