Search the FAQ Archives

3 - A - B - C - D - E - F - G - H - I - J - K - L - M
N - O - P - Q - R - S - T - U - V - W - X - Y - Z
faqs.org - Internet FAQ Archives

Rec.Bicycles Frequently Asked Questions Posting Part 4/5
Section - 8i.8 Fretting damage in Bicycle Mechanics

( Part1 - Part2 - Part3 - Part4 - Part5 - Single Page )
[ Usenet FAQs | Web FAQs | Documents | RFC Index | Restaurant inspections ]


Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 4/5
Previous Document: 8i.7 Bikecurrent FAQ
Next Document: 8i.9 Left hand threads
See reader questions & answers on this topic! - Help others by sharing your knowledge
Date: Fri, 11 May 2001 16:35:42 PDT

Fretting or to fret: to eat or gnaw away, to erode.

In machinery, fretting is the micro-motion of tightly fitting parts
that superficially appear immobile with respect to each other.
Classically, transmission shafts and gears or axles with a press fit
show evidence of motion on disassembly by the presence of rouge, rouge
being iron oxide particles that are generated in such interfaces by
micro-motions far smaller than conventional measuring equipment can
resolve.

On bicycles such an interface occurs between the square taper on the
pedal crank and its spindle, where rouge is evident on the face of the
steel spindle regardless of whether it was assembled with grease or
not.  That fretting occurs is also evident by the need for a retaining
bolt to prevent crank disengagement from its spindle and of pedals
from their crank.  Removing a crank requires substantial force with an
extractor, yet continual fretting will disengage the crank in the
absence of a retaining bolt.  Likewise pedals are not easily removed,
but without a left hand thread on left pedals, they will unscrew.

In addition to disengaging the press fit of a crank, fretting moves
cranks up the taper until the preload of the retaining and
installation bolt matches the press times the slope of the taper.
That is to say, fretting relaxes surface friction loads in the
interface.  Additionally, load distortion of a crank causes it to move
away from the face of the retaining bolt, up the taper of the spindle.

Pedals have similar relative motions in the attachment thread and
pressure face on the shoulder of the spindle.  This is also a dynamic
joint that appears to be static.  In the case of the pedal, fretting
motion is directional and can cause precession by the "wandering" load
whose center of pressure rotates in the crank thread opposite to the
rotation of the crank.  Even without clearance, elastic deformation of
the crank and pedal spindle cause micro motions that, if not countered
by an appropriate thread direction, will unscrew the pedal.  The
presence of a left hand thread on the left pedal and on many bottom
bracket right side bearing cups is proof that fretting occurs.

If these motions did not occur, then bolt locking devices, such as
cotter pins, lock nuts and lock washers would not be necessary.  Most
nuts and bolts so secured do not come loose in service and therefore
should not rotate.  Presence of locking means gives evidence that
fretting is more ubiquitous than most people (mechanics and engineers
included) believe.

Fretting in bearings is a different but similar effect, that is the
bane of steering gears and other mechanical devices that are intended
to rotate but are primarily used in a fixed position (straight ahead).
Automotive patents for anti-fretting steering gears abound.  Saginaw,
Gemmer, and Ross steering gears come to mind.  In bicycles this effect
is seen in the bearings of the fork, or head bearings, that are meant
to rotate but often experience straight ahead, non rotating use.

Because fretting involves invisibly small motion, it remains difficult
to understand and hard to convey to the user who suffers fretting
symptoms on a piece of machinery.  It was long believed that impact
cause Brinelling of bicycle head bearings even though mechanics who
installed cottered cranks should have noticed an inconsistency in that
pounding in cotters with a large hammer with all the shock taken up by
one 1/4" ball under the crank spindle never caused a dent, yet 20
balls loaded by a much smaller force through a rubber tire was
believed to cause dimpled head bearings.  Beyond that, the top bearing
that carries practically no load and receives no impact, also became
dimpled and, like the bottom load bearing one, did so in the fore and
aft quadrant.  These dimples were not shiny as Brinell indentations
are, but are milky finish typical of tear-outs from asperity welding.

Ball bearings operate in two modes that became apparent in the
computer disk business because their data actuators often move step by
step from track to track, with a radial arm about 1" long, there being
more than 20,000 tracks per inch.  Servo control engineers must
analyze bearing drag to be overcome for this purpose.  In such small
motions, ball bearings are essentially locked solid with their
lubricant film, the bearing appearing as welded balls acting as
springs.  This "pre-roll" stage of motion is the one that causes the
dimples in the bicycle head bearings because they, unlike the disk
bearings, have been lubricant depleted from fretting, not having made
a larger motion for a longer time, motion that would replenish
lubrication between ball and race.

Ball bearings roll on a film of oil that is so thin that it does not
present liquid properties, being several mono-molecular layers thick
as it adheres to ball and race.  If it weren't for this behavior, oil
would not remain in the interface.  However, with fretting, oil is
displaced and pin point welding takes place.  Bicycle head bearing
fretting is caused by fore and aft rocking of the fork crown, a motion
that lies below visible resolution, and is small enough to not
replenish lubricant.  Bearing damage appears as dimples from myriad
asperity contacts that welded and broke loose as the ball fretted in
place, leaving a milky finish.

Road bicycles are more subject to this damage than off road bicycles
because they spend more time traveling straight ahead, especially when
coasting downhill.  Fretting damage occurs during these times, because
lubrication is not replenished by steering motions.  The compound
bearings offered by Shimano seem to have greatly reduced the problem
by taking up fork crown rocking motion in a plain steel on aluminum
spherical cup that is not prone to metal to metal contact, while
steering rotations are borne in a pre-loaded full complement angular
contact ball bearing supported by this plain bearing.

User Contributions:

1
Report this comment as inappropriate
Oct 15, 2019 @ 6:06 am
so are we widening reduce compared to the Opioid high incidence

leader Trump questioned due to cbs television studios get together trends rob Glor just after Helsinki SummitPart 2 created by organizer due to jesse Glor interview J. Trump airs at some point on cbs.

hbo to push out a documented regarding successive Podcast's Adnan SyedA 4 hour Adnan Syed, A Baltimore regional citizen who was discovered guilty while in the kill together with a ex girl in high school, Will be released merely hbo.

Amtrak training traffic and as well,as well as the gets rid of person In MarylspokeswomanAmtrak Beth K. tuesday active in the Bowie local area. typically learn affected appeared to be on its way caused from Richmond, virginia, To birkenstock boston. the places four or five people on the streets are already struck.

precisely rings regarding goodness Triumphed compared to WWE to train [url=https://medium.com/@patrickbrock0526/is-charmdate-scam-true-my-personal-review-towards-charmdate-com-d74194c1db92]CHArmDate SCAM[/url] Madison sq Gardenrelated to Greg Gilleland G1 Supercard, timetabled on Madisto do with sq storage wednesday WrestleMania by 2019.

Acuna Homer robbing collect facilitates Braves fight NatsCombining clutch selling, extended periods of time golfing ball heading to and moreover Ronald Acuna deft credential inside of the outfield, The Braves beat the excellent 8 3.

Bartolo bowel moves A motorola milestone phone In center Of a difficult 2018 SeasonWith your man's 246th vocation suceed in, Bartolo intestinal tract start resenting it transferred formerly Dennis Martinez which are more wins in history through a latina western derived glass pitcher, an impressive feat for or even a pitcher. The assortment has to be a 10 anxiety attack big pegs competitor because confronts each triathletes considering mental and physical troubles for a chance to change that stays almost forever.

frugal flyer points: the way to get To Reykjavik without the need started BrokeDaydreaming further than last week? Here work most effectively prices at airline tickets so that it will Reykjavik, Iceland simply inside July the fall of associated 2018.

fresh xmas crackers so that you can pizzas: 8 outstanding Capitol slope small-businesses to determine OutRestaurants, sporting goods rungs, motor cycle the malls. advisable attractions gain a tantalizingly delightful frozen reduce.

cheapest your home and family gatherings with regard to Easter 2018 In new york, DCFrom Easter ovum hunts regarding sessions whilst Easter rabbit, area capitol has plenty of wife and kids risk-free disasters to gain enjoying the Easter fun day.

5 formulas of remarkable st. Patrick's Day Drinkstreethese boozy beverages are inclined to rotation type. Patty Day right into a bash that can sometimes st. patrick on his own definitely enhance a wine glass inside.

is when I keep playing excerpt from the Amy k. Sederer, md, suggests in the event we now mounting desensitized for that opioid crisis.

cbs the nearest work: Filmmaker Matthew HeinemanMatthew Heineman analyzes our emerging number in Showtime "currently the exchange punches,

5 alarming surgery reports From 2017Here a directory of from the just that series year the way in which scientific disciplines is now far as well as incredible (And a little low!) it may.

10 indispensable Tips for girls to be able to comfortable around the internet

Six self-defense ideas every woman should know

ByLloyd my wife and i. a fact I put on have another large questionnaire to indicate, my favorite give good results mandates that I look out for this high incidence your levels revealed it and that i promote rest to work hard at it the identical.

are blessed with all risen numbing to those who are demise day after day? To the households thrown back to pain dependency to cigarettes yields? to a hellish budget and simply social results for all communities, specifically in epicenters with all the outbreak?
(...)
2
Report this comment as inappropriate
Oct 17, 2019 @ 7:07 am
Marr viewers back 'outstanding' Nigel Farage over fiery BBC interview

Andrew Marr viewers back 'outstanding' Nigel Farage over fiery BBC interview as Brexit Party leader complains questions were 'entirely unrelated' to the Euro elections but some say it was right that he be put on the spotNigel Farage clashed with Andrew Marr live on BBC One yesterday morningHe was questioned over past phrases on the NHS and Vladimir PutinToday said that BBC asked him about issues 'entirely unrelated to this election'By David Wilcock, Whitehall writer For Mailonline

published: 17:29 BST, 13 May 2019 kept up to date: 18:03 BST, 13 nicely 2019

Viewers have leapt to the defence of Nigel Farage after he hated a hostile BBC interview that brought up past comments about the NHS and Russian autocrat Vladimir Putin.

The Brexit Party leader clashed with Andrew Marr when he appeared on live television yesterday [url=https://ukrainianwomen.home.blog/2019/06/17/dating-in-ukraine5-great-tips/]beautiful ukrainian women[/url] ahead of the ecu elections in which is party is currently ahead on the polls.

It made for comfy viewing as the two men talked across each other, The interviewer refusing to stop asking them questions and the politician angrily denouncing the exchange as 'ludicrous'.

Twitter users bombarded the BBC, Saying that the job interview had been a 'hatchet job' and Mr Farage himself complained today that it had broughtup subjects 'entirely unrelated to this election'.

Piers Morgan was the who took the side of Mr Farage, Saying repeatedly with former Labour spin doctor Alastair Campbell that 'hysterical' critics were helping propel Farage 'into Downing Street'.

But other twitting users were less sympathetic, With many saying it was right that he be held to account and some advice that he appeared on the BBC too often.

Mr Farage objected to the line of questioning during the programme and his team reportedly hated it afterwards.

Campaignfound ing found in Pontefract, Yorkshire immediately, Mr Farage described: 'We were discussing many different things that were entirely unrelated to this election and, Here's the particular, The BBC is a public software broadcaster, in which we all pay 150 quid a year.

'Up until soon, despite the fact this party had gone from nothing to leading in the polls, Up until soon, Not a single associated with the Brexit Party had appeared on any of their programmes.

'You may well thought there was a story to tell there, You would have thought there were questions regarding how did the party do this, Who are the job hopefuls for the party, What's it saying with these elections, And then to be challenged if we have on those points.

RELATED ARTICLES recent 1 Next

Nigel Farage says its his 'duty to face as MP at the next. Theresa May is ready to let MPs decide on how to break.

'We had little or no of that. What we had were a whole series of quotes and misquotes from things I'd said up to 10 years ago that were utterly unrelated to what is going on on Thursday week.

'This is a national election that is swirling on Thursday week and, all ready, The BBC has not had a proper debate of it.

'I think that an outrage.'

But jerr Keen, A producer on the Andrew Marr session, Defended its working with of the Brexit Party leader.

making on Twitter he said: 'It is not true Marr ''didn't ask Nigel Farage anything tightly related to EU elections'' Andrew questioned him for 9 mins on: The mandate for no deal (Farage's main policy) (with) Whether 2nd ref or a Brexit deal that keeps us close to EU is definitely ''betrayal'' (One of his key reasons).or,--

And the BBC's editor of political programs, take advantage of Burley, supplied: 'Andrew Marr did very tough interviews with Theresa May and Jeremy Corbyn at party conference.

'Nigel Farage is the leader of a party and was treated as earnestly and with as much rigour.'

Mr Marr insisted it was reasonable to ask Mr Farage about previ (...)

Comment about this article, ask questions, or add new information about this topic:




Top Document: Rec.Bicycles Frequently Asked Questions Posting Part 4/5
Previous Document: 8i.7 Bikecurrent FAQ
Next Document: 8i.9 Left hand threads

Part1 - Part2 - Part3 - Part4 - Part5 - Single Page

[ Usenet FAQs | Web FAQs | Documents | RFC Index ]

Send corrections/additions to the FAQ Maintainer:
iglesias@draco.acs.uci.edu (Mike Iglesias)





Last Update March 27 2014 @ 02:11 PM