Mark Simpson

Cleaning and Chasing Threads

Mark Simpson
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Duration:   3  mins

We’ve all been there, you’re assembling a project when suddenly you discover the thread inside the hole you are trying to insert the bolt into is either clogged with paint and debris or worse yet has been damaged. Naturally the best solution is to chase the threads with a tap, but sometimes you just don’t have a tap the right size and thread pitch to get the job done. But all is not lost and if you only need to chase one hole it’s seldom cost effective to run to the store searching for that one tap.

We join Mark Simpson in the shop to give us a quick solution on how to quickly modify a bolt to efficiently clean and restore threads. Simpson demonstrates how to use a hand held cut-off tool to modify a hardened bolt with slots to effectively clean threads. This process is often necessary when threads become worn, corroded, dirty or otherwise damaged, making it difficult to thread fasteners into them. He further adds, “this is not a replacement for quality tap and dies but rather a low cost quick way to keep your project moving forward”.

Tools and Materials

Bolt: You’ll need a hardened (grade 5 or better yet grade 8) bolt with the same thread size and pitch as the damaged threads you want to repair.

Lubricating Oil: To reduce friction and ease the threading process.

Wrenches or Sockets: To turn the bolt.

Cleaning Tools: Such as a wire brush or a toothbrush for removing debris and rust from the damaged threads.

Safety Gear: Always wear safety glasses and gloves when working with tools.

Steps to Modify a Bolt to Clean and Chase Threads

Select and Modify the Appropriate Bolt: Choose a hardened bolt with the same thread size and pitch as the damaged threads. The diameter and thread pitch must match to ensure a proper fit. modify the as seen in the video by grinding an edged groove in the length of the bolt on 1-3 sides (much like the flutes in a tap). Also modify the end bolt with a taper to make starting the bolt easier.

Clean the Damaged Threads: Use a wire brush or a toothbrush to clean the damaged threads on the workpiece or in the threaded hole. Remove any dirt, debris, rust, or old thread-locking compounds.

Apply Lubricating Oil: Apply lubricating oil to the damaged threads to reduce friction and make the threading process smoother.

Insert and Turn the Bolt: Thread the selected bolt into the damaged threads by turning it counterclockwise then counter clockwise in several steps, again using the same process as you would use a tap. Because the bolt lacks the hardness of a tap, taking shorter steps can help ensure success. Consider turning in one 1/4 turn and turning out 1/8 turn and repeat. This action will help remove any remaining debris and rust while also reshaping and cleaning the threads. Apply gentle and even pressure, and avoid forcing it.

Inspect the Threads: Periodically inspect the threads for signs of improvement. If you encounter resistance or difficulties, back the bolt out a bit and then turn it back in. Continue this process until the threads are clean and functional.

Remove the Bolt: Once you’re satisfied with the cleaned threads..

Reassemble: You can now reassemble your fastener, such as a nut or another bolt, onto the cleaned and chased threads. The restored threads should provide a secure and functional connection.

In summary, modifying a bolt to clean and chase threads is a practical and cost-effective way to repair damaged threads, improving the functionality and longevity of threaded connections.

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