drill/tap in frames

On 7/14/2018 2:01 AM, John B Slocomb wrote:
On Fri, 13 Jul 2018 20:53:33 -0500, AMuzi wrote:

On 7/13/2018 8:14 PM, Ralph Barone wrote:
John B. Slocomb wrote:
On Fri, 13 Jul 2018 12:49:33 +0000 (UTC), Ralph Barone
wrote:

John B. Slocomb wrote:
On Fri, 13 Jul 2018 00:10:02 +0200, Emanuel Berg
wrote:

James wrote:

Then you should definitely not just drill
and tap the frame tube itself.

Why not?

The material is too thin.

Is it more thick at the bottom of the bottom
bracket shell and at the bottom-mid section of
the down tube where I have seen this numerous
times, and also the chainguard stays to the
chainguard intersection?

A bottom bracket is usually specified as 7 - 8 mm thick.
--

Cheers,

John B.


Maybe 3-4 mm. Are you quoting the difference between the OD and ID, or the
wall thickness?

I just looked at their catalog which red, for example:
"LB100R - For 22.2mm Chainstays. 60.30x62.30x7\ufffd.
No guides or cut-outs".
or
"LB109R - With Oval 30x17mm. Chainstays.
Angles 60x64x7.30\ufffd. No guides or cut-outs."

Given that the first two numbers were obviously length and breadth
assumed the last was thickness. Not so?



I don't know. I just thought that 7mm wall thickness for a bottom bracket
shell appeared to be overkill to me. I did some web searching and nobody
publishes data on the OD of bottom bracket shells (probably because it
doesn't matter to a first approximation). However, looking through a bunch
of diagrams, I did see that many of them had a 7mm deep pocket to hold the
bearings. Perhaps that's where your 7 came from.

Aha! This BB shell has a 38 mm OD and a 1.370" ID, which gives about 2mm
wall thickness.
https://framebuildersupply.com/produ...od-made-in-usa


Say that again, slowly. The O.D. is 38mm and th I.D. is 1.370??

Just measured a cast 1982 Cinelli and an unknown vendor on a
1978 Bianchi Superleggera at 3mm. Both are m36x24 on
vintage frames being repaired.

A new mid-1970s RFG pressed shell is 3mm. A new 1976 Nikko
Sangyo pressed shell is 4mm but heavy and klunky in other
aspects as well. Both 1.370"x24.

That's a quick check with a vernier so depending on your
purpose you might subtract thread depth. Or not. Regarding
threaded holes, I've seen a lot of drilling, piercing,
slots, tapped holes and so on on every kind of steel BB
without notable failure attributable to that. They do break,
just not from holes in the bottom. Classic British bikes
have a coarse threaded hole on top LH for a bearing oiler.
Cracks don't form around those either.

Say that again, slowly. The O.D. is 38mm and th I.D. is
1.370??

That would be 38mm overall, 34.8mm at thread peaks or ~33.8
at thread root leaving about 4+mm dia or 2+mm at the radius
theoretically. Which comports roughly with actual
measurements yesterday. Surely not 7mm on any modern (not
cast iron) threaded BB shell.



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