X axis not stopping at the same point

Howdy -
(Apologies if this is not the proper place)

I was drilling a test for a 3 person cribbage board when suddenly, the middle track does not keep an even path.
In the image below the Y axis travels Left to Right and X axis travels Top to Bottom.
I checked the GCode and the X Axis numbers are identical along the path, yet as you can see they are not lining up. It is my thought that the machine isn't stopping at the right spot.

Sound legit? (I'm asking for validation before I start to mess with the Acceleration and stuff in the Config file)





Thanx~!

I would also check for mechanical play (backlash) eg couplings and lead screw nut.

Chris M

Howdy -
Interesting idea. Yes, I do have a slight rotation in the spindle as it travels up-and-down along the Z-Axis. It was rather noticeable at first, but I worked on it. I built the CNC from a set of plans I borrowed; a set of plans that I no longer have. (They were borrowed from a friend who borrowed them from someone he knew, etc...),
I know what the source of the vertical spiraling is; There is a slight difference in alignment between the shaft on the Z-Axis stepper motor and the threaded rod that acts as the travel gear. It was pretty noticeable earlier and I managed to make an adjustment to it and there didn't seem to be a problem.
I guess until now.

The shaft is attached to a plastic bridge that connects to the router, allowing it to travel up-and-down along two shafts with bearing wheels. In theory, I should be able to separate the router and drill a larger hole in the plastic bridge, allowing for more space/wiggle room to center the the travel gear. (If that doesn't work, I don't know what to do next)

Thanx for the ideas...!

Well, I *think* I fixed it.

I don't take very good photos with my cell phone but here they are....

The top of this photo has the stepper-motor. As you can see its shaft is clamped with a hose, which is on a threaded rod which goes through a T-nut that I have screwed into a plastic brace. The brace extends to the router chassis, which I have locked into place with 4 washers and two nuts on a threaded rod that is drilled into the wooden spacer between the two pipes.



This photo is a closer view (with solution)
I noticed as the Z motor turns, the threaded rod is slightly off-set causing the plastic bridge to slightly 'jiggle' in a circular motion. Originally I had the wooden spacer, one washer, plastic bridge, washer two nuts - and I snugged them down tightly. What I did was add one washer to each side of the plastic, and when I snugged the nuts back down, I did it so the plastic bridge had barely enough play to move on its own without effecting the chassis the router was attached to.



Initial testing shows that it seems to work well; no spiral descent and ascent from the router. Next up = I will re-load that cribbage board program and see how it looks...

Thanx~!

>>> Sterl

I *did* fix it, but the above was not the solution!

The X-axis is controlled by two threaded rods, one on either side of the machine, controlled by a single stepper motor and a belt that moves them simultaneously. Apparently, one side had a bit of play in it, so it would 'shift'. It was just a smidgen, but it was enough.
So that was tightened down and now all I have left is figure out a 'traveling depth' problem.
When the machine I travel from the back to the front (X0 -> X21) it looses 1/8" of depth. (Meaning; that at the back of the machine I can set the Z axis to cut down -0.25" and then travel along the X for 20". It does so, but by the time it reaches the end, the depth is now -0.125"
I'm pretty sure that the pipes that it travels along can be adjusted...however; I don't know if that is a good idea at the moment.

I am in Minnesota and we are experiencing above-average temperatures. Presently it is 37 degrees, the snow is melting and I work in the garage. The air is humid.

I do have some non-uber-precise things I can work on. Maybe I'll get to them first thing tomorrow AM.

Thanx~!

>>> Sterl

If your "pipes" can move, they probably have.

Todd -
Oh yea, correct you are! The rails on either side are black pipes, each one mounted on a 2x6 via three short threaded rods. Spacing is controlled/adjusted by nuts on the rods. So in theory, to even things out all I need to do is give them a couple turns (lower the back/raise the front, etc...)

John -
Hydralic hose? Okay...I will look into it, thanx!

...This sure is a learning process (It's my 3rd career change...I guess you *can* teach an old dog new tricks!)

Thanx again~!

>>> Sterl