I have a bicycle brake disk that I wish to mount on a (bicycle) hub. The
disk is RH threaded and is meant to mount on the left side of the hub, so
when the brake is applied it screws down onto a shoulder on the hub. My
application means I need to mount this disk on the right side.

So what I think I'll do is make a shouldered collar threaded RH on the
outside, and LH on the inside, and cut LH threads on the hub. The disk will
run up to the shoulder on the collar and the collar will run down to the
shoulder on the hub.

How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.

"jtaylor" wrote in message
...
I have a bicycle brake disk that I wish to mount on a (bicycle) hub. The
disk is RH threaded and is meant to mount on the left side of the hub, so
when the brake is applied it screws down onto a shoulder on the hub. My
application means I need to mount this disk on the right side.

So what I think I'll do is make a shouldered collar threaded RH on the
outside, and LH on the inside, and cut LH threads on the hub. The disk
will
run up to the shoulder on the collar and the collar will run down to the
shoulder on the hub.

And I presume the shoulder would be on the outside of the disk? That should
work OK, since the tendency will be for the disk to screw to the shoulder,
and the LH threads inside will tend to screw the collar inboard.


How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.

The hub is probably the limiting element for strength of a threaded section.
You probably won't like the machining characteristics of it, but you'll be
better off with stainless for the collar. Otherwise, you'll get nasty
dissimilar metals corrosion in the union, almost right away.

You didn't say how thick was the brake disk. That plays into how small a
difference you can live with between the hub o.d. and the disk hole i.d.

I have no idea how much force a bike wheel exerts on the disk, so please
accept my cornball estimates as just a way to solve the problem.

Figure a reasonable working strength on the stainless similar to mild
steel - say 40kpsi to keep it conservative. If the disk were, say, 3/16"
thick, then the 'adapter' portion of the collar would be 3/16" wide,
shoulder to end - 0.1875 inches. Say the disk exerts a torque of 1000
inch-lb at the hub (ymmv). Then you need 1000/40000 of a square inch of
metal in the cross-section of the adapter - 1/40th square inches. At .1875
wide, that's 0.1333 inches thick (between thread valleys). Add the thread
depths of both the inside and outside threads to that to get the major o.d.
and i.d.

Likely, the threads would fail before the collar squirmed out of the hole.
One rule of thumb says at least five buried threads to maintain the
characteristic strength of the metal. A 3/16" thick disk doesn't give you
that many buried threads at 24tpi, unless it has a thicker hub.

LLoyd

It sounds to me as if it would be as easy to make a complete new brake
disk. You would only have to cut one thread.

Dan


jtaylor wrote:
I have a bicycle brake disk that I wish to mount on a (bicycle) hub.
The
disk is RH threaded and is meant to mount on the left side of the
hub, so
when the brake is applied it screws down onto a shoulder on the hub.
My
application means I need to mount this disk on the right side.

So what I think I'll do is make a shouldered collar threaded RH on
the
outside, and LH on the inside, and cut LH threads on the hub. The
disk will
run up to the shoulder on the collar and the collar will run down to
the
shoulder on the hub.

How thin can I make the collar? - there's a limit to how far I can
reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably
make
the collar from either brass or mild steel; and the hub is some kind
of
aluminium alloy.

wrote in message
oups.com...
It sounds to me as if it would be as easy to make a complete new brake
disk. You would only have to cut one thread.

Actually, he'd have to make a new disc and a new hub. Still, that would
probably be a better solution than the collar idea.

When it comes to brakes, you don't want to mess around and risk failure.
Even on a bicycle (imagine having it fail at a busy traffic intersection at
the bottom of a grade).

The makers of the commercial brake have invested considerable time and money
to insure that their design works as intended. Will the OP be able to say
the same thing about his collar?

If he copies their design, using the same materials, dimensions, and
tolerances, but simply reversing the thread direction, he can be fairly sure
he'll have no problems. But a makeshift collar will be an unknown factor.
Not to mention that it introduces additional points for out-of-roundness,
out-of-plane, out-of-balance, etc. All the things a person wouldn't want in
a disc brake.

Of course, the other option is to solve the problem that's preventing the OP
from mounting the brake on the left side of the hub as intended.

Regards,
Michael

"DeepDiver" wrote in message
...

Of course, the other option is to solve the problem that's preventing the
OP
from mounting the brake on the left side of the hub as intended.


Not an option; the hub is a on a stub axle mounted on the left side of a
trike, and so the disk has to be inboard.

On Mon, 11 Apr 2005 10:34:31 -0300, jtaylor wrote:

I have a bicycle brake disk that I wish to mount on a (bicycle) hub. The
disk is RH threaded and is meant to mount on the left side of the hub, so
when the brake is applied it screws down onto a shoulder on the hub. My
application means I need to mount this disk on the right side.

So what I think I'll do is make a shouldered collar threaded RH on the
outside, and LH on the inside, and cut LH threads on the hub. The disk will
run up to the shoulder on the collar and the collar will run down to the
shoulder on the hub.

How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.


If I understand it correctly, the threads are taking all the torque load
when the caliper clamps onto the rotor. So as long as you remove the
unthreading action (from reversing the RH thread on R side), nothing will
have changed as far as safety and function is concerned.

So, howzabout pinning the hub, rotor and lock collar in place? The pin can
be relatively small diameter since its only function will be to prevent the
collar from backing off. Can you match drill after assembly and pin or even
thread and install a small bolt??
--
Skuke
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jtaylor wrote:

How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.

Don't use brass with aluminum. Bicycles are outside things and get wet.
Brass+aluminum+wet=corrosion.

Ted

On Tue, 12 Apr 2005 22:36:11 GMT, Ted Edwards
wrote:

jtaylor wrote:

How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.

Don't use brass with aluminum. Bicycles are outside things and get wet.
Brass+aluminum+wet=corrosion.

Ted

Ditto stainless and aluminum, and probably mild steel and aluminum.
Best to anodize the aluminum, or check out this stuff from Brownell's:
http://tinyurl.com/6kfz4

On Tue, 12 Apr 2005 23:31:23 -0500, Don Foreman wrote:

On Tue, 12 Apr 2005 22:36:11 GMT, Ted Edwards
wrote:

jtaylor wrote:

How thin can I make the collar? - there's a limit to how far I can reduce
the hub diameter. The disk is threaded 1.375 x 24TPI; I'll probably make
the collar from either brass or mild steel; and the hub is some kind of
aluminium alloy.

Don't use brass with aluminum. Bicycles are outside things and get wet.
Brass+aluminum+wet=corrosion.

Ted

Ditto stainless and aluminum, and probably mild steel and aluminum.
Best to anodize the aluminum, or check out this stuff from Brownell's:
http://tinyurl.com/6kfz4



Any decent bike will have aluminum hubs & rims, stainless spokes and brass
nipples. All three of the materials are in direct contact with each of the
other. Aluminum crank arms are in contact with chromoly or Ti pedal and
bottom bracket spindles. The list goes on. Granted, the aluminum is
probably anodized and the brass is usually plated.

Also, the OP only said he's using bike parts, not making a bicycle so it may
or may not be an "outside thing". It may not even get wet.
--
Skuke
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