Helicoil jam on screw

[dchu129]

Having problem with screw jam when installing into helicoil and cannot be turn anymore.

When I force the jammed screw out, the helicoil will be remove from its insert thread.


Here are the spec

Screw: .190-32 UNJF-3A Perfect Thread
Helicoil: .190-32 Fine Thread
Helicoil Insert Thread: .190-32 UNF-3B

 

[rb1957]

i'll assume the hardware is appropriate.

does it jam immediately (as the screw starts to engage the heli-coil) or later ?

 

[dchu129]

It gets tight immediately, but as I turn deeper, it will eventually be stuck halfway through the screw

 

[hydtools]

The Helicoil threads are tapped incorrectly. Inspect them for correct size and no taper.

What is the screw material?

Ted

 

[dchu129]

You mean the helicoil itself or the insert thread for helicoil?

Screw is of 15-5 stainless steel

The helicoil is also coated with dry film lube, could the build up from the dry film cause the problem too?

 

[rb1957]

the way i read the helicoil product guide your helicoil should be !!91-3C?###, where
!! should be 35, T1 or 11 depending on type
? should be N or blank
### is the length

 

[Tunalover]

You might want to check that the UNJF and UNF threads are compatible at all. If I remember right, the UNJF threads have chamfered threads while the UNF have rounded threads. Is there a conflict?


Tunalover

 

[hydtools]

Tapered or undersize, the thread for the insert. Not the insert.

Ted

 

[Tmoose]

I think Tunalover's concerns are correct. Although the UNJ screw has the rounded roots.

From this site -

http://www.ring-plug-thread-gages.com/ti-UNJ-vs-UN.htm

PRODUCT COMPATIBILITY
UN Bolt into UN Nut = No problems.
UNJ Bolt into UNJ Nut = No problems.
UN Bolt into UNJ Nut = No assembly problems. Functional problems are possible.*
UNJ Bolt into UN Nut = In most cases an interference fit at the thread minor diameter. Functional problems are also possible.*​

 

[zekeman]

dchu129 ,

Why don't you call up the Helicoil Corp and get the answer.
Since they have been in business at least 70 years maybe they know a little bit about their product and perhaps can help you
better.