Motor Reversing

Page 7 of 8  
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 resistor.
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wrote:

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On Tue, 12 Oct 2010 22:25:50 -0400, "J. Clarke"

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snipped-for-privacy@snyder.on.ca says...

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 15" wheel.
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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 15" wheel.
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If it "works like a charm" then why can't it slow a dado fast enough to meet EU regulations?

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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?
says...

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says...

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.

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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.
says...

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On Wed, 13 Oct 2010 18:15:40 -0400, "J. Clarke"

under the saw table and in the path of the saw-dust and have it work reliably??? Not going to happen - guaranteed.
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As I stated posters seem to lean towards the technology they are comfortable with.
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 reliably??? Not going to happen - guaranteed.
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says...

So tell us how to wire an induction motor to make the "contactor and resistor" work.

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On Wed, 13 Oct 2010 23:16:27 -0400, "J. Clarke"

resistor 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.
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snipped-for-privacy@snyder.on.ca says...

So now you have to add a power supply and controls.
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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.
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.
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wrote:

a brake caliper for the application.
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snipped-for-privacy@snyder.on.ca says...

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 mechanism.
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On Wed, 13 Oct 2010 23:15:27 -0400, "J. Clarke"

I've also rebuilt a few tilting arbour saws - both belt drive, gear drive, and direct drive..
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snipped-for-privacy@snyder.on.ca says...

And yet you see a problem.
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On Thu, 14 Oct 2010 08:27:07 -0400, "J. Clarke"

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