Kickback

[joez]

Saw this on another forum, there is a video at the end something everyone should watch.

Kickbacks! - NewWoodworker.com LLC

be safe


joez

[Grandad-5]

That's a real wake-up call, for both beginners and seasoned TS users.

He says people call him an idiot for doing that experiment. Perhaps.
I believe it shows that people who feel very comfortable using this equipment, such as himself and many others including myself may not be fully aware of just what can happen and operate under a mistakem impression that we can control the chain of events.

I admit to having been guilty of removing the riving knife on occasion.
Never again.

Thank you for posting.

Jim

[BobL]

The guy is an idiot.

A major contributor to the kick back he experienced that he fails to acknowledge is his blade is set too low

As far as TSs are concerned, I consider them "full face shield "machines. Push blocks are for blind cuts, otherwise its 2, foot long push sticks for pushing stuff between fence and blade - that is a really dumb ahrse place to put your hand.

BTW I took my riving knife off my TS in 2007. I would use one if my TS had a retractable one.

[Wongo]

Kickback is real, very dangerous and this bloke is an idiot. Such demo has been done before but it was done in a much more intelligent and safer way. He obviously can't work out what is dangerous and what is not.

[mic-d]

It's catching lately:
Curves on a Table Saw » Highland Woodworking Blog

Cheers
Michael

[wm460]

Thanks for posting joez.
I am glad this bloke done this experiment, in my extremely limited use of table saws I have heard of kick back but fortunately never experienced it, this video will stay in my mind.

BobL, what is wrong with the blade set low?

[mic-d]

Thanks for posting joez.
I am glad this bloke done this experiment, in my extremely limited use of table saws I have heard of kick back but fortunately never experienced it, this video will stay in my mind.

BobL, what is wrong with the blade set low?

Blade set low is OK for crosscutting, but for ripping they provide a lot of teeth travelling in the wood and against the direction of travel. With the blade set high for ripping, the teeth direction provides downforce not so much horizontal force and fewer teeth in the wood providing motive power.

Cheers
Michael

[Grandad-5]

Raising the blade for ripping is contrary to what I was taught as well.
Blade should just clear the gullet. Reason given at the time was that the forces of the blade were pushing the timber along the table whereas a higher blade pushed the front of the work down and the back up increasing the chances of kickback.
Being curious, I thought I'd Google it to see what the answer really is. After a pleasant interlude of reading, it would appear there are as many advocates of raised blades as there are lowered, for all kinds of reasons.
Sounds like it might be a matter more of preference than hard and fast rule perhaps.

Jim

[BobL]

Raising the blade for ripping is contrary to what I was taught as well.
Blade should just clear the gullet. Reason given at the time was that the forces of the blade were pushing the timber along the table whereas a higher blade pushed the front of the work down and the back up increasing the chances of kickback.

With the blade set high the back of the blade may well be lifting the timber up but with the blade set low it is much easier for the timber to climb up onto the blade and be thrown back at the operator. With the blade set high the front of the blade does a much better job of holding the timber down onto the table whereas with the blade set low the blade is partially pushing the work away from itself towards the operator. This was how I leaned it from the timber mill where kickback might involve a railway sleeper size lump being thrown back at the operator. The other reason was not to do with kickback but related to saw motor loading, minimizing the number of teeth in the cut.

[mic-d]

I guess the other thing to it as well, and you can see it from that video and the link I posted, when the blade is low it doesn't take much movement for the piece to get up on top of the blade and then it cannot be stopped. I don't buy the argument about the high blade pushing down on the front and lifting the back, for one thing, the piece is flat and for another, one push stick will be holding the back down. Furthermore, you want the front pushed down, it's the front where kick back begins. Beside the riving knife and the high blade the other best thing you can do is use an accessory rip fence that ends about the centre of the blade so there is no possibility of pinching between the fence and the back of the blade.

Cheers
Michael

[BobL]

I don't buy the argument about the high blade pushing down on the front and lifting the back, for one thing, the piece is flat and for another, one push stick will be holding the back down.

???? are you suggesting the reverse occurs.

Of course push sticks will mitigate the problem but the source of the problem has to be investigated without referring to push sticks or push blocks.

At the mill where no push sticks or push blocks were/could be used and lots of green wood under tension was being cut the foreman fitted a narrow riving knife to a 24" saw and showed us the back of the saw clearly lifting some of the wood.

[mic-d]

I was replying to post #8 where a reason NOT to use a raised blade was given as pushing down on the front and lifting the back. I was saying that it IS a reason to use a high blade, it pushes down the front... along with my other explanation. We are on the same page Bob.

Cheers
Michael

[A Duke]

I didn't see any mention of a blade guard at all and you can have one that incorporates hold down and anti kick back devices.
Regards

[Grandad-5]

I was replying to post #8 where a reason NOT to use a raised blade was given as pushing down on the front and lifting the back.

And I'm not necessarily disagreeing with you Michael.
I was just repeating what I was taught, and I guess I'm of the vintage that can still remember the rule was, when your teacher speaks, you shut-up & listen.
You have to earn the right to disagree, which I reckon I now have.

The thing about that video the OP so kindly posted for us was that it demonstrated the use of the riving knife in a way I'd never considered.
It was called a splitter in the shop where I started off and its function....so I was told....was to prevent the board being ripped closing up again after being cut. Thus its name. It was something that was automatically removed on every TS in the shop.

Seeing that video has made me see how it can also prevent the board coming into contact with the rear of the blade.

Having said all that, its funny that the only instance of kickback I've ever personally experienced was in that first shop, ripping a piece of 8x4 backing sheet. The blade was high at the time and I didn't bother to lower it before starting. I wasn't dead steady feeding the sheet in, it caught and ripped out of my hands. My boss, who was also my FIL ripped shreads off me for not lowering the blade. I guess its a lesson I learnt well, and have never questioned until now.

Cheers
Jim

[BobL]

. . . . We are on the same page Bob.
l