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Description
Angle to the axis20°
Diameter range12–20 mm
InsertTCMT 16T304
Length100 mm
Indexable countersink 12x20 mm – 20° chamfer mill for a TCMT insert
Technical data and dimensions – 16 mm Weldon shank
| Technical data | |
|---|---|
| Cutting edge angle to the axis | 20° (40° cone) |
| Minimum diameter D2 | 12 mm |
| Maximum diameter D1 | 20 mm |
| Max. cutting depth | 11 mm |
| Flute length l | 30 mm |
| Overall length L | 100 mm |
| Shank diameter d | 16 mm, Weldon |
| Number of inserts Z | 1 |
| Insert | TCMT 16T304 |
| Insert screw | M3.5x10, Torx T15, 2.7 N·m |
| Manufacturer | Smoxh, Turkey (HF20 TC16 D12-20) |
Indexable countersink 12x20 mm Smoxh chamfers hole and slot edges at 20° to the axis. It cuts with one TCMT 16T304 insert over diameters from 12 to 20 mm. The insert has three cutting edges. A dull edge is replaced by rotating the insert through 120°, without resharpening the tool.
The 20° angle is measured between the insert edge and the tool axis. As the insert rotates, it sweeps out a 40° cone. For every millimeter of plunge depth, the diameter increases by 0.73 mm. The chamfer is long and narrow: its axial length is approximately 2.7 times its width. The entire feed is taken by one cutting edge, so a lower feed per revolution is selected. The 16 mm shank has a Weldon flat for the holder screw, which locks the tool in the holder.
Applications – hole and slot chamfers at a 20° angle
20° chamfer mill operations
The tool chamfers edges at 20° to the axis. A hole is chamfered with an axial movement, while a slot is chamfered by feeding along the slot. The same insert edges cut in both operations. The countersink machines holes and slots wider than 12 mm.
Hole edge chamfer
The countersink plunges axially into a hole larger than 12 mm. The insert chamfers the edge at 20° to the axis. The chamfer width is set by the plunge depth. Each millimeter of downward travel adds 0.73 mm to the chamfer diameter, up to 20 mm.
Chamfer on both slot edges
The tool is guided along the center of a slot from 12 to 20 mm wide. The insert chamfers both upper edges in a single pass. Chamfer width is set by the plunge depth. This method is used to chamfer keyway and guideway edges.
Hole chamfer – depth and diameter
How deep to plunge to obtain the required chamfer
The countersink cuts from 12 mm to 20 mm in diameter. At a 20° angle to the axis, the diameter increases by 0.73 mm for each millimeter of downward travel. The maximum plunge depth is 11 mm – at this depth, the chamfer reaches a diameter of 20 mm. This range accommodates medium-series clearance holes for M12–M16 screws according to ISO 273.
Calculator: Z-axis plunge depth for chamfer diameter
Plunge depth is measured from the workpiece surface to the insert corners at a diameter of 12 mm. Plunge depth = (chamfer diameter − 12 mm) ÷ 0.73, e.g., (16 − 12) ÷ 0.73 ≈ 5.49 mm. The value 0.73 is the diameter increase per 1 mm of plunge depth at an angle of 20°.
▲
Hole wider than 12 mm
The countersink cuts from a diameter of 12 mm, so the chamfer extends around the entire circumference of a hole wider than 12 mm.
TCMT 16T304 insert – three edges and indexing
Triangular insert to ISO 1832, Torx T15 screw
The insert code is interpreted according to ISO 1832. T indicates a triangle, so the insert has three cutting edges. C indicates a 7° clearance angle: the insert has positive geometry and cuts freely. M is the tolerance class, and the next T indicates a countersunk screw hole and a chip breaker on one side. 16 indicates an edge of approx. 16.5 mm, T3 a thickness of 3.97 mm, and 04 a corner radius of 0.4 mm.
The insert's 60° angle does not determine the chamfer angle. The 20° angle results from the insert's orientation in the body. The store offers the TCMT 16T304 H6310 insert from the Korean brand Horn. Grade H6310 is a general-purpose grade for steel and stainless steel. The countersink is sold without inserts.
Changing edges step by step
1Loosening the screw
Key: Torx T15
2Indexing the insert
Rotation: 120°
3Cleaning the insert seat
Chips: removed
4Tightening the screw
Torque: 2.7 N·m
✓Test chamfer
Check: diameter
M3.5x10 screw and T15 key according to the Smoxh catalog
With one insert, each indexing operation provides a new edge across the entire 12–20 mm range. A chip under the insert shifts the edge and changes the chamfer diameter, so the insert pocket must be cleaned before installation.
Cutting data – starting values
Cutting speed and feed per tooth – conservative ranges
The ranges are based on milling with an entering angle of 45° according to ISO 513. At an angle of 20°, these are starting values: begin at the lower limit and increase the values while monitoring the chips and spindle sound.
| Workpiece material | Cutting speed vc [m/min] | Feed per tooth fz [mm] |
|---|---|---|
| P Structural and alloy steel | 150–220 | 0.10–0.22 |
| M Stainless steel | 80–140 | 0.08–0.18 |
| K Gray cast iron | 180–300 | 0.10–0.28 |
Calculating spindle speed and feed rate – Ø 20 mm chamfer in steel
Spindle speed is calculated for the largest diameter engaged in the material, here the full chamfer diameter of 20 mm. Spindle speed = 1000 × cutting speed 150 m/min ÷ (3.14 × diameter 20 mm) ≈ 2380 rpm. Feed rate = feed per tooth 0.10 mm × 1 insert × 2380 rpm ≈ 230 mm/min. These two values are entered into the machine tool program.
Higher spindle speeds and lighter pressure work well for countersinking. Low speeds with heavy pressure cause vibration. When machining stainless steel, coolant protects the hole edge from overheating.
Indexable countersink 12x20 mm Smoxh chamfers holes and slots at 20° to the axis. The diameter range is 12–20 mm, and the maximum plunge depth is 11 mm. It cuts with one TCMT 16T304 insert with three edges. The 16 mm Weldon shank prevents the tool from rotating in the holder.
Questions about the 12x20 indexable countersink
Chamfer, inserts, depth, CNC program
An angle of 20° to the axis produces a 40° cone. A chamfer at this angle is machined when specified on the workpiece drawing.
TCMT 16T3 inserts to ISO, e.g., TCMT 16T304 with a 0.4 mm corner radius. The store offers TCMT 16T304 H6310 Horn for steel and stainless steel. The insert is secured with an M3.5x10 screw with a Torx T15 socket.
One TCMT 16T304 insert. The insert has three edges, providing three usable edge positions.
Enter a 40° countersink with a tip diameter of 12 mm in the tool table. Measure the tool height to the insert corners. Plunge depth = (chamfer diameter − 12 mm) ÷ 0.73.
Product accessories
Carbide insert TCMT 16T308 H6310 Horn
Reference: 0000006146 In stock > 10 items
€3.68
€4.53 brutto
Carbide insert TCMT 16T304 H6310 Horn
Reference: 0000007829 In stock > 10 items
€3.68
€4.53 brutto
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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