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post #1 of 23 (permalink) Old 12-13-2009, 02:21 PM Thread Starter
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Angry Tips for Tapping Threads?

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!

C
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post #2 of 23 (permalink) Old 12-13-2009, 03:04 PM
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Quote:
Originally Posted by Crobins365 View Post
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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Last edited by flitecontrol; 12-13-2009 at 03:07 PM.
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post #3 of 23 (permalink) Old 12-13-2009, 03:07 PM
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Quote:
Originally Posted by Crobins365 View Post
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. No! You need control and would lose it using a power tool....when cutting new threads, you turn/cut clockwise half turn then counter clockwise to clear cutting grooves then repeat 'til finished. That would be hard to do with a power tool.
2. What is the best lubricant to use when tapping? PB Blaster? Something else? Oil...preferably cutting oil
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? No...use helicoils....google it to learn more.
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. Yes, tap & bolt are same size.

Thanks in advance!
I'm sure Lance or others have more precise responses....above are my thoughts
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post #4 of 23 (permalink) Old 12-13-2009, 03:19 PM Thread Starter
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Thanks, everyone, for the quick replies. Here's a nice link I found for using helicoils: http://www.roadstarmagazine.com/modu...rticle&sid=233

Still wasn't sure what exactly the "coil" part was, but I found a few links elsewhere on the web. If I'm not mistaken, it looks like the coils go into the new hole and serve as the threads for the bolt?

C
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post #5 of 23 (permalink) Old 12-13-2009, 03:21 PM
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Yes.

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post #6 of 23 (permalink) Old 12-13-2009, 04:14 PM
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When tapping the threads for the helicoil or new threads. Once the tap has gone in one full turn of cutting. turn 1/2 turn in then 1/4 turn back and continue this way especially in non ferrous metals like aluminum and brass. This will keep the threads from tearing and break off the cuttings to clear the cut as you go. Use plenty of light oil to lube the tap and flush out some of the cuttings. Yes the helicoil becomes a thread spacer once installed. There are special taps made for use with an electric drill. For most of our applications I do not recommend their use as the cut would be too fast. Another option would be inserts if the hole has been fubared too much for helicoils.

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post #7 of 23 (permalink) Old 12-13-2009, 04:37 PM
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When getting the taps, be sure you have the right size, as there are taps made to tap the holes over-sized.
These are designated by an 'H' number... i.e. 1/4-20 H3.
H3 is usually nominal size and H4 and up are over-size.

A great oil to use is called Tapmagic. They have one formula for aluminum one for steel, one for universal use etc.



And Antiq is spot on with his description of how to tap!!
The biggest thing to remember is TAKE YOUR TIME!! If the tap starts to be really hard to turn, you went too far before backing it out some.
If it's a deep hole, about every 1/4 of depth, completely remove the tap to clean out the hole and tap.


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post #8 of 23 (permalink) Old 12-13-2009, 06:42 PM
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Both my father and older brother were machinists so growing up in that household I was constantly told 'the right way to do it'. Having a lathe and a mill in the shop was nice too (wish I had them now).

All good advice above. I'd say go slow with our soft metals too. The cutting oil is worth it and you can filter it out and reuse it if you catch it under your work area. A blow gun on a compressor works great to keep the tap and threads clean when cutting. Did I say go slow?

Good luck,

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post #9 of 23 (permalink) Old 12-13-2009, 07:45 PM Thread Starter
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I think at this point I will be learning how to install helicoils. lol What a mess. I'm great with using a dye on the external threads, but the internal ones are new to me. Maybe I can go mess something else up so I can try again!

C
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post #10 of 23 (permalink) Old 12-13-2009, 08:31 PM
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Quote:
Originally Posted by Crobins365 View Post
I think at this point I will be learning how to install helicoils. lol What a mess. I'm great with using a dye on the external threads, but the internal ones are new to me. Maybe I can go mess something else up so I can try again!
the key is holding the tap straight ... helicoil is a lil easier but its also easier to screw up the helicoil u get a fresh slate after u drill it out to acccept the coil... take your time and and keep things at 90 degrees ... good luck !!!



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