Description
External threading turning tool SER 25X25-22 Varel
Right-hand tool holder SER-2525M22 for 22 ER inserts
| Technical data | |
|---|---|
| Manufacturer designation | SER-2525M22 |
| Machining operation | External threading |
| Design | Right-hand (R) |
| Shank cross section | 25x25 mm |
| Overall length | 150 mm |
| Distance from cutting edge to back of shank | 32 mm |
| Insert family | 22 ER |
| Thread types with the appropriate insert | Metric M – 60° Whitworth BSW – 55° Unified UN – 60° Trapezoidal Tr – 30° |
| Metric pitch range | 3.5–5.5 mm Depending on the selected 22 ER insert |
| Trapezoidal thread pitch range | 4–5 mm |

The photo shows the SER-2020K16 tool holder from this family.
The table data applies to the SER-2525M22 variant.
The insert shown in the photo is not included with the turning tool.
SER-2525M22 – external thread turning in practice
The workpiece rotates while the cutting edge moves along its axis
External threading turning tool SER 25X25-22 Varel is a right-hand holder for turning threads on shafts, journals and sleeves. The 25x25 mm shank is clamped in a suitable lathe tool post. With the appropriate 22 ER insert, you can cut metric M and inch UN threads with a 60° profile, as well as inch Whitworth BSW threads with a 55° profile.
The metric pitch range is 3.5–5.5 mm, depending on the selected insert. For inch BSW and UN threads, select an insert to match the profile and threads per inch (TPI). Example: a UNC 1 1/2 thread has 6 threads per inch and falls within the range of the 22 ER N60 insert (7–5 threads per inch). This is an indexable turning tool: when the cutting edge wears out, only the insert is replaced and the body is retained.
The thread diameter is determined by the shaft being machined, not the holder. The same 22 ER 4 ISO insert can therefore cut, for example, M36 x4 and M64x4. This is why a threading tool replaces a set of dies for fine threads and large diameters.
Schematic diagram. Typical setup of a right-hand turning tool in front of the lathe axis.
How does an external threading tool work?
The insert deepens the same profile with each successive pass. The feed remains synchronized with spindle rotation. For a single-start thread, tool travel per revolution equals the thread pitch.
In a typical setup, a right-hand turning tool cuts toward the lathe chuck. The R symbol itself identifies the holder design. The hand of the resulting thread also depends on the tool setup, spindle rotation and feed direction.
22 ER inserts – selecting the thread profile and pitch
One holder, different tasks with the appropriate insert
Full profile 22 ER ISO
A full-profile insert, such as 22 ER 4 ISO, is designed for a specific pitch. It machines the thread flanks, root and crest. A different pitch requires the appropriate insert version.
Example: metric profile, 4 mm pitch.
Partial profile 22 ER N60
A partial-profile insert, such as 22 ER N60, covers pitches of 3.5–5 mm (7–5 threads per inch). It does not finish the thread crests. The outside diameter of the workpiece must be prepared beforehand with a suitable tool.
Selection: profile, pitch range and insert grade.
Choose a full-profile insert for production runs of the same thread. The crest is formed together with the flanks, without a separate operation, ensuring a repeatable profile. An N60 insert with a 60° profile or an N55 insert with a 55° profile covers several pitches, making it useful for short runs and one-off parts. The crest then depends on the previously turned diameter, so profile control is less precise. With a 22 ER TR insert, you can cut a Tr trapezoidal thread with a pitch of 4–5 mm.
The final “22” indicates the insert size, not the diameter of the thread being cut. The thread profile and pitch depend on the selected 22 ER insert. 16 ER and 22 IR inserts are not direct substitutes for each other.
Threading with a turning tool on a lathe – setup and feed
Short overhang, correct cutting edge height and synchronized motion
Set the cutting tip at spindle center height. Check the alignment of the insert profile relative to the workpiece axis. Minimize shank overhang to reduce susceptibility to vibration. Remove chips from the pocket and support surfaces before mounting.
Select the cutting speed and number of passes according to the insert, material and clamping rigidity. The SER body alone does not determine cutting data for steel, stainless steel or aluminum.
The external threading turning tool SER 25X25-22 Varel requires a tool post for a 25x25 mm shank that allows the cutting edge height to be set correctly. When selecting it, also check the clearance around the workpiece. The overall length of 150 mm describes the body, not the permissible working overhang. Inspect the final thread size according to the requirements of the part drawing.
Feed for a 4 mm pitch
Pitch P is measured along the axis between corresponding points on adjacent thread turns.
For a single-start thread, the tool moves axially by 4 mm for each spindle revolution.
Feed per revolution:
fn = P = 4 mm/rev.
Example: spindle speed n = 150 rpm
vf = n × P = 150 × 4
600 mm/min
Feed rate
150 rpm is a calculation example, not recommended cutting data. The threading cycle requires the feed to be synchronized with the spindle.
Thread turning with a turning tool – approach, cutting pass and retraction
Each pass uses the same four movements, going slightly deeper each time
The thread is formed in several passes. In each pass, the tool follows the same cycle of four movements, and the 22 ER insert cuts slightly deeper each time until the profile reaches full depth. The diagram shows one pass in a typical right-hand SER turning tool setup.
Single-pass cycle
Schematic diagram, top view. Red line – cutting movement, the insert is cutting. Dashed lines – rapid movements without cutting.
The tool moves from the starting point in front of the shaft end face and feeds in perpendicular to the axis to the depth of this pass. This is a rapid movement without cutting.
The insert cuts while moving along the axis toward the chuck. For each spindle revolution, the tool advances by the thread pitch P, for example 4 mm.
At the end of the thread, the tool rapidly retracts from the shaft. At a workpiece shoulder, it does this in the thread relief groove before reaching the shoulder face.
The retracted tool rapidly returns to the starting point. It begins the next pass with a slightly deeper infeed.
Set the starting point in front of the shaft end face. The insert then enters the material with the feed already equal to the pitch. Metric thread depth is approximately 0.61 × P, or approximately 2.45 mm for a pitch of 4 mm. At a workpiece shoulder, machine a thread relief groove at least 1.05 × P wide, or approximately 4.2 mm, and at least as deep as the thread.
Tool infeed and number of passes in thread turning
The infeed direction determines which insert edge cuts
Infeed is the movement that takes the insert deeper on the next pass. Its direction determines which insert edge cuts and how the chip flows. In the diagrams, red lines show successive positions of the insert tip, and the arrow shows the infeed direction. The numbers 1–5 and progressively darker bands indicate successive passes, or the layers of material removed in each pass. The bold line shows the insert edge that is cutting.
Radial infeed
The insert feeds straight toward the axis and cuts with both edges. This is the simplest method. It works well for fine pitches, short-chipping materials and hardened materials.
Modified flank infeed
The tool moves diagonally along the flank, or side of the profile, at an angle a few degrees less than 30°. One edge does most of the cutting, while the other does not rub against the thread flank. Manufacturers recommend this method as the first choice for most threads.
Alternating flank infeed
The tool alternately moves along each flank of the profile, so both edges wear evenly. This method helps with coarse pitches and long-chipping materials. It requires a program that is not available on every lathe.
Select the number of passes according to the pitch and material. For a pitch of 4 mm, insert manufacturers' catalogs specify 10–20 or 11–18 passes; harder materials require more passes. The first pass is the deepest, and each subsequent pass is shallower, keeping the chip cross section similar. The final pass should not be shallower than approximately 0.05 mm, or the edge will start rubbing instead of cutting.
SER 25X25-22 – selection and application questions
Key information before selecting a holder
The holder accepts right-hand external threading inserts from the 22 ER family. These include full-profile inserts, such as 22 ER 4 ISO or 22 ER 6 W, and partial-profile inserts, such as 22 ER N60 and 22 ER N55. Select the profile, pitch and grade suitable for the job.
Up to 5.5 mm for metric threads, for example M56 x5.5 with a 22 ER 5.5 ISO insert. The 22 ER N60 and 22 ER N55 inserts cover pitches of 3.5–5 mm, or 7–5 threads per inch.
Yes, with a 22 ER TR insert installed. The holder can cut Tr trapezoidal threads with a pitch of 4–5 mm, such as Tr 20x4 or Tr 24x5. The trapezoidal profile has an angle of 30°. The range includes 22 ER TR inserts with pitches of 4 and 5 mm.
With full-profile 22 ER inserts, you can cut coarse threads from M30 x3.5 to M60 x5.5. For example, M36 x4 requires a 22 ER 4 ISO insert, and M48 x5 requires an 22 ER 5 ISO insert.
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