Stripped BB threads

Tom Paterson wrote:
From: "Phil, Squid-in-Training"

Ahh... Thank you for the informative response. Does retapping
threads cause a lot of heat, though?

Especially with a motor driven pipe vice (not fast but easier than
Armstrong power), you can hear the lard sizzle when threading pipe.
Hot enough? --TP

I had in mind retapping BB threads manually.

--
Phil, Squid-in-Training

Unless you are power taqpping, heat is never noticed but it does happen
at that microscopic point where metal becomes a chip, it will get hot.
And if the cutting oil cannot lubricate, the tap or finished quality
will suffer.

Sulfurated oils on carbon steel tend to work best. I found hypoid lube
to be the only acceptable substitute for hand tapping of steels. I had
used Tap Magic for steel but ran out. Hypoid lube is sulfurated and
stays in place so I use it.

The worst brazing material has a tensile strength of 6000 PSI. The
best epoxy wonder material is 4000 PSI. Good luck.


--
Weisse Luft

Weisse Luft wrote:
Unless you are power taqpping, heat is never noticed but it does
happen at that microscopic point where metal becomes a chip, it will
get hot. And if the cutting oil cannot lubricate, the tap or finished
quality will suffer.

Sulfurated oils on carbon steel tend to work best.

What about BB threads by hand? We use the Park cutting oil at work.

--
Phil, Squid-in-Training

"peter.kidwell" wrote in message
...
A friend of mine has stripped threads on the adjustable cup side of his
English bottom bracket.
The advice I have given is to fit a Stronglight threadless BB but I have
no experience of these are they successful or is there any other answer

PK



It would appear that the poor state of some BB threads and other bicycle
threads are due to not using the correct lubrication for cutting them.
I will give out the advice offered here i.e. to run a sharp tap through the
thread with cutting tool lub. but I have my doubts if it will work as you
cannot put back the missing metal of the stripped thread .
I have sourced some old stock oversize cups which may be the solution i.e.
just screw them in, not cut an OS thread in the BB.

PK

From: "Phil, Squid-in-Training"

[heat produced in threading operation]

What about BB threads by hand? We use the Park cutting oil at work.

Let's put it this way: If you tried to run that tap in far enough to really
chase the threads with no lube, it would get nice and hot (before it jammed),
even by hand.

I looked for a "contents" page for Rigid Dark, similar to the one A. Muzi
posted for the "Emblem" brand of cutting oil. No dice. Never used that brand
(by name anyhow) or the Park product, but suspect someone else supplies for
Park. Maybe these others are even better than Rigid oil. I'm happy to know from
experience that whatever the R-stuff has in there (sulfur, lard), it is the
stinkiest, nastiest, and works the best of the three or four brands I've used
on the job, by *far* (including three years doing "new work" residential/light
commercial construction, threading a fair amount of pipe). We guessed it was
the lard content, from the smell, FWIW.

(Sigh...) When you have a job like a damaged BB shell on a nice bike frame, why
**** around with gear oil or anything else? Put down a catch pan, cardboard
under, use the best oil you can get, copiously and deliberately (second guy
applies cutting oil), thread in just far enough to "catch" all the threads on
the BB cup, thoroughly clean/brush chips out, lube the hell out of everything,
use a BB cup that has a nice long threaded section and "snug fit" (you hope),
run it in tight and hope for the best! All you need to do is pick up enough
thread material to hold that cup in place-- the threads can look awful, etc.;
as long as they hold, they hold.

The next solution(s) get a lot more expensive-- more labor, Italian BB cups,
Mavic/Stronlight BB w/labor costs, brazing/paint and then a retap, all with a
chance of failure.

Rigid comes in a nice Tip-Spout quart size bottle, and might be available in
surprising places-- local hardware store, H. Depot, Lowes, even Target shows as
carrying at least some Rigid products. Done, I hope. Lunchtime. And the NFL.
Happy Halloween. --TP

On 2004-10-31, Weisse Luft wrote:

Unless you are power taqpping, heat is never noticed but it does happen
at that microscopic point where metal becomes a chip, it will get hot.

FWIW, I often see smoke even when turning taps by hand.

And if the cutting oil cannot lubricate, the tap or finished quality
will suffer.

Sulfurated oils on carbon steel tend to work best.

But don't use a sulfurated oil on aluminum.

I found hypoid lube
to be the only acceptable substitute for hand tapping of steels. I had
used Tap Magic for steel but ran out. Hypoid lube is sulfurated and
stays in place so I use it.

Half a liter of real cutting oil is just a few bucks at the local hardware
store...

--

-John )

On 2004-10-31, Phil, Squid-in-Training wrote:

Weisse Luft wrote:
Unless you are power taqpping, heat is never noticed but it does
happen at that microscopic point where metal becomes a chip, it will
get hot. And if the cutting oil cannot lubricate, the tap or finished
quality will suffer.

Sulfurated oils on carbon steel tend to work best.

What about BB threads by hand? We use the Park cutting oil at work.

Standard cutting oil is sulfurated; I'd be surprised if Park's wasn't.

--

-John )

From: "peter.kidwell"

I will give out the advice offered here i.e. to run a sharp tap through the
thread with cutting tool lub. but I have my doubts if it will work as you
cannot put back the missing metal of the stripped thread .

Repeating, I have a frame that I ran the wrong "side" tap through (English)
(the sins of youth), then chased what remained of the threads with the correct
tap. True, not "stripped" but then maybe even worse... The left side does not
look the same as the right, that's for sure, but holds 100% with Campy steel
(N. Record) cups, used many miles for loaded touring, fixed gear. Phil (alu?)
rings did not work. IMHO, certainly worth a shot, with "real" BB cups. If the
tap just"falls" in, finds no purchase, well, you'll know right away it's not
use, right? g. "Easiest first". --TP

Cutting oil takes heat out of the cut more quickly than motor oil
does, so the cutting edges stay sharp longer. Plain water is even
better--great for cooling, but crap for lubrication, so you'd likely
break taps all over the place if you tried to use it. Cutting oil is
right down the middle--good enough cooling and just enough
lubrication.

Phil, Squid-in-Training wrote:
Ahh... Thank you for the informative response. Does retapping threads cause
a lot of heat, though?

Cutting metal at any normal speed indeed does involve a lot
of heat. Ideally both the chip and the coolant are carrying
much of it off the work.,

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"peter.kidwell" wrote in message
...
A friend of mine has stripped threads on the adjustable cup side
of his English bottom bracket.
Some of my cycling buddies have said to use oversize cups, are these
still available.

A Muzi wrote:
Yes, plus 0.5mm oversize cups were once available for all
threads, but no longer.
http://www.yellowjersey.org/photosfr...t/CA746AOS.JPG

Phil, Squid-in-Training wrote:
-snip- thread diameter are meausured from the OD of the
threads? Is it this way for all designations?

Yes, that's right.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971