Electric brake for tablesaws?

[Robert Chapman]

Yesterday I did something dumb in the shop and spent an hour in the ER as a result. I was ripping some 3/4 inch plywood on my TS, had turned off the saw after a cut and was moving the large remaining piece when I touched the still rotating blade with two fingers of my right hand. I know - the blade guard was in the corner - also dumb.

So here is my thought - if the motor on the TS had been equiped with an electric brake I might not have two fingers throbbing and bandaged. Do any TSs have electric brakes on the motor? If not why not? My PC circular saw has one. Seems like a good safety feature.

I know - if I had a Sawstop I would not be writing this post.

[Sonny Edmonds]

Depends on your motor.
But here is one or two you might use (http://www.grainger.com/Grainger/wwg/productIndex.shtml?operator=prodIndexRefinementSea rch&originalValue=Motor+brakes&L1=Brakes%2C). :eek:

Heal fast, do NOT repeat your mistakes. :rolleyes:

[J.R. Rutter]

You could look around for a VFD - (variable frequency drive). This would let you set things like time to bring blade up to speed (no more thump) and time to stop the motor (brake speed). Of course you can also vary the speed of the motor, but this has limited use on a table saw unless you are getting very creative. Depending on your motor HP, these can be had for a couple hundred dollars, just do some googling.

[Charles Lent]

Robert,

Sorry to hear about your "incident" and I hope you have a full recovery.


There are two types of motors that are most commonly used on table saws.

A universal type motor, which is the type used in most hand tools, actually becomes a generator when it is spinning. If you could short together the motor leads immediately after you removed the input power, the motor would stop very quickly. This is the technicue employed by the hand tool manufacturers to add braking to their tools. They simply add another set of contacts to the power switch that connects the motor leads together when the power switch is turned off.

An induction type motor, which is what is most commonly found in the larger table and cabinet saws, does not generate any significant energy when it is spinning, like the universal motors, and so the brake that was described above will not work. It is possible to electrically brake this type of motor, but a much more sophisticated braking circuit is required. Basically a stationary magnetic field has to be created in this type of motor to brake it. A VFD could be used, but would need to remain powered on during the braking cycle and they can't be used on all motors.

Neither of these braking schemes will stop the motor/blade as fast as the Sawstop system.

Charley

[Greg Sznajdruk]

I could be all wrong and it wouldn’t be the first time but if I recall the reason they don’t use dynamic braking on table saw is that the breaking action could loosen the arbour nut.

Greg

[Sonny Edmonds]

That is entirely possible, Greg.
The kinetic energy of the blade could conceivably backlash the arbor nut loose or even off.
Good point! ;)

[Steve Rozmiarek]

Robert, if you get a chance to look at Felders system, I think it is what you are thinking of. Not sure what the electrons are doing in all those components, but the motors all have soft start, which I love, all have variable speed adjusted electronically, which I also love, and all have superb braking, which is phenominal. I have a 12" WW2 in the saw now, and it stops in 2-3 seconds. The shaper takes a bit longer, and the planer is 2-3 as well. To make all of this work, there is a huge circut panel, completely full of Lenze components.

I actually did something similar to what sent you to the ER about a week after I got my new combo, but when my finger touched the riving knife, the blade had stopped moving. Just a big reality check, no blood.

The way that Felder, and apparently Altendorf, deals with the braking and the inertia of the saw blade, is to add two pins outside the arbor nut. The whole assembly is FAR different then any unisaw clone.

[Ed Bamba]

Been there, done that. But fortunately my injury was was minor. Don't get me wrong, it was still painful. Learned something on that day; never assume that the blade is at a full stop, and avoid reaching for off-cuts with bare hands. Best to use a push stick. Get well soon.

Ed

[Charles Lent]

Greg,

If you stop the motor too quickly, the arbor nut will definitely loosen up. In 1965 I made a braking circuit for my old contractors saw that used an induction motor, and the first time that I tried it the motor stopped very quickly, but the blade kept turning. The arbor nut had loosened and the blade was spinning freely, although it was turning a lot slower then it had been when the saw was running. Reducing the braking voltage and pulse duration left the nut tight, but the motor would then spin about 5 revolutions before fully stopping, still better than the normal coast, but not as good as the Sawstop, which grabs the blade and self destructs both the blade and the brake unit. My brake was never intended to stop the saw that quick. I had technical difficulties keeping my home made brake circuit working and eventually gave up on it. It was just a DC power supply and a pulse duration control circuit, but I didn't have the technology in 1965 to make it reliable enough. Semi-conductors are much better now.

Charley

[Jeff Bratt]

You are correct - European saws are required to use dynamic braking. And this is why they are not allowed to mount dado stacks. The braking action can be adjusted to stop a 10" (or 12"?) blade without loosening the arbor nut, but dado stacks have too much mass. For larger diameter saws, there are little stubs on the arbor and matching holes in the blade to keep the arbor nut from loosening.

[Robert Parrish]

I have been wondering about this very problem for years. My compound miter saw has a blade break and the arbor nut doesn't come off. I spend a good of my shop time waiting for the TS blade to stop or sometimes I just force it to stop!! It seem like something that would sell very well as an add-on.

[Nissim Avrahami]

Sorry to here about your accident.....I wish you fast recovery....

That' exactly the reason that the EU imposed "The blade must stop within 10 seconds" since year 2000 or so (on my saw it stops within 6 seconds, so I just count to 10)...and from this year, on all the metalworking and woodworking machines without permanent guard.


That is entirely possible, Greg.
The kinetic energy of the blade could conceivably backlash the arbor nut loose or even off.
Good point! ;)

Grag and Sonny
You are correct, now you can understand why on the Euro saw the use of dado blade is prohibited (Mass).

Best Regards
niki

[Ben Rafael]

I used a General or General International(cant remember which) TS once where the blade would stop very quickly when powered down. It was a very nice feature.

[Nissim Avrahami]

What Jeff Bratt said...I think that it's mandatory for 12" or more blade even though my table saw is designed to 10" max blade dia.

On the blade there are 2 holes that each of them can fit to the pin.

Personally, I removed the pin to be able to use older blades without holes.

niki
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[Steve Rozmiarek]

Sorry to here about your accident.....I wish you fast recovery....

That' exactly the reason that the EU imposed "The blade must stop within 10 seconds" since year 2000 or so (on my saw it stops within 6 seconds, so I just count to 10)...and from this year, on all the metalworking and woodworking machines without permanent guard.



Grag and Sonny
You are correct, now you can understand why on the Euro saw the use of dado blade is prohibited (Mass).

Best Regards
niki

Is it legal to use the "dado" cutter that works more like a shaper cutter than a blade there? I have one of those, horrible for plywood, great for solid, but it goes on the saw arbor. It also brakes as well as the regular blades. It would work with the 30mm shaper spindle too, I think.

What brand is that saw you posted a photo of?

[Nissim Avrahami]

Hi Steve

I don't know about any "shaper like" dado blade but, I think that only the blade can be installed on the arbor that is so short that anything more than 3mm cannot fit (the arbor is 30mm dia according the EU regulations)

The table saw on the pic is "Elekra Beckum" (owned by Metabo) but some 1 year ago, everything is Metabo and the name Electra Beckum remained only on the older production line - but it's the same TS just with new label...

Here is a general view - the sliding table is original and you can see a few of my improvements...

Regards
niki
108046108047

[Peter Quinn]

I use a Griggio (Italian) at work that stops in under 4 seconds, costs around $10, 000. Its a small slider, maybe a 60" stroke? Very nice machine. It accepts a dado stack and a stacked scoring blade, they have overcome the 'no dado' problem with a serious locking collar on the arbor unlike anything on an American saw. If you've seen a shaper arbor with the lock ring for reverse rotation, its a little like that but has a key way involved and two pins on the arbor collar. I would not try to break a standard US made TS as the blade spinning off is a much worse scenario than waiting for it to stop. Having the blade break on that slider is a real convenience, wish they all had that but glad I didn't have to pay for that saw. My slot mortiser has a breaking motor that stops in a few seconds which is also a real nice feature for safety and quick set up changes.

I'm sorry to hear of your injury but in all honesty a wound inflicted by lack of patience and adherence to a strict safety protocol (don't reach over the blade to retrieve a work piece, wait for the blade to stop before working around the saw, etc) os only tenuously an accident to the extent that it wasn't intentional. It falls in my book close to drunk driving accidents, not intentional but a highly likely outcome from risky behavior.

[Robert Chapman]

Thanks guys for your informative,sympathetic and constructive responses to my dumb accident. I'm going to check out some of the electric brake options. And a special thanks to Peter Quinn for equating my accident to drunken driving - thanks Pete - really helpful.

[Peter Quinn]

Didn't mean to irk you there Robert. It sucks to be injured, I am concerned for your safety and I hope you never see the ER again. But...

Way I see it there are two kinds of accidents. There are those unforeseen kind like a kick back from release of tension or a hidden defect in a board, or a serious machine malfunction, and there are those completely avoidable ones we all give ourselves, like nicking a finger on a blade or shoving a screw driver into the palm of one's hand (I still have a scar from one of those). I work in a cabinet shop where risky behavior is not tolerated, and I'm not sure if that's to protect the employee's or the owners insurance policy or both. Maybe something about decreased productivity too. But if you get caught doing something stupid, or about to, you get told quick. The most effective safety device available is not bolted to a machine, it sits under your hat. There is a zero sympathy policy on avoidable accidents. It doesn't always feel good but it does promote safe work habits pretty quick.

And the reason drunk driving is a crime is that behavior risks injury to others, unlike most things you do with a wood working machine which typically only injure the user. I didn't mean to insinuate that you are a criminal, but I do feel that the two behaviors share many similarities. And I have ben guilty of operating machinery under the influence of stupidity more times than I care to think about, thank God I was never caught. I am slowly reforming my ways.:D

[Robert Chapman]

OK - thanks Pete - I just reacted to the drunk driver analogy. At least in my shop I only directly hurt myself [but here's where the drunk driver analogy holds true] I also hurt my wife and others who care about me. I think that I have apologized about 10 times to my wife for my stupidity[she accepts my apologies]. On we go - lesson learned and stupidity realized. Guess I'll have a beer.

Bob Chapman

[Steve Rozmiarek]

Hi Steve

I don't know about any "shaper like" dado blade but, I think that only the blade can be installed on the arbor that is so short that anything more than 3mm cannot fit (the arbor is 30mm dia according the EU regulations)

The table saw on the pic is "Elekra Beckum" (owned by Metabo) but some 1 year ago, everything is Metabo and the name Electra Beckum remained only on the older production line - but it's the same TS just with new label...

Here is a general view - the sliding table is original and you can see a few of my improvements...

Regards
niki
108046108047

Thanks for the info Niki, I've never seen a saw like yours before. Sure looks like it ought to work well. It's interesting to see what we are missing on this side of the pond. Have a good day,

Steve

[Larry Edgerton]

You are correct - European saws are required to use dynamic braking. And this is why they are not allowed to mount dado stacks. The braking action can be adjusted to stop a 10" (or 12"?) blade without loosening the arbor nut, but dado stacks have too much mass. For larger diameter saws, there are little stubs on the arbor and matching holes in the blade to keep the arbor nut from loosening.

I have a european model saw with the shot arbor, but I have a stub spindle/stabilizer/nut that converts the 1" arbor to 1 1/4" that I use with dado blades. I had Forrest bore an eight inch dado stack for me. I like it because I can take the whole stack off on the adapter.

[Rod Sheridan]

Yesterday I did something dumb in the shop and spent an hour in the ER as a result. I was ripping some 3/4 inch plywood on my TS, had turned off the saw after a cut and was moving the large remaining piece when I touched the still rotating blade with two fingers of my right hand. I know - the blade guard was in the corner - also dumb.

So here is my thought - if the motor on the TS had been equiped with an electric brake I might not have two fingers throbbing and bandaged. Do any TSs have electric brakes on the motor? If not why not? My PC circular saw has one. Seems like a good safety feature.

I know - if I had a Sawstop I would not be writing this post.

Hi Robert, I'm very sorry to hear about your preventable accident.

Although I'm sorry to see you get injured, your injury is probably one of the most common, caused by two issues;

1) Lack of a guard.

2) Lack of patience.

I find the problem with tablesaw guards is that they can't be used for non through cuts, so we remove them. The correct method is to not use the TS for non through cuts since it's not designed for that. (Always use the correct tool for the operation).

The other solution is an overarm guard, I happen to have an Excalibur and like it.

So from a safety perspective, use the machine as designed, or replace the guard with a suitable one, that can stay on the machine for all operations. If you can't use a guard, don't perform that operation on that machine.

The patience aspect has always been an issue in industry, and some machinery has electrical braking of the motor via a VFD , DC injection or electrically operated mechanical brakes.

When I worked in the wood industry, we had "Coasting Blades Bite" safety posters with the top of the blade re-drawn as a snake with it's fangs exposed, posted in most areas of the plant. Even then we three coast down accidents while I worked there.

Since patience can't be regulated, blade brakes and usable guards are required in the EU, fortunately we will also follow suit, however as usual, later rather than sooner.

I notice than the MAN and MECH designations for cutters required in the EU are spreading to North America, the last shaper cutter I purchased was labled MAN for hand feeding. So some of the safety aspects are crossing the pond.

Sorry to hear that you were injured, however reading your post I see that you'll be more careful in the future.

Regards, and best wishes for your recovery.......Rod.

[Chip Lindley]

- if I had a Sawstop I would not be writing this post.

Hmmmm! I have to Wonder! Inquiring Minds Want to Know! Does the emergency braking function of the SawStop remain functional AFTER the motor is turned off, and the blade is COASTING? Those hotdogs are nicked Under Power!

As for dynamic/electronic brakes loosening of arbor nuts, those can be adjusted to allow a short coast time. There is no need to have a blade stop in a split-second! Belt-driven tablesaws stop faster than direct-drive saws. Radial arm saws coast FOREVER! Especially the big ones. Dynamic braking has been used successfully on those for a long time, accomplishing the purpose it was designed for.

Sorry about your mishap, Robert! I, too, have scars from stupidity and inattention! At least WE both have all our fingers! In the final analysis, the Individual is responsible for his Own safety!

[Tom Godley]

I went to a wood show not long ago -- they had a Sawstop and I wanted to know the same thing. Unfortunately no one was around and I was not at the show long enough for the afternoon "demonstration".

A brake on table saws and band-saws should be mandatory .... IMO.

[Joe Chritz]

According to the manufacturer the safety system is still energized and will work while the switch is off and the blade is coasting to a stop.

Since tablesaws rarely injure anyone but the operator I am not a big fan of .GOV intervening and making features mandatory. The UL will most likely make a lot of those features mandatory by not listing saws without them in the future.

Hope your hand heals fast, we are all guilty of breaking the rules from time to time. Sometimes you get bit some times you don't. The only incidents I have had have been kickbacks but they still did some damage.

Joe

[John Callahan]

Do any TSs have electric brakes on the motor?

My Porter Cable 3812 jobsite saw has an electric brake which works pretty well and a feature I appreciate- I had the same type of accident some years ago though not as severe on my old contractor's saw. It got my attention :eek: and like Peter I am (still) slowly reforming my ways. Fwiw Grizzly has introduced revised versions of two models in their bandsaw line (G0531B/G0566B) that have have a magnetic brake- it will be interesting to see how well they work and if the technology filters down to the tablesaw line. Hope you are well on the mend.

[Karl Brogger]

The most effective safety device available is not bolted to a machine, it sits under your hat. There is a zero sympathy policy on avoidable accidents. It doesn't always feel good but it does promote safe work habits pretty quick.

Thank you for posting that Peter. I grew up with the idea that ignorance should be painfull, if it isn't painfull it should be expensive.

Accidents happen though, but to my line of thinking the guards make people too relaxed. A guard isn't a guarantee that you won't mangle your digits, only keeping your head out of your butt is. I've stuck my head up my butt, and paid for my mistake in stitches because of it too, so your not alone Robert.

Hey, if you were there an hour couldn't have been too bad.