Bolt hole circle

In article <[email hidden]>,

!Jones said:

In G-code programming, the parameters to the bolt hole circle (bhc)
procedure are radius, angle from vertical to first hole, and number of
holes. My point is that when anyone but a cyclist talks about a bhc,
he or she universally specifies a *radius*, not a diameter.

So, a 110 bhc should be 55!!!

Jones

Well, that's fair, but the actual most useful in-the-field measure, as
Sheldon points out somewhere, is the distance from bolt to bolt for a
given BCD and bolt pattern*.

Bolt-bolt centres are an easy thing to measure, while the diameter is
hard to directly measure.

Also, BCD feels relevant to cyclists because it constrains the smallest
number of teeth a ring on that bolt circle can have (about 39 for 130 mm
BCD, barring heroic efforts).

*bolt pattern being a distinction that was hardly necessary until the
advent of 4-bolt MTB cranks

--
Ryan Cousineau [email hidden] http://www.wiredcola.com/
"I don't want kids who are thinking about going into mathematics
to think that they have to take drugs to succeed." -Paul Erdos

in rec.bicycles.tech Ryan Cousineau said:

Well, that's fair, but the actual most useful in-the-field measure, as
Sheldon points out somewhere, is the distance from bolt to bolt for a
given BCD and bolt pattern*.

Oh, I agree. If I ever had to solve a BHC, I'd start with that as the
easiest measurement to take; then I count the holes and pull out my
calculator. My point is that, mathematically, a circle is defined by
a radius. I was cutting a chain ring the other day and I accidentally
plugged in 110 is what brought it to mind. I hadn't ever really
thought about it, but we're the only bunch I know of to use a
diameter.

Jones

!Jones said:

In G-code programming, the parameters to the bolt hole circle (bhc)
procedure are radius, angle from vertical to first hole, and number of
holes. My point is that when anyone but a cyclist talks about a bhc,
he or she universally specifies a *radius*, not a diameter.

So, a 110 bhc should be 55!!!

Jones

But cyclists don't talk about BHCs. They talk about BCDs.