Motor Reversing

[clare]

Like I said.

[Steve Turner]

After I already said it.

[Robatoy]

In article ,

On an average wheel, that would be 330+ mph (Or therabouts ± 50 mph)

I don't think you'd want to stop that tire in one rotation.

[Steve Turner]

Valid point, but again, we're not talking about a Saw-Stop equivalent here, only a "convenience" brake that stops the blade in a second or two. Unless you've dangerously under-tightened the arbor nut (or ridiculously over-engineered the brake) that's not likely to cause enough centrifugal force to loosen the arbor nut.

[clare]

stop the blade

caliper probably

Most definitely.

[-MIKE-]

1. It wouldn't be running.
2. What I'm talking about could hardly be considered a load.

[-MIKE-]

Neither of us is trying to stop the blade that fast.

I seriously doubt that was even the slightest consideration for the inventor of the SawStop.

[Markem]

Would make a great cartoon to pass about the Internet, if twas done in animation might even go viral. But you might want to have a huge catchers mitt behind the punchee.

Mark

[Lee Michaels]

Is Wiley Coyote available as a spokesperson?

[Stuart]

If a car wheel has a rolling diameter of, say, 17", the car will travel about

4.45 feet per revolution. 5000rpm means the car will be travelling at 22,251 ft/min or 252mph. I'm not surprised given the car probably weighs upwards of a ton.

However, as anyone who has done much driving before the advent of ABS will tell you, it is quite easy to lock up the wheels of a car if you stamp on the brake hard enough.

Because the energy in a rotating saw blade is bugger all compared with a moving car.

[Josepi]

Spoken like a true woodworker...LOL

[Josepi]

That happens freuently to my Milwalkee 12V drill. The brake stops the insides but the chuck wants to keep on going and undoes itself and the bit falls out. The chuck even appears to have a dual gear ratio tightening mechanism.

"Steve Turner" wrote in message news:i97mc6$uo9$ [e-mail]... Valid point, but again, we're not talking about a Saw-Stop equivalent here, only a "convenience" brake that stops the blade in a second or two. Unless you've dangerously under-tightened the arbor nut (or ridiculously over-engineered the brake) that's not likely to cause enough centrifugal force to loosen the arbor nut.

[clare]

From what I was told it WAS.

[Josepi]

OMG! Now we need to put an ABS system on our saw brake so it doesn't cause any arbor damge from stopping to quickly?

LOL

scott

"HeyBub" writes:

[Josepi]

I have no idea what EU regulations state or why they would care about a gradual stop of a saw blade.

Are these regulations involved in convenience stopping of a table saw blade and what do they state?

[Josepi]

Maybe not. Somebody has to take one for the team. Induction motors typically have enough back emf generation to cause some, if not enough braking to stop most motors.

Somebody try it. With the saw blade running full speed, pull the plug (do

**NOT** turn off the switch) and stick the two plug contacts (line and neutral) across the metal table top and short it out.

Tell us what happens and what kind of motor you have.

The DC injection will involve a little more circuitry.

I have experienced both with different motors. They ranged from 1hp AC to

5hp DC units. The DC injection could make them stop in a turn or so but with such large motors the torque was brutal.

In article , [e-mail] says... On an induction motor the process is a bit different. Instead of aresistor across the motor to stop it you use "DC Injection" - in other words throw about 40 volts DC across the winding for about 2 seconds.

[Josepi]

Nobody wants to stop a saw blade in one rev. Convenience stop only.

This was barked at when the SawStop came into comparison.

A car brake is designed to avoid locking up, yet that's exactly the behavior you would want with a sawblade, and you'd want it to lock in much less than a single revolution.

[J. Clarke]

Seriously that's how you compress the piston on the brakes on a Jeep-- put a c-clamp on it.

[J. Clarke]

The state that the blade must spin down in 10 seconds or less or else the saw has to have permanent guard. The method they normally use won't spin dado blades down in 10 seconds, so saws without permanent guards are made with short arbors that can't take a dado.

[J. Clarke]

Because the blade masses a tiny fraction of what the car does.

If a car brake doesn't ever lock then the car doesn't stop. In any case, absent ABS it's possible to lock the brakes on any car on which the brakes are in good condition. Don't believe me, put both feet on the pedal and shove hard. If you have ABS then pull the fuse on it first.