Can someone offer some general Do's and Don'ts for tapping threads (internal)? I just picked up a tap set to clean up some master cylinder threads, but have already made a mess of things.
Here are some questions:
1. Can I use an electric drill to tap threads? I'm guessing "no" but I'd like to hear it (and why)from someone who knows these things.
2. What is the best lubricant to use when tapping? PB Blaster? Something else?
3. If I fu-bar my threads, can I plug the hole with JB Weld and try it again? If not JB, is there something else that's workable?
4. I'm assuming that the "proper tap size" is equivalent to the bolt that would go in the hole - e.g., if the bolt is a 5mm x .80, I need a tap that's labeled as such. I'm reading this little Sears guide and it's suggesting...I'm not sure what, but I want to make sure there's no trick to selecting the right tap.
Thanks in advance!
1. No. The electric drill will probably turn the tap too fast, either causing it to wallow out the hole or possibly snap the tap off. The tap is hardened steel, but is comparitively brittle. The tap set should come with a T handle for turning the taps by hand once the hole has been drilled to the proper diameter. The T handle helps keep the tap from getting off vertical. An adjustable wrench can be used to turn the tap, but it increases the chances of not tapping the threads straight.
2. They make (thread) cutting oil, but almost any fluid will suffice when cutting threads by hand. I've used penetrating fluid, 3-in-1 oil, and automotive oil. Anything to make turning the tap and cutting the threads easier.
3. Not sure about JB Weld, but it might work if you can get all the oil out and the hole properly cleaned first. Brake or carb cleaner might work. They make a material you can mix, pour into the buggered hole, coat the bolt with a supplied releaser, and thread the bolt into the hole. Think you leave the bolt in until the product dries. Might be called ThreadRestorer or something like that. But you can only apply 80% of the recommended torque to threads treated with this product IIRC. Another alternative is go up one size in tap and bolt, if that is an option.
4. Yes, the tap and bolt need to be the same. As mentioned above, if starting from a solid block of metal, the thread hole needs to be drilled to a certain diameter. Not too small to allow the tap to work properly, and not so large that the threads on the bolt will not fully engage in the cut threads. The hole would need to be drilled square, which is difficult with a hand held drill.
Hope this helps.
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