helicoil fight

[Rooster]

Great stuff, Bob. It's good to hear this stuff from someone who REALLY knows, instead of talking out their ass.
Thanks for your input, I always pay attention when you speak.

[T. Cotten]

I'm sorry Mr. Cotten but you are incorrect, taps do not size the minor diameter. I am aware they do make a drill/ tap combination for production work but we are not talking that here. Even if what you are saying could be remotely correct, which it isn't, if you read post #3 you will see he took the lead off of the tap. So what you are saying is that from now on I do not need to use the correct size drill as stated in the machinery handbook or on any tap/drill chart hanging on every machine shop wall across the globe, this will be some sad news for the drill manufacturers. DCoul could also have a depth issue but why in the hell would you not make the minor diameter of the tap the correct size?

Please look at taps, Bob!

Please note the lead-in taper that that relieves and finishes the inside diameter of the hole, if the pilot hole is proper, or under-sized.

If your pilot drill is too big, it will indeed cut the inside diameter of the threads.

This is pretty basic, Bob!

[BigLakeBob]

Please look at taps, Bob!

Please note the lead-in taper that that relieves and finishes the inside diameter of the hole, if the pilot hole is proper, or under-sized.

If your pilot drill is too big, it will indeed cut the inside diameter of the threads.

This is pretty basic, Bob!

Pretty basic is that what your arrows point to is the lead to cut the threads not the minor diameter. Just like a drill usually has a 118* or 135* point or lead cutting angle, flat bottom drills don't cut like ones with the standard points. They make taper taps, plug and bottom taps which each has their purpose. And of course if the drill cuts oversize it would cut the minor diameter, that is why there is a tolerance on minor diameters. A standard tap cuts the threads NOT the minor diameter. Well, this afternoon I have to drill and tap 104 1/4-20 holes in H13 mold steel, I probably won't use your suggestion in drilling undersize and letting the tap size the hole. Complete BS! I'm done discussing this with you. DCoul good luck and please post your results with your fixed engine case.

[T. Cotten]

For those Folks who don't believe me,...

Drill a deep hole with the prescribed drill for your tap size, then feel its slop in the hole.
Then tap the hole, and inspect it again with the same bit.

....Cotten

[DCoul]

My tap didn't cut deep enough good to use the whole Helicoil insert. I then ground off the tip of the Helicoil so I could get it deeper in the hole which only bought me maybe another 1/8". I don't think I can get it deeper but I don't think I need to as it just holds the oil pumb to the bottom of the case with 4 1/4" bolts. I then cut a couple threads off the insert which worked on the first hole but not the next. My theory is, and this is a Helicoil rookie speaking here, that the tips of the threads in the tapped hole are too tall. I'll need to ream to take those off and re-tap. The depth of each thread is, I'm thinking, determined by the width of the tap, and since the hole is too small, the threads of the hole are too tall.
I appreciate you guys helping with this. If I had paid closer attention to the package, I obviously wouldn't have screwed this up. It says in Bold letter 1/4-24, smaller lettering below: Drill Size/Diam.Trou/Tamano de la broca: 17/64 (.2656). Sometimes I get in a hurry.

Details, details, details.

[larry]

Grinding the drillbit in this manner will prevent grabbing. Not as nice as a reamer but will work.

[BigLakeBob]

Good suggestion Larry, I was taught to do that when drilling brass.

[larry]

Brass and plastic.

[DCoul]

I can't quite tell what you did there Larry.What surface is ground? Is this is?661631.jpg Like the one on the right correct?

[T. Cotten]

Just web-search "drill bit angles", Folks!

Wikipedia has a handy chart for different materials, if you missed it in your highschool text book.

....Cotten
PS: I thought everybody had seen toys like these...

[DCoul]

I bought a Sawzall quite a few years ago and my wife says " don't you have enough tools..."? Uh, no.

[T. Cotten]

I bought a Sawzall quite a few years ago and my wife says " don't you have enough tools..."? Uh, no.

DCoul!

Next time, remind her that the most important tools are the ones that make more tools.

Hopefully, she will see the 'economics'.

...Cotten

[BigLakeBob]

I can't quite tell what you did there Larry.What surface is ground? Is this is?[ATTACH=CONFIG]20978[/ATTACH] Like the one on the right correct?

Not to speak for Larry which brought up the good point (no pun), the leading (or cutting) edge is dulled or given a negative rake. To explain negative and positive rake is easiest when thinking of a lathe tool, the cutting point is on center but the chip flow is either downward (positive) or upward (negative). It is the way the insert or cutting tool is positioned. With a drill the lead cutting edge is against the chip flow, I guess that is a way to explain it, so it doesn't dig or draw itself into the work piece. Larry, I didn't mean to answer for you and correct me if I'm wrong or if different from your knowledge.

[DCoul]

Like this?polyc6.jpg

[T. Cotten]

I don't want to speak for Larry either,...

And I couldn't copy his pic for an arrow either, so I have attached my own.

I hope I am correct that Larry wanted to illustrate a chip-breaker-grind shown on the right in my attachment upon a tortured Caterpillar bit.

Its ugly, probably hand-carved, but graphically demonstrates the technique.

....Cotten