K40 with C3D and LB giving me squiggly lines

For some reason my machine is giving me squiggly lines on vertical lines. The horizontal seem very good, but the vertical just keep giving me problems. I’ve tried adjusting belt tension and mirrors but nothing seems to be helping. Anyone have any ideas?

Lens loose in the holder?

I don’t believe so. Should be pretty snug in there but I’ll double check it this evening.

Your acceleration settings (or speed) might be too aggressive. The wobbles appear to be after taking the corner. Also check to make sure your rails are free of dirt.

It seems like it happens no matter what speed I use. Is there something I should change in the config file to set the acceleration different? And if so what’s a recommended speed?

There’s a value in the config file called “acceleration”. Check what yours is set to and try dropping it by about 25%. Run a test and if it’s still wobbling, drop it another 25%. Start with that.

Alright, well, I modified the config file, it was at 2000mm/s acceleration. Took it down to 1500 then 1000 and still seems the same.

I just came across the new smoothieware for the C3D mini so i updated that as well as updated lightburn to the latest version. Then i went through lightburn and turned all the maximum speeds down under device settings, but i assume all this does is limit the speed you can input on the cuts and engraves in the cut menu, doesnt actually effect the machine.

Any other suggestions?

Edit: It seems if i slow the machine WAAYYYYYY down, to like 20mm/s or lower i can get very straight vertical lines. Almost as nice as the horizontal lines. However I dont think i should have to go that slow right?


Obviously that’s one of the first things I did. I think that goes without saying. If your machine is dirty you’re going to have issues. I keep my machine spotless. If it was something so simple I most likely would have figured it out on my own.


So obvious, you completely ignored it here. My bad.

You know what? You’re right. My apologies.

I cleaned the rails. No change. Anything else?

Check that the pulleys are tight on the stepper shafts, there is a little setscrew that may have backed off.

Mechanical vibration was my problem with lines like that. After checking everything, it was the darn air pump that was on the same shelf as the laser. I use a small airbrush compressor. There was enough vibration transferred to cause the problem. I fixed by moving to a different shelf and better isolation.

Can’t say that is your problem but it was mine.


If you did this on the “Additional Settings” page it will have no effect on your controller.

You are correct that 20mm/sec is way slower than should be necessary. Jim might be onto something here though - Do you have a fair, air pump, or anything else mounted in or near the machine that could be causing vibration? Do you feel vibration on the machine when it’s running? Do your steppers make a lot of noise? Having the stepper motor current set too high can cause resonance too.

I have my air pump mounted underneath the shelf on the cart that my laser is on, I also have my chiller on the lower shelf of the cart, so there are vibrations around the laser. But it does the squiggly lines whether the air pump and chiller are on or not. So i cant see that being the problem. My stepper on the Y axis are a little louder than on the X axis, so maybe thats the problem. Which setting changes the current for the stepper and what should i set it to?

The laser does the squiggly lines whether the air pump is on or not, so i dont think that is it. Good suggestion though!

It’s in the config.txt file - Look for beta_current (I think). Alpha is X, Beta is Y.

Alpha_Current and Beta_Current are both set to 1.5. I have no idea what they should be. Does this seem like an OK value?

Also, one thing i have noticed is that the right side of the Y axis has a little bit of up and down play. I can see it has a roller over there but it doesn’t seem to be eccentric like the ones on the x carriage so i dont have a way to make it not move. I don’t see how it would be moving up and down during use anyways, just thought it was noteworthy. Maybe this is normal?

Check the squareness of your gantry. Any misalignment on this will cause your “2 rail axis” to be out of alignment and can cause DRAG, which will in turn cause the exact problem you are experiencing! Also, have you lubed the bearings with something light like sewing machine oil?

I will check the squareness this evening. I believe it should be pretty square.

I do lightly coat the rail with the bearings with some oil.