Z Axis Dropping

I have been using my new MK2 CNC for about two months now.
I had a MK1 and never had these issues before.

When I am drilling a series of holes, the Z Axis drops after the first 15 or so holes. This has happened multiple times, in multiple projects, and same sort of problem.
I have made sure the collet is tight, and it is not the bit slipping.
I have attached a picture of the project before I stopped it and you can see the gradual progression of the z axis moving down.

Any suggestions on how to remedy this?

I have a couple thoughts/observations.

Are you sure it’s not dropping sooner, maybe the whole time? The reason I ask is because you have to eat up the Z gap above the material before the bit starts to drag and it makes more sense to me if it’s happening a little bit on each hole then all of a sudden after a bunch of holes.

Have you checked the coupler between the Z motor and threaded rod? I have a MK1 with the belt but I think the MK2 has the motor inline, on top of, the threaded rod with a coupler like the other axis. I wonder if it can slip there without just falling out? The other axis can slip at those couplers, without falling totally apart, but they aren’t vertical.

I can double check your G-Code if you post it but if it looks right in gSender it most likely is not the G-Code IMHO.

You’re probably right about it slipping the whole time. Didn’t think about that.
I will have to check my connection to the lead screw.
Thank you and appreciate the suggestion.
I am also using easel by inventables as opposed to GSender but never had this issue with my MK1 and that software.

Was just looking at the MK2 on Onshape and it looks like it could slip on the motor side of the coupler without falling apart. I would think that if it slipped too much on the lead screw side of the coupler the lead screw would fall out, along with the router.

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@ShopTeacher What router are you using, Eric? Is it the same one that you were using in your Mk1?

It is the same. The Makita


Thank you for the suggestion!
Tightened things up tonight, ran a test and it seems to be working normally again!
Thank you again for the help!

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@ShopTeacher Since you have solved your problem, Eric, I am closing this topic.

Have fun.