Schlumpf button fixings

Ok, I've had my Schlumpf for about 4 months now, and have lost 4
buttons* so far - which at £6 each, is turning in to quite a high
running cost.

The last one I lost was one of the original plastic ones, which I think
I may have over-tightened, but that was my last reserve one, so I've
had to commute in 1:1 mode this week while I wait for the replacements
to be shipped over :-(

Does anyone have any tips on how to attach them securely? The
instructions say *tighten the screw within the button very firmily
(torque 1.1Nm) *and then goes on to say *Please check that you can't
unscrew the buttons by hand. If so, you will loose them soon!* Now,
I'm not exactly sure what 1.1Nm translates to in terms of brute force,
but I'm sure I've done at least that, and they certainly haven't been
undoable by hand.

Any suggestions? Oh, and bare in mind that they will need unscrewing
if/when I change my cranks over.

Or should I just put a 'please return to...' note on the inside of each
one?

STM




* Ok, so one of them I managed to find by retracing my path, so I could
reuse that


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Let's play fast and loose with units so it's easier rather than
distinguishing mass and force. I'm guessing you have no torque wrench.
I don't know what units you prefer but let's say that pounds, kilograms
and Newtons "weigh" something for simplicity. A Newton, which is a
force unit, is equivalent to about a quarter pound and about a tenth of
a kilogram. Let's use 11cm instead of 1.1m so the distance is
manageable and is about 4.5 inches or so. Picture putting a wrench on
this screw with a handle that is 11cm or 4.5 inches long. Put something
that is 2.2 pounds or a kilogram on the end of the handle. That's
applying 1.1-N-m of torque. Not a lot.

I don't have a Schlumph so I don't know what this screw looks like.
From the required torque I would guess in is an Allen head cap screw or
button head screw that is of order M2. A small screw, perhaps easily
stripped. Is there a reason that you cannot use Loctite or the British
equivalent if it is different? That's a way to keep the screw from
coming out, maybe even when you're bopping it with your heel. E-mail
Florian and ask him if it would be OK. You can also nick (score) the
last 2 threads toward the head so they bind when tightened but I would
tend to avoid that. Well, I would do it but I would recommend that you
avoid doing it because you have to answer to Herr Schlumph.


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harper wrote:
...A Newton, which is a force unit, is equivalent to about a quarter
pound...



My Physics 101 professor once suggested we go to McDonald's and order a
"Newton Burger".

That's my 2 cents.


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hell-on-wheel wrote:
My Physics 101 professor once suggested we go to McDonald's and order a
"Newton Burger".

That's my 2 cents.


That's a very bad joke, but I get a pretty good laugh out of things
like that


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For those that don't know, the Schlumpf button fixing is an either M2 or
M3 grub screw. It screws into the middle of the button, and pushes
against the shifting rod. This pushes the button outwards, so that the
button is stuck onto the threads holding the button on and won't
unscrew. It comes with a special tool (or a pair of pliers does the
job) that lets you hold the button still whilst you do up the
grubscrew.

I'm not sure if loctite would help, as at the point the button loosens
off, it's not that the screw has come loose, it's that the button has
managed to come unscrewed slightly.

It is possible to overtighten it, as mine came like that, and it wasn't
possible to undo without drilling it out.

I tighten my buttons by using allen keys on both at the same time, so
I'm tightening them against each other. I find this better than using
the special tool to tighten them up, or using pliers to hold the button
still.

Joe


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This might be obvious, but just to check, you are holding the button
still when tightening the grub screw aren't you?

Joe


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well, harnessing all the raw power of Microsoft Paint, coupled with my
technical drawing abilities, I've come up with the following diagram
for those that don't know how the buttons are fixed;

22979

The last button I lost was secure for quite a while, but it was the
older plastic type, and it had been sitting in a warm room for quite a
while. Then, on Monday night I took it out on a bitterly cold ride, so
I guess that probably had something to do with it.

The buttons are held still while I tighten the grub screw, but I like
the idea of tightening it against the grub screw on the other side. I
think I'll treat myself to a torque wrench this weekend and give that a
go.

STM


+-------------------------------------------------------------------+
|Filename: Schlumpf button.JPG |
|Download: http://www.unicyclist.com/attachment/22979 |
+-------------------------------------------------------------------+

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Seems too obvious so I've probably completely missed the point, but
couldn't you loctite the button to the shaft it screws onto, rather
than the grub screw? Is there some reason why that would be bad, such
as the shaft being free-turning so you'd never be able to unscrew the
button if it were loctited on?

Rob


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rob.northcott wrote:
, such as the shaft being free-turning so you'd never be able to unscrew
the button if it were loctited on?




Yes it is free turning. If it gets stuck on because of the grub screw,
you can drill it out, but if the button itself is stuck on, you'd have
to unbuild the wheel and send the hub to Switzerland.

Joe


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I knew there'd be a catch. Still, I would think you'd get away with a
bit of low-strength threadlock, just to stop it falling off so quickly
if the grub screw came loose. Couldn't you hold the shaft from the
other side to unscrew the button?

On second thoughts, perhaps it's too far recessed to be able to hold it
from the other side.

Rob

EDIT: It would be better if there was a slot in each end of the shaft
so you could hold it still with a screwdriver from the other side, then
you could use threadlock on the buttons without so much worry of
getting them stuck. You could get the first button off by holding the
other button still with pliers or the special tool, then hold the shaft
still with a screwdriver to get the second button off.


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