About Trapezoidal Tap
The trapezoidal tap is a cutting tool specially designed for the machining of trapezoidal threads with an isosceles trapezoidal shape (the angle of the threads is usually 30° or 29°). It is mainly used for processing threaded connections that require high load carrying capacity, transmission accuracy and wear resistance, such as screw nuts and elevating mechanisms.
There are two main types:
1. Metric trapezoidal thread (Tr type), such as Tr20×4 (diameter 20mm, pitch 4mm).
2. Imperial trapezoidal thread (ACME type): such as 1″-5 ACME (1 inch diameter, 5 teeth per inch).
Trapezoidal taps are widely used in the following fields due to their high transmission efficiency and good load carrying capacity:
1. Mechanical transmission: such as machine tool screws, CNC equipment feeding system.
2. Heavy-duty equipment: jacks, hydraulic cylinders, presses and so on.
3. Lifting mechanism: elevator, lifting platform, screw conveyor.
4.Valves and pumps: adjusting screws, sealing drive components.
5. Repair and customized processing: repairing worn trapezoidal threaded holes or making non-standard parts.
Difference with normal thread：
| Thread Type | Pitch Type | Main Application | Feature |
| TR/ACME | 30°/29° | Transmission, Heavy Duty | High bearing, bi-directional force |
| MM/UNC | 60° | disable connection | Anti-loosening, easy to disassemble |
| G/NPT | 55° | Sealed Ducts | leak-proof, pressure-resistant |
How to use trapezoidal tap:
(1) Preparation
Select the right tap: Confirm the thread specification (e.g. Tr20×4).
① Calculate the diameter of the bottom hole: the bottom hole of the trapezoidal thread is larger than that of the ordinary thread, calculation formula:
Metric trapezoidal thread (Tr): bottom hole ≈ nominal diameter - pitch (e.g., Tr20×4, bottom hole ≈ 20-4=16mm)
② Inch ACME threads: you need to look up the table or use the special formula.
③ Choose a suitable drill bit and drill the hole to ensure that the hole wall is smooth.
(2) Cutting steps
① Fix the workpiece: Make sure the workpiece is stable and prevent it from shifting.
② Lubrication: Use cutting oil (e.g. tapping oil, vulcanized oil) to reduce friction and prolong tap life.
③ Tapping method:
- Manual tapping: use tap wrench, keep it vertical, and back off half a turn after every 1~2 turns to break chips.
- Machine tapping: Use floating tapping chuck on drilling machine or CNC, low speed cutting (recommended speed 50-200 RPM).
④ Step-by-step machining (deep holes or hard materials):
- Rough first with a coarse taper (head taper), then finish with a fine taper (second taper).
(3) Check threads
Use a trapezoidal thread plug gauge to check thread accuracy.
If the thread is not smooth, use the tap back to correct.
Notice
(1) Avoid tap breakage:
Keep the tap perpendicular to the hole to avoid skewed force.
Do not force tapping, encounter resistance should back off the knife to clean the chips.
Hard materials (such as stainless steel) are recommended to use **spiral fluted taps** for easy chip removal.
(2) Choose the cutting fluid correctly:
Steel/stainless steel: sulfurized cutting oil, special oil for tapping.
Aluminum/Copper: kerosene or special cutting fluid for aluminum.
Cast iron: can cut dry or use light oil.
(3) Tap Maintenance:
Clean and apply anti-rust oil after use.
Taps with serious wear should be replaced in time, otherwise the thread quality will be affected.
Trapezoidal taps are a key tool for machining high load drive threads for machine tools, heavy-duty machinery and precision equipment. Proper selection of the bottom hole, control of cutting parameters and good lubrication can significantly improve thread quality and extend tool life. For high volume production, it is recommended to use Machine Trapezoidal Tap + Tapping Machine to improve efficiency.