Alexei Volkov
Stripped bolt threads are a common issue that can occur due to friction, corrosion, or misalignment during fastening. Repairing stripped threads in plastic can be done through various methods, and this text will outline some of the most popular techniques. One common method is to use a tap and die kit, which allows users to cut new threads or reshape old ones. Other methods include using a thread repair kit, soldering iron, or epoxy to fill and reshape the threads.
How to rethread a plastic bolt hole
| Characteristics | Values |
|---|---|
| Tools | Tap and die set, pin vise, thread repair kit, soldering iron kit, plastic welder kit, plastic welding rods, plastic repair kit, thread cutting tool, thread file grooves, rethreading tap, rethreading kit |
| Materials | Oil, epoxy, grease, Vaseline, JB Weld, plastic, stainless steel, brass |
| Techniques | Clamp bolt in a vise, cut threads, reshape threads, clean out the hole, measure the hole, drill, cut new threads, rotate and back off the tap, dislodge debris, align holes, wrap teflon around the screw, use a soldering iron, dimple the plastic, heat the screw, cool the screw, use a piece of tape to hold the bolt down |
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What You'll Learn
Using a tap and die kit
Next, you need to determine the number of threads per inch (TPI) to select the correct tap and/or die for the bolt. Most tap and die systems include a gauge to help you match the TPI of the bolt. After determining the TPI, you can select the corresponding die. Keep in mind that these sets come in both metric and SAE, so choose the appropriate type for your project.
Once you have the correct tap and die, it's time to start the rethreading process. Place the tap into the provided wrench and secure it. Then, carefully align the tap with the bolt hole, ensuring that it is straight to the hole. As you begin to rethread, use lots of oil to lubricate the tap and back it out frequently to remove any debris that builds up in the threads.
If you are dealing with completely damaged threads, you may need to drill out the hole and re-tap it for a larger bolt. This will require a larger tap and a new bolt that matches the new size. Alternatively, you can fill the hole and re-tap it.
It's important to note that taps are used to create new threads, not to clean up damaged threads. For cleaning up damaged threads, you may want to consider using a thread chaser or a rethreading tap and die that is specifically designed for thread repair.
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Drilling to a larger size
Once the hole has been enlarged, threads can then be cut into the new hole using a tap and die set. A tap is a shaft of metal that cuts threads into a hole, and a die is used to cut threads onto a shaft, like a bolt. When using a tap, it is important to use cutting oil to lubricate the process. The tap should be turned a half turn and then backed off by a quarter turn. This process can be done by hand or with a tap screwdriver, also known as a "tritap," which typically comes in sizes 6-32, 8-32, and 10-32.
After the new threads have been cut, a larger diameter bolt can be used to secure the connection. It is important to choose a bolt that is large enough to grip the material securely but not so large that it becomes incompatible with surrounding components. This method of drilling to a larger size and rethreading is a common and effective way to repair stripped threads in plastic bolt holes.
It is worth noting that there are alternative methods to rethreading a plastic bolt hole without drilling to a larger size. One option is to use a self-tapping screw that is slightly larger than the current screw. This option may not be as aesthetically pleasing but can be a cost-effective solution. Another alternative is to use a threaded rivet, although this may require additional tools and clearance.
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Using a thread repair kit
Thread repair kits are a cost-effective way to repair a tapped hole without removing the part containing the damage. They typically consist of a drill bit, tapping tool, insertion tool, and threaded insert. An air or electric drill and a tap wrench are also required but are not usually included in the kit.
One popular type of insert is the Helicoil® insert, which has a tightly wound spring design with a diamond cross-section. This type of insert is simple to install and relatively low-cost, but may not be suitable for screws or bolts that will be under constant load, high temperatures, or high torque.
Another option is to use a ProMAXX® thread repair kit with ProMAXX® ProSerts™. This kit provides stronger holding power than the original factory hole and requires no additional steps when machining to accommodate the ProSert™. Simply drill the hole, apply Loctite®, and twist in the insert using the included ProMAXX insert tool.
When repairing stripped threads, it is important to clean out the hole and measure it to determine if a new pilot hole needs to be drilled. The insert can then be placed into the tapped hole using an optional drive tool to create a strong fastening. After repairing the stripped threads, use new hardware for your fastenings to ensure superior grip strength.
Additionally, if you are repairing a bolt, you can mount it in a vise or chuck to keep it secure. With the correct pitch facing the screw, file at the same angle as the threads. If the thread damage is minimal, you may be able to reform the threads by running a nut up and down them, but this runs the risk of the nut fusing to the thread.
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Soldering
While soldering irons are mentioned as a potential solution for repairing stripped threads in plastic, the sources do not provide detailed instructions on how to do this. However, the general process of rethreading a plastic bolt hole involves the following steps:
- Clean out the hole and measure it to determine if a new pilot hole needs to be drilled.
- If the hole is too damaged, you can drill and tap it to a larger size, using a larger bolt.
- Alternatively, you can use a thread-cutting tool called a tap to rethread the hole. Use lots of oil and turn the tap a half turn, then back it off a quarter turn.
- If you cannot use a larger screw or bolt, you can use a product called Helicoil, which is a helical coil insert used for stripped thread repair.
- Another option is to coat the screw or bolt threads lightly with grease, so the threads are still prominent, and then fill the hole with an epoxy of your choosing. Put the bolt back into the hole and let the epoxy set overnight. The epoxy will take the shape of the bolt threads, creating a perfectly threaded hole.
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Using a thread restoration kit
Thread repair kits have become increasingly popular due to supply chain shortages and the rising cost of replacement parts. They are a cost-effective way to repair damaged threads in a tapped hole without removing the part or parts containing the damage.
Thread repair kits are typically made up of a drill bit, tapping tool, insertion tool, and threaded insert. An air or electric-powered drill and a tap wrench are also required but are not usually included in the kit.
To use a thread repair kit, start by finding the thread count or pitch. Clean out the hole and measure it to determine whether a new pilot hole needs to be drilled. If the threads are badly damaged, you may need to drill out the hole to the next size bolt size. You can then use the tapping tool to cut new threads into the hole. When using the tap, use lots of oil and turn it a half turn, then back it off a quarter turn. Finally, use the insertion tool to screw the threaded insert into the hole.
It is important to work slowly and carefully when rethreading a bolt hole to avoid damaging the bolt.
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Frequently asked questions
The easiest way to rethread a plastic bolt hole is to use grease, Vaseline, or epoxy. Coat the bolt threads lightly with grease or Vaseline so the threads are still prominent, then fill the hole with epoxy. Put the bolt back into the hole and let the epoxy set up overnight.
A tap is a shaft of metal that will cut threads into a hole. You can use a tap and die set to rethread a bolt hole. If the threads are badly damaged, you may need to use a tap to drill out the hole to the next size bolt.
A die cuts threads onto a shaft, like a bolt. You can use a tap and die set to rethread a bolt hole.
You can repair stripped threads in plastic using a plastic welding kit, a soldering iron kit, or a thread restoration kit.
A thread restoration kit can be used to restore stripped threads. A full set will include both metric and SAE thread counts. To use it, start by finding the thread count (SAE) or pitch (metric) and use the tap or die to reshape the threads to their original condition.
