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Description
DIAMETER Ø25 mm
LENGTH 250 mm
INSERT TNMG 1604rr
ANGLE κr 93°
Technical specifications of the S25S MTUNL 16 boring bar
| Technical data | |
|---|---|
| ISO designation | S25S MTUNL 16 |
| Shank diameter (d) | Ø25 mm |
| Effective height (h) | 23 mm |
| Overall length (L) | 250 mm |
| Functional overhang (f) | 18 mm |
| Min. bore diameter (D_min) | Ø32 mm |
| Entering angle (κr) | 93° |
| Clearance angle | 0° (negative) |
| Clamping system | ISO — combination (M) |
| Insert type | TNMG 1604rr |
| Cutting direction | L — left-hand (R version available) |
| Shank material | Steel (S) |
| Manufacturer | Smoxh |
Boring bar S25S MTUNL 16 – for internal turning of bores
Internal turning tool for machining bores from Ø32 mm
Boring bar S25S MTUNL 16 is an indexable boring bar designed for longitudinal turning and roughing and medium machining of bores with diameters from 32 mm. The round steel shank with a diameter of Ø25 mm and a length of 250 mm provides cutting stability even with greater tool overhang. The geometry with an entering angle of 93° allows turning along the wall with simultaneous light facing.
In the combination clamping system (M), the TNMG 1604rr insert is held simultaneously by a top clamp and a pin in its hole. The negative geometry of the 60° triangular insert with 6 cutting edges is suitable for roughing and medium machining, providing high cutting edge strength and cost efficiency thanks to its double-sided design. The boring bar is compatible with TNMG 16 inserts in various carbide grades — select the grade to match the workpiece material.
Decoding the MTUNL designation of the S25S MTUNL 16 boring bar
What the individual letters in the ISO designation mean
Decoding the designation MTUNL
M
CLAMPING
Combination (M)
The top clamp and pin secure the insert simultaneously
T
INSERT SHAPE
60° triangle 60°
TNMG insert — negative, double-sided, 6 edges (3 per side)
U
ENTERING ANGLE
κr = 93°
Longitudinal turning inside the bore with light facing
N
CLEARANCE ANGLE
α = 0° (neg.)
Negative geometry — double-sided inserts, edges on both sides
L
DIRECTION
Left-hand (L)
Feed to the right — from the spindle toward the tailstock
Shank: Ø25 mm (S25S, steel) · Insert: TNMG 1604rr
Typical applications of the S25S MTUNL 16 boring bar
Cutting operations:
| ▸ | Longitudinal boring — enlarging and finishing cylindrical bores from Ø32 mm |
| ▸ | Roughing and medium machining of bores — negative TNMG geometry provides a strong cutting edge; for finishing, select an insert with a finishing chip breaker |
| ▸ | Internal taper turning — bearing seats, internal chamfers, Morse tapers |
| ▸ | Light facing — the 93° angle allows machining the face inside the bore |
| ▸ | CNC production runs — repeatable cutting edge positioning and quick insert replacement in the holder |
Included
Package contents for S25S MTUNL 16
Package contents:
| ✓ | Boring bar body S25S MTUNL 16 | 1 pcs |
| ✓ | Combination clamp (clamp + pin) | 1 pcs |
| ✓ | Hex key for insert replacement | 1 pcs |
| ✗ | TNMG 1604rr cutting insert (sold separately) | — |
Compatible TNMG 1604rr insert
TNMG 1604rr
The cutting insert is not included in the set — must be purchased separately. TNMG insert. Negative geometry means that the insert is double-sided and has 6 cutting edges, providing a stronger cutting edge and twice as many edges as a single-sided insert.
Select the insert grade to match the workpiece material: P (structural steels), M (stainless steel), K (cast iron), N (aluminum). You can find compatible inserts in the section "Related products" below.
Insert installation and replacement for the S25S MTUNL 16 boring bar
Instructions for combination clamping (M)
Insert replacement procedure step by step
1 Loosen the clamp
Loosen the clamping screw 2-3 turns
2 Clean the insert seat
Remove chips and debris
3 Install the insert
Fit onto the pin and press down
4 Tighten the clamp
Torque 2.0–3.5 Nm
Important: Do not exceed the recommended tightening torque — this may damage the thread in the seat or crack the insert.
Checks before starting work:
| ▸ | Tool overhang — do not exceed 4×d (100 mm) without support; use vibration damping for greater overhang |
| ▸ | Cutting edge height — set the cutting edge at spindle centerline height |
| ▸ | Insert seat condition — check that the contact surface is not damaged or worn |
| ▸ | Secure clamping — the insert must have no play in the seat |
| ▸ | Indexing — when an edge wears out, rotate the insert to a fresh edge (6 edges in total) |
Note: Use internal coolant (through the spindle) for boring whenever possible. When machining without coolant, reduce cutting parameters by 20–30%. Long tool overhang promotes vibration — if vibration occurs, reduce the depth of cut and increase the feed.
Frequently asked questions — S25S MTUNL 16
The minimum bore diameter is Ø32 mm. In smaller bores, the tool head interferes with the machined wall, preventing proper cutting.
For a steel shank of Ø25 mm, the recommended maximum overhang without damping is 4×d, or 100 mm. Above this value, vibration may occur — reduce the depth of cut or use a vibration-damped boring bar.
The TNMG insert has negative geometry (clearance angle 0°), which means it is double-sided with 6 cutting edges. When one edge wears out, rotate or flip the insert to use the next edge — this significantly reduces tooling cost per part.
Product accessories
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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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