DIYbanter - View Single Post

J. Clarke[_2_]

In article , says...

J. Clarke wrote:

I suspect that a small pyrotechnic pressurizing one of the calipers off
my '76 Lincoln might surprise you.

Bill
When it snapped (seriously)? I'm not an engineer, so I don't know for
sure. I just wouldn't be surprised. Maybe someone else can opine.

J. Clarke
Why would something that can stop a 4000 pound car "snap" when called on
to stop a 3 pound saw blade?

Bill
"Pyrotechnics" rather than a master cylinder with brake fluid?

J. Clarke
To stop the saw in a fraction of a revolution, you need rapid
application. A pyro will build pressure rapidly.

That is what I what I might expect to increase the probability of failure.

Given blade radius and density, and rpm, you could probably integrate to
compute the (foot-pounds of) energy that need to be stopped in a small
fraction of a second (I hope that the dust on the blade won't be an
issue). I've seen you post in another "forum" so I believe you are
up to the calculation. I do not have engineering background to back me
up, I'm just thinking it through with you and everyone else who is
reading. Evidently, you'll need to generate the equivalent of an equal
and opposite amount of energy. This means, I think, that you only get
the benefit of a "projection" (dot product) and not all of the force you
can apply to the side of the blade. My reasoning could definitely be
off, maybe a physicist or engineer could help out?

Disk brakes work by friction. The energy comes off as heat. Apply F to
the brake, k * F is the braking force where k is the coefficient of
friction.

Back of the envelope it looks like the Lincoln brake at Lincoln pressure
can stop it in about 1/3 revolution. Don't know how much higher
pressure that caliper can take--at 2x the pressure might be able to do
it in 1/6 revolution, which puts it in Sawstop territory.