weird laser behavior on Y axis

[Joseph Abenhaim]

Hi Dave,

I should have mentioned before but my Y is the gantry axis (engraving axis) the only movement there is on a linear rail driven by 1 motor and no drive shaft, there can't be a twist because it goes back and forth on the same rail. so essentially my gantry runs vertical and moves left to right, so i engrave top to bottom if that makes sense. The issue here is happening on that axis alone, if i draw 2 lines, one of top of another, and one cuts moving up, it cuts clean, if i then cut toward the bottom, it cuts blurry.

[Dave Vigness]

Ah, so your X and Y are reversed from most smaller lasers. Have to think about that.

I would still vote for a bearing problem. The key being it only happens in one direction. I would look at the leading side of the direction it's happening in. Is the belt pulling parallel, in other words, does the attachment point on the gantry line up with the top of the idler / drive pulley feeding it? I tend not to say something is loose only because you have not mentioned any 'wiggle' in the line, only out of focus.

[Jeffrey Aley]

Hi Dave,

I should have mentioned before but my Y is the gantry axis (engraving axis) the only movement there is on a linear rail driven by 1 motor and no drive shaft, there can't be a twist because it goes back and forth on the same rail. so essentially my gantry runs vertical and moves left to right, so i engrave top to bottom if that makes sense. The issue here is happening on that axis alone, if i draw 2 lines, one of top of another, and one cuts moving up, it cuts clean, if i then cut toward the bottom, it cuts blurry.

That's interesting. I'd like to see a photo of your laser, if you don't mind. Like Dave, I had assumed that the problem occurred when the gantry was moving.

[Jeffrey Aley]

So here's my latest hypothesis:
When the laser head is moving, the friction comes from the bearing block.
The applied force comes from the belt.
I assume (please verify) that the belt is not attached directly to the bearing block; it is usually attached to a different point on the laser head.

This would create a torque such that the head could rotate (slightly) depending on which direction the belt is pulling. Such a rotation would cause a misalignment of the beam in one (or the other) direction.

Test: hold the bearing block in place. Then see if you can wiggle the tip of the nozzle in the Y direction (or any direction, for that matter). There should be no movement AT ALL.


Let us know...

[Dave Vigness]

You are correct in that there should be no tilting movement. For the rest of us, the X takes the brunt of the movement / abuse. For you it sounds like it's the Y. I have no idea why your X and Y are swapped. Unless someone plugged the plugs in the wrong port on the controller and was too lazy to change them or didn't realize that is what they did.

You are most likely to get the slop in one direction. The good part is that since it's only one direction, it's just a matter of replacing the bearing block. Pick and and that is the easiest to get all the other stuff out of the way, slide to old one off and the new one on and put everything back together... only a few minutes job, ROTF LMAO

This would also be a good time to evaluate how parallel your belts are. The attachment point vs that edge of the respective pulleys.

[Joseph Abenhaim]

You are correct in that there should be no tilting movement. For the rest of us, the X takes the brunt of the movement / abuse. For you it sounds like it's the Y. I have no idea why your X and Y are swapped. Unless someone plugged the plugs in the wrong port on the controller and was too lazy to change them or didn't realize that is what they did.

You are most likely to get the slop in one direction. The good part is that since it's only one direction, it's just a matter of replacing the bearing block. Pick and and that is the easiest to get all the other stuff out of the way, slide to old one off and the new one on and put everything back together... only a few minutes job, ROTF LMAO

This would also be a good time to evaluate how parallel your belts are. The attachment point vs that edge of the respective pulleys.

So it's not a mistake, its just part of the design, I don't have the gantry running left to right, my gantry runs top to bottom. My X rails are left to right and 1500mm long.

So in the past week theres been a few changes, for one thing I've replaced the V Wheels running left to right (1200mm axis) for linear rails. I've also replaced my gantry which was 2040 extruded alum for a 4060. I figured much wider will be more stable and rigid. In any case i'm also using a brand new linear rail / block on the y axis as well. Still the problem is always there, If i do a shape clockwise it's all messed up, counterclockwise much better. but always going down on the Y seems to be the culprit.

[Dave Vigness]

Okay, from your description, is this machine flat, it is this a vertical? Does your rail / belt run on the face or top of the gantry? Does the belt return stay on the outside of the gantry or inside?

Lastly, I'm assuming you have the standard belt on toothed drive and idler pulleys. Have you looked at Russ' set up reversing the belt so it's smooth idlers and no tooth other than over the drive pulley?

With power off, is there any restrictions in movement that you can feel? You've probably checked all of this, but I'm asking to get a good picture in my head.

[Joseph Abenhaim]

Dave, you can see the machine here https://i.ytimg.com/vi/07FFSKnJv0I/maxresdefault.jpg so that should give you an idea, I think the problem is mostly gone now, i've beefed up the gantry, motors, and switched from 2 motors to drive the X to 1 with a rod that extends the length. Don't even ask why in the heck this was designed with one motor for each side of the x.

[Dave Vigness]

The two motors means the guy that designed it was used to designing 3D printers. I have never gotten close to justifying the two sides not be physically tied together somehow, not with the tolerances required for the laser cutting over the distances we cut.