You must be a controls or P&C guy with WNH!
Use a DC motor and a DPDT switch with a big resistor across the "stop"
terminals to short the motor when you shut it off. Stop a 10 inch
blade from 3600rpm in less trha a second with a dead short (if the
switch can handle it) or in about 2 seconds with a good "soft" braking
The electornic way would be so much gentler and easier to implement. They
work like a charm.
Maybe only because of the background of the guys proposing it.
Why would it be "impractical on a 10" saw? The brake rotors on that car
are IIRC 11.5 inch diameter and the whole brake assembly fits inside a
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?
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.
I assume these regs are not enforced on saw sales then?
I know my sliding saw (cheapo) has a dynamic brake in it that slows it down
after a few seconds of power down but I do not have a T/S. The ones I have
seen (probably old units) spin forever after power off.
As I stated posters seem to lean towards the technology they are comfortable
The mechanics would be a nightmare to me, also. To others the electronics
would be a nightmare.
Contactor and resistor?...way too complicated.
You want to put that monstrosity on a tilting arbour saw, mounted
under the saw table and in the path of the saw-dust and have it work
Not going to happen - guaranteed.
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
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.
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.
It works reliably on a tilting Lincoln wheel in the path of rain, road
dust, and whatever else mother nature can throw at it, so why does a
nice, dry saw cabinet present such problems?
Do yourself a favor, pull a wheel off your car and _look_ at the
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