Table Saw Motor Question

[Thomas Williams]

I have a Craftsman hybrid table saw with 1 3/4 hp motor. After I hit the stop switch it takes the blade a fair amount of time to come to a stop. How long should it take for the blade to stop? Is there any braking in a TEFC motor? It has never bothered me, but LOML thinks it takes too long.

[glenn bradley]

Mine takes a long time as well. The motor has no brake that I am aware of. If it is any consolation, my saw stops much sooner than my big table router ;-) In both cases I have decided that patience save fingers. There is always something to do while you wait for the blade to stop. Just build that wait time into your method of work and enjoy your shop time. Clear off the bench or sweep a little. Hang some tools back up or return them to their proper spot. There's all sorts of ways to pass the time.

[Tom Veatch]

I have a Craftsman hybrid table saw with 1 3/4 hp motor. After I hit the stop switch it takes the blade a fair amount of time to come to a stop. How long should it take for the blade to stop? Is there any braking in a TEFC motor? It has never bothered me, but LOML thinks it takes too long.

I've never put a stop watch on my 10" 3HP cabinet saw, but it takes a fair amount of time - 15-20 seconds at least with a thin kerf blade, much longer with an 8" dado set. I've never really paid that much attention to the stop time, just been careful to keep clear until it does stop.

The TEFC designation of an electric motor simply indicates that the motor is totally enclosed within a metal shell and cooling is accomplished by air blown over that shell rather than directly across the motor's windings. That designation doesn't address whether or not the motor might incorporate braking provisions.

Definitions of traditional motor enclosure terminology can be found here (http://www.compressors.com/Documents/documents/NEMA-motor-enclosures-traditional.pdf).

[Tom Veatch]

...After I hit the stop switch it takes the blade a fair amount of time to come to a stop. How long should it take for the blade to stop? ...

Timed mine this morning. 10-12 seconds from switch off to blade stopped.

[Ken Fitzgerald]

Tom....on the 2 tables saws I have owned in my lifetime that is about the time it takes for those two to spin down. Without a brake, it's simply spinning mass versus the friction of the bearings.

[Mike Marcade]

We like to call it inertia. ;)

[Tom Veatch]

Tom....on the 2 tables saws I have owned in my lifetime that is about the time it takes for those two to spin down. Without a brake, it's simply spinning mass versus the friction of the bearings.

Exactly. Moment = (Rotational Moment of Inertia) X (Angular Acceleration)

I've heard there are some standards in Europe that put limits on the length of time it takes the blade to stop spinning which is why (as I've also heard) that stacked dado blades can't be used on European saws.

Don't know how true that is, but it is certainly true that with the spinning mass of my 8" stacked dado, it seems to take forever for the blade to stop spinning. Just to satisfy curiosity, I'll have to time it next time I've got my dado blade mounted.

[Bruce Page]

Looking on the bright side…your bearings are good!
My Unisaw takes awhile to stop as well.

[Chuck Burns]

There are electrical means that a tool manufacturer can use toslow the blade down quickly. I had such a sytem on a 16" Dewalt RAS. It worked for a while when the saw was new. After it stopped working we got it fixed under warranty; twice. After the warranty expired and it stopped working for the third time we decided to live with it.

Now you want to talk about a blade taking a while to stop....this puppy took the cake. Spinning a 1/4" blade you could turn the saw off and still crosscut a doug fir 4x6 while coasting down.

[Gary Curtis]

My cabinet saw takes about 6-8 seconds to spool down to a stop. You are being reasonable to worry about continued spin on your blade.

In an excellent article by Kelley Mehler in Popular Woodworking he compared the design and features on European tablesaws. He considers them far superior, especially when it comes to safety. European law mandates that power machines come to a stop within 5 seconds of cutting power.

I wish I had such equipment. North American equipment will have to meet those standards by 2012.

Gary Curtis

[Mike Marcade]

Exactly. Moment = (Rotational Moment of Inertia) X (Angular Acceleration)

I've heard there are some standards in Europe that put limits on the length of time it takes the blade to stop spinning which is why (as I've also heard) that stacked dado blades can't be used on European saws.

Don't know how true that is, but it is certainly true that with the spinning mass of my 8" stacked dado, it seems to take forever for the blade to stop spinning. Just to satisfy curiosity, I'll have to time it next time I've got my dado blade mounted.

You are probably right about the European standards, in the early 90s I was designing an electric hedgetrimmer to sell in Europe and it needed a mechanism to stop the blade within 0.5 seconds of releasing the trigger. The chain saws needed something similar.