What's new
What's new

Tap cutting over size

lol? Helicoils are bad? Helicoils are one of the most awesome things around. I wish I invented that.

Don't think of it as a crappy repair thing. Sometimes they are purposely designated and engineered into a product. Excellent for aluminum components because you can put in steel insert threads that last a long time, with the lightweight aluminum body. Thats why the aerospace industry uses it, spec-ed some of the time and not as a repair item.
 
Some good info here, thanks all for chipping in. I ended up thread milling. Have adjusted D wear .0004 after 120 holes, god I love aluminum. Next time will look a little harder for a better tap and try that again. Better off anyway, since I would have had to finish by hand with a tap ground to have no lead threads. Yea let's put a max hole Dia depth of 0.430 with a min full tap depth of 0.400. Greeeaaat, thanks engineer.
 
You better warn the entire aerospace industry that helicoils are bad!! You might save millions of lives!! :rolleyes5:

The entire aerospace industry? I find it hard to believe that the same people calling out class 3 J threads, just slap a helicoil in there. Yea, they might possibly use one here and there under the table but, seriously. The helicoil is a quick fix for the guy without proper tools.
 
OK Thats just completely untrue. As already stated, helicoil are often specifically called for in a design. Helicoil is not always used in the perspective of fixing broken threads. In fact, that is the very reason why they are used. Why did those cheap threads get striped? Because they are crappy low toughness and resilience materials that make up the thread. The reason why helicoils are used is the threads are built to last many cycles of use that exceed the expected service time of the product. They are very much superior than normal threads in certain applications.

Imagine you are designing an aluminum cover on a jet that is often serviced by ground personnel. So lots of bolt and unbolt cycles. These are shop guys who will overtorque this stuff too. You need aluminum for its strength to weight, yet using tapped aluminum threads will not survive repeated cycling. But with a steel helicoil insert, that part will now last millions of cycles. Now you have an aluminum structure with threads that last.
 
The entire aerospace industry? I find it hard to believe that the same people calling out class 3 J threads, just slap a helicoil in there. Yea, they might possibly use one here and there under the table but, seriously. The helicoil is a quick fix for the guy without proper tools.

Its more than obvious you have NEVER even seen an aerospace part.....
 
I'm going to give Jlaugh the benefit of the doubt here. Do you work in a job shop or repair place? Many moons ago when I was in a job shop the helicoil was just a repair type item, we seldom saw it specced on a print, but then again we weren't doing aerospace at that place. As to being embarrassed about it in your box ... :rolleyes5: I remember a journeyman back when I started my apprenticeship saying the same thing about the easy out tools too.... now that I look back I see alot of stuff he said/did makes me think he was an uppity "I never make mistakes" kind of guy. Now that I do some 'other' work I see that helicoils are in fact very widely used from the design up as the other guys said. Why do you think they make helicoils on rolls and pneumatic installation tools, for the super fast automated repairs? :D
 
helicoils are standard items used in softer metal like aluminum to strengthen a thread area especially if part is not threaded very deep. i have seen them on drawings for new parts plenty of times
.
i have often seen it on drawings even on cast iron parts to strengthen thread area by spreading the thread load to od of helicoil which is bigger diameter it ultimately gives greater screw holding strength.
 
I guess I don't have the expierience I thought I did. No. I don't work in a job shop. Yes, my view of helicoils was a crappy, cobble job of a repair item. Now that my erronous thinking has been pointed out, I can see how a helicoil could be very useful in large aluminum (and other soft metal) aerospace parts. I'm very much humbled by the communities' education. I'm quickly learning inside the industry of machining there is a wider diversity than I previously thought.

JMC, You would be suprised at the stuff I make, as I'm sure I would be just as amazed at the stuff you make.

cncdumm, thanks for the education.

Larry Dickman what do yall use on the finish passes for your Inconel parts. We are currently having issues with the finish quality on an Elgiloy medical part.
 
I guess I don't have the expierience I thought I did. No. I don't work in a job shop. Yes, my view of helicoils was a crappy, cobble job of a repair item. Now that my erronous thinking has been pointed out, I can see how a helicoil could be very useful in large aluminum (and other soft metal) aerospace parts. I'm very much humbled by the communities' education. I'm quickly learning inside the industry of machining there is a wider diversity than I previously thought.

JMC, You would be suprised at the stuff I make, as I'm sure I would be just as amazed at the stuff you make.

cncdumm, thanks for the education.

Larry Dickman what do yall use on the finish passes for your Inconel parts. We are currently having issues with the finish quality on an Elgiloy medical part.

Well said Jlaugh. It takes a certain someone to admit when they are wrong (no matter what the cause). Bravo dude!
 
Larry Dickman what do yall use on the finish passes for your Inconel parts. We are currently having issues with the finish quality on an Elgiloy medical part.

You mean for the threads, or on the part in general? For cut threads I use OSG VC-10 taps, or Micro-100 threadmills for milled threads. For milling, I use either Data Flute or Gaar 5 fluters
 
Rerally

I'm aware that taps come in different tolerance limits. I assumed, maybe mistakenly, that a tap to install a helicoil was entirely outside of the standard oversizing categories. Helicoil's are one of those tools I would be embarrassed to have in my box, comparable to easy outs. I have no expierience with them and do not care to. When I hear that a tap is of the brand helicoil, it makes me assume that it is for a helicoil. Although, if helicoil has the machinery to produce taps to allow the use of their product it would only make financial sense to produce taps in the standard size range as well. I am curious of if they do or not.

I have no expierience with them and do not care to. maybe that is why you do not understand them, it is very common to use them many many parts use them andhave used them for years. I am sure Helicoil does not make their own taps but there are companies out there capable of making specials I have had many made in the past.
 
I'm not a machinist. I retired from an engineering job in the semiconductor equipment biz that put me close to real machinists often enough to have a lot of respect for the breed. I never want to stop learning and got a bunch of good info from this thread.
What I'd suggest here is that when all else fails try an asymmetrical approach to the solution. There are plenty of ways for the smart design engineer to get around the wet dreams of some ISO bureaucrat half a world away and at the same time make a genuine improvement in quality (whatever that is; and for anybody who wants to get into that please lead us to the appropriate forum)
That last employer of mine usually used helicoils (One old German engineer whose designs always worked insisted on Keenserts and nobody was ready to argue with him) in aluminum vacuum chamber parts outside the vacuum area (Inside they create virtual leaks.) Best design practice was to only specify the Helicoil's type and installed thread, its length and the maximum tap drill depth from the datum that was the most truly functional. The machine shop installed the helicoils and then cleaned and packaged the parts for clean room assembly. (an expensive process) The field service guys were big fans of thread inserts. For ISO type quality control the best answer for the machine shop would be to get a written statement from the insert manufacturer supporting any deviation from their recommended installation practice. ......... Ed Weldon
 
I do not do machining for a living, this is just my hobby. But I am a mechanical engineer as well. Years ago I used to work for a military supplier, producing surface fighting and supporting vehicles. Absolute majority of them were constructed of aluminum alloy. Most of the threaded holes were inserted by design to make them stronger and more resistant to damage. Guess what, none of the inserts were of a Helicoil type. Some of them were Keeinserts, some were other types but no Helicoils. At that time I did not know why it is done this way.

Recently I had to use pretty big Helicoils (1.25" diameter thread) to repair damaged threads in the very expensive casting. The casting material was not aluminum, but steel, so it can make a difference. The repair went very well and casting was assembled into the compressor, but upon disassembly it was discovered that most Helicoils were pulled out by the screws a turn or two. I have to admit the screws were torqued to about 800 ft-lbs. When Helicoil tang is broken out, there is no easy way to wind it back into the hole. So we replaced the inserts. The subsequent disassembly caused the same problem with Helicoil pullout. We did everything we could trying to immobilize the inserts including welding at the top thread and permanent Loctite. Nothing worked...
Helicoil technical support is clueless as to what can be done to make it work. Obviously there will be no more Helicoils for me in a similar application.
I thought it would be useful to see this subject from the user's prospective...

Mike
 
Good thread I like taps especially when they behave by cutting right and do not break. I check for runout and try to think about the right tap for the application. Whether or not to use coolant or molly dee or whatever tapping fluid is also important. Yet the basics of good spot drill good drill (that drills round and on size and being the correct drill size for the tap) and then the right kind of tap.


I personally do not like using two fluted taps much at all which is my preference. Sometimes taps will cut under or over depending upon the material. I have also had this problem if the program has the thread pitch feed slightly off. That has happened a few times.

There is plenty to read about proper tapping and if you do a little research you can quickly figure it out. Most is just basic. Reading your post I was not sure if you were Tapping or thread milling. Thread milling is much better to me especially when cutting tapered threads in a mill. That can't be beat. Many outfits do not do this because they feel the tooling is too expensive. I disagree yet will do it their way.

If you are thread milling and it is oversize it is a programming issue. If you have comp on the diameter and the program picks it up and activates it then it is as easy as making a offset input. Also check for run out on the tools. Make sure to take your tools out and to inspect your collets to be sure there is not a chip inbedded there on the collet or the taper inside the tool holder or even the taper in the spindle.

Always one hundred percent of the time you must be sure every chip is cleaned out of any tool holder always. If you do this you rise one position higher to being a great Machinist.
 
I would stay away from form taps for Helicoils. Is it technically okay to use them Yes. But
you will have a lot more problems installing the coils. If you ever have looked at the profile of a roll formed thread
you will understand why they cause problems. The ridge that it creates causes the coils to hang up occasionally.
If you can't get cut taps to work I would thread mill. You have total control over size.
As far as brands go if you ever use Kato tang less coils you will never go back to Heli-Coil brand.
I have installed thousands in my career and the Kato system kicks Helicoils butt hand down.
 
Alright, so I'm going to end up thread milling to hold pitch diameter but figured this could be a helpful thread depending on the answers. Situation I have is as follows: Material is 6061 aluminum. Thread call out is 10-32 3B, must tap for thread insert. Pitch spec is 0.210-0.212. Tapping 0.400 deep. Using a H2 tap. After tapping, the no-go flies in. Rigid tapping, tried a "floating" tap head as well. Tried putting in a few lead threads in machine then finish by hand tapping, still oversized. Any tricks out there to make a tap cut to size? Thanks all.
Is your threaded insert the same class fit as your tap? Usually mass produced inserts are a class 2 or, general fit. This may explain why it flies through your class 3 hole. Use the 3 wire measurement method or optical comparator to verify the class fit of your inserts.
Thread milling will give you maximum control for a proper fit, however.
 
I do not do machining for a living, this is just my hobby. But I am a mechanical engineer as well. Years ago I used to work for a military supplier, producing surface fighting and supporting vehicles. Absolute majority of them were constructed of aluminum alloy. Most of the threaded holes were inserted by design to make them stronger and more resistant to damage. Guess what, none of the inserts were of a Helicoil type. Some of them were Keeinserts, some were other types but no Helicoils. At that time I did not know why it is done this way.

Recently I had to use pretty big Helicoils (1.25" diameter thread) to repair damaged threads in the very expensive casting. The casting material was not aluminum, but steel, so it can make a difference. The repair went very well and casting was assembled into the compressor, but upon disassembly it was discovered that most Helicoils were pulled out by the screws a turn or two. I have to admit the screws were torqued to about 800 ft-lbs. When Helicoil tang is broken out, there is no easy way to wind it back into the hole. So we replaced the inserts. The subsequent disassembly caused the same problem with Helicoil pullout. We did everything we could trying to immobilize the inserts including welding at the top thread and permanent Loctite. Nothing worked...
Helicoil technical support is clueless as to what can be done to make it work. Obviously there will be no more Helicoils for me in a similar application.
I thought it would be useful to see this subject from the user's prospective...

Mike

There are thread inserts that are designed to lock in place or be locked in place during installation. There is also an "old school" machining technique of "staking" the hole that can help lock inserts in place. Finally, in some applications, it is acceptable to use thread locking compound during the installation of the thread inserts.

Helicoil is just one brand/type of thread insert available. Its name is very popular because it was marketed to the general public. The brand name of the product became the substitute for the actual name of the item, similar to Xerox for photocopies and photocopiers or Crescent for an adjustable jaw wrench. While the beginning tapped hole size does effect the size of the installed thread insert, the installed size of the thread insert is the more critical dimension.
 








 
Back
Top