# motor braking



## tvrgeek (Nov 19, 2013)

I was wondering while waiting for the table saw to spin down, why don't most of the power tools have some sort of braking? There are several ways to use back EMF to slow an SC motor. I have seen mechanical brakes on band saws, but nowhere else. I wonder how many accidents happen because of not waiting for a tool to stop.

My old Delta chop saw has a brake, but it is a brush type motor. Induction motors are a little harder, but not much.


----------



## wildwoodbybrianjohns (Aug 22, 2019)

Just fyi, all table saws for european market must have electronic braking now by law.


----------



## Mike_in_STL (Dec 8, 2016)

My Laguna Platinum Dovetail cab saw has some kind of brake. There is a noticeable "thunk" as the motor spins down and the blade changes speed quite rapidly after the "thunk".

You pose a good question. The RAS I inherited from the grandfather has a manually applied brake on the motor housing and it was manufactured in the late 70s/ early 80s.


----------



## JohnMcClure (Aug 24, 2016)

This would be interesting to try.
A relay connected across the motor's terminals, that closes about 1/2sec after the power switch is opened, would probably do the trick. 
Coastdown doesn't bother me enough to find out, but it would be a neat experiment. If someone tries it I'd be happy to hear about it!


----------



## Lazyman (Aug 8, 2014)

The reason is probably mostly cost. Unless they are required to add it like they are in Europe, they most likely won't add the cost and if ever are required, they will probably pass on double the cost to the consumer.


----------



## MrUnix (May 18, 2012)

+1 to what Nathan sez…

Margins are so slim that even a few pennies can make a big difference with mass produced machines. I can do braking on my Unisaw, but it's 3-phase. Not as easy on a single phase machine.

Cheers,
Brad


----------



## Harryn (Apr 25, 2011)

My 1960's Craftsman radial arm saw has braking, it consists of two back to back diodes in the motor end caps. Have replaced them twice over the years.


----------



## Scap (Aug 7, 2018)

On these items that have brakes, do the arbor nuts have any type of mechanical device to keep them from loosening on shutdown?


----------



## tvrgeek (Nov 19, 2013)

Now that is a good question. My Delta chop saw does not, but the braking is not that hard.

Looking on WIKI about induction motor braking, three phase is easier than single phase.



> On these items that have brakes, do the arbor nuts have any type of mechanical device to keep them from loosening on shutdown?
> 
> - Scap


----------



## tvrgeek (Nov 19, 2013)

That would have been a brush type motor. Very different from an induction motor. You could pretty much just short the brushes and the back EMF would brake it.



> My 1960 s Craftsman radial arm saw has braking, it consists of two back to back diodes in the motor end caps. Have replaced them twice over the years.
> 
> - Harryn


----------



## PPK (Mar 8, 2016)

I guess spindown has never bothered me. Doesn't even seem like a huge safety issue. I've always figured that if you're in such a hurry to do something that you can't wait for the blade to stop spinning, you're working too fast and don't have safety in mind anyway. Further, your hand shouldn't be by the blade when it's plugged in to begin with, no? It takes a few seconds to unplug, and that's always enough for me to let the blade stop. On belt driven machinery (with the exception of the bandsaw) its only a few seconds after shutting down. That's my opinion for what it's worth!

Chop saw is a different story I guess. It would be a pain to have to wait for a chopsaw to spin down, since those cuts are repeated and you often use the blade to line up the next cut. But I haven't seen a chopsaw w/out a brake.


----------



## tvrgeek (Nov 19, 2013)

Double would be cheap. Look into actual production cost and how it relates to retail cost. A lot higher.
If they have it in the EU, then the engineering and production investment has already been done. I would not buy only to get it, but might be a tie breaker. As an example, between the 14 inch Laguna and Rikon band saws. Can't go wrong with either. Only tie breaker is the sale this month may be a lunch better on the Rikon.



> The reason is probably mostly cost. Unless they are required to add it like they are in Europe, they most likely won t add the cost and if ever are required, they will probably pass on double the cost to the consumer.
> 
> - Lazyman


----------



## bigblockyeti (Sep 9, 2013)

My Unisaw has three drive belts and needs to run a good five minutes before getting any heat in them, as a result it slows pretty quickly even with a heavy, full kerf blade installed. My Delta Milwaukee RAS has an electronic three stage brake that starts slowing the blade ~0.3 seconds after power is removed from the motor, after the final stage it might still be spinning 300 rpm or so but with new bearings recently installed, it slows fast enough after that, BTW, it's single phase.


----------



## tvrgeek (Nov 19, 2013)

As I have a "new" drill press, I can experiment with the old. Basically, measure the DC resistance of the motor to determine the "normal" equivalent current to the AC RMS current, Then build a DC power supply with the voltage that would be the same current. Basically, just a single phase rectifier, a few resistors and a suitable cap. Looks like a fun little project.

Three phase motors can play games using one phase to generate the current to brake on another. Can't do that on a single phase.


----------



## ibewjon (Oct 2, 2010)

My grandfather's 1950's green DeWalt RAS had a braking system. It had a box on the saw containing vacuum tubes. Unfortunately the saw was lost in a flood and scrapped. Unfortunately Europe is far ahead of the US on safety. My DeWalt table saw doesn't have a riving knife, but the European model does. DeWalt didn't want to pay for the US testing from what I have read.


----------



## MadMark (Jun 3, 2014)

I play a game when I turn off the saw. Can I get the blade cranked down before it stops spinning. You DO keep the blade retracted for safety, don't you?


----------



## tvrgeek (Nov 19, 2013)

When finished with what I am doing, yes. After every cut, no.



> I play a game when I turn off the saw. Can I get the blade cranked down before it stops spinning. You DO keep the blade retracted for safety, don t you?
> 
> - Madmark2


----------



## Mike_in_STL (Dec 8, 2016)

> I play a game when I turn off the saw. Can I get the blade cranked down before it stops spinning. You DO keep the blade retracted for safety, don t you?
> 
> - Madmark2


Nope, and my guns are loaded too.


----------



## bigblockyeti (Sep 9, 2013)

> Unfortunately Europe is far ahead of the US on safety. My DeWalt table saw doesn t have a riving knife, but the European model does. DeWalt didn t want to pay for the US testing from what I have read.
> 
> - ibewjon


I don't read additional regulation as being unfortunate. Sure the availability of safety equipment FOR THOSE WHO WANT IT certainly isn't a bad thing but having it forced upon everyone and subsequently everyone having to pay for it doesn't sit well with me. Europe is so far ahead they don't allow dado blades. Back in 1773 their oppressive regulation didn't work out too well culminating a hiney whoopin not quickly forgotten just a few years later.

I'll take my freedom and select my safety as I see fit.


----------



## tvrgeek (Nov 19, 2013)

I don't see a downside to either a riving knife or a blade brake, where the idiot-proof SawStop I can see how it would cause issues frequently. ( and a lot of $70 shoes and $100 blades ) No dados is just symptomatic why England left the EU. Woodworking is dangerous, OK, I accept that, but there are things that are easy and pretty cheap that can help maybe 80% and not have any effect on your use of the tool or a significant cost.

Anyway, I broke down and asked for advice from a real engineer as I was just a lab rat. No luck searching the WEB for how it is commonly done on EU machines.


----------



## ibewjon (Oct 2, 2010)

Do you have seat belts and shoulder harness in your car? Don't use it because it is required? Sorry, but you are mostly wrong. Then make the riving knife parts for my saw available. I don't like others telling me that I can not have or buy safety equipment or features. You don't use safety glasses or hearing protection either because eyes and hearing along with fingers and other body parts are available on line? Safety on the job and at home are extremely important. I will gladly pay because safety is cheaper than a doctor or ER.


----------



## bigblockyeti (Sep 9, 2013)

Mostly wrong? Facts please.

I never stated I don't like some safety features, I did state I don't like having them forced on me!


----------



## ibewjon (Oct 2, 2010)

Sorry, but I like safety and want the features available, not put on a shelf because a company is trying to make more money. If ALL companies were FORCED to have the same safety standards, as in the EU, then the machines would be priced by quality and other features, not on leaving out safety. We disagree on this, so let's end the discussion.


----------



## JackDuren (Oct 10, 2015)

> I play a game when I turn off the saw. Can I get the blade cranked down before it stops spinning. You DO keep the blade retracted for safety, don t you?
> 
> - Madmark2


No….


----------



## Fettler (Dec 6, 2012)

.


----------



## tvrgeek (Nov 19, 2013)

I'll get back when I have some design or results and leave the controversy out of it.


----------



## AndyJ1s (Jan 26, 2019)

At the beginning of my 2nd semester of high school woodworking (late 1970's), they had purchased a new, larger RAS. The brake was too strong, and it sent a brand new 14" saw blade across the shop floor, embedding itself in the opposite wall. Luckily they were testing it when no students were present. Nobody was hurt, thankfully.

They had to wait for several weeks to get a replacement brake and a factory technician to install and calibrate it.

Count me in the group that prefers less government control, and more competition. When the market demands a product (or product feature) industry will produce it. I especially abhor a manufacturer that lobbies the government for new 'safety requirements' which only that manufacturer can satisfy. Now we have competition, not regulation, and more options are coming available. As it should be.


----------

