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Are full kerf blades more dangerous than thin kerf ?

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Forum topic by Carloz posted 12-04-2017 02:13 PM 541 views 0 times favorited 17 replies Add to Favorites Watch
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Carloz

967 posts in 427 days


12-04-2017 02:13 PM

I would guess that the ability to give in some would decrease a chance of pinching the wood between the blade and the fence.
Another thing is that when the blade does grab the wood the wider tooth has more wood to push against and as the result the wood will be thrown with bigger force. Thinner kerf would simply cut into the wood more and the wood would get less acceleration. You can picture it as cutting a watermelon with a thin and thick swords. The thin one will leave the watermelon halves in place but the thicker one will throw them to the side.
These are all purely my imagination that could be far from the real state of things.


17 replies so far

View jonah's profile

jonah

1451 posts in 3134 days


#1 posted 12-04-2017 03:40 PM

It’s your imagination. The only difference is that full kerf blades are likely stiffer, which would actually make them safer, not more dangerous, because they’d be less likely to deflect away from and then back into a pinched work piece.

Either one, when spun at ~5000rpm by a 1.5-5HP motor, will fling a piece of wood through a wall (or the operator of the saw).

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Lazyman

1503 posts in 1223 days


#2 posted 12-04-2017 03:46 PM

Everything else being equal, besides the width of the blade, the biggest factors that cause risk are how well the saw is setup and the skill or stupidity of the operator.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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DalyArcher

101 posts in 955 days


#3 posted 12-04-2017 03:53 PM

I doubt that is it actually measurable to any degree, but my thought would be the same as Jonah, full kerf blades may actually be safer. Again though, I doubt it is actually a measurable difference. Kickback will happen no matter the thickness or diameter of the blade if there is an error in operation. When I finally (hopefully by spring) get my 5 hp cabinet saw set up and running it will be sporting full kerf blades and Jess-Em stock guides.

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Fred Hargis

4756 posts in 2329 days


#4 posted 12-04-2017 04:13 PM

You’re comparison the the thin/thick sword isn’t valid, as I see it. A saw blade removes the material to make way for it to pass though the wood, a sword doesn’t do that. Regardless, any difference would only be measurable with laboratory instruments and of no consequence to a hobbyist.

-- Our village hasn't lost it's idiot, he was elected to congress.

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Carloz

967 posts in 427 days


#5 posted 12-04-2017 04:15 PM



, because they d be less likely to deflect away from and then back into a pinched work piece.

- jonah


What do you mean by “and then back into a pinched work piece” ?

View pintodeluxe's profile

pintodeluxe

5461 posts in 2649 days


#6 posted 12-04-2017 04:27 PM

If anyone has the impression that full kerf blades are more dangerous, I’ll bet it’s because they sometimes slow down on underpowered saws. Back when I was using a 1.75 hp contractors saw, I felt much better using a thin kerf blade because it was a better match to my saw.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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jonah

1451 posts in 3134 days


#7 posted 12-04-2017 04:48 PM


, because they d be less likely to deflect away from and then back into a pinched work piece.

- jonah

What do you mean by “and then back into a pinched work piece” ?

- Carloz


Full kerf blades are thicker. Being thicker, it’s harder to deflect one to the side. A blade deflecting away from the fence and then back into it (maybe due to a knot, or work fed improperly, for example) could cause a kickback.

View rwe2156's profile

rwe2156

2711 posts in 1316 days


#8 posted 12-04-2017 04:52 PM

Anything that causes you to push the stock harder increases the risk of an accident a lot.

This includes dull blades, underpowered saws, wood binding in the cut, poor quality fences, etc.

So I can see where a full kerf blade in an underpowered saw would be more dangerous when the blade gets a little dull.

How much more dangerous than a thin kerf? Who knows?

-- Everything is a prototype thats why its one of a kind!!

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runswithscissors

2562 posts in 1861 days


#9 posted 12-04-2017 10:47 PM

I would never cut a watermelon with a sword. An axe, maybe, but never a sword.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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Carloz

967 posts in 427 days


#10 posted 12-05-2017 12:03 AM


Anything that causes you to push the stock harder increases the risk of an accident a lot.

This includes dull blades, underpowered saws, wood binding in the cut, poor quality fences, etc.

So I can see where a full kerf blade in an underpowered saw would be more dangerous when the blade gets a little dull.

How much more dangerous than a thin kerf? Who knows?

- rwe2156


It is not a matter of power. Wood offers more resistance when pushed against a full kerf than against thin keft. (That’s why thin kerf exists in the first place,to create less resistance to underpowererd saws) According to the Newton’ Second Law the amount of force is equal to the amount of counterforce, ie full kerf blade pushes the wood harder than thin kerft does. The difference is not small as we need more powerful saws to work with full kerf blade.
So if the blade pushes harder it would throw a piece of wood with higher force.
If you go to the extreme and make the blade razor thin it would not be able to create any kickback, it would just cut into the wood.

I did not expect unbiased answer here though.

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jonah

1451 posts in 3134 days


#11 posted 12-05-2017 12:29 AM

I’m not sure where and when you learned your physics, but Newton’s second law of motion describes how the velocity of an object equals its mass times acceleration (F = ma). It has nothing whatever to do with “counterforce.”

It’s not really clear from your “explanation,” but I think you’re talking about the third law of motion, which is that every force results in an equal and opposite reaction.

If you pick up a full kerf blade and a thin kerf one, you’ll see what while the full kerf one is a bit heavier, the difference isn’t all that much as a percentage of its total mass. Thus a full kerf and thin kerf act with substantially similar force on a piece of wood.

I assure you, a 1.5HP electric motor is plenty powerful enough to fling a 1lb piece of wood fast enough to kill you.

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Tony_S

766 posts in 2919 days


#12 posted 12-05-2017 12:33 AM

You’re splitting hairs.
There probably would be some correlation between thin kerf and standard kerf vs. speed of ejection. But the massive amount of different scenario’s that could take place would take an engineer and a mathematician years to calculate.
Kerf width, HP, rpm’s, blade heights, material size, density, any gravitational forces applied….and on and on…

All to find out that the table leg knocked your teeth out at 138mph in stead of 141mph. You still have no teeth.

Tune your saw up properly and use it within it’s capabilities, safely…..it shouldn’t even be a consideration.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Rick_M's profile

Rick_M

10618 posts in 2216 days


#13 posted 12-05-2017 01:44 AM

Lot of interesting thoughts. I’m not sure the question can be answered unless you define what you want to know and how it will be measured. If all you want to know is if a full kerf requires more power to do the same work, assuming all other factors are equal, then yes. But to decide whether that’s more or less safe, you need something to measure.

-- http://thewoodknack.blogspot.com/

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knotscott

7785 posts in 3211 days


#14 posted 12-05-2017 12:49 PM

I think the danger factor is probably pretty minor between kerf widths. If your saw is underpowered, you might be more prone to push harder with a full kerf blade simply because it poses more resistance, but otherwise I don’t think the full kerf blades are inherently more dangerous. From a safety standpoint, it’s far more important to use good technique, safety devies, have the saw setup well, a sharp blade that’s correct for the task, and to use flat and square stock that doesn’t fight you.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

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Kazooman

867 posts in 1788 days


#15 posted 12-05-2017 01:08 PM


I would never cut a watermelon with a sword. An axe, maybe, but never a sword.

- runswithscissors

Good point. Reminds me of the time when I was a kid when a group of us chipped in and bought a whole watermelon. Lacking a knife we cut it into pieces on the edge of a stop sign. Worked like a charm. I do not recall if it was a thin kerf stop sign or the standard full kerf model. I do recall that it was red.

PS: The stop sign lacked a riving knife and yet there was no kick back. We did use a pair of watermelon Grippers to protect our fingers.

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