X-Axis travel Issue?


(Cory) #1

Hi all, Cory here. Hope everyone is having a good start to the week!

Needing a little help but please bare with me. CNC is very new to me and what a rabbit hole it is!

Please note this happening is from initial assembly, right out of the gate. I (what I seem to think) am having an issue with my x-axis travel. It seems to be jumping at regular intervals but it does not seem to follow any pattern relating to circumference of the drive gear?? I can actually feel the jump or skip happen when slowly pushing the assembly left or right along the x-axis but the drive gear does not seem to be in the same position every time it happens? This problem presents itself when milling as well. Curves along the y-axis become straight lines for a small span and this happens in the same spot with every pass. Squares become rectangles with the shorter side running the x-axis.

Heeeelp!


(Josh) #2

Is the z-axis belt guitar string tight? I don’t have the shapeoko assembled (working on restoring an older one, but have been on the forums for a bit now) but this seems to be one of the main issues that come up. I’d check that out.


(William Adams) #3

The basic points of adjustment for a machine are:

Beyond that it’s usually a matter of ​https://wiki.shapeoko.com/index.php/Calibration_and_Squaring_the_Machine c.f., http://docs.carbide3d.com/shapeoko-faq/how-to-calibrate-the-machine-for-belt-stretch/

Make sure that your feeds and speeds are correct and you’ve made a suitable endmill selection: http://docs.carbide3d.com/support/#tooling-support — see: https://precisebits.com/tutorials/calibrating_feeds_n_speeds.htm for one technique to adjust these.


(Cory) #4

Thanks Josh, i’ll give that a go. Could the z-axis belt tension really cause this tho?


(Cory) #5

Thank you Will. So pretty much checked all of this with the exception of really buckling down on the calibration/sqauring. Though I’m leaning towards there is obviously something wrong here other than the machine being out of perfect square…


(William Adams) #6

Check and see if both Y-axis motors are rotating properly?


(Cory) #7

They seem to be. Have not had any issues there. See attached pic of a 2in square I did in carbide create. Measures 1.984 in the y direction, 1.746 in the x direction after milling.


(mikep) #8

That would indicate you’re belt tension is still pretty loose (ie. it’s taking way more steps to get to 2inches than it should)

Because the two (x and y) aren’t even close to each other, that’s going to be a huge contributer to an out-of-round circle.

I think there is also something else going on here though, because you should get an oval if all it is is belt tension. You got something a bit pointy, which indicates some backlash too.


(Cory) #9

Hey Mike, i guess i can have another go at tightening the belts and going through the belt stretch calibration. I have no accurate way to measure how tight these are getting and am fearful of over-tightening. Any suggestions here?

As far as the backlash, how do you mean? Mechanically, everything is screwed down pretty tight…


(William Adams) #10

Backlash is usually when the machine moves in one direction, then one moves in another direction and it has to take up slack or something to get things to mesh for the move, so it’s less than it ought to be.

https://wiki.shapeoko.com/index.php/Glossary#B

Any kind of unexpected play in an axis due to clearance or looseness of mechanical parts. Check for it by moving an axis in one direction, stopping the unit, then noting how much movement is necessary in the opposite direction to begin moving the machine.


(mikep) #11

There’s -something- in there that is requiring distance to be taken up before it moves. Does the Z carriage rock left and right? That would indicate the v-wheels on the bottom aren’t adjusted properly. Does the router rock left and right with respect to the plate? That would indicate the aluminum router clamp isn’t tight to the plate. It can be a little hard to find. Sometimes it’s the pulleys turning very slightly on the stepper shafts, sometimes its looseness in the Z axis belt because the bottom screw wasn’t tight enough.

Belts: Set up the belt so that the screw to attach the bracket >barely< reaches the bracket, which some force stretching the belt by hand. Then tighten the screw. That should be about right. You may ask how I could come to the conclusion that the belts aren’t tight enough…and would be right to ask :slight_smile: The 1.746in dimension is quite a bit less than 2in (about 15%). The tighter the belt is, the further apart the cogs are, and therefore, the fewer steps are required for a given distance…which means if the belt is not stretched enough, the same number of steps won’t take you as far as it would if the belt was stretched more. You’re short, which means not stretched enough.

Given that the Y direction is almost 2in, that one is about the right tension, and you can just correct out the rest with a belt step adjustment for that axis. The X direction would require the default of 40 to be adjusted to ~ 46 or so, which is a pretty big delta, and that indicates the belt is too loose.


(Cory) #12

Sorry for the late response all. Life has a habit of getting in the way.

So it’s definitely looking like it was still too loose on the belts. Obviously these things can take a LOT more than i thought. So cheers!

Thanks all!