Stepper motor moves short, but only on first “step”

I’ve had the x-carve for nearly two years. Have not used it nearly as much as I wish I could. I am getting better and so am trying to do more accurate cuts. As part of the process I was checking stepper motor distance accuracy and found an interesting problem.
On the x axis, the first move after changing directions is short (.086 instead of .100).
Example: move +x, get .086. Move +x again, get .100. Move -x, get .086. Move -x again, get .100…
In actuality, the second step is a little short. Maybe .002. But by the 3rd step it is always .100.
So the question is, what’s the issue? Software settings? Hardware?

Yes, sounds like backlash to me.

Thanks for the tips guys. I am just now getting to be able to check things, here is what I did:
-I cleaned the v wheels
-tighten the belt
-updated the firmware
-checked the little setscrews on the pulley and one is missing the other seemed a little loose. I thought for sure that would solve it. Nope!
-all this made things better. But the first step is now .094-ish (instead of .086)
-so, I opened the x-controller and checked voltage
-also tried a couple settings on the dip switch. Each setting changed distance, but short first step persisted I put it back to 1/8 step, which is what I’ve had it on.
-I started checking at .001” Increments instead of .100. Same issue just smaller numbers. Oddly though it took four or five steps in one direction before being accurate. Hmm
-I swapped one stepper from the y-axis and…you guessed it…still didn’t fix it!

So it has to be software right?! Some setting? So weird!

I found the solution!! The problem was with my nuts! Let me back up.
After I switched stepper motors with the T-shirt, I knew it had to be from some other part of the system. So I ordered new belting and saw they had an eccentric nuts upgrade kit, and I ordered that too. As I waited I came across this post: Is that what they call "BACKLASH"? is it Normal?, which discusses loosening the eccentric nuts and messing with the voltage.
I loosened my nuts and instead of being .012 short on the first step, it was .004. Whoa!! (I never touched the voltage for the record)
I installed the upgrade kit, which allows for tightening the lock nut independent of the eccentric nut. This removes the temptation to over tighten to keep your nuts from getting loose and let’s you dial in the v-wheel tension. I’ll see if I can get under .004, but for what I do, that’s good enuf.
I hope this helps someone out there…happy cutting!

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Random update: It says “T-shirt” in my last post. I’m pretty sure that was supposed to be y-axis. Oops.