ECN Forum
Posted By: davelloyd Electric brakes - 03/12/05 06:40 PM
Hello,

I have a circular sa that has an electric brake.

I have a set of dado cutters that I wish to fit to this but the dado manufacturer says thes should not be fitted to a machine that has an electric brake.

My problem is that I REALLY need this set up and even if I go out and by a new machine then it will still have the brake.

How do these things work and can they be disabled?

Thanks

David Lloyd

{Message edited to add one word "brake".}

[This message has been edited by Trumpy (edited 03-13-2005).]
Posted By: pauluk Re: Electric brakes - 03/12/05 08:42 PM
I can't say I've ever owned a circular saw with an electric brake.

I can think of two possibilities:

1. A physical brake pad arrangement held on by springs with a solenoid to pull the brakes off when the trigger is operated.

2. Switch contacts which re-arrange the motor connections when the trigger is released to short the armature to achieve braking (similar to the rheostat braking used on electrio trains).

I can't think why an add-on accessory would have a problem with brakes though.

[This message has been edited by pauluk (edited 03-12-2005).]
Posted By: davelloyd Re: Electric brakes - 03/12/05 09:01 PM
I've had these saws to pieces for repairs in the past and there is no physical brake. It's the way it's wired that cause the saw to stop quickly.

I can't see any reason why there should be a problem and spoken to a few others who use this set up in the States.

Seems to me that the U.K. has gone safety barmy over the last few years. I now have to wear so much safety gear I'm starting to wonder if it's more dangerous.

Seems like the manufacturers are covering themselves for every eventuality, however remote.

Hard hat, falls off every time I lean over. High visi jacket that gets tangled with every thing. Leash on my harness that I keep tripping over every time I turn round in the cherry picker and so on.

So, could the electric brake be wired out?

Dave

[This message has been edited by davelloyd (edited 03-12-2005).]
Posted By: Trumpy Re: Electric brakes - 03/13/05 08:01 AM
Hi there Dave,
I know what you are talking about here.
I do know that a Dado-cutter, will not work properly, if there is a brake on the blade.
A Dado cutter has two blades, one for each side of the dado.
Am I wrong Dave?.
We use what is called a "Drop Saw" here in NZ on Construction sites for the cutting of timber and all of them have a brake on them.
Now, as far as I'm aware, they have a Universal(Series) motor driving them, the larger sizes do have an Induction motor.
What causes the braking in the Series motor is that when the trigger is released, the Back EMF of the motor is used to stop it.
The Induction type use a system of DC injection to effect the slowing of the motor.
Posted By: davelloyd Re: Electric brakes - 03/13/05 04:15 PM
Trumpy,

You are right about the dado. It has 2 blades, one on either side and four chippers in the middle.

I can't imagine what effect the brake has on this. The only thing I can think is it loosens itself when the brake is applied or the torque created due to the weight of the cutters might damage the arbor of the motor.

The saw in question is a Makita 5903R. Does this mean anything to you?

I'm almost sure it's a series motor. So can the wiring be altered to disable the brake?

Thanks

Dave
Posted By: Trumpy Re: Electric brakes - 03/13/05 04:41 PM
Dave,
All I can say at this stage is who is the manufacturer of the dado blade?.
Also have you contacted Makita to see if this sort of modification is even safe?.
Reason I say that Dave is because if you disable the electric braking system, you could also be disabling any sort of speed controls too.
The speed and stop systems could be controlled by the same Triac/Diac or SCR's.
To have an out of control Series motor would be very dangerous. [Linked Image]
Posted By: Trumpy Re: Electric brakes - 03/13/05 05:00 PM
Oddly enough Dave I have the Service Manual for that saw here.
I just found it in my pile of Manuals that I have here.
According to the manual, it has a Series motor and it should not be used for anything other than a Circular saw.
My advice would be to buy a dedicated Dado cutter.
Posted By: davelloyd Re: Electric brakes - 03/13/05 05:52 PM
Trumpy,

Thanks for the help.

Taking your advice I'm going to look for a different model saw, older probably, and forget about modifying the one I have.

Makita would say not to use the saw for anything than what it's designed for. However, I see the Americans doing this sort of mod all the time because a dedicated dado machine runs to around £3000 which, for me, a simple carpenter, is just out of the question.

If I ever do get round to this then I'll make sure it's as safe as can be made, substantial guards etc.

Regards

Dave
Posted By: pauluk Re: Electric brakes - 03/13/05 09:23 PM
Hmmm...... Good point on the speed controls on series motors. They are great for generating high starting torque, but can speed dangerously under no load if not constrained by design or regulation.

Disabling the braking would be pretty easy if it's just an on/off trigger switch, but is there actually a speed control on this model? That would certainly make it a little more complex.

P.S. I agree completely that HSE and their cronies are getting stupid on some things these days.



[This message has been edited by pauluk (edited 03-13-2005).]
Posted By: davelloyd Re: Electric brakes - 03/14/05 05:38 AM
pauluk,

There is no speed control as such, just a simple on / off trigger.
So, would it be dangerous to disable the brake? Obviously it would be more dangerous because the blade kept spinning after the trigger was released but what about this thing with the motor running out of control?
I've got a picture in my mind of it accelerating out of control til it just disintegrates :-)

I'm glad you agree with me on the Health and Safety thing. They have made a big difference on the larger sites for the better. I can see this when I go to some small domestic extension and see how crazy the the way they are working is.
Just seems to me that they starting to go that bit too far, too silly, so losing the respect of the blokes and spoiling what should be a good thing

Dave
Posted By: pauluk Re: Electric brakes - 03/14/05 04:58 PM
Sounds as though it's probably just a regular series motor then, where the top no-load speed will be limited by the design of the motor.

It shouldn't be too difficult to disable the electric braking, although you'd need to trace the wiring to make the necessary changes. Maybe Trumpy's service manual he found has a wiring diagram. How about it Mike? [Linked Image]

The electric braking doesn't come into play until you release the trigger, at which point you have already cut off power, so there's no danger of the motor taking off if you disable the brake!

I can't see any safety concerns, other than the obvious one that the blade will continue rotating for longer when you release the trigger.

But then as you're not a HSE inspector, you'd use common sense and not grab it until it stopped wouldn't you? [Linked Image]



[This message has been edited by pauluk (edited 03-14-2005).]
Posted By: davelloyd Re: Electric brakes - 03/14/05 06:50 PM
pauluk,

I think I'm just gonna look for an older model without a brake and cut that up to make the mods.

To alter it I'm gonna need an electrician. Firstly 'cos I'm a thick chippie and second 'cos I can see most electricians not wanting to do this from the safety point of view. i.e. if I do something daft and get hurt they might get the blame for overiding a safety feature.

Where are you based? :-)

Dave

[This message has been edited by davelloyd (edited 03-14-2005).]
Posted By: pauluk Re: Electric brakes - 03/15/05 11:53 AM
Quote
Firstly 'cos I'm a thick chippie
Well, I reckon you'd probably make a better job than the "pro" who did this wiring. [Linked Image]

Quote
Where are you based? :-)
Norfolk coast, about 20 miles NE of Norwich.

Whereabouts are you? Don't think any of us have thought to ask yet.
Posted By: Trumpy Re: Electric brakes - 03/15/05 02:23 PM
Guys,
As far as Service Manuals go, this one has to be one of the more useless ones.
In fact to be honest the only real info it had was how to replace the brushes.
Sorry but no circuit diagram, you have to plead poverty before the manufacturer will give you them these days.
But, I did note that the trigger switch has 6 wire terminals.
Now I'm only guessing here, but it sounds to me like the trigger switch may have a momentary set of contacts that reverse the field or armature windings when the trigger is released, thereby slowing the motor.
Just a thought. [Linked Image]
Posted By: davelloyd Re: Electric brakes - 03/15/05 08:59 PM
Both,

I'm in the West Midlands. Lucky aren't I?

I thought about asking that guy about rewiring my saw for about two seconds :-)

Freud, the manufacturer say not to use the dado with a breked machine because the sudden stop could cause the nut to loosen....

Now I'm thinking the simple answer would be to us twn nuts. One to hold the dado and a second to lock the first nut into place.

Dave
Posted By: Trumpy Re: Electric brakes - 03/16/05 02:29 AM
Dave,
Just to be on the safe side,
I'd use a bit of Loctite thread-locking adhesive on the thread.
I'm not that keen on the idea of modifying the safety parts of electrical appliances, especially Power tools.
I'm reminded of a guy that mucked around with a Bench grinder here recently.
When he started it up, the excessive speed caused the grinding wheel to shatter and a piece of it flew through the corrugated iron wall behind the bench, leaving a large ragged hole.
The guy just stood there reflecting on what had just happened. [Linked Image]
Electric motors can't tell what is on the end of them, they just drive it.
Good luck with the Dado saw!. [Linked Image]
Posted By: gideonr Re: Electric brakes - 03/17/05 12:15 AM
I looked up the Makita 5903R and it seems to be a handheld circular saw? A dado set in one of those looks to me like a quick suicide route! 8-) Never mind it being overloaded?

A spindle moulder with a wobble saw or adjustable groover and a high fence, or just with a router cutter adaptor? Again a bit pricey though. I take it a router is out of the running?

A lot of distributers seem to have stopped selling dado sets, but Dewalt still seem to be making them, so try their saws. They certainly make dado fitting parts for their radial arm saws and table saws, and they won't cost you £3000.
Posted By: davelloyd Re: Electric brakes - 03/17/05 03:25 AM
I know this sounds scary

I need something like in the picture but not quite as extreme!
http://www.thesitebuilder.net/yoxall/skildado1.jpg

Dave
Posted By: pauluk Re: Electric brakes - 03/18/05 09:27 PM
That looks like the worm-drive Skilsaw in that pic. Never used one, but I've heard good reports on them.
Posted By: davelloyd Re: Electric brakes - 03/19/05 03:32 PM
It is an old 10" wormdrive saw. I have a couple of 7 1/4" ones and find them really good. Far better than the sidewinders we can only get in the U.K. No looking over the top of the machine to see the blade.

These were hard to get so I don't want to start altering them as they're just too useful for everything else.

Dave
Posted By: kiwi Re: Electric brakes - 03/20/05 11:24 AM
Last year a man was killed in NZ when a piece of a shattered angle-grinder wheel shot into his chest. Power tools are to be taken seriously.
Posted By: Trumpy Re: Electric brakes - 03/26/05 09:04 PM
Kiwi,
Quote
Power tools are to be taken seriously
Yeah I agree. [Linked Image]
I've always had the upmost respect for any Electrical tool that uses a spinning part to perform it's work.
Especially where that part contains things like sharp teeth and bits that can cause you real harm.
Sometimes the Electrical hazard of these tools pales in comparison to what could happen to you!. [Linked Image]


[This message has been edited by Trumpy (edited 03-26-2005).]
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