Summary of key knowledge about CNC thread processing

March 16 17:25 2023

Metal cutting thread processing methods mainly include turning, milling, tapping, etc. Today, the Anebon team brings you a summary of the most common thread turning important technical knowledge in production and shares it with everyone.

1. Important basic knowledge of thread processing1.1 Definition of terms

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①Bottom of tooth ②Side of tooth ③Top of tooth

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1.2 Helix angle:– The helix angle depends on the diameter and pitch of the thread.- Adjust the flank relief of the blade by changing the shim.- The blade inclination angle is γ. The most common bevel angle is 1°, which corresponds to a standard shim in the holder.

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1.3 Cutting forces when entering and exiting the thread:– The highest axial cutting forces in threading operations occur during entry and exit of the cutting tool into the cnc machining workpiece.- Cutting data that are too high may lead to movement of an unreliably clamped insert.

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1.4 Tilt the blade for clearance:The bevel angle can be set with a shim under the blade in the handle. Refer to the chart in the tool catalog to select which shim to use. All holders come with standard shims set at 1° rake angle.

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Choose the shim according to the bevel angle. Workpiece diameter and thread pitch affect the rake angle. As can be seen from the figure below, the diameter of the workpiece is 40mm and the pitch is 6mm, the required shim must have a 3° bevel angle (standard shims cannot be used).

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Markings for threading inserts and shims:

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Thread shape and its application:

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2.1 Thread insert type and clamping scheme2.1.1 Multi tooth blade

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advantage:- Reduce the number of feeds- very high productivityshortcoming:- Requires stable clamping- Requires sufficient retraction space after threading2.2 Full profile blade

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advantage:- Better control over thread shape- Fewer glitchesshortcoming:- One type of insert can only cut one pitch2.3 V-profile blade

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advantage:- Flexibility, the same insert can be used for several pitches.shortcoming- Can cause burrs to form and require deburring.Clamping solution i-LOCK:– Extremely rigid threading with fixed inserts- Guided by the guide rail, the blade is positioned in the correct position- The screw presses the insert on the guide rail back to the radial stop at one of the contact surfaces (red contact surface) in the insert holder- Reliable insert interface ensures longer tool life and higher thread quality

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Various handles:

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3. Three different types of feeding methodsThe method of feed can have a significant impact on the threading process. It affects: Cut control, insert wear, thread quality, tool life.3.1 Improved side feedMost CNC machine tools can use this method of feeding through cycle programs:- Chips vs. conventional turning types – easier to form and guide- Axial cnc cutting force reduces vibration risk- Chips are thick but only in contact with one side of the insert- Reduced heat transfer to the blade- First choice for most threading operations

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3.2 Radial infeedMost common method – the only method that older non-cnc lathes are able to use:- Produces hard “V” shaped chips- Uniform blade wear- The insert seat is exposed to high temperatures, which limits the depth of entry- Suitable for machining fine threads- Potential vibration and poor chip control when machining coarse threads- First choice for work hardened materials

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3.3 Alternate feeding- recommended for large teeth- Uniform insert wear and maximum tool life when machining very large pitch threads- Chips are guided in two directions and are therefore difficult to control

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4. Methods to improve processing results

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Decreasing depth of cut (left), constant depth of cut (right)

4.1 The depth of cut decreases layer by layer (the chip area remains unchanged)Able to achieve a constant chip area, which is the most commonly used method in NC programs.- The first pass is the deepest- follow the recommendations on the feed table in the catalog- More “balanced” chip area- The last pass is actually about 0.07mm4.2 Constant depth of cutEach pass has the same depth regardless of the number of passes.- Higher requirements for blades- Ensures optimum chip control- Not applicable when the pitch is greater than TP1.5mm or 16TP4.3 Finish thread crests with extra stock:No need to turn stock to exact diameter prior to threading, use extra stock/material to finish thread crests. For finishing crest inserts, the previous turning machining process should leave 0.03-0.07mm of material to allow the crest to be properly formed.

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4.4 Recommended external thread feed value (ISO metric system):

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4.5 To ensure workpiece and tool alignment:Use a maximum centerline deviation of ±0.1mm. Too high a cutting edge position and the relief angle will decrease and the cutting edge will be scratched (cracked); too low a cutting edge position and the thread profile may not be correct.

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5. thread turning application skills success1) Before thread turning, check whether the workpiece diameter has the correct machining allowance, and add 0.14mm as the crown allowance.2) Precise positioning of the tool in the machine tool.3) Check the setting of the cutting edge relative to the pitch diameter.4) Make sure to use the correct insert geometry (A, F or C).5) Ensure a sufficiently large and uniform clearance (blade-tilted shim) by selecting the appropriate shim to obtain the correct flank clearance.6) If the thread is unqualified, check the entire setup including the machine tool.7) Check available NC programs for thread turning.8) Optimize the feeding method, number of passes and size.

5.1 When selecting tools for thread turning operations, consider:- Check overhangs and any clearances required (e.g. shoulders, sub-spindle, etc.)- Minimize tool overhang for quick set-up- For less rigid setups, select inserts with lower cutting forces- High precision coolant extends tool life and improves cutting control- Easy access to coolant with plug-and-play coolant adapter- In order to ensure productivity and tool life, multi-profile inserts are the first choice, single-edged full-profile inserts are the second choice, and V-profile inserts are the option with the lowest productivity and shortest tool life.

5.2 Insert wear and tool life:Feed method, optimize the feed method, number of passes and depthBlade inclination to ensure a sufficiently large and uniform clearance (blade-tilted shim)Insert geometry, make sure to use the correct insert geometry (A, F or C geometry)Blade material, choose the correct material according to the material and toughness requirementsCutting parameters, if necessary, change cutting speed and number of passes.9) Ensure correct cutting speed to meet application requirements.10) If the pitch of the workpiece thread is wrong, check whether the pitch of the machine tool is correct.11) Before cutting into the workpiece, it is recommended that the tool should start with a minimum distance of 3 times the pitch.12) High-precision coolant can extend tool life and improve chip control.13) The quick change system ensures easy and fast clamping.

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