[CR]Re: Classicrendezvous digest, Vol 1 #1892 - 23 msgs

(Example: Racing:Jean Robic)

From: "Stephen Barner" <steve@sburl.com>
To: <classicrendezvous@bikelist.org>
References: <20021124195400.17180.84128.Mailman@phred.org>
Subject: [CR]Re: Classicrendezvous digest, Vol 1 #1892 - 23 msgs
Date: Sun, 24 Nov 2002 17:58:29 -0500

When calculating the amount of thread engagement, you need to take into account the tolerances and allowances for the various parts. Tolerance is the amount of variation in size that is acceptable by the manufacturer. Allowance is the amount of clearance engineered in the mating parts. If the male and female parts were exactly the same size, it would be extremely difficult to thread them together.

It is likely that you would get significantly less than 75% engagement under the best of conditions. I have seen Stronglight cranks strip out even when Stronglight extractors were used. The extractor has less engagement thread than a Campagnolo or Japanese crank, the fit usually seemed sloppy to me, the aluminim Stronglight used was pretty soft, and they sometimes seized on the axle, all factors that lead me to never try extracting a Stronglight crank without a puller designed specifically for Stronglight cranks.

Does anyone besides me have a Stronglight 93 crossover drive on a tandem? Ok, truth is I reverse threaded standard cranks to make it work.

Steve Barner, looking at a foot of snow in Bolton, Vermont.


----- Original Message -----


> Date: Sun, 24 Nov 2002 10:16:17 -0500
> To: classicrendezvous@bikelist.org
> From: "H.M. & S.S. Sachs" <sachs@erols.com>
> Subject: [CR]49D and TA extractor tools
> Cc: Toni.Theilmeier@t-online.de, jerrymoos@sbcglobal.net
>
> Jerry Moos and others have commented on the difference between these. I
> can help a little bit with the question of whether it is safe to use the TA
> on early Stronglight cranks:
>
> JM:
> The thread diameter on Stronglight is 23.35 mm while the TA is 23.0 mm.
> HS:
> My measurements were a bit different, but same difference between them;
> gotta get that dial(or my eyes) calibrated. I got 23.2 and 22.8,
> respectively. Key is a 0.4 mm difference in diameter.
> JM:
> Both have the same pitch, I believe.
> HS:
> According to Sutherland's 2nd, essentially everything used a 1 mm pitch --
> except early Lambert at 24 TPI (1 mm = 25.4 TPI).
> JM:
> The TA extractor will thread into the Stronglight arm, but will not
> completely engage the threads.
> HS:
> Beloved Spouse reminded me which trig function to use. Given 60 degree
> included angle (except 55 for Italian?) and 1 mm pitch, the depth of the
> thread would seem to be 0.866 mm [depth = (0.5*pitch)/(tan 30deg)]. In
> fact, there is a flat valley at the bottom, and the ridge is chopped off,
> so the depth is somewhat less. Let's call it 0.8 mm. Now double that,
> since we have only one side (radius) and have to think about whole
> diameter: 1.6 mm. This is 4 times the 0.4 mm differrence in
> diameter. So, the good news is that the TA covers 75% of the thread depth
> of the Stronglight. But, the bad news is that it is the "thin" 75%, not
> the thick root of the pitch. The worse news is that the puller is strong
> steel and the arm is weaker aluminum. Guess which set of threads would
> pull out.
>
> So, I'm heartened that Tony Theilmeier has had good luck:
> "Jerry Moos kindly warned the group not to use TA extractor tools on
> Stronglight cranks. Maybe I have just been very lucky, but I have
> disassembled many a 49D equipped b/b, and I have always used a TA tool. It
> has always worked."
>
> As for me, I'll use a TA in a stronglight in an emergency (since I have
> spare arms), but won't do it when I can avoid it.
>
> harvey sachs
> mcLean va - and pleased I remembered that it was a trig problem!