I have the same issue. I have noticed sawdust clinging to to vac hose like iron filings to a magnet. Why would this only impact the Z axis? I have no issues with X and Y. I still am going to try to enlarge the dust boot hole so the router moves smoother.
It happens on XY too
as @gwilki said, the crv file would help. Did you set a flat depth for your v-carve? I always use 0.2" as a flat depth when using v-bits.
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It’s not any single file but all of them. I was doing a test cut for a new project today. I set the Z, used the GO TO Z ZERO button on gsender and it went down and barely touched the surface, moved the Z up, attached the dust shoe, sent the router to Z again and it dived into the work piece (router off). It just made a small hole so no big deal. I’m convinced it’s a static issue. Mine might be limited to the Z as the hose when attached to the dust shoe is fairly close to the Z motor and wiring. I need to work on grounding the vac hose.
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@StuartG I very much doubt that it is static since you have nothing running between the two Z movements. Just my opinion, though.
One thought is: when you raise the Z gantry to install the dust shoe, are you by chance hitting the top of the Z movement? If so, then your Z0 is now off.
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When I’m attaching the dust shoe I am not moving the Z axis. Im purposefully avoiding the belt and pullys on top of the gantry.
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@StuartG I’m not being clear.
In your previous post, you said that you “moved the Z up, attached the dust shoe”. So, I took that to mean that you had previously set Z0 to the surface. You then, in your words, “used the go to Z zero button” and the bit “barely touched the surface”. So far, so good, yes?
Then you “moved Z up” to attach the dust shoe. Then, finally, you “sent the router to Z again”, presumably meaning that you used the go to Z zero button. At that point, it “dived into the work piece”.
I was/am trying to say that when you “moved the Z up” to attach the dust shoe, could you have moved it up enough to hit the top? If so, this would explain the subsequent problem when you again hit go to Z zero and it dived into the work piece.
I am not trying to be argumentative. I am just repeating what you set out as your process.
Thanks for the clarification. When I said I moved the Z up I used the gSender Z+ button to move it up just enough to get the dust shoe on. Usually 1-2 inches.
Stuart
Graham makes some valid points. It is also worth noting that this is what Sienci says about grounding and erratic movement
" IMPORTANT: EMI does not cause the LongMill to lose position or move erratically. It is a very common misconception that grounding your machine will help prevent missed steps, stalling, or positioning issues. EMI only causes CNC machines stop completely or disconnect from the computer. If your machine is not moving the way you think it should, it is a mechanical issue or an issue in your gcode. If you are experiencing these issues, please start with double checking the mechanics of your machine."
I post this because the grounding maybe a rabbit hole you are going down.
@StuartG Understood. As I said at the outset, and as @Mickus has elaborated on, I don’t believe that this is noise related. Some weird mechanical thing is going on. (Don’t you just love that technical talk? 
)
If it were me, I would try this. I would do just as you have done to get the bit just touching the material. Up until then, you are fine. I would then raise the bit the usual amount to install the dust shoe. Here is where I would vary from your process. I would not install the dust shoe.I would jog in X and/or Y so that if the bit does “dive” in the next step, it does not actually bury itself in the material.Then, I would jump to your next step and click on “go to Z zero”.
If the bit just stops at the height of the material again, clearly the act of putting the dust shoe on is somehow causing your problem. If the bit goes below the top of the material, even without the dust shoe installation step, then something is going on when you jog Z+.
I think you nailed it here. Today when I was putting on the dust shoe I had to adjust it’s height a bit. The magnets are pretty strong and I noticed out of the corner of my eye that the belt and pully were moving when I was adjusting the shoe. It was then that I realized that my left hand was pushing down on top of the router moving the carriage down a bit.
I removed the shoe and moved the XY so the bit would be out of the way of any material and I hit the go to Z button and the bit dived to below the material surface. I reset the Z again, replaced the shoe being careful not to touch the router and have been running today without issue.
I think we got it!
Thanks for everyone’s input. I still think I should ground that hose as it does build up quite a bit of static over time in the cold dry winters.
Stuart
@StuartG I’m glad to hear that you solved it. These things can be a #$%@ to figure out some times.
I was not suggesting that you don’t ground things. I’ve got more ground wires than power cords, I think. As you say, things are most pronounced in our dry winter heating season. I have a room humidifier in my shop just for that reason.
As you have resolved your issue, I am closing this thread. Don’t hesitate to start a new one if/when new issues arise.