Bottom bracket shell, head-tube tube, angles?

Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.

I have some scrapheap bikes to cut up for parts, and, specifically, for
the bottom bracket shell and head tube. But I'd really rather not have
old scrap bits in it. And in any case they have 73mm shells and I'd
rather have a 68mm to keep the Q down. So, does anyone know where I can
get a piece of aluminium tube of the right internal diameter for a
bottom bracket shell? What _is_ the right internal diameter - 1.37
inch?? Is getting hold of this so hopelessly difficult that I'd be
better off just cutting up my scrap?

And similarly, the head tube. When you talk about a 1 1/8" headset, is
the measurement the outside diameter of the steerer tube or the inside
diameter of the head tube - or something else altogether? What,
exactly, should the inside diameter of the head tube be?

Finally, those of you who have built your own frames: Obviously the
bottom bracket axle wants to be /exactly/ parallel to the rear axle,
and /exactly/ at 90 degrees to he head tube axis. But in practice how
carefully do I have to jig this? How far off is too far off?

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

Age equals angst multiplied by the speed of fright squared.
;; the Worlock

Simon Brooke wrote:
Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.

I missed what kind of bike this will be. Or are you keeping it as a
surprise? :-)

I have some scrapheap bikes to cut up for parts, and, specifically,
for the bottom bracket shell and head tube. But I'd really rather not
have old scrap bits in it. And in any case they have 73mm shells and
I'd rather have a 68mm to keep the Q down. So, does anyone know where
I can get a piece of aluminium tube of the right internal diameter
for a bottom bracket shell? What _is_ the right internal diameter -
1.37 inch??

Yes, see http://www.sheldonbrown.com/gloss_bo-z.html

Is getting hold of this so hopelessly difficult that I'd
be better off just cutting up my scrap?

And similarly, the head tube. When you talk about a 1 1/8" headset, is
the measurement the outside diameter of the steerer tube or the inside
diameter of the head tube - or something else altogether?

Outside diameter of steerer.

What,
exactly, should the inside diameter of the head tube be?

According to Sheldon Brown, for 1 1/8", "frame cup outside diameter" is
34.0 mm. I'm not sure if that's the head cup itself or the tube inside
diameter--which I would expect to be a touch smaller to make an
interference fit.

Info: http://www.sheldonbrown.com/gloss_ha-i.html - scroll down.

~PB

in message , Pete Biggs
') wrote:

Simon Brooke wrote:
Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.

I missed what kind of bike this will be. Or are you keeping it as a
surprise? :-)

One with two wheels and pedals.

Gearing isn't finalised (and won't be until we've done some testing) but
current plans are for a lowest gear of 49.7 inches and a highest of
155.3 inches. Oh, and did I say it was a monocoque?

I have some scrapheap bikes to cut up for parts, and, specifically,
for the bottom bracket shell and head tube. But I'd really rather not
have old scrap bits in it. And in any case they have 73mm shells and
I'd rather have a 68mm to keep the Q down. So, does anyone know where
I can get a piece of aluminium tube of the right internal diameter
for a bottom bracket shell? What _is_ the right internal diameter -
1.37 inch??

Yes, see http://www.sheldonbrown.com/gloss_bo-z.html

That's what I was looking at, but the Great Sheldon also quotes 1.375
(mind you, 5 thou bigger is not a lot, but then the threads on a BB
shell are not very deep).

And similarly, the head tube. When you talk about a 1 1/8" headset,
is the measurement the outside diameter of the steerer tube or the
inside diameter of the head tube - or something else altogether?

Outside diameter of steerer.

What,
exactly, should the inside diameter of the head tube be?

According to Sheldon Brown, for 1 1/8", "frame cup outside diameter"
is
34.0 mm. I'm not sure if that's the head cup itself or the tube
inside diameter--which I would expect to be a touch smaller to make an
interference fit.

Info: http://www.sheldonbrown.com/gloss_ha-i.html - scroll down.

Ah, thanks, hadn't seen that.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/
Windows 95:
You, you, you! You make a grown man cry...
M. Jagger/K. Richards

Simon Brooke wrote:
Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.

Cool. Carbon the way of the future is mmmmm! ;-)

I have some scrapheap bikes to cut up for parts, and, specifically, for
the bottom bracket shell and head tube. But I'd really rather not have
old scrap bits in it. And in any case they have 73mm shells and I'd
rather have a 68mm to keep the Q down. So, does anyone know where I can
get a piece of aluminium tube of the right internal diameter for a
bottom bracket shell? What _is_ the right internal diameter - 1.37
inch?? Is getting hold of this so hopelessly difficult that I'd be
better off just cutting up my scrap?

www.framebuilding.com if you can bear to buy new. Peter is very helpful
and has no minimum order (Although I recommend buying everything you
think might be useful at once to balance out the carriage costs!).

Do you have access to the appropriate thread cutters for a BB? It's
worth mentioning that the ones commonly used to clean existing threads
are apparently not much cop at cutting new ones.

And similarly, the head tube. When you talk about a 1 1/8" headset, is
the measurement the outside diameter of the steerer tube or the inside
diameter of the head tube - or something else altogether? What,
exactly, should the inside diameter of the head tube be?

The OD of the steerer. Are you thinking of going 1 1/8th? I only ask
because I have both a head tube reamer and facer and crown race cutter
for 1" which you'd be welcome to borrow.

Finally, those of you who have built your own frames: Obviously the
bottom bracket axle wants to be /exactly/ parallel to the rear axle,
and /exactly/ at 90 degrees to he head tube axis. But in practice how
carefully do I have to jig this? How far off is too far off?

It depends on how comfortable you want the bike to be to ride. Hooves 1
was fine for shortish distances, but for rides of 40+ miles, the wonky
BB (Around 2 degrees out left to right I think) had a habit of
exacerbating groin strain. This was probably not helped in any way by
the excessively high gearing.

I still dream of getting my hands on some cones for centering tubes, but
I've yet to find a source, and our otherwise pretty good machine shop at
work does not include a lathe!

Jon

Simon Brooke wrote:

Gearing isn't finalised (and won't be until we've done some testing)
but current plans are for a lowest gear of 49.7 inches and a highest
of 155.3 inches. Oh, and did I say it was a monocoque?

I won't ask what you'll be slipstreaming with that monster gear ;-)

/snip
Yes, see http://www.sheldonbrown.com/gloss_bo-z.html

That's what I was looking at, but the Great Sheldon also quotes 1.375
(mind you, 5 thou bigger is not a lot, but then the threads on a BB
shell are not very deep).

Looking at the table carefully, it's 1.370 for British and 1.375 for ISO.
SB says "British and I.S.O. are interchangeable".

~PB

in message , Pete Biggs
') wrote:

Simon Brooke wrote:

Gearing isn't finalised (and won't be until we've done some testing)
but current plans are for a lowest gear of 49.7 inches and a highest
of 155.3 inches. Oh, and did I say it was a monocoque?

I won't ask what you'll be slipstreaming with that monster gear ;-)

Dead easy cycling if my[1] acronyms[2] can help[3].

[1] or 'mysterious'.
[2] or 'aerodynamics'.
[3] but probably not with prototype #1.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/
Wannabe a Web designer?
URL:http://userfriendly.org/cartoons/archives/97dec/19971206.html

in message , Jon Senior
jon_AT_restlesslemon_DOT_co_DOT_uk ('') wrote:

Do you have access to the appropriate thread cutters for a BB? It's
worth mentioning that the ones commonly used to clean existing threads
are apparently not much cop at cutting new ones.

I don't, but I think Marcus has. I'll check in the morning.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; It's dangerous to be right when the government is wrong.
;; Voltaire RIP Dr David Kelly 1945-2004

"Simon Brooke" wrote in message
...
get a piece of aluminium tube of the right internal diameter for a
bottom bracket shell? What _is_ the right internal diameter - 1.37
inch??

If you're cutting threads in it, no.

1.375" is the (nominal) dimension of the "screw" - the part with the threads
on the outside. To determine the correct size for a matching internal
thread you need that number, the thread pitch, the thread form, and a figure
for the percentage of a full thread.

For a 1.375" 24 tpi 60 degree thread with a flat crest and root (standard
form) and 80% thread the correct figure would be 1.3316986666666665, more or
less a few Ångströms.

Simon Brooke wrote:
Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.



I'm sure you have considered everything, but it would be remiss of me
not to relate a coutionary tale. A friend of mine had an extremely
nasty accident on his first serious ride on the carbon monocoque he
made. Judging from the state of the frame (he has no memory of the
incident) the head tube tore somewhat through the carbon composite and
he fell off.
Remember to make that bit really strong!!!

LGF

in message . com,
') wrote:

Simon Brooke wrote:
Well, the material for the monocoque of my new bike has arrived here
today, so it's time to get off my arse, stop drawing and start
building. But there are still things I'm short of, or, to be more
precise, could do better.

I'm sure you have considered everything, but it would be remiss of me
not to relate a coutionary tale. A friend of mine had an extremely
nasty accident on his first serious ride on the carbon monocoque he
made. Judging from the state of the frame (he has no memory of the
incident) the head tube tore somewhat through the carbon composite and
he fell off.
Remember to make that bit really strong!!!

Thanks, I will. But this isn't actually a bike you can fall /off/,
precisely...

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Women are from Venus. Men are from Mars. Lusers are from Uranus.