thread class of heli-coil screw lock 1

[cervantes]

Hi all,

I was wondering - "standard" Heli-Coil insert thread class is defined at 6H tolerance

when we are talking about screw "lock" insert version - GO gauge does not pass, which is rather normal situation because it's tighter

I am wondering - how to verify if thread class in screw lock version is correct? (assuming it shall be also 6H or this assumption is wrong) ?

thanks in advance

 

[drawoh]

cervantes,

A locking helical thread insert has a coil bent into a hexagonal pattern that violates all the screw tolerances. The locking section does not comply with H6 or anything else. The rest of the insert might.

Any time I have specified locking helical thread inserts, everyone has hated me for it.

--
JHG

 

[pylfrm]

cervantes,

Standard practice is to inspect the threaded hole before installation of the insert. It shouldn't be necessary to gage the installed insert.

I believe HeliCoil recommends class 4H5H for screw-locking applications. Their catalog has more detailed information about tolerances and gaging.


pylfrm

 

[tbuelna]

I would agree with pylfrm's comment about only needing to gage the threaded hole prior to installation. The quality of the installed helicoil insert relies on strict compliance with the controlled process described by the helicoil's manufacturer. In other words, if you prepare/inspect the threaded hole and install the insert exactly per the manufacturer's instructions, you will get an acceptable result.

 

[Tunalover]

I disagree with pylfrm and tbuelna. The function of the end-item obviously has less to do with the position of the installation hole than it does with the position of the end-item screw thread position. I purchase parts containing captive hardware by delineating the end-item screw thread positions at MMC. It is the supplier's responsibility to meet the end-item positional tolerances even if he tries to point a finger at his fastener supplier.

Tunalover

 

[drawoh]

tunalover,

We had problems in the distant past with helical thread inserts that did not work. We bought helicoil thread gauges. We removed the thread inserts and we inspected the holes. It turned out to be the vendor's fault. He was using old, dull taps.

The OP wants to know how you determine that a locking insert meets H6 tolerances. As noted above, I claim that the insert works by violating this tolerance. You cannot verify that it meets H6, because it doesn't.

--
JHG