Roll your own Rohloff cog wear gauge?

Discussion in 'Cycling Equipment' started by Rick Onanian, Jan 30, 2004.

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  1. Rick Onanian

    Rick Onanian Guest

    How does a Rohloff cog wear gauge work? Could I duplicate it? It looks very similar to a chain
    whip, even simpler, it just appears to be a single short length of new chain with one end
    attached to a bar.

    I googled r.b.t. for the subject, and didn't find any ideas on alternative ways to check a
    sprocket for wear.

    If a worn sprocket is used with a new chain, will the chain wear faster? I ask because Jobst said
    this in an old thread:
    >...sprocket wear a don't-care dimension, I assumed he meant chain wear. It makes no difference how
    >badly sprockets are worn. If the chain skips on them, they are worn out... ...In other words, a new
    >chain is the test instrument, no measurement tool makes any sense...
    but he didn't say if doing that will wear the chain excessively.
    --
    Rick Onanian
     
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  2. Tim McNamara

    Tim McNamara Guest

    Rick Onanian <[email protected]> writes:

    > How does a Rohloff cog wear gauge work? Could I duplicate it? It looks very similar to a chain
    > whip, even simpler, it just appears to be a single short length of new chain with one end attached
    > to a bar.

    The bar has a "foot" that goes between two teeth and allows you to set tension on the chain. IIRC,
    on worn cogs only the one or two rollers nearest the bar are pressed against the teeth, and you can
    just flip the loose end of the chain off the cogs.

    > I googled r.b.t. for the subject, and didn't find any ideas on alternative ways to check a
    > sprocket for wear.

    The old way as a 1/4" dowel placed between the teeth, to eyeball wear. I haven't done this in years,
    and I'm not sure if it would be reliable with modern ramped and pinned and wedged and shaped and
    profiled teeth. I just replace cogs when a new chain skips on them.
     
  3. Jobst Brandt

    Jobst Brandt Guest

    Rick Onanian writes:

    > How does a Rohloff cog wear gauge work? Could I duplicate it? It looks very similar to a chain
    > whip, even simpler, it just appears to be a single short length of new chain with one end attached
    > to a bar.

    > I googled r.b.t. for the subject, and didn't find any ideas on alternative ways to check a
    > sprocket for wear.

    > If a worn sprocket is used with a new chain, will the chain wear faster? I ask because Jobst said
    > this in an old thread:

    >> ...sprocket wear is a don't-care dimension, I assumed he meant chain wear. It makes no difference
    >> how badly sprockets are worn. If the chain skips on them, they are worn out... In other words, a
    >> new chain is the test instrument. No other measurement tool makes any sense...

    > But he didn't say if doing that will wear the chain excessively.

    Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if it
    is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do you
    imagine will affect the chain?

    Jobst Brandt [email protected]
     
  4. meb

    meb New Member

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    I was always told and accepted the assertion that a worn sprocket would accelerate chain wear, but I can’t see any specific reason why that should be so to confirm the premise is valid or rather myth.

    However-

    A chain slides up the tooth of a partially worn sprocket increasing friction slightly. More so on a heavily worn sprocket, occurring at stages prior to the sprocket slipping.

    Also, small transient effective ratio changes occur due the inconsistent engaging of the adjacent teeth, more noticeable on smaller 11T or 12T sprockets (kind of like a random biopacing).

    Some persons change sprockets whenever they change chains. Many assume 2:1 chain/sprocket wear. A slightly worn sprocket is suitable for most applications.
     
  5. spamski-<< How does a Rohloff cog wear gauge work? Could I duplicate it? It looks very similar to a
    chain whip, even simpler, it just appears to be a single short length of new chain with one end
    attached to a bar. >><BR><BR>

    Yes, the lever end is placed between cog teeth and the remaining chain length placed on some cogs.
    Pull the lever taught and see if the chain at the end is loose, which if it is, assumes the cogs are
    worn. Good tol but for hyperglide only.

    Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
    (303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"
     
  6. <[email protected]> wrote:

    > Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if
    > it is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do
    > you imagine will affect the chain?

    Isn't it a misnomer to say that a worn sprocket is "out of pitch"? The pitch remains constant as the
    teeth wear.

    Certainly, the air gap between teeth increases, but significantly only at the base of the teeth -
    not in the area towards the tips of the teeth. This is what causes skipping when it becomes
    pronounced enough. And because a fixed-gear setup (anything without a chain tensioner, in fact)
    doesn't permit skipping, a badly-worn sprocket on such a setup could cause accelerated chain wear.

    John
     
  7. Jobst Brandt

    Jobst Brandt Guest

    John Henderson writes:

    >> Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if
    >> it is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do
    >> you imagine will affect the chain?

    > Isn't it a misnomer to say that a worn sprocket is "out of pitch"? The pitch remains constant as
    > the teeth wear.

    As the chain wears, it's pitch elongates causing it to ride higher on the sprocket where it wears
    home positions part way up the teeth. A new, in-pitch chain will roll into these positions of
    greater pitch diameter under load making engagement of incoming links impossible. Thus the chain
    skips forward into the next engagement only to repeat the sequence if the load on the chain
    remains. This is why filing or grinding the tips of sprocket teeth has no merit. That doesn't alter
    the pitch of the wear pockets on its teeth that are too great. To do any good, the seat at the root
    of the tooth would need to be reshaped but this wouldn't do much good because the case hardening
    would be gone.

    > Certainly, the air gap between teeth increases, but significantly only at the base of the teeth -
    > not in the area towards the tips of the teeth. This is what causes skipping when it becomes
    > pronounced enough. And because a fixed-gear setup (anything without a chain tensioner, in fact)
    > doesn't permit skipping, a badly-worn sprocket on such a setup could cause accelerated chain wear.

    The base circle is practically unchanged by all this. The reason the chain skips under load is that
    it rides in the wear pocket of a larger pitch, making engagement of following links impossible.

    Jobst Brandt [email protected]
     
  8. daveornee

    daveornee New Member

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    I think the chain rollers will roll more and the bushings that they ride on will wear more when you but a new chain on a worn cassette.
    I don't understand Jobst's explanation otherwise.
    I think a new chain does a good job of exposing worn cogs.
     
  9. <[email protected]> wrote:

    > As the chain wears, it's pitch elongates causing it to ride higher on the sprocket where it wears
    > home positions part way up the teeth. A new, in-pitch chain will roll into these positions of
    > greater pitch diameter under load making engagement of incoming links impossible.

    I see we're in agreement on the basic problem, but may be splitting hairs about terminology when it
    comes to "pitch".

    > Thus the chain skips forward into the next engagement only to repeat the sequence if the load on
    > the chain remains. This is why filing or grinding the tips of sprocket teeth has no merit. That
    > doesn't alter the pitch of the wear pockets on its teeth that are too great. To do any good, the
    > seat at the root of the tooth would need to be reshaped but this wouldn't do much good because the
    > case hardening would be gone.

    I wasn't aware that the teeth were case-hardened. I expect you're right, but I've certainly found
    that grinding away the offending unworn part of the old teeth makes sprockets run like new again. I
    haven't measured the "new lease of life" in terms of mileage, but it didn't appear overly short.

    > > Certainly, the air gap between teeth increases, but significantly only at the base of the
    > > teeth - not in the area towards the tips of the teeth. This is what causes skipping when it
    > > becomes pronounced enough. And because a fixed-gear setup (anything without a chain tensioner,
    > > in fact) doesn't permit skipping, a badly-worn sprocket on such a setup could cause
    > > accelerated chain wear.
    >
    > The base circle is practically unchanged by all this. The reason the chain skips under load is
    > that it rides in the wear pocket of a larger pitch, making engagement of following links
    > impossible.

    Agreed. But in a non-derailleur set-up where it's *skipping* that's impossible because the chain
    doesn't have enough play to climb out over the outer edge of the sprocket, we have a different
    scenario. So with a new chain under peddling pressure, what must "give" is the inevitability of the
    chain riding in the wear pocket. For at least part of each tooth engagement, it must move back, and
    instead ride on the protruding part higher up on one or more teeth (further back around the
    sprocket). In these circumstances (which I've tried), you can hear the noise of the new chain
    protesting.

    John
     
  10. "daveornee" wrote:

    > I think the chain rollers will roll more and the bushings that they ride on will wear more when
    > you but a new chain on a worn cassette. I don't understand Jobst's explanation otherwise. I think
    > a new chain does a good job of exposing worn cogs.

    If the old sprocket isn't worn enough to make the new chain want to skip, then there's no increased
    wear. That's been my understanding of meshing dynamics, and I believe that's what Jobst is saying.

    John
     
  11. meb

    meb New Member

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    The pivoting exit link is ostensibly under the same tension whether it is pulling on one tooth or several teeth further down the chain.

    The chain wear is occurring with pivoting of that loaded exit link.

    Since the tension on the exiting pin is immaterial to how many teeth the load is distributed to, and because the other wear variable-pivot angle is the same with a new or used sprocket since the base circle is unchanged-the chain wears the same independent of the sprocket condition.

    Chainwear is not a dependent variable of skipping. Skipping is a dependent variable of sprocket and chainwear.

    So the proposition that an old sprocket substantially wears chains faster is myth.
     
  12. "meb" wrote:

    > The pivoting exit link is ostensibly under the same tension whether it is pulling on one tooth or
    > several teeth further down the chain.
    >
    > The chain wear is occurring with pivoting of that loaded exit link.
    >
    > Since the tension on the exiting pin is immaterial to how many teeth the load is distributed to,
    > and because the other wear variable-pivot angle is the same with a new or used sprocket since the
    > base circle is unchanged- the chain wears the same independent of the sprocket condition.
    >
    > Chainwear is not a dependent variable of skipping. Skipping is a dependent variable of sprocket
    > and chainwear.
    >
    > So the proposition that an old sprocket substantially wears chains faster is myth.

    For derailleur systems, I agree. But I believe it's different with the new chain, badly worn
    sprocket, combination on a fixed gear system.

    In this set-up, the chain is forced to advance and retard, around the sprocket, to accommodate
    misshapen teeth. The chain audibly chatters and rattles when pressure is applied. Only a few weeks
    ago, I put a (properly adjusted) new chain onto a badly-worn rear sprocket on my internally-geared
    bike just to test the behaviour. It was noisier than I had anticipated.

    John
     
  13. Jobst Brandt

    Jobst Brandt Guest

    John Henderson writes:

    >> The base circle is practically unchanged by all this. The reason the chain skips under load is
    >> that it rides in the wear pocket of a larger pitch, making engagement of following links
    >> impossible.

    > Agreed. But in a non-derailleur set-up where it's *skipping* that's impossible because the chain
    > doesn't have enough play to climb out over the outer edge of the sprocket, we have a different
    > scenario. So with a new chain under peddling pressure, what must "give" is the inevitability of
    > the chain riding in the wear pocket. For at least part of each tooth engagement, it must move
    > back, and instead ride on the protruding part higher up on one or more teeth (further back around
    > the sprocket). In these circumstances (which I've tried), you can hear the noise of the new chain
    > protesting.

    On fixed gear operation, the main problem is on the incoming chain that is forced to snap into place
    on the sprocket, the pitch circle on which the chain tries to ride being too big for the in-pitch
    new chain. In that event, silence can be achieved by rounding off the teeth but it would not work
    with a derailleur where the chain will ride high and not be forced to engage. It will still skip.

    Jobst Brandt [email protected]
     
  14. <[email protected]> wrote:

    > On fixed gear operation, the main problem is on the incoming chain that is forced to snap into
    > place on the sprocket, the pitch circle on which the chain tries to ride being too big for the
    > in-pitch new chain. In that event, silence can be achieved by rounding off the teeth but it would
    > not work with a derailleur where the chain will ride high and not be forced to engage. It will
    > still skip.

    I've actually reshaped badly worn sprockets several times - grinding the teeth on a derailleur
    freewheel so that it runs smoothly without skipping or noise with a new chain.

    I just remove material from the non-load-bearing area, making the teeth which looked like this:

    \ /
    | |
    | |
    | \
    | |
    | /
    \___/

    look like this instead:

    \ /
    | |
    | |
    | |
    | |
    | |
    \___/

    noting of course that these diagrams exaggerate the amount of wear in the "pocket" at the base of
    the teeth. It doesn't *have* to be visible to the eye to cause skipping.

    John
     
  15. A Muzi

    A Muzi Guest

    [email protected]> wrote:
    >>Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if
    >>it is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do
    >>you imagine will affect the chain?

    John Henderson wrote:
    > Isn't it a misnomer to say that a worn sprocket is "out of pitch"? The pitch remains constant as
    > the teeth wear.
    >
    > Certainly, the air gap between teeth increases, but significantly only at the base of the teeth -
    > not in the area towards the tips of the teeth. This is what causes skipping when it becomes
    > pronounced enough. And because a fixed-gear setup (anything without a chain tensioner, in fact)
    > doesn't permit skipping, a badly-worn sprocket on such a setup could cause accelerated chain wear.

    It's not a misnomer.

    I didn't follow your argument but a worn tooth cannot wear a chain. It is the reverse that actually
    happens. Worn chains erode teeth. As the roller gets farther away from the root of the tooth, the
    tooth's face is worn away.

    --
    Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
     
  16. "A Muzi" wrote:

    > I didn't follow your argument but a worn tooth cannot wear a chain. It is the reverse that
    > actually happens. Worn chains erode teeth. As the roller gets farther away from the root of the
    > tooth, the tooth's face is worn away.

    In suggesting that worn sprockets might accelerate chain wear, I'm thinking only of the special case
    where the chain wants to skip, but can't because it's a "fixed gear" set-up. The new chain is
    properly adjusted, so that it cannot skip.

    As I mentioned, this can result in very noisy running - it certainly sounds stressed.

    John
     
  17. Rick Onanian

    Rick Onanian Guest

    On Fri, 30 Jan 2004 22:30:59 GMT, [email protected]
    wrote:
    >> If a worn sprocket is used with a new chain, will the chain wear faster?
    >Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if it
    >is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do you
    >imagine will affect the chain?

    I didn't know that the chain only bears force on the exiting tooth.

    I was under the impression that the chain's load is distributed on each contacted tooth; and if that
    was the case, and the teeth were worn, it would be possible that the chain is not well supported,
    and the rollers or plates would be caused to elongate until the chain becomes better supported
    (through it's better, stretched fit).

    However, knowing now that it's already only bearing load at one link, I see that it's not an issue.

    The practical upshot is that, as I spend a bunch of money replacing most of my drivetrain so I can
    make my double crank triple, I can use my existing cassette and needn't worry about premature chain
    wear, which in turn would prematurely wear the new chainrings.

    I doubt the cassette is worn anyway...just making sure.
    --
    Rick Onanian
     
  18. Rick Onanian

    Rick Onanian Guest

    On Mon, 2 Feb 2004 00:31:13 +1100, "John Henderson"
    <[email protected]> wrote:
    >For derailleur systems, I agree. But I believe it's different with the new chain, badly worn
    >sprocket, combination on a fixed gear system.

    For the record, the context of my question was on a common derailer bike.

    That said, I'm glad you decided to speak up; it resulted in a very informative thread. I got a
    general [and very basic] idea of chain wear dynamics.
    --
    Rick Onanian
     
  19. Jobst Brandt

    Jobst Brandt Guest

    Rick Onanian writes:

    >>> If a worn sprocket is used with a new chain, will the chain wear faster?

    >> Worn sprockets cannot affect chain wear because the chain only bears on the exiting tooth and if
    >> it is doing that on a new or an out of pitch sprocket makes no difference to the chain. What do
    >> you imagine will affect the chain?

    > I didn't know that the chain only bears force on the exiting tooth.

    That is the primary load bearer. That can be deduced from elastic considerations, the sprocket being
    more rigid than the chain. The chain, in theory, bears on all teeth, when new and perfectly in
    pitch, but because it has elasticity, any strain will leave primarily the tooth on the working end
    loaded. This is more evident on chainwheels where the chain can be moved manually a few teeth from
    the end while pushing on the crank.

    > I was under the impression that the chain's load is distributed on each contacted tooth; and if
    > that was the case, and the teeth were worn, it would be possible that the chain is not well
    > supported, and the rollers or plates would be caused to elongate until the chain becomes better
    > supported (through it's better, stretched fit).

    A worn chain causes damage primarily to aluminum chainwheels because it rides higher on the teeth
    where they are thinner. With an elongated chain, all load is concentrated on one tooth at the
    engagement point rather than the first three or four that would be with a new chain where elasticity
    of the aluminum sprocket, being greater than the chain, distributes load over more teeth.

    > However, knowing now that it's already only bearing load at one link, I see that it's not
    > an issue.

    > The practical upshot is that, as I spend a bunch of money replacing most of my drivetrain so I can
    > make my double crank triple, I can use my existing cassette and needn't worry about premature
    > chain wear, which in turn would prematurely wear the new chainrings.

    If the chain does not skip there should be no problem. Besides, chains are expendable and relatively
    inexpensive compared to cassettes and chainwheels.

    > I doubt the cassette is worn anyway...just making sure.

    You'll soon find out. Frequently used sprockets wear fast.

    Jobst Brandt [email protected]
     
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