Reply 1 (by DMGtech_Europa):
The rotary table seal leak on the DMU 50 third generation is unfortunately something a lot of shops hit around the 5-7 year mark, especially in production environments running aggressive coolant concentrations. The culprit is almost always the Simrit labyrinth seal at the A-axis trunnion interface — DMG Mori switched to a slightly different seal compound around 2019 on the 3rd gen but the design is still vulnerable to certain biocide chemicals in modern synthetic coolants that swell and then crack the seal lips over time. Before you order parts, check what coolant you're running and whether it's compatible with the seal material — there's a compatibility chart in the machine maintenance section of the documentation portal and it's genuinely useful. If you're using a high-biocide semi-synthetic, switching to a full synthetic like Blaser Swisslube B-Cool 755 has solved the recurring seal issue for several shops I know.
Reply 2 (by Precision_Shop_NorCal):
We replaced the trunnion seal on our DMU 50 in-house last year and I'll say it's a manageable job if you're comfortable with the machine and have DMG Mori's service documentation. The critical thing people mess up is the torque sequence on the trunnion bearing retaining ring — there's a very specific angular torque and preload spec that if you ignore it, you'll have table runout problems that you didn't have before. DMG Mori's local service team will tell you it must be done by them but honestly any competent maintenance tech with the documentation can do it. Budget about a full day for the job, order the Simrit seal kit and the O-ring set together because the secondary seals are cheap and foolish not to replace while you're in there. The seal kit part number has changed twice since 2020 so verify directly with the DMG spare parts portal.
Reply 3 (by ManufacturingEngineer_IL):
One thing worth adding — if you have a coolant leak at the rotary table and you've been running it while waiting for parts, pull the table apart and inspect the angular contact bearing races for rust staining before you just replace the seal and button it back up. Coolant that gets past a leaking seal sits in the bearing cavity and corrosion can start within weeks, especially with water-based coolants that have degraded past their recommended concentration. We had a DMU 50 where we did a seal-only repair and six months later had to do a full bearing replacement because we didn't catch the early corrosion, and a full trunnion bearing job is a much bigger number than a seal kit. A borescope inspection of the bearing cavity takes ten minutes and can save you a very expensive lesson.
Reply 4 (by 5AxisShop_Bavaria):
For what it's worth, DMG Mori released a revised labyrinth seal design for the DMU 50 and DMU 65 monoBLOCK platforms in early 2025 that's supposed to address the chronic leak issue with a wider lip geometry and a different elastomer compound. It's sold as an upgrade kit rather than just a replacement part and the pricing from DMG is reasonable if you compare it to downtime cost. We installed it on two machines in our facility during scheduled maintenance and so far no leaks after 14 months of production use, which is better than any previous seal we've run on those platforms. If you're still on the original or first-replacement seal design, the upgrade kit is genuinely worth doing proactively at your next major PM rather than waiting for another leak event.
