True wheel has slack spoke, doesn't stay true

Phil, Squid-in-Training wrote:
wrote:


I've removed flat spots from my rims several times. It didn't take a
car jack. I used a bench vise and blocks of wood.

I took a piece of 1" x 4" board, perhaps 10" long, and fastened a
block cut from 2" x 4" on each end. The blocks have an angled
surface, to match the rim's angle. This supports a span of the rim
from the outside. Another block of wood presses against the flat
spot on the inside (i.e. hub side), with several spokes removed for
clearance.

The sandwich fits into my bench vise. I tighten bit by bit, loosening
occasionally to check if I've moved the rim enough. It's a bit fussy,
but not too bad. Way easier than buying new components and building a
new wheel, and much cheaper.

- Frank Krygowski

I can almost visualize, it but I can't figure out how all the parts hold
together without flying apart. Do you have a schematic/pictures?

Sorry, no digital camera lives here. I can try with ASCII art -
tedious as that is!

Here's a top view. The rim would be horizontal, the hub toward the top
of the page.

Sqeezing the vise shut makes the rim more concave upward in this
sketch.


| vise jaw |
| ___________|
------------
| | wood block bearing on
"inside" rim surface
----------

- - - -- -Rim goes here - - -

---------- ----------
| \ / |
Two wood blocks
| \ / |
fastened to 1 x 4
----------------------------------------------------------------
| 1 x 4 |
---------------------------------------------------------------

---------------------
| |
| vise jaw |

- Frank Krygowski

dvt wrote:
jim beam wrote:

1. bike shops don't always allow for the elongation in tension that
revos exhibit compared to other spokes. that often leaves then a
little too long for their application, so it can be hard, particularly
on a revo, to get any more tension if the thread is bottomed out -
because they just twist.


Assume: 300 mm spoke length, modulus 200 GPa, spoke tension 100 kgf

Variable: 1.5 mm vs 2.0 mm spoke diameter

Difference in elongation: 0.36 mm

so instead of rounding a spoke length calc that was x.43mm upwards, it
would now be x.79 and get rounded down. or at least would be if the
shop didn't just use the same length for both gauges, which is my
experience. and it created the situation i described - that of thread
nipple thread binding because the revos were just too long.

On Wed, 07 Dec 2005 20:49:00 -0800, jim beam wrote:

so instead of rounding a spoke length calc that was x.43mm upwards, it
would now be x.79 and get rounded down. or at least would be if the

So between .0 and .5 gets rounded up and between .5 and .0 gets rounded
down? That's a very interesting discontinuous function you've created.

shop didn't just use the same length for both gauges, which is my
experience.

It should, if it was actually rounding things off. That's how rounding
works. Given that a fraction of a millimeter too long is much more crucial
than a fraction of a millimeter too short, you should probably round down
to the nearest millimeter when possible.


Jasper

"dvt" wrote in message
...
jim beam wrote:
1. bike shops don't always allow for the elongation in tension that
revos exhibit compared to other spokes. that often leaves then a little
too long for their application, so it can be hard, particularly on a
revo, to get any more tension if the thread is bottomed out - because
they just twist.

Assume: 300 mm spoke length, modulus 200 GPa, spoke tension 100 kgf

Variable: 1.5 mm vs 2.0 mm spoke diameter

Difference in elongation: 0.36 mm


And assuming a 2-56 thread on the spoke, that's 56 * (.36/25.4) =
..7937-something of a turn.

Not really anything to worry about for sensible folk.

Jasper Janssen wrote:
On Wed, 07 Dec 2005 20:49:00 -0800, jim beam wrote:


so instead of rounding a spoke length calc that was x.43mm upwards, it
would now be x.79 and get rounded down. or at least would be if the


So between .0 and .5 gets rounded up and between .5 and .0 gets rounded
down? That's a very interesting discontinuous function you've created.

er, yes. you are right - other way around.



shop didn't just use the same length for both gauges, which is my
experience.


It should, if it was actually rounding things off. That's how rounding
works. Given that a fraction of a millimeter too long is much more crucial
than a fraction of a millimeter too short, you should probably round down
to the nearest millimeter when possible.

that's what i was trying to say.



Jasper

On Thu, 08 Dec 2005 06:11:32 -0800, jim beam wrote:
Jasper Janssen wrote:

er, yes. you are right - other way around.

Ah, that makes more sense.

It should, if it was actually rounding things off. That's how rounding
works. Given that a fraction of a millimeter too long is much more crucial
than a fraction of a millimeter too short, you should probably round down
to the nearest millimeter when possible.

that's what i was trying to say.

Of course, many shops stock spokes only in 2 mm increments rather than 1
mm increments, in which case a pure round down function might be
problematic, but a pure rounding function (0-1 to 0 and 1-2 to 2) might
also be unsuitable.

P'raps 1-1.5 down and 1.5-2 up. At least for those terribly elastic types
of spokes.


Jasper

wrote:

I've removed flat spots from my rims several times. It didn't take a
car jack. I used a bench vise and blocks of wood.

I took a piece of 1" x 4" board, perhaps 10" long, and fastened a block
cut from 2" x 4" on each end. The blocks have an angled surface, to
match the rim's angle. This supports a span of the rim from the
outside. Another block of wood presses against the flat spot on the
inside (i.e. hub side), with several spokes removed for clearance.

The sandwich fits into my bench vise. I tighten bit by bit, loosening
occasionally to check if I've moved the rim enough. It's a bit fussy,
but not too bad. Way easier than buying new components and building a
new wheel, and much cheaper.

There is a commercial tool for pressing flat spots out of a rim.
It works similarly, but the various blocks are metal and attached
to a metal frame, with a screw handle for doing the pressing.
I don't know if it is made any longer or who made it - my old LBS
in Santa Cruz had one hanging on the shop wall.

wrote:
I've removed flat spots from my rims several times. It didn't take a
car jack. I used a bench vise and blocks of wood.
I took a piece of 1" x 4" board, perhaps 10" long, and fastened a block
cut from 2" x 4" on each end. The blocks have an angled surface, to
match the rim's angle. This supports a span of the rim from the
outside. Another block of wood presses against the flat spot on the
inside (i.e. hub side), with several spokes removed for clearance.
The sandwich fits into my bench vise. I tighten bit by bit, loosening
occasionally to check if I've moved the rim enough. It's a bit fussy,
but not too bad. Way easier than buying new components and building a
new wheel, and much cheaper.

wrote:
There is a commercial tool for pressing flat spots out of a rim.
It works similarly, but the various blocks are metal and attached
to a metal frame, with a screw handle for doing the pressing.
I don't know if it is made any longer or who made it - my old LBS
in Santa Cruz had one hanging on the shop wall.

This one? It's well made, easy to use.
http://www.yellowjersey.org/photosfr...st/RIMTRUE.JPG

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

A Muzi wrote:
wrote:
There is a commercial tool for pressing flat spots out of a rim.
It works similarly, but the various blocks are metal and attached
to a metal frame, with a screw handle for doing the pressing.
I don't know if it is made any longer or who made it - my old LBS
in Santa Cruz had one hanging on the shop wall.

This one? It's well made, easy to use.
http://www.yellowjersey.org/photosfr...st/RIMTRUE.JPG

The one I saw was very like that, I think not identical, but
in materials a similar age and style. Thanks for posting the
picture. I always wondered if this tool would work on the
deeper sectioned rims that are more common now, as well
as typical single-wall or box section rims.

I can imagine home brewing a similar tool by nailing sections
of wood (about 1x1 strips) to a flat board, and using a large
C-clamp with a wood block to do the pressing.

wrote:
Phil, Squid-in-Training wrote:
wrote:


I've removed flat spots from my rims several times. It didn't take
a car jack. I used a bench vise and blocks of wood.

I took a piece of 1" x 4" board, perhaps 10" long, and fastened a
block cut from 2" x 4" on each end. The blocks have an angled
surface, to match the rim's angle. This supports a span of the rim
from the outside. Another block of wood presses against the flat
spot on the inside (i.e. hub side), with several spokes removed for
clearance.

The sandwich fits into my bench vise. I tighten bit by bit,
loosening occasionally to check if I've moved the rim enough. It's
a bit fussy, but not too bad. Way easier than buying new
components and building a new wheel, and much cheaper.

- Frank Krygowski

I can almost visualize, it but I can't figure out how all the parts
hold together without flying apart. Do you have a
schematic/pictures?

Sorry, no digital camera lives here. I can try with ASCII art -
tedious as that is!

Here's a top view. The rim would be horizontal, the hub toward the
top of the page.

Sqeezing the vise shut makes the rim more concave upward in this
sketch.


| vise jaw |
| ___________|
------------
| | wood block bearing on
"inside" rim surface
----------

- - - -- -Rim goes here - - -

---------- ----------
| \ / |
Two wood blocks
| \ / |
fastened to 1 x 4
----------------------------------------------------------------
| 1 x 4 |
---------------------------------------------------------------

---------------------
| |
| vise jaw |

- Frank Krygowski

Nice, Frank... I see it now.
--
Phil, Squid-in-Training