Hey Stefan, I have the same desktop scanner as you, the Open Technologies Deluxe, and I use Exocad, I do full arch cases all the time with it and they come out pretty much passively perfect, but I don't mill metal, just Zirconia and PMMA. Definitely some things to watch out for though to verify your scan accuracy. This is what I'd do:
First, just good practice, verify the model analogs are clean and not distorted because they've been reused/bent. Often I found Dr's will reuse a bent/warped analog to save money only screw up the master model because the scan marker won't seat evenly in it.
Sometimes the scan markers might not thread in perfectly. It may feel right when you screw down, but then when you unscrew it kind of 'pops' out, because it was torqued down but got in a bind and not evenly seated. Pay close attention to feeling this and if something didn't feel right, chances are it probably wasn't
Verify under magnifier that the scan marker is truly all the way seated. I had a case not long ago where a DESS titanium scan marker didn't fully seat because it kind of gets in a bind and you think its solidly down, but it's not quite. Double check.
If your scan markers seat evenly in the analogs, go ahead and scan away. I always, always verify that the alignment of the master model and the alignment of the scan markers overlay perfectly. If you are using the Revenge software, after you align your scans, left click your master model scan, then select your scan marker scan by holding control click. This will show you how they both are aligned to each other. When you do this, if you see the image shift, even slightly, then it's not perfectly aligned, You will need to perform some techniques to get them to perfectly align which I can go into detail if you don't know how to do this.
Ok, assuming you got all your scan markers in one scan, if you are having misalignment problems in different implants from different scans, that tells me that most likely the problem is your scan marker matching in exocad. When you select your abutment library and match to the scan marker, there is a little slider to the right. In my experience, I always adjust the slider upwards because other wise It might be trying to match too much data and actually misalign at this step. When it comes to accurate alignment, often less is more. I told a digital Dr. guru (I'll withhold his name) this tip while he was presenting Exocad dentistry to our study club, and I had to correct his case in front of the study club because I could tell his scan marker alignment was off
Because it was for a live patient, he was very grateful for the tip! Basically, after your orange scan marker placement is overlayed on the green scan marker of the model, they both need to be perfectly matched. Often I will see they are not if I do not adjust the slider upward. If you don't see even orange/green splotchy mottling across the top of the scan marker, then it's vertical is off, and it also might be tilted. This is the most crucial CAD verification step to implant passivity. Play around with the slider until you get a perfect alignment, if you can't achieve that then you need to rescan your marker because there is not enough data for exocad to get an accurate alignment.
Finally, if you are still not getting passivity, then it could be the CAM, however I doubt it based on my experience, it's usually in the desktop scan alignment or CAD alignment. If I were you I'd double check by milling your full arch out of pmma. If that fits the same as your metal, then you can rule out your cam as the problem.
Hopefully this sorts it out for you!
-Matt