Twotrees TTC450 CNC Mastery: How a Trunnion Adds Two Axes

• 1
  What the TTC450 Actually Adds to a 3-Axis Machine
• 2
  Finding the Rotary Centerline Before You Cut Anything
• 3
  Planning Toolpaths Around a Trunnion Work Envelope
• 4
  Which Materials and Part Shapes Suit This Conversion
• 5
  Where the Error Budget Goes on a Trunnion Conversion
• 6
  Step by Step: Commissioning a Trunnion Conversion
• 7
  Trunnion Conversion vs True 5-Axis vs 3-Axis With Fixtures

A 3-axis router moves the tool in X, Y and Z. The workpiece stays put. The TTC450 changes that by mounting a rotating table and a tilting head on the machine bed, so the part itself can rotate under the cutter. The rotating table is the A axis. The tilt head is the B axis. Together they form a trunnion, and the two motions let the tool reach faces that would otherwise need a second setup.

This is not the same as a simultaneous 5-axis machining center. On a true 5-axis machine, all five axes are interpolated in one continuous motion, and the controller compensates the tool tip in real time. On a TTC450 conversion, the controller usually moves the rotary axes as positioning moves between cuts, then runs the cut in three linear axes. The distinction matters because it decides what kind of surface you can produce.

The trunnion adds two things: reach and repeatability. Reach, because a tilted part exposes side faces and angled holes to a short tool. Repeatability, because once the rotary centerline is dialed in and stored, you can return to the same angle on the next part without re-indicating. That second benefit is often worth more than the first on small production batches.

What it does not add is stiffness. The trunnion sits on top of the existing table, so every cutting force now travels through an extra interface, an extra bearing set, and an extra clamp. The base machine still sets the ceiling. A light router with a TTC450 will still behave like a light router.

• 1
  A axisRotating table, rotates the part about the X direction.
• 2
  B axisTilt head, tilts the part about the Y direction.
• 3
  Positioning vs simultaneousMost hobby conversions position, then cut in 3 axes.
• 4
  Stiffness ceilingSet by the base machine, not by the trunnion.

Every rotary table has a center of rotation, and the controller needs to know where that center sits in machine coordinates. If the number is off, every tilted cut is off by the same amount, and no amount of tool compensation will hide it. This is the single step that separates a working conversion from a frustrating one.

The usual method is to indicate a precision pin or a ground dowel held in the chuck. Sweep the pin with a dial test indicator as the A axis rotates. Adjust the work offset for the Y and Z values until the runout reads as low as your indicator allows. For a machine in this class, getting the pin to within 0.02 mm is a realistic target, and 0.01 mm is achievable with patience and a good indicator.

Once the centerline is known, store it as a permanent offset in the controller. Do not re-find it every job. Re-finding it introduces variation, and variation is what kills batch consistency. Check it monthly, or after any crash, but treat it as a fixed datum in between.

The B axis needs the same treatment. Tilt to a known angle, indicate a reference face, and confirm the actual angle against the commanded angle. Small angular errors grow with part size: a 0.1° error is roughly 0.09 mm of displacement 50 mm from the center, and 0.17 mm at 100 mm. On a 200 mm part, the same error is closer to 0.35 mm.

• 1
  Indicate, do not assumeSweep a pin to find the true A-axis center.
• 2
  Store the offsetTreat centerline as a fixed datum, not a per-job task.
• 3
  Check the B axis tooVerify commanded angle against an indicated face.
• 4
  Angle error scales with radius0.1° is 0.17 mm at 100 mm from center.

A trunnion eats work envelope. The rotating table and tilt head occupy space that used to belong to the part, and the part swings through an arc that must clear the machine frame at every angle. Before you program anything, measure the usable envelope with the trunnion installed and the table tilted to your extreme angle. Write the numbers down and keep them next to the machine.

Tool length is the next constraint. A long tool reaches further into a tilted part, but it also deflects more. On light routers, tool deflection is often the largest single error source, larger than the trunnion itself. Keep the tool as short as the geometry allows, and prefer a stub-length cutter with a reduced neck over a long reach tool when both can reach the feature.

Programming style matters as much as the hardware. For positioning work, post the rotary moves as separate blocks, let the machine clamp, then cut. For contoured work that needs the rotary axis to move during the cut, expect the controller to lag, and reduce feed accordingly. Many hobby controllers cannot maintain a commanded feedrate while interpolating a rotary axis with a linear one, so the actual chip load drifts.

A practical rule: if the feature needs the rotary axis to move during the cut, halve your normal feed and take a spring pass. If the feature can be cut with the rotary axis locked, treat it as a normal 3-axis cut and use your usual parameters. Most parts on a conversion of this class fall into the second category.

• 1
  Measure the real envelopeTilt to the extreme angle and check clearance.
• 2
  Short tools winDeflection usually exceeds trunnion error.
• 3
  Position, clamp, cutLock the rotary axes whenever the feature allows.
• 4
  Halve feed on rotary cutsControllers often cannot hold commanded feedrate.

The TTC450 sits in the hobby and light-production class. That puts aluminum, brass, plastics and modeling board squarely in range. A 6061 part with a 6 mm cutter, 1 mm depth of cut, and moderate feed will run cleanly if the trunnion is rigidly mounted and the part is well supported. Plastics and machinable wax are even more forgiving and make good practice stock for learning the offsets.

Steel is a different conversation. Mild steel 1018 can be cut on a light machine, but the cutting forces scale with material strength, and the trunnion interface is the weakest link. Expect chatter, expect to reduce depth of cut to a few tenths of a millimeter, and expect tool life to drop. If your part is steel and needs real 5-axis contouring, this is not the right platform.

Part shape decides more than material. A part that is roughly cubic, fits inside the trunnion swing, and has features on four or five faces is ideal. A long shaft or a thin plate is a poor fit: the trunnion swing limits length, and a thin plate needs support that the rotating table does not provide without a fixture.

Holes at compound angles are the classic win. A hole that would need a tilted fixture on a 3-axis machine becomes a simple A-plus-B positioning move. That single capability is why many shops add a trunnion in the first place, even when they never run a simultaneous 5-axis toolpath.

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  Good fitAluminum, brass, plastics, cubic parts, compound-angle holes.
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  Marginal fitMild steel, thin plates, long shafts.
• 3
  Poor fitHardened steel, tight-tolerance contouring, large parts.
• 4
  Best use caseMulti-face features that would otherwise need two setups.

When a part comes off a conversion out of tolerance, the trunnion is rarely the only suspect. Build an error budget before you blame the hardware. The main contributors are centerline offset error, angular positioning error, tool deflection, thermal growth, and workpiece movement in the fixture. On light machines, tool deflection and fixture movement usually dominate.

Centerline error is a constant offset. If a feature on a tilted face is consistently shifted in one direction, and the shift scales with the tilt angle, the stored centerline is wrong. Re-indicate and correct the offset. If the shift does not scale with angle, look at the fixture instead.

Angular error shows up as a taper or a mismatch between two faces cut at different tilt angles. Measure the actual angle on the part with a sine bar or a height gauge and compare it with the commanded angle. If the error is repeatable, apply an angular correction in the controller or in the post.

Tool deflection is the one error you can hear. Chatter marks, a poor surface finish on one side of the part only, or a taper that grows toward the bottom of a deep cut all point to deflection. Shorten the tool, reduce the radial engagement, or add a spring pass. On light routers, this single change often recovers more accuracy than any adjustment to the trunnion.

• 1
  Constant shiftSuspect the stored rotary centerline.
• 2
  Angle-dependent shiftSuspect angular calibration or the post.
• 3
  One-sided finish problemSuspect tool deflection or fixture movement.
• 4
  Drift over a long runSuspect thermal growth in the spindle and frame.