Alexei Volkov
Tapping a thread into a plastic pipe is a challenging task that requires careful preparation and the right tools. The process involves cutting internal threads into the pipe to create a pressure-tight joint. This can be achieved using a tap, which is a tool designed to cut threads into materials. The tap needs to be very sharp, and it may help to put the pipe in the freezer to stiffen it before threading. It is also important to support the pipe with a collar to prevent the walls from expanding. In some cases, it may be necessary to strip away some of the inner plastic coating to expose the aluminium layer before tapping.
| Characteristics | Values |
|---|---|
| Pipe tap type | Standard, High-hook, Medium hook, Low-hook, Extension, British Standard, Interrupted thread, Spiral flute |
| Pipe tap coating | Bright, Nitride, Oxide, Titanium Nitride |
| Pipe tap thread type | BSPT (British Internal Tapered Parallel Pipe Threads), PTF-SAE (short internal threads), NPT (National Pipe Thread Taper) |
| Pipe tap thread size | 1/⁄ 8 , 1/4 , 3/⁄ 8 , 1/2 , 3/4 , 1, 1 1/⁄ 4 , 1 1/2 , 2 inch |
| Pipe material | PVC, Nylon, PTFE, Nylon, Bronze, Cast Iron, Polyethylene, Steel, Aluminium |
| Tapping technique | Using sharp taps, collar support, two taps (small and large), removing inner plastic coating, freezing pipe, soldering wire, expanding bush, glue, lubricant |
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What You'll Learn
Using a steel tap to cut threads through the inner plastic pipe
First, it is essential to have a very sharp steel tap. The sharpness of the tap is crucial to cutting through the plastic pipe effectively. Consider putting the pipe in the freezer for a while before starting, as this will stiffen the pipe and reduce the tendency of the plastic to smear around the cutting points.
When using the steel tap, it is recommended to support the pipe with a collar. Without this support, the pipe walls may expand and deform as the tap bites into the plastic. Even with a collar, the tap may not cut through the plastic cleanly, and a larger tap might not enter the pipe directly. To address this issue, you can use two taps: a smaller one to create a pilot thread, followed by a larger one to cut through the plastic and penetrate any aluminium sheath within the pipe.
If your plastic pipe has an aluminium sheath, achieving good electrical contact with the aluminium layer can be challenging. One possible solution is to remove some of the inner plastic coating with a tool like a Dremel to expose the aluminium before tapping. However, this method can be time-consuming and may require additional steps to ensure a clean electrical connection.
There are alternative methods to tapping the pipe. One suggestion is to create a makeshift self-tapper by cutting flats into a bolt and threading it in and out of the hole. Another method is to use a propane torch to soften the hole edges and then thread in your homemade tap or a bolt with a taper. However, this method should be approached with caution, as it can produce toxic chemicals and is not suitable for PVC pipes.
Lastly, when tapping the plastic pipe, it is essential to consider the specific type of plastic and the size of the pipe. Different plastics may require different techniques and tools for effective threading. Additionally, the tap you use should be appropriately sized for the pipe you are working with.
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Exposing the aluminium layer by cutting away the inner plastic
Exposing the aluminium layer in a plastic pipe is a crucial step in creating a strong and durable connection. This process involves carefully removing the inner plastic coating to reveal the aluminium surface underneath. Here are the detailed steps and considerations for completing this task:
First, it is important to understand the composition of the pipe you are working with. Plastic pipes, such as PEX pipes or APC (Aluminum Plastic Composite) pipes, are commonly used in various applications, including plumbing and heating systems. These pipes typically have multiple layers, including an inner layer of plastic and an outer layer of aluminium.
To expose the aluminium layer, you will need the right tools. A sharp tap designed specifically for cutting plastic is essential. A tap with carefully sharp edges will help you cut through the plastic cleanly and effectively. It is also recommended to use a pipe cutter or a specialised cutting machine for APC pipes to ensure clean edges and a tight fit.
Before cutting, consider placing the pipe in a freezer for a while to stiffen it. This step helps reduce the tendency of the plastic to smear or deform around the cutting points, making it easier to achieve a precise cut. Additionally, using a collar or a similar supporting tool can help prevent the pipe walls from expanding during the tapping process.
Now, you can begin the process of cutting away the inner plastic. Start by clamping the pipe securely to provide a stable base for cutting. Align your sharp tap with the area you want to expose and begin cutting slowly and carefully. It is important to take your time and apply consistent pressure to achieve a clean cut.
As you cut through the plastic, you may need to use multiple taps of different sizes. Start with a smaller tap to create a pilot thread, and then switch to a larger tap to penetrate the aluminium layer. This two-step process can help you create a more precise and effective thread.
Finally, once you have cut away the inner plastic and exposed the aluminium layer, you can further improve the connection. One suggestion is to create an expanding bush by stripping off the inner plastic coating and using a short tube with saw cuts along its length. Alternatively, you can use a compression fitting by removing the outer plastic sheath, allowing the aluminium to pass through the stop ring in the fitting.
Remember, when working with plastic pipes and aluminium layers, it is essential to prioritise safety and precision. Take your time, use the right tools, and follow the appropriate installation techniques to ensure a successful and secure connection.
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Using a sharp tap to prevent pipe walls from expanding
Tapping plastic pipes is a challenging operation that requires accuracy and special techniques. When tapping a plastic pipe, the tap's sharpness is essential to prevent the pipe walls from expanding. Even with a carefully sharp tap, the pipe walls may still expand as the tap bites into the plastic. To mitigate this issue, it is recommended to use a collar to support the pipe.
To create a clean electrical contact, one must carefully remove the inner plastic coating to expose the aluminium layer. This process can be tedious and prone to errors. A Dremel tool can be used, but it may remove aluminium faster than plastic, potentially compromising the thin aluminium barrier. An alternative approach is to use a sharp Stanley knife to expose the aluminium, followed by scraping and applying oil to prevent oxidation.
Another technique to prevent pipe wall expansion is to utilise the pipe's temperature. By placing the pipe in a freezer, the plastic stiffens, reducing the tendency to smear around the cutting points. However, this method has limitations as the pipe quickly warms up, and the advantage is lost.
When tapping plastic pipes, it is essential to consider the challenges and employ techniques like using sharp taps, supporting the pipe with a collar, and manipulating the pipe's temperature. These methods can help prevent pipe wall expansion and ensure a successful tapping operation.
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Applying teflon tape to limit corrosion on the threads
Teflon tape, also known as PTFE thread tape or plumber's tape, is an easy and safe way to limit corrosion on the threads of plastic pipes. It is especially useful for pipes that don't have a built-in rubber seal, like shower heads, toilet fittings, and kitchen fittings.
Before applying Teflon tape, it is important to clean the pipe threadings with an all-purpose cleaner to remove any dirt, grime, or old sealant. Be sure to clean both the male threads of the pipe you're applying tape to and the female threads of what you're screwing the pipe into. Wait until the threadings are completely dry before applying the tape.
When applying the Teflon tape, start on the second thread from the end of the pipe so that it doesn't block the opening. Pull the tape tight and wrap it in the same direction as the threads, usually with 2-3 wraps to cover the threading. Work away from the end of the pipe, overlapping the tape as you go. For most pipes, 4-6 wraps are sufficient, but do not wrap more than 6 times as it can cause hazards and prevent pipes from joining properly.
If you're working with pipes that have pressured water or gas, it is recommended to add a layer of pipe dope or pipe joint compound over the Teflon tape for extra protection against leaks. Pipe dope fills in the gaps between threads and can be used in addition to tape on water supply lines and fixtures. However, when using another type of threading sealant, avoid using Teflon tape as well, as it can overload the threads and affect the seal.
Teflon tape is not suitable for all types of pipes. It is recommended for brass fittings unless they come with a rubber gasket. It is also meant for use on tapered pipe threads and should not be used on fluid power (hydraulic) systems.
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Using a standard nylon M4 screw with a caged nylon nut
Tapping threads into plastic pipes can be a challenging task, but using standard nylon M4 screws with caged nylon nuts offers a practical solution. This method provides several advantages over traditional tapping methods, including increased speed, improved strength, and the convenience of replaceability.
When working with plastic pipes, it is essential to use sharp taps and provide adequate support to the pipe during the threading process. A collar, for instance, can help prevent the pipe walls from expanding outwards as the tap bites into the material. Additionally, consider chilling the pipe in a freezer before threading to make the material stiffer and reduce smearing around the cutting points.
The standard nylon M4 screw with a caged nylon nut provides a stronger and more durable thread than 3D-printed alternatives. The caged nut design ensures that the nut remains securely in place, even if the assembly is shaken or inverted. This feature is particularly advantageous in applications where regular removal and replacement of the nut are necessary.
To use a standard nylon M4 screw with a caged nylon nut, follow these steps:
- Ensure that the plastic pipe is securely clamped or held in a vice to provide a stable base during threading.
- Create a tap drill-sized hole in the pipe at the desired location. This hole should be slightly smaller than the outer diameter of the screw's threads.
- Use a sharp tap to cut the threads into the pre-drilled hole. Go slowly and apply firm, even pressure to create a clean and consistent thread.
- If needed, use a small tap to create a pilot thread, followed by a larger tap to achieve the desired thread size.
- Once the thread is cut, insert the standard nylon M4 screw into the hole, ensuring that the screw's threads align with the newly cut threads in the pipe.
- Secure the screw in place by tightening the caged nylon nut onto the screw's threads. The nut will prevent the screw from loosening or falling out.
Remember to consider the specific requirements of your project when selecting the appropriate locking nut type and size. Standard nylon M4 screws and caged nylon nuts are typically suitable for most domestic applications, but heavier-duty alternatives may be required for industrial or high-torque applications.
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