[flongo]

I recently machined a 3d vector from vector art 3d using their supplied 3d cam software. After the machining was finished I noticed there was a recessed line that ran the length of the material. After contacting the company and sending the G-CODE, the technician said that the code checked out and didn't seem to be a problem on their end. He suggested I post a question on a cnc forum for further questioning. I have attached multiple pictures to show the end product. Thanks for all the help as I am not really sure what happened on this piece.
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[ger21]

Looks like your Z axis lost steps and lost position.
Either that, or you have a loose coupler on the Z axis.
Make sure everything is tight. If it is, try reducing the Z axis acceleration by 50%.

[FMTcncs]

Looks a lot to me like the machine didn't pull up before going back to ramp into that bottom section. If you can, run the program again and watch it and where this happens. I can almost guarantee it just spit out one line of code that didn't bring the Z up at all. If you find that, you can manually change it or just run through your program and make sure it's moving at least 2 inches after each ramp-out.

[twoartistic]

Since your machine ran several passes at a lower Z position than the rest of the code, then corrected, I would check several things;

1) Like one other person said, your coupling on the Z axis. In my experience, once you have a mechanical slip, it continues to slip in the same direction until it hits a stop. So this is unlikely, but not impossible.
2) Error in the code. This design looks like it rises out of the material to a common depth and plunges into the material at a close to common depth around the perimeter. Open the code in a spreadsheet or in notepad, and do a search for the deepest plunge. If your code is bad (regardless of what the supplier noticed), you will see a few z line instructions that have a greater value than the rest of the code.
3) I had a similar issue when I first started to run my CNC to carve out shaped cuts. My machine was trending shallower (missing plunge steps) as the part was machined. Turned out it was a combination of three things, the wrong encoder cable for the distance from my control panel to the Z encoder, running the power cable for my spindle in part of the same wire chase as my Z axis motor wiring, and static discharge from my dust collection vacuum hose. Because it was a multi aspect issue, it was really difficult to troubleshoot. I had to solve each issue independently, but once I did, the machine has ran for years and always returns to home with no measurable variance and carves perfectly.

Good Luck!