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#142885 03/12/05 02:40 PM
Joined: Nov 2004
Posts: 24
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Member
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).]

#142886 03/12/05 04:42 PM
Joined: Aug 2001
Posts: 7,520
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Member
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).]

#142887 03/12/05 05:01 PM
Joined: Nov 2004
Posts: 24
D
Member
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).]

#142888 03/13/05 04:01 AM
Joined: Jul 2002
Posts: 8,407
Member
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.

#142889 03/13/05 12:15 PM
Joined: Nov 2004
Posts: 24
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Member
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

#142890 03/13/05 12:41 PM
Joined: Jul 2002
Posts: 8,407
Member
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]

#142891 03/13/05 01:00 PM
Joined: Jul 2002
Posts: 8,407
Member
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.

#142892 03/13/05 01:52 PM
Joined: Nov 2004
Posts: 24
D
Member
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

#142893 03/13/05 05:23 PM
Joined: Aug 2001
Posts: 7,520
P
Member
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).]

#142894 03/14/05 01:38 AM
Joined: Nov 2004
Posts: 24
D
Member
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

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