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Description
Angle to the axis45 degrees
Diameter range5–21 mm
InsertTPMN 160308
Length110 mm
Indexable countersink 5x21 mm – 45° chamfer mill for a TPMN insert
Technical data and dimensions – 16 mm Weldon shank
| Technical data | |
|---|---|
| Cutting edge angle to the axis | 45° (90° cone) |
| Minimum diameter D2 | 5 mm |
| Maximum diameter D1 | 21 mm |
| Max. cutting depth | 8 mm |
| Flute length l | 40 mm |
| Overall length L | 110 mm |
| Shank diameter d | 16 mm, Weldon |
| Number of inserts Z | 1 |
| Insert | TPMN 160308 |
| Insert clamping | TP-16 clamp, L4 key |
| Manufacturer | Varel |
Indexable countersink 5x21 mm Varel cuts recesses for M5–M10 countersunk screw heads and chamfers hole edges. It cuts with one TPMN 160308 insert over diameters from 5 to 21 mm. The insert has three cutting edges. A dull edge is replaced by indexing the insert by 120°, without sharpening the tool.
The 45° angle is measured between the insert edge and the tool axis. As it rotates, the insert sweeps a 90° cone. This matches the head angle of a metric countersunk screw. For every millimeter of plunge depth, the diameter increases by 2 mm. The entire feed is carried 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 – countersunk screw seat and slot chamfers
Operations with the 90° countersink
The same insert edges cut the screw head recess and the chamfer. The countersink also works as a 45° chamfer mill. Only the tool path and plunge depth change. The countersink machines holes and slots wider than 5 mm.
Countersunk screw seat
The insert sweeps a 90° cone, matching the screw head specified in DIN 7991. The countersink feeds axially into the clearance hole to the calculated depth. It accommodates M5, M6, M8, and M10 heads with diameters from 10 to 20 mm. The head sits flush with the workpiece surface or 0.1 mm below it.
Chamfer on both slot edges
The tool is guided along the center of a slot from 5 to 21 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.
Screw head recess – selection and depth
Which screws fit and how deep to plunge
The countersink cuts from 5 mm to 21 mm in diameter. A complete recess requires two conditions. The clearance hole must be larger than 5 mm. The screw head must be less than 21 mm in diameter.
Calculator: Z-axis plunge depth for recess diameter
With a 90° cone, each millimeter of downward travel adds 2 mm to the diameter. Plunge depth is measured from the workpiece surface to the insert corners at a diameter of 5 mm. Plunge depth = (recess diameter − 5 mm) ÷ 2, e.g., (12 − 5) ÷ 2 = 3.5 mm for an M6 head.
▲
Clearance hole wider than 5 mm
The countersink cuts from a diameter of 5 mm. In a clearance hole wider than 5 mm, e.g., 5.5 mm for M5, the recess is complete and the head seats fully.
TPMN 160308 insert – clamp instead of a screw
Triangular insert without a hole to ISO 1832
T indicates a triangle, so the insert has three cutting edges. P indicates a 11° clearance angle: the insert has positive geometry. M is the tolerance class, and N indicates an insert without a hole or chip breaker. 16 indicates an edge of approx. 16.5 mm, 03 a thickness of 3.18 mm, and 08 a corner radius of 0.8 mm.
The insert without a hole is held by a TP-16 clamp tightened with an L4 key. The clamp presses down on the insert from above and pushes it against the seat walls. The countersink is sold without inserts.
Changing edges step by step
1Loosening the clamp
Key: L4
2Indexing the insert
Rotation: 120°
3Cleaning the insert seat
Chips: removed
4Tightening the clamp
Clamp: TP-16
✓Test recess
Check: with the screw head
Clamp and key according to the Varel catalog
With one insert, each indexing operation provides a fresh edge across the entire 5–21 mm range. A chip under the insert shifts the cutting edge and changes the recess diameter, so the insert seat must be cleaned before installation.
Cutting data – starting values
Cutting speed and feed per tooth – conservative ranges
The values are based on conservative milling ranges with a 45° entering angle according to ISO 513. Start 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 – M6 recess in steel
Spindle speed is calculated for the largest diameter engaged in the material, here the 12 mm head. Spindle speed = 1000 × cutting speed 150 m/min ÷ (3.14 × diameter 12 mm) ≈ 3970 rpm. Feed rate = feed per tooth 0.10 mm × 1 insert × 3970 rpm ≈ 390 mm/min. These two values are entered in 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 5x21 mm Varel cuts 90° recesses for M5, M6, M8, and M10 heads. It also chamfers holes wider than 5 mm and slot edges. It cuts with one TPMN 160308 insert over diameters from 5 to 21 mm. The 16 mm Weldon shank and 110 mm length fit standard milling tool holders.
Questions about the 5x21 indexable countersink
Recess, inserts, depth, CNC program
For 90° countersunk screws to DIN 7991: M5, M6, M8, and M10. Their head diameters are 10, 12, 16, and 20 mm, and their clearance hole diameters are 5.5; 6.6; 9, and 11 mm. The calculator above gives the plunge depth for each of these screws.
TPMN 160308 inserts: triangular, without a hole, with a 0.8 mm corner radius. They are held by a TP-16 clamp tightened with an L4 key.
One TPMN 160308 insert. The insert has three edges, providing three usable edge positions.
Enter a 90° countersink with a tip diameter of 5 mm in the tool table. Measure the tool height to the insert corners. Plunge depth = (head diameter − 5 mm) ÷ 2, plus approx. 0.1 mm.
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