Table saw kickback

[transatlantic]

Why isn't the user getting kickback in this video?

https://youtu.be/qG4v0weIo2s?t=68

I'm refering to the second cut where the 2 pieces finally come apart.

From my understanding, you get kickback when you have a piece that is cut free and can be wedged into the far end of the blade causing it to flip back (notice he also has no riving knife).

I can see he is holding the smaller bit down with his thumbs, but I doubt that would help if it kicked.

 

[NazNomad]

Why isn't the user getting kickback in this video?

1. He's set the saw & fence up perfectly, it can't pinch the workpiece.

2. He's Matthias... the woodworking love-child of Albert Einstein & Chuck Norris.

 

[Fitzroy]

It's not a 100% chance of occurring, but if it does your likely screwed so you put in place measures to eliminate it as a possibility.

 

[transatlantic]

Why isn't the user getting kickback in this video?

1. He's set the saw & fence up perfectly, it can't pinch the workpiece

From my understanding, that wouldn't help. Its about the kerf cut in the wood closing, which could happen even if both the blade and fence were parallel

 

[lurker]

He makes a living broadcasting this stuff
He is hardly likely to broadcast himself making mistakes is he?

You need to ask yourself how much material is on the digital cutting room floor.

 

[Adam9453]

If the wood is stable and the user has good technique then kickback is far less likely to occur.
However if the wood is not stable and has stresses within it that are released during the cut, forcing it to pinch between the fence and back of the blade then it will bite you if you don't have a riving knife or some other device to stop it.
Safest route is to have a riving knife, crown guard and well setup fence.
Americans generally have a more relaxed approach to table saw safety but so did we years ago. We're just a little farther along the safe usage journey lol
Let the arguments begin.... :twisted:

 

[Bodgers]

Why isn't the user getting kickback in this video?

https://youtu.be/qG4v0weIo2s?t=68

I'm refering to the second cut where the 2 pieces finally come apart.

From my understanding, you get kickback when you have a piece that is cut free and can be wedged into the far end of the blade causing it to flip back (notice he also has no riving knife).

I can see he is holding the smaller bit down with his thumbs, but I doubt that would help if it kicked.

Do a search for the video where he tries to induce feedback...

 

[monkeybiter]

Do a search for the video where he tries to induce feedback...

Is that like kickback? :twisted:

Probably correct as typed.

 

[NazNomad]

Why isn't the user getting kickback in this video?

1. He's set the saw & fence up perfectly, it can't pinch the workpiece

From my understanding, that wouldn't help. Its about the kerf cut in the wood closing, which could happen even if both the blade and fence were parallel

Watch this and get back to me ... https://www.youtube.com/watch?v=Fbca0Km8Q5E

 

[transatlantic]

Watch this and get back to me ... https://www.youtube.com/watch?v=Fbca0Km8Q5E

Sure, I get that. But just having the blade and fence perfectly parallel without a knife only helps if the piece between the blade and the fence is always pushed firmly against the fence. That seems unlikely, especially when using push sticks or with think offcuts. Another point I brought up was if the wood was to move after the cut, as I believe thin bits can become instantly bowed, due to stress relief.

Of course, I may be talking complete nonsense

 

[Fitzroy]

To be honest I do not think that the linked video really shows kickback, it only shows a mild version of the off-cut being accelerated out of the saw. For me the link at the end shows what kickback can really be like.

If you're interested here is my thought experiment on kickback; lets consider the effects that could be/are involved:
- The rear of the saw blade is rising out of the table, if it contacts the work-piece it will try to lift it. The contact could be between the teeth and the work-piece or the blade body and the work-piece.
- The teeth are designed to cut, so long as the cutting force is less than the downwards force on the work-piece the teeth will cut not lift the piece. Cutting force will increase the larger the cut the rear of the blade is tying to take and the duller the teeth are.
- The body of the blade cannot cut the work-piece, friction between the body and the work-piece will always try to lift the work-piece. the force will increase the tighter the piece is pinched between fence and blade body.
- The centre of the saw blade is moving towards the front of the table, if it contacts the work-piece it will try to move it in that direction.
- The saw blade velocity is greater at the edge compared to the centre. Typically a saw blade is at 150ft/s (100mph) at the edge, this velocity drops off linearly with distance from edge to arbour.

If you put all these things together then the potential outcomes of a work-piece contacting the back of the blade are twofold:
Minor contact - Rear blade teeth cutaway incremental material, saw continues to spin freely. Small amount of energy is imparted on the work-piece. Once the offcut is free the saw slowly accelerates the off-cut out the front of the saw.
Major contact - Rear blade teeth or body of the blade cannot cut away the material in contact with the blade, saw begins to stall. Large amount of energy is imparted into the work-piece as momentum is transferred from saw to work-piece. Work-piece begins to rise off of the table making contact with top edge of the saw blade where velocity in the direction of the front edge of the table is maximum. Work-piece is violently kicked off the table.

Though experiment outcomes:
- In a 'major contact' the situation will worsen rapidly, as the work piece rises it will contact more teeth that are inherently 'more grippy' allowing a greater transfer of energy/momentum from the saw to the work-piece.
- A blunt blade is more likely to grip, lift and throw the work piece than cut away any excess.
- Any contact with the blade body, due to a hideously miss aligned fence or wood movement as stresses are relieved, is more likely to lift the work-piece and result in a major contact event.
- Once the work-piece is past the blade and in contact with the riving knife the opportunity for the work-piece to make a major contact with the blade is virtually eliminated.
- A blade guard over the blade not only prevents the operators hand contacting the top of the blade but also prevents the work-piece getting on top of the blade where the velocity towards the front of the saw is greatest.

https://www.youtube.com/watch?v=u7sRrC2Jpp4

Just my way more than 2p worth.

Fitz.

PS. I have a very old TS with no riving knife nor over blade guard and I now know why I hate using it so much!

 

[woodpig]

I thought someone on here said the biggest cause of table saw accidents in the US is due to the fence being too long?

http://www.hse.gov.uk/pubns/wis16.pdf

 

[Sawyer]

Why isn't the user getting kickback in this video?

1. He's set the saw & fence up perfectly, it can't pinch the workpiece

From my understanding, that wouldn't help. Its about the kerf cut in the wood closing, which could happen even if both the blade and fence were parallel

Also, the wood twisting slightly in the cut, being grabbed by the up-running teeth at the back of the blade and so climbing up on top of it and being ejected backwards. Nasty. Another reason why table saws need a riving knife & crown guard.

 

[custard]

He's Matthias... the woodworking love-child of Albert Einstein & Chuck Norris.

 

[monkeybiter]

Also, the wood twisting slightly in the cut, being grabbed by the up-running teeth at the back of the blade and so climbing up on top of it and being ejected backwards. Nasty. Another reason why table saws need a riving knife & crown guard.

That's the only condition under which I've caused/experienced kickback, 2'x2' 30mm worktop offcut shot back into my gut at astonishingly high speed. Quite enlightening.