I have found at least small (<#4) split ring spring washers to be unreliable for high vibration environments. I agree that they certainly do not deserve the label "lock washer", and if you consider the physics in this situation you will probably agree: If the vibration environment is such that the spring washers become unloaded or nearly unloaded, then on the opposite side of the vibration waveform they will attempt to yank the fastening out. If the screw rotates during that re-loading even the tiniest amount, then you are doomed. I only use nylon lock nuts or thread locking compound. BUT, qualification is qualification, and this seems a large enough change to have the qualification test repeated. Sometimes we find surprises, and that is the reason there are tests. I would certainly be ready to place big money on the nylon lock nuts passing the quals with flying colors if installed properly, but the tests must be re-done. Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Tuesday, June 26, 2007 2:35 AM To: [log in to unmask] Subject: Re: [TN] To lock or not to lock? We have used the selflocking plastic insert nuts for twenty years with no problems, and we shock and vibration test a lot according to MIL specs. The disadvantage with split-ring washers is that they can corrode in harsh environment and lose some of the good locking properties. E.g. imagine that you do service maintenance in field, and have to reuse the lock washers. In such a situation, plastic insert nuts are better. As most locking is based on friction and material constants, one has to select bolts, nuts, screws and washers after the actual construction. If you want very reliable lockings, and there is no quick-service demand, use Flange nuts with plastic inserts. These nuts have a larger friction area, and also grooves that make a tremendous grip. Sometimes, they are too good: you nearly can't unlock. And, as I said, you need do selections from the materials you use. Locking bolts and nuts is an art! Inge -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of - bogert Sent: den 26 juni 2007 00:07 To: [log in to unmask] Subject: [TN] To lock or not to lock? June 25, 2007 Folks, we have an OEM who designed and qualified an assembly for military (NAVY shipboard) shock and vibration requirements via performing shock and vibration testing. His qualified design used split ring lock washers. To save $ (assembly time primarly), the OEM proposes to replace the split ring lock washers with Nylok type locking nuts. Question is, would the OEM need to repeat the shock and vibration qualification testing. My understanding is that although split-ring washers are sometimes called lock-washers, in fact, they do not "lock" the fasteners in place, as is specifically stated in the applicable MS standard/mil spec for the washers. Apparently the Nylok locking nuts that have the plastic (nylon??) insert are true locking devices and as such perform better as a locking feature than do split-ring lock washers. Therefore, there should be no need to repeat shock and vibration qualification testing if the OEM changed from split-ring lock washers to use Nylok type locking nuts. The only possible concern I am aware of is that the locking nuts can only be used (removed and re-installed) a specified number of times (e.g., 10 to 15 times?). I would like any Technet folks information on the above. Thanks. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------