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Description
External threading turning tool SEL 20X20 16 Smoxh
Left-hand SEL 2020 K16 holder for 16 EL indexable inserts
| Technical data | |
|---|---|
| Manufacturer designation | SEL 2020 K16 |
| Machining operation | External threading |
| Design | Left-hand (L) |
| Shank cross section | 20x20 mm |
| Overall length | 125 mm |
| Distance from cutting edge to back of shank | 20 mm |
| Insert family | 16 EL (also 16 IR) |
| Thread types with the appropriate insert | Metric M – 60° Parallel pipe G – 55° Unified UN – 60° |
| Metric pitch range | 0.5–3.5 mm Depending on the selected 16 EL insert |
The photo shows a mirror image of the SER 2525 M16 body.
The data in the table apply to the left-hand SEL 2020 K16 holder.
SEL 2020 K16 – external thread turning in practice
The workpiece rotates while the cutting edge moves along its axis
External threading turning tool SEL 20X20 16 Smoxh is a left-hand holder for turning threads on shafts, journals and sleeves. The 20x20 mm shank is clamped in a suitable lathe tool post. By selecting the appropriate 16 EL insert, you can cut metric M and inch UN threads with a 60° profile, as well as G parallel pipe threads with a 55° profile.
The metric pitch range is 0.5–3.5 mm, depending on the selected insert. For G and UN inch threads, select the insert to match the profile and threads per inch (TPI). Example: a G 1/2 thread has 14 threads per inch and falls within the range of the 16 EL AG55 insert (48–8 threads per inch). This is an indexable turning tool: when the cutting edge wears out, only the insert is replaced, while the body is retained.
The thread diameter is determined by the shaft being machined, not the holder. The same 16 EL 3.5 ISO insert can therefore cut, for example, M30 x3.5 and M33 x3.5. This is why a threading tool can replace a set of dies for fine threads and large diameters.
Illustrative diagram. Left-hand turning tool, left-hand thread, feed toward the tailstock.
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.
The left-hand turning tool has a mirror-image design and uses 16 EL inserts. It is primarily intended for left-hand threads. The hand of the resulting thread also depends on the tool setup, spindle rotation and feed direction.
16 EL inserts – selecting the thread profile and pitch
One holder, different tasks with the appropriate insert
Full profile 16 EL ISO
A full-profile insert, such as 16 EL 1.5 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, 1.5 mm pitch.
Partial profile 16 EL AG60
A partial-profile insert, such as 16 EL AG60, covers pitches of 0.5–3 mm (48–8 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 AG60 insert with a 60° profile or an AG55 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. The left-hand holder also accepts 16 IR inserts, which have the same shape as 16 EL inserts.
The final “16” indicates the insert size, not the diameter of the thread being cut. The thread profile and pitch depend on the selected 16 EL insert. The 11 EL and 16 IL inserts are not direct substitutes for each other. The full profile of a 16 IR insert corresponds to an internal thread, so choose 16 EL inserts for external threads.
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 to suit the insert, material and clamping rigidity. The SEL body alone does not determine cutting data for steel, stainless steel or aluminum.
The SEL 20X20 16 Smoxh external threading turning tool requires a tool post for a 20x20 mm shank that allows the cutting edge height to be set correctly. When selecting the tool, also check the clearance around the workpiece. The overall length of 125 mm describes the body, not the permissible working overhang. Check the final thread dimensions against the requirements on the part drawing.
Feed for a 1.5 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 1.5 mm for each spindle revolution.
Feed per revolution:
fn = P = 1.5 mm/rev.
Example: spindle speed n = 400 rpm
vf = n × P = 400 × 1.5
600 mm/min
Feed rate
400 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. During each pass, the tool repeats the same cycle of four movements, and the 16 EL insert cuts slightly deeper each time until the profile reaches its full depth. The diagram shows one pass of a left-hand SEL turning tool cutting a left-hand thread, with feed toward the tailstock.
Single-pass cycle
Schematic diagram, top view. Red line – cutting movement, the insert is cutting. Dashed lines – rapid movements without cutting.
1
Approach
The tool moves from the starting point in the groove at the shoulder and feeds in perpendicular to the axis to the depth for this pass. This is a rapid move without cutting.
2
Cutting pass
The insert cuts as it moves along the axis toward the tailstock. For each spindle revolution, the tool advances by the thread pitch P, for example 1.5 mm.
3
Retraction
Beyond the end face of the shaft, the insert exits the material and the tool rapidly retracts away from the axis.
4
Return
The retracted tool rapidly returns to the starting point in the groove. It begins the next pass with a slightly deeper infeed.
The left-hand turning tool starts the thread from the shoulder side, so the groove at the shoulder is the starting location. It accommodates the insert tip and a short lead-in where the feed synchronizes with the pitch before the insert enters the material. The metric thread depth is approximately 0.61 × P, or approximately 0.92 mm at a pitch of 1.5 mm. Make the groove deeper than the thread and wider than 1.05 × P, or approximately 1.6 mm, because it must accommodate both the insert and the lead-in.
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 1.5 mm, insert manufacturers' catalogs specify 5–11 or 6–10 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.
SEL 20X20 16 – questions about selection and applications
Key information before selecting a holder
The holder accepts left-hand external threading inserts from the 16 EL family, such as 16 EL AG60 and 16 EL AG55. It also accepts 16 IR inserts with the same shape, such as the partial-profile 16 IR AG60. Select the profile, pitch and grade to suit the application.
Up to 3.5 mm for metric threads, such as M30 x3.5 and M33 x3.5 with a 16 EL 3.5 ISO insert. For inch threads, the 16 EL AG60 and 16 EL AG55 inserts cover up to 8 threads per inch.
For G parallel pipe threads according to ISO 228-1, from G 1/16 to G 6. These sizes have 28, 19, 14 or 11 threads per inch. Each thread count has a corresponding full-profile insert, such as 16 EL 19 W for G 1/4 and G 3/8.
Yes, with a 16 IR/EL grooving insert installed. It fits size 16 left-hand SEL external holders, so no separate turning tool is needed. Select the insert width to match the groove width on the part drawing, and check the permissible depth in the insert data sheet.
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