Moving parts from a lathe to a mill is a recipe for error. We explain how Mill-Turn (Multi-Tasking) technology eliminates stack-up errors, guarantees concentricity, and reduces the total cost of complex CNC parts.
There is an old saying in manufacturing: “Don’t let go of the part.”
In the traditional workflow for a complex round part (like a hydraulic manifold or an aerospace connector), the process looks like a bucket brigade:
Op 10: Turn the profile on a Lathe.
Move: Operator takes it out, puts it in a bin.
Op 20: Clamp it in a Mill to drill cross-holes and mill flat surfaces.
Move: Operator flips it to machine the back side.
Every time that part is unclamped, moved, and re-clamped, you introduce Error. A tiny chip in the vise jaws, a slight misalignment in the fixture, or human variation—suddenly, the cross-hole is no longer perfectly centered on the turned diameter.
At Sureton, we believe the best way to hold a tight tolerance is to never let go.
That is why we invest heavily in Turn-mill machining services (Mill-Turn Centers).
Here is the engineering logic behind why “One-and-Done” machining is superior to the traditional “Lathe + Mill” combo.
1. The GD&T Reality: Concentricity is King
The biggest victim of the multi-machine process is Concentricity (and Runout).
Imagine you are making a motor shaft. The bearing journals are turned on a lathe. The keyway is cut on a mill.
If you move that part to a mill, you have to “find center” again. Even with a Renishaw probe, there is a margin of error.
The Mill-Turn Advantage:
In a Mill-Turn center, the part spins (C-Axis) while a milling head (B-Axis) comes in to cut the keyway. The part never leaves the main spindle.
The Result: The keyway is mathematically perfect relative to the bearing journal. The geometric relationship is locked in by the machine’s rigid mechanics, not by an operator’s setup skill.
2. The “Sub-Spindle” Hand-Off
“But what about the back side of the part?”
This is where the magic happens.
Advanced Mill-Turn machines have a Sub-Spindle (a second spindle facing the main one).
The Main Spindle machines the front.
The Sub-Spindle moves in, grabs the part, and the Main Spindle lets go.
The Sub-Spindle pulls back and finishes the rear operations.
This “spindle-to-spindle” transfer happens in seconds, fully synchronized. The part’s spatial relationship to the machine coordinate system is maintained continuously, guaranteeing unmatched back-side concentricity.
Sureton’s Capability: We can take a raw bar of material (e.g., stainless steel, aluminum, brass) and drop a completely finished, deburred part into the collection bin without a human ever touching it. This process unlocks the true “lights-out” manufacturing potential for high-volume precision components.
3. The Economics: Higher Rate, Lower Cost
4. When Should You Use Mill-Turn?
Not every part needs this technology. If you need a simple washer, a standard lathe is cheaper.
But you should specify Multi-tasking CNC machine capability if your design features:
Off-Center Features: Holes or slots that are not on the centerline (e.g., a flange with a bolt pattern).
Complex Angles: Angled holes that require 5-axis simultaneous movement (e.g., medical bone screws).
Hex or Flat Features: A round shaft with wrench flats milled onto it.
High Precision Requirements: Any part where the critical relationship between turned and milled features is tighter than ~0.05mm (50 microns).
5. The “Done in One” Philosophy
In modern manufacturing, handling is waste.
Every time a human touches a part, cost goes up and quality risk increases.
At Sureton, our goal is to feed raw stock in one end and get a perfect, inspected component out the other. Mill-Turn technology is how we achieve that for our most demanding aerospace and hydraulic clients.
Have a complex round part?
Don’t split it across three drawings. Send the STEP file to Sureton. Let us show you how combining operations can simplify your supply chain and improve your quality.
