Brake on a table saw?

[heimlaga]

I am littlle by little cleaning the rust of an old rip saw and collecting the parts that I will need to get it into part time professional use. I will make modern guards for it and convert it from line shaft driven to have it's own motor. Essentially it is a big table saw with a 600mm blade and no height adjustment.

I am planning to power it with a 7,5kW three phase motor with star-delta start.
The questions are:
Does it need to have some kind of brake to stop the blade spinning after switching off the motor in order to fullfill the new European safety regulations?
How could I get or make a brake system on the cheap?


By the way I don't listen to people telling me that this is illegal since my home made guards aren't CE approved. After a lot of quarreling with local safety inspectors and insurance clerks I made them accept home made guards on my old machines provided that the guards function the way they should.

 

[wallace]

Some options are VFD or a DC injection break, both are expensive new for that size of motor.

 

[MMUK]

WOW! That's roughly 13HP! Are you sure that's big enough? :roll: You planning on felling an entire forest? :shock:

 

[woodfarmer]

you need to short the windings out intermittently when it powers off. some sort of triac for each of the three windings.

 

[deema]

That's one big motor your looking to stop. I believe the regulations state that you have to stop the blade I a certain time if you employ people, it does not state how this has to be achieved. If you have no employees I don't believe as a sole trader you need to be compliant.

If you do need to stop the spindle, one option I had seriously looked at was attaching a cable operated old brake drum to the spindle. I didn't have access to a small trailer brake set that would fit into the saw, otherwise it would have been my solution.

 

[nev]

I can confirm that thumbs are NOT a good solution!
post885256.html#p885256

 

[heimlaga]

Thanks.
I got a quote for a DC brake and it was way too expensive for me at 800 euros. I will probable use a traditional star-delta starter with a star position in teverse too and a return spring that returns the swith to zero as loon as it is not held in the star-reverse position. Than the star-reverse position would act as a brake.
A switch like this would cost a little over 300 euros.

 

[MMUK]

As an added precaution, could you spring load the blade guard so it drops down to the deck as soon as the material is out of the way?

 

[Limey Lurker]

What's wrong with using a disc brake calliper on the blade? It would not be disallowed by the regulations!

 

[deema]

A brake calliper on the blade would I believe cause either the blade to distort or slip on the spindle as it's only held by friction to the spindle. Adding a brake disc and calipers would be feasible, however they are normally hydraulically operated.