Repairing a damaged thread bolt normally takes some experience. Some methods are also better, and some thread repairs are easier than others. This is a good thing, because bolts have different applications, and some bolt applications are more intense than the rest. Using the best method means that you can repair the damaged bolt at your comfort level.
Ideally, however, compromising the strength of the bolt by shaving off too much steel is a no-no. Every bolt follows specifications and standards set by industry experts. While all thread repair methods can get the job done if properly performed, your high priority should be about keeping the bolt’s strength.
So, considering how to repair the bolt thread damage and apply the best method means some factors have to be considered before repairing the thread bolt.
Joint Stability and Bolts
The bolt together with the nut and surrounding components exerts a clamping force that compresses the entire joint. The joint is important to keep the structure of the object steady, especially given that there are many mechanical components. We refer to this as ‘stiffness of the bolt’ and ‘balance of joint’.
Imagine a joint assembly on a kitchen table where the screw is not inserted properly. What happens? The whole table is not stiff or balanced. This means you have to re-do it, or if the screws have problems, would need to be replaced or fixed. This is because the joints are not ‘compressed’ enough, and do not clamp the bolt.
Clamping Force and Bolts
In order for the bolt to balance the joint, the bolts have to have an amount of force, too. This is what is referred to as ‘pre-load‘. The pre-load must be able to carry the force from the load, so that the bolt will not succumb under the load. Think of having a poor back–if you have a poor back it’s hard to keep your balance. That’s because your spine is acting like the bolt which carries the clamp of the spine components and supports the rest of your body.
Pre-load develops because the bolt is inserted and it is screwed into the joint. Bolts are precision tools and machines which require precision work, too. The pre-load comes from the torque of the bolt when it is stretched and rotated. The torque is the force which is the amount of rotation in an object.
Usually, the calculations are that 85% to 90% of the tension load is exerted on the bolt. The whole tension cannot exceed the performance of the bolt, which would affect the stability of the structure.
The geometry of the threads, the diameter and size of the bolt, and friction all determine the pre-load on the bolt.
The clamping force depends on the threads as well. This is where the use of the right methods of repairing bolts come in. Using the right tools are important, too. Ensuring that the components of the bolt and the joint will work together depends on the threads performing well.
High and Low Torque Applications
When you encounter a stripped thread bolt for repair work, consider if your bolt is under high or low torque. High torque applications require precision work, because the torque of the bolt needs to be at the level where it can withstand the load. Otherwise, there won’t be enough clamp on the joint, and the bolt might be a weakness on the structure. Furthermore, if the repair work is poorly done, this means rework, and also a possibility that the bolt will fail.
Low-torque applications, on the other hand, can work with bolt repair methods that are less sensitive. Depending on your requirements, choose the method best for your project.
Below are some of the general applications with high and low torque.
High torque applications:
- Dynamic and heavy loads
Low torque applications:
- RV Water Heater
- Fire Hydrant
- Plastic caps
Usually, low torque applications are for household usage. These are items or appliances which do not necessarily go through too much vibration, weight, or duress.
Repairing your Damaged Thread Bolt
Here are some of the methods which depend on the torque application:
- Tap and Dies. This can give you the benefit of using a larger bolt, if you need to install a new one. Drill into the hole, and make sure to use the correct drillbit. As mentioned, the key thing is to maintain the balance of the joint. Tapping too much metal might affect the overall strength of the clamp components. You also run the risk of not doing it right the first time, and the threads might not match with the bolt, or that the threads might get damaged with the excessive use of the dies.
- Epoxy. This is recommended only for low-torque applications. Using epoxy, you can contour the inner threads using the epoxy on the bolt and the hole. Make sure to use a release agent for easy release of the bolt. This can work fine for household usage.
- Thread Files. Recommended for low-torque applications, because this is time consuming for bolts with large diameters. No professional experience required, but you have to remember to use the correct size for the pitch or you’ll ruin the threads.
- Rotary Thread. Rotary thread can be used for both low torque and high torque applications. Using a precision spin, it can work with your bolts to repair all kinds of corroded, hardened, or damaged thread bolt. The strength of the bolt is also not compromised, as Rotary Thread works with a precision mechanism. It is accurate and easy to handle compared to a thread file. The following are the applications for Rotary Thread:
- DIY projects
- Home Improvement
- Farm & Ranch Projects
- Technical Projects
- Industrial Projects
Damaged thread bolts are some of the parts of the project that cannot be overlooked. When considering damaged bolt threads, keep in mind if it is in a heavy application or not. This way, you can decide which method to use. To simplify, you may use Rotary Thread which works and repairs any inch, metric, or pipe.