Thread Tapping Suggestions and Recommendations

[JETS 81 DMC]

Anyone use these thread forming chip free taps?

Sounds like this might be a better one to use from the description.

https://www.mcmaster.com/standard-ta...e03189k222zjbz

[Ethan Rode]

Taps are meant to cut threads, not necessarily restore them.

Since it's a blind hole, you'll need to evacuate the chips at least once during any thread cutting or restoring operation, otherwise the risk of binding the tap, or overloading the threads is high. No need for specialized taps, just good practices.

If the threads in the head are still intact, a thread chaser is the best option.

If the threads aren't intact, a HeliCoil, or other thread insert will need to be set. Time-Serts are an excellent option too, but require more base material to be removed, and the bolts should only be torqued 7 ft/lb.; well within the capability of a HeliCoil.

[David T]

Actually taps and dies are meant to "form" threads, cutting them is one way and rolling them is another. Cutting them is weaker than forming, you are cutting the grain structure, rolling induces compressive stress and is a much stronger way to form threads. For this application cutting is more than enough and yes, good practice is to stop and clear chips often during threading. If you allow too many chips to accumulate you will wind up tearing the threads out and breaking the tap. Two flute taps are not meant to be used in blind holes. They shoot the chips ahead of the tap so they should only be used in through holes so the chips can get out. You should also use cutting fluid to lubricate and cool as you tap. Doing this kind of repair work you should work slowly and carefully checking that you are perpendicular and backing the tap out often to check the threads and clear the chips. No need for a bottom tap, just make sure you go deep enough so the bolt or the insert doesn't "bottom out". Use Never Seize so this doesn't happen again. Because you have steel bolts in aluminum you get corrosion once the plating on the bolt corrodes. The bolts holding the intake manifold are at an awkward angle so you must check and double-check that you are drilling and tapping at the correct angle. Stick a bolt in a nearby cylinder bolt hole and use a square or protractor if necessary. Take your time, fixing a messed up job will take a LOT longer to fix than doing this slowly but right.

[DMC1890]

I cringe when I watch the guys on 'Forged in Fire' - they crank away on taps as if they were cranking on a can opener. Ditto to Bitsyncmaster and David T comments. Go a half turn in, then a quarter turn out, and back out the tap totally every couple of turns. Use cutting oil, or any kind of oil.

[David T]

Those guys on that program are blacksmiths whose specialty is knives. Watch a machinist, they know how to cut threads. With the right equipment you CAN blast threads, it is done all the time in mass production. You just aren't cutting a 75% or higher thread. You oversize the hole so you don't cut deep threads. A whole different story when doing repair work. It is all done by hand and not usually under fully controlled conditions. That is why I say go slowly and carefully, 1/2 turn at a time like you said and frequently removing the tap to clear the chips.

[mr_maxime]

I cringe when I watch the guys on 'Forged in Fire' - they crank away on taps as if they were cranking on a can opener. Ditto to Bitsyncmaster and David T comments. Go a half turn in, then a quarter turn out, and back out the tap totally every couple of turns. Use cutting oil, or any kind of oil.

I've seen some people at work do it with drills...

[Rich_NYS]

How's it going with this, Nick?

[AugustneverEnds]

How's it going with this, Nick?

Zero progress so far. Stupid work has kept my car out of commission since early September. I need to re-evaluate my priorities! Thanks for posting the video, I have been watching it in segments. I am going to a professional industrial supply store this afternoon to see their taps. If nothing looks good there I will buy from McMaster, trying to shop local if possible.

[Nicholas R]

I've had pretty good luck with mcmaster, however even those taps I've had teeth break off of. I've never broken one completely though. Locally I usually go for Irwin taps. They're not the best but I think they're still made in the US and much better than anything from HF. At Lowes they usually even come with the bit you need. I only use HF taps for chasing threads, and even then I'm weary.

I remember using helicoils on some of those M7 bolts with Cliff Schmucker years ago. The kit was great; came with the drill bit, tap, helicoil, and installation tool. Timeserts are also pretty great. Just be sure to use threadlocker on whatever you use.

Regarding milling and drilling with taps, you can definitely do that, HOWEVER, machine taps are different than hand taps/general taps and shouldn't be interchanged.

taps-four.jpg

In this photo, the two taps in the center of this photo are both machine taps. The spiral fluted one is for blind/bottoming holes so that the chips naturally are pulled up, and the one next to it is for through holes because the chamfered relief at the bottom pushes chips down and out the bottom of the hole. A hand tap in a mill is usually a recipe for a bad time. I've come close to this by accidentally grabbing the wrong tap on my mill and not realizing until it started binding in the hole.

Don't get me started on forged in fire. I love the show, but usually end up cringing every time I see one of them try to operate a mig welder or a hand tap...