I know this is an older post but I thought I would post my experience that I had last night and tonight. I had literally the EXACT same problem with millbox but my machine was a DWX51D. My implant/hybrid crown was 11.54mm tall, I put it in a 14mm disc and machined with broken margins. Then I redesigned and tried again in a 14mm disc. Broken margins. I milled all of my other crowns with perfect margins. So I re-marked the margins in millbox and tried again. Broken margins. I came here to see if anybody else had had this problem. I saw your post about the 18mm disc working. I tried that and I had success. I have milled 14 other crowns since then, all with perfect margins. I have been milling with millbox for 7ish years and have never had this problem. If anybody else has a solution, I would love to hear it! Thank you for this post!!!