Is that what they call "BACKLASH"? is it Normal?

Hello there.

As I learn the wonderfull world of CNC with the goal of making 2 sided PCBs (printed circuit boards), I discovered that my x-Carve has some backlash (0.04mm) on the Y and 0,105mm on X axis, wich would explains some of the inconsistencies I found on my first PBC tries.

Test conditions:

My tension is 5.5lb on the X belt for a 34mm belt lenght between belt roller and belt attach. The tension-meter raise the belt 1/2" over the extrustion. that makes a 34x17x17 triangle. (See pics)

I intalled a “microscope” on my xCarve. (see pics)

To reproduce the bug, I put a mm ruller aligned on my wasteboard.
I measure movements in 1mm increments and measure the backlash.

Results: the first movement in another direction after direction change (ie.: moving X+ than X-) is shorter that the subsequent moves, that are as expected at 1mm each.

Is there a way to fix that? I checked the tension (I feel I can’t tighten the X belt anymore without risking to break it, but this is not an educated guess so input is welcomed!) The rollers etc are no loose, they are pretty tight.

Is it normal for the x-Carv to show this kind of bakclash? is there a way to program g-sheild to take care of it?
Here are some pics:

Tension measuring setup:

Actual measurement:

USB “microscope” setup (sorry I had to remove the “inventable” logo to fit the holders…)

Check out this thread on reprap: Eradicate backlash
"I think i have narrowed it down to the Y axis carriage. It is twisting side to side just a hair when reversing direction just enough to cause the backlash. "

So perhaps the X axis stiffing mod and some Y axis stabilizing brackets would help?

@JocelynBouchard… I have exactly this same problem. Each time their is a direction change, the X axis only moves 0.5mm when I jog it 1mm. In my case, it doesn’t lose steps… 5mm will go 5mm despite the first half-step. It’s like the second step catches up. I can produce perfect squares, rectangles, triangles… Just no circles. The stutter-step causes the circle to have a slight bulge at about the 2:00 and 8:00 positions–right where it changes direction on the X axis. I can actually see the belt stretch each direction change, no matter how tight I have adjusted the belt tension. This happens equally in both directions.

Any ideas for getting rid of this backlash would be really helpful as a big percentage of what I need the X-Carve for involves circles.

Here is (shortly) what I did to get an acceptable backlash of about. 0,033mm to 0,045mm.

On my machine, the excentric bolts were way too tight. Now, I can slip-move the V-wheels (without moving the carriage) if I apply about the same strenght as if I would open a plastic pepsi bottle. (I know it’s not very precise but I have nothing to measure this kind of movement).
The drawback is that I have to re-tight them often, as vibration looses them quickly. I’ll try to find some lock-tite like stuff that would block the set and can be easily broken to readjust. This too much tightness was causing the mecanisme to loose about. 0.15mm on direction change. This works very well for very light work (I’m engraving PCBs) I don’t know what this “slack” will cause when I’ll try tougher works like cutting wook or aluminum. probably

I also realised, using my microscope to measure movement lengfht per step, that each step did not move the same len. This was solved by raising current with the potentiometers on the X and Y axis (also did on the Z, although it was moving fine) They were originally set to 11 o-clock. They are now set to 2 o-clock. Be sure to have some cooling on the motor drivers (fan or heatsink) as more current to the motors means more heat.

Hope my english is understandable. Feel free to ask questions if unclear.

Vive la France (et le Quebec)