This is the question that causes most of the wrong orders in driven tooling. The machine model on the nameplate does not tell you the mounting — the turret does. And the two systems are not variations of the same idea; they mount in completely different ways.
| VDI | A cylindrical shank goes into a bore in the turret disc and is pulled in by a serrated drawbar. Standardised in DIN 69880. Sizes VDI16 to VDI60. |
|---|---|
| BMT | A flat flange bolts onto the face of the turret with four screws, plus a curvic or key location. BMT is an industry de-facto standard, not an ISO or DIN standard. Sizes BMT45, 55, 60, 65, 75, 85, 110. |
Two lathes with the same model number can leave the factory with different turrets. Builders offer turret options, and they change them across production years and across regions. A model sold in one market as VDI40 may be BMT55 in another.
This is why Mongtec asks for the turret, not just the machine. On the machine pages of this site the turret interface is published where it is known, and where a builder offers more than one, the page says so instead of guessing.
BMT sizes are not interchangeable between builders in the way a standard would guarantee. Because BMT is a de-facto standard rather than a written one, a BMT55 from one machine builder can differ from a BMT55 from another in bolt pattern, drive position or coolant port. The size is a starting point, not a guarantee of fit.
VDI, being written into DIN 69880, is more consistent — but the drive dog position and coolant arrangement still vary.
If you send the machine make, the model and a photograph of the turret face, that is usually enough. If you have a holder already on the machine, the article number stamped on it is enough on its own.