From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: What is Loctite and were can I get it
Date: 22 Jun 1998 18:12:02 GMT

John Serafin writes:

>> It might have occurred to you that in production assembly, no
>> Loctite is used on the millions of bicycles shipped to customers.

> Does this mean that Campagnolo cranks shipped to OEMs don't come
> with Loctite on the bolts?

> I'm not advocating Loctite on crank bolts, but the bolts on the (new
> in box) Campy cranks I bought recently had Loctite on them.

Loctite on a new product is, with rare exception, a major design flaw.
Properly designed screwed connections allow enough elastic preload
that the part in question that it will never unload the thread in use.
Therefore, the tread cannot unscrew.  For this reason, critical joints
used strain bolts, or other elastic components, to maintain position.
Screws that should hold, even if loose, such as brake anchor bolts,
should have elastic stop nuts.  These have the disadvantage that they
resist turning on installation, but for such applications this
tradeoff is acceptable.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: What is Loctite and were can I get it
Date: 23 Jun 1998 17:54:08 GMT

Frank Krygowski writes:

>> Loctite on a new product is, with rare exception, a major design
>> flaw.  Properly designed screwed connections allow enough elastic
>> preload that the part in question that it will never unload the
>> thread in use.  Therefore, the tread cannot unscrew.  For this
>> reason, critical joints used strain bolts, or other elastic
>> components, to maintain position.  Screws that should hold, even if
>> loose, such as brake anchor bolts, should have elastic stop nuts.
>> These have the disadvantage that they resist turning on
>> installation, but for such applications this tradeoff is
>> acceptable.

> I disagree with the statement that Loctite use indicates a major
> design flaw.

> A successful design is one that achieves its objectives.  If the
> objective is to fasten something in place and not have it loosen,
> what would be the advantage of a strain bolt over Loctite?  One may
> be perhaps more elegant, in an engineering sense, but engineers
> typically don't go for elegance as much as for getting the job done.

Controlling the dosage, the cleanliness of the joint and that it gets
into the assembly at all are major production headaches.  As I
mentioned, in machine design, products are rated in motions during
assembly with multiplying factors.  Low scores are better in
assessment of "design for assembly" and adding any glue, filler or
paste carries a high penalty.  For this reason, fasteners that do the
job without glue are greatly preferred.

> 50 years ago, Loctite didn't exist.  People invented a wide, wide
> array of devices to prevent loosening of threaded fasteners.  If
> every instance of the use of lockwashers, jam nuts, special thread
> forms, etc. indicated a major design flaw in your eyes, you have
> high standards indeed!  Higher than almost anyone else, in fact.

Loctite was invented as a fix for otherwise unreliable designs.  Its
main role is in aftermarket applications for faulty machinery.  There
are applications where it is used in lieu of precision cartridge
bearing mounting by having a clearance bore whose gap is filled with
Loctite.  Even these are better designed to not be glued.

> While I admit to being something of a retro-grouch, I see Loctite as
> a useful technology that can simplify life both for the designer and
> for the end user.

You probably mean the lazy engineer and the person who has to use his
design.  The term end user evokes Scott Tissue, 400 sheets per roll.

Jobst Brandt      <jbrandt@hpl.hp.com>