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Helicoil jam on screw

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dchu129

Mechanical
Jan 30, 2012
18
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

 
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i'll assume the hardware is appropriate.

does it jam immediately (as the screw starts to engage the heli-coil) or later ?
 
It gets tight immediately, but as I turn deeper, it will eventually be stuck halfway through the screw
 
The Helicoil threads are tapped incorrectly. Inspect them for correct size and no taper.

What is the screw material?

Ted
 
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?

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

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

From this site -

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.*
 
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.
 
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