UNJ threads

[Mgrenier]

Hello all,

 

We have over 800 .750-16UNJF STI and 5/16-24UNJF STI holes to machine in nitronic 50 material. We called Emuge and asked them for UNJF taps and they told us that these kind of taps do not exist. They told us tu use standard UNF taps but to drill the hole bigger to assure the clearance of the bolt. Is this true or are there UNJF taps out there on the matket?

 

Also, How big should be the tap drill?

 

Anybody can give me some pointers on that, we are king of lost here.

 

Thanks in advance,

[crazy^millman]

You might try Widell they will make just about anything you want. I also might look at a thread mill if doing that many in that Material.

 

HTH

 

This from the Machinist Handbook 24th Edition Page 1639.

quote:

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This British Standard (B.S. 4084:1978) aries from a request originating from within the British aircraft industry and is based upon specifications for Unified screw threads and American Military Standard MIL-S-8879

 

These UNJ threads, Having ab enlarged root radius, were introduced for applications requiring high fatiuge strength where working stress levles are high, in order to minimize size and weight, as in aricraft engines, airframes, missles, space vechiles and similar desgins where size and weight are critical. To meet these requirements, the root radius of external Unified threads is controlled between appreciably enlarged limits, the minor diameter of the mating internal threads being appropriately increased to insure the neccsarry clearence. The requiremtn for high strengeth is futhers met by restricting the tolerances for the UNJ threads to the highest classes, Classes 3A and 3B, of Unified screw threads.

---

HTH

 

Oh yeah thank you for bringing that up learned something there and also would seriously look at millthreading these parts. Trying to tap a Class 3 fit is a %%^%%^$. It is hard enough trying to thread profile them on a CNC lathe much less try to tap them and hold it.

 

[ 05-25-2004, 12:30 PM: Message edited by: Millman^Crazy ]

[McRae]

I hope that you haven't cut anything yet... The STI means "Screw Thread Insert" similar to a Helicoil - and this is something that you will have to find from the manufacturer of the the insert. Talk to the customer and make sure you do it right.

[Mgrenier]

Andrew,

 

I know what the STI means, I was just wondering if UNJF taps existed and if there was a chart of somesort for the tap drill size.

 

quote:

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Talk to the customer and make sure you do it right.

---

Yeah but that implies that the custommer knows what he wants. Which, of course, is not the case.

 

Keep the suggestions coming, please......

 

Have a nice day,

[Mike Whitten CAD/CAM Contractors]

Marting,

 

Emuge is correct. UNJ is a spec for modified root. It has more material in the shatrp V area as the bottom of the thread on the male thread only. This is why the female thread can be made with the normal tap. You must have a bigger TDS in order to clear the Root of the male thread.

 

UNJ is and areospace thing becasue it adds strength to the fasteners.

 

Look in machinery handbook

 

I have a hot job and a machine sitting. I will look for the spec at lunch, in about 1 hour.

 

Mike

[Mike Whitten CAD/CAM Contractors]

Oh yea, I have to think about the STI thing at lunch

 

Mike

[CR]

Martin

Andrew is right you need to use a 3/4-16 STI tap(also called helicoil tap)(of course is not the regular 3/4-16 tap)

you need a tapped hole for a 3/4/16 helicoil insert, some time later somebody has to insert the 800 helicoil inserts into the tapped holes once the insert is assembled, it accomodates any standart male threaded bold or screw (MIL-S-7742 and MIL-S-8879 controlled radius)

Need to know what type of insert will be using.

the class of fit goes by the letter "H"

[Mike Whitten CAD/CAM Contractors]

Marting,

 

I was slow on this one,

 

The other guys already had it for you.

 

Did you get the STI thing figured out yet?

 

I am guessing they just have special inserts for this.

 

Thanks

[Mgrenier]

quote:

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I am guessing they just have special inserts for this.

---

That is the thing, the custommer calls for a standard insert from the helicoil catalog. That only makes us more confused. The only thing that the custommer tells us in "make UNJF threads".

 

Thanks for your input and keep em coming if you have anything else.

 

Have a nice day,

[Mike Whitten CAD/CAM Contractors]

Call Heli-coil

 

Here is the number for Heli-coil Canada:

 

514-333-8080

[McRae]

http://www.i-logic.com/pwa355/page28.htm

http://www.panamericantool.com/family.cfm?...erospace%20Taps

http://www.spstech.com/aero/prod_lit/insert_brochure.pdf

 

Clearly this is an aerospace part and the implication that your customer doesn't know what they want simply makes we want to walk...

 

I suggest that the Insert will contain the proper UNJF thread and the onus on you will be to provide the thread for the insert only (which for some inserts can be unique on its own.

 

Tap Drill Chart - Titex (a Sandvik Company)

http://www.titex.com/SANDVIK/3432/Internet...ochtabellen.pdf

[stan z]

who has thread gage for this???????????

HA HA

[gcode]

quote:

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who has thread gage for this

---

You can buy STI thread gages.

The insert will take the characteristics of the threaded hole.

If your tapped hole was oversized, the installed

insert's pitch diameter will be oversized as well.

I've never seen STI inserts installed in nasty

stuff like Nitronic 50 before.

[crazy^millman]

Again Widell makes Thread gauges also here is their Link: Widell Tap Company

 

Florida Boys have all kind of Contacts.

 

HTH

[Mgrenier]

Andrew,

 

Thanks for the links, that proved to be very usefull. I also want to thank everyone for their input. I will follow all that info to the client so that he can tell us what he really wants.

 

Have a nice day,

[jplecan]

Hello Martin,

Kennametal makes a good tap in their series K-NI STI for the 5/16-24 STI thread. I agree with everyone about the J thread distiction, use a regular UNF STI tap, but the minor dia of the hole is larger. Kennametal doesn't show a 3/4-16 STI tap in that series, would probably be better to generate with a thread mill.

Jim