# Why are dado blades considered unsafe?



## MrRon (Jul 9, 2009)

I keep hearing people say dado blades are dangerous, but never heard the reason why. I use a dado blade all the time and have never felt that by doing so, I was placing myself in danger. If there is something I don't know, please enlighten me.


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## JAAune (Jan 22, 2012)

I would guess because some people attempt to do too much with them and are subjected to powerful kick back forces. Plowing a 3/4"x3/4" dado through oak is probably overdoing it.

The way I use them, I've never had any incidents. I just keep the cuts shallow enough that I'm not feeling any strong resistance to the cuts. Deep dados are done in multiple passes.


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## BArnold (May 20, 2013)

I've never had any bad incidents using a dado set. I'm curious to see what the responses are to your post. Like JAAune said, using a dado improperly can lead to problems just as with many other tools.


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## knotscott (Feb 27, 2009)

Probably because of the amount of material removed in the event of an accident….a full dado stack could really mangle flesh.


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## MrRon (Jul 9, 2009)

Using a dado blade can be as dangerous as using a plain blade, but why such a strong reaction by European safety associations? I can just see "VERBOTEN" printed in saw owner manuals.


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## NiteWalker (May 7, 2011)

What scott said.


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## Manitario (Jul 4, 2010)

big ass blade + large potential for kickback


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## roman (Sep 28, 2007)

you keep hearing nonsense

in my experience & as limited as some might think that is

they r as safe as apple pie

the blades are never a problem

people are


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## bullhead1 (Mar 29, 2012)

"VERBOTEN" is "forbidden" in English for those that haven't looked it up yet. My only guess is that the safety police in Europe are jumping on the US attorneys band wagon of thinking all consumers are entitled to be compensated for their carelessness. I assume their reasoning is that you have to run it with the guard off.


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## longgone (May 5, 2009)

*They are perfectly as safe as any other tool if you are careful and use common sense*.


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## rg33 (Dec 1, 2012)

speaking of dadoes and potentially being unsafe, I have a question…
Im building a simple tv stand that will have one shelf in the middle. This shelf will be glued to the sides having dadoes about halfway up. My question is as follows, is it safe to cut the dadoes (for 3/4" plywood) crosscut wise on the table saw using the fence? 
Before you think me a noob about to do something unsafe let me clarify the following, the pieces that will get the dadoes aren't actually that much longer than they are wide: 20"X17" with the dado being put up about halfway up the 20" length. I have a stacked dado set that I just got, but wanted to get others' inputs before I try this. Otherwise I do have a 1/2" router bit that I could use with two passes but it just seems like that would be much more of a hassle since I dont have a router table yet.


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## wormil (Nov 19, 2011)

Europeans love their riving knives which don't work with dado blades.


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## mojapitt (Dec 31, 2011)

Everything we use can be dangerous if you aren't careful. That's why woodworkers are very common in the Emergency Department. Know your guidelines and follow them.


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## knotscott (Feb 27, 2009)

In addition to taking a bigger chunk of flesh, the skeptic in me also thinks someone who was well positioned to profit from it probably made tons of money by passing those laws in Europe. Greed and the urge for the few to control the many is pretty is an ugly part of human history.


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## Bullet (Apr 14, 2009)

Dado sets are perfectly safe… As long as you're using them on a Saw Stop.

Sorry. Couldn't resist.


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## moonie (Jun 18, 2010)

In the past 5 years I have been using my grandfather's craftsmen table saw and it has a ¾ hp on it .
But I do all my dado's with it but I only go a ¼ " deep and a ¼ " wide and that's Oak too. I wont try this on my big saw it has a 2 hp .


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## BJODay (Jan 29, 2013)

Isn't harder to adjust the height of a dado, (the depth of the cut), on a table saw? I use a router table. It has a lift with a measuring wheel and I can precisely set or adjust the depth of the cut. On my table saw, I turn the crank and have to manually measure the height of the blade. I know a TS would be faster once set.

BJ


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## helluvawreck (Jul 21, 2010)

I personally haven't had any bad problems with dado blades. I would say that it is important to keep them sharp. Of course that goes with any saw blade.

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com


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## TheDane (May 15, 2008)

I've never even had any safety concerns with dado stacks on my TS. I use a sacrificial fence, featherboards, and push blocks to keep control of the stock, and limit the depth of cuts.

I'd rather take two, three, or four shallow cuts to get to the depth I want than try to plow out the full depth in a single pass.

I'd like to get hear from some of our LJ brothers & sisters across the pond on this issue … I have always wondered why myself.


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## PurpLev (May 30, 2008)

dado blades has added risk compared to regular blades for the following reasons :

1. dado blade full width could mean that the nut tightening the blades on the arbor doesn't have enough threading to and could potentially come loose (abnormal - and if you follow proper guidance should not be a factor - but done by someone less educated, and this scenario is a potential reality)

2. no splitter/riving knife can be used (properly) which increases the risk of a kick back as there is nothing behind the blade to prevent wood from being pushed onto the back of the blade

3. non through cuts - requires the removal of blade guard on 99% of factory supplied TS (unless you have an overarm guard which are usually after market guard solutions). again, reducing the amount of safety protection one run this TS with


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## moonie (Jun 18, 2010)

Well BJ I dont think so its easyer than a router but I set my blade at a 1/4" to start and take it all out at one time.


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## WoodDweller (Aug 29, 2013)

Id like to see the european safety regulations concerning table saws and dado blades. Otherwize its hard to tell fact from fiction. I did not find it but here is some type of summary of the UK table saw safety regulations.

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

"Rebating and grooving. A circular saw should not be used for cutting a rebate or groove unless the blade is effectively guarded. This is because the normal saw guard cannot be used"

(More info might be on http://www.hse.gov.uk/woodworking/wis.htm)


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## CharlieM1958 (Nov 7, 2006)

@rg33: Based on the size of your work piece, I think you would be okay using the fence. If it was much longer, though, I would use a miter fence or a sled.


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## MrFid (Mar 9, 2013)

I had heard this too, and am interested and agree with what most of the comments on here have said so far. Here are a couple observations from someone who uses my dado set a lot.

1. Riving knives and blade guards go out the door pretty much. (+1 PurpLev)
2. Removing more material in one swipe can be dangerous if done improperly.
3. Heavier blades result in more wear-and-tear on your TS motor, especially if you take deep cuts.
4. My saw (Ridgid R4511) at one point had a recall because dado sets were being spun off the arbor and being thrown around the shop. Mine wasn't an affected serial number, but it certainly gave me pause for a moment the first time I spun a dado after reading that. Not really a problem with dadoes in particular, but rather with the saw itself I guess.
5. The older model dado blades (that oscillate as they spin, don't remember the name) freak me out. Not for any particular reason I can think of, but they scare me a bit.
6. They are harder to have ZCIs for. A while back I batch cut about 10 Zero Clearance Inserts of my TS, and most of those are now cut for different width dadoes. I always have a spare blank or two that I can dedicate to a random width dado if necessary. But if you don't have the time invested in making many ZCIs and having a few blanks around, you might be running a dado with an oversized ZCI, or even worse, no insert at all. Can't even imagine how scared I would be to cut a dado without a TS insert.


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## teejk (Jan 19, 2011)

I would guess the reason is wanting to keep a lot of downward pressure at the point of cut. One mis-step and your fingers are vulnerable. When I'm in doubt I borrow the push pads from the jointer. As for adjusting height, I keep a collection of cut-offs that I marked with their thickness…place the desired one next to the blade and raise lower until the highest tooth is even with the top.


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## lumbermeister (Dec 24, 2012)

Because there is not through-cut, the risk of the wood binding on the blade is nearly non-existent (i.e., the workpiece portion that has already been cut cannot collapse on itself as it is not a through-cut). One if the projects that I posted are shelves, that include 3/4" x 3/" dadoes cut through Padauk on my R4512 saw with Freud SD206 set - I took it slowly and felt no unusual resistance.

I agree with Knottscott - a cut with a dado set at full width/depth is sure to mangle an awful bit of skin and bone.


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## NiteWalker (May 7, 2011)

Bailey, a few of your points need clarification.

3. " Heavier blades result in more wear-and-tear on your TS motor, especially if you take deep cuts." 
Most table saws were designed for use with dado sets as well as regular blades. I could see this being true if the only blade ever used in the table saw is a dado set, but even then, the amount of wear and the effect on longevity would probably not be much.

5. "The older model dado blades (that oscillate as they spin, don't remember the name) freak me out. Not for any particular reason I can think of, but they scare me a bit." 
Wobble dadoes. They're not any more dangerous than stack dado sets, but the quality of the cut is vastly inferior compared to a stack set.

6. "They are harder to have ZCIs for. A while back I batch cut about 10 Zero Clearance Inserts of my TS, and most of those are now cut for different width dadoes. I always have a spare blank or two that I can dedicate to a random width dado if necessary. But if you don't have the time invested in making many ZCIs and having a few blanks around, you might be running a dado with an oversized ZCI, or even worse, no insert at all. Can't even imagine how scared I would be to cut a dado without a TS insert." 
There's a few ways around this. A dado doesn't need a zci for every cut. Groves or edge rabbets don't really have much tearout, if any. Even for some dado cuts where the material can be used with a backer, tearout isn't an issue. So just using an insert that's the same size or slightly bigger than the needed dado will work fine. I use two sizes mostly; a 3/4" for most cuts and a 3/8" for 1/4" or smaller dados.

Another option is to make a single zci with replaceable inserts. Spending the time to make one of those would probably take the same time to make your 10 inserts, but when you need a new strip, it's pretty easy to pop out the insert and slip a new one in.


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## TheDane (May 15, 2008)

Here is my zero-clearance throat plate with replaceable inserts:


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## MrFid (Mar 9, 2013)

NiteWalker- Thanks for the info. I guess I just figured that because some saws can get bogged down taking deep cuts with a normal blade, it made sense that they might get bogged down taking deep dadoes. I generally don't cut enough out with a dado to feel or hear this change, but I've had it happen with a standard blade (even thin-kerf) when cutting say 8/4 or 12/4 purpleheart. Figured it would apply here as well. Are you saying that when the blade slows that it's not causing motor wear? What about belt wear? If neither of those assumptions are true then that's good news for me.
I also agree about ZCIs and rabbet cuts. Not much tearout on the bottom of mine usually. More so on the back if I don't back up with workpiece. It was just as easy for me to use a piece of half inch ply to make 10 ZCIs and store them in a drawer until it's showtime than to make a replaceable insert for one throat plate.
Yes wobble dadoes! Thank you. The stack makes so much more sense to me, and I agree that the quality of the cut would seem to pale in comparison. I'd never trade my stacked set. Thanks again!


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## TerryV (Jun 30, 2012)

The requirement in commercial workshops in the UK is that machines are designed and suitable for the job, and that they are effectively guarded. Saws have to come to a stop within 10 seconds.

A dado set usually prevents guarding (unless a special guard is used). A saw that isn't guarded is not deemed suitable or safe enough for commercial use. The same applies to the standard blade if used for rebates and grooves.

A heavy blade set will increase the stopping time.

We have a different approach to safety over here. The idea is to design out the risk where possible. This is because employees kept getting hurt. Saw guards and riving knives reduce the number of injuries, although it is always possible to work without them and not necessarily get hurt.

All this means that commercial shops either ignore the regulations (common enough) or use another machine for rebates and grooves.


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## joeyinsouthaustin (Sep 22, 2012)

OP has said, "I keep hearing people say dado blades are dangerous"

This is true, they are not, however, Unsafe. Most have pointed out they are as dangerous as other blades. Here is my simple 2cents.

Drag is what causes a TS blade to bind causing a kickback, either drag from pinching of the wood after cut (this is mitigated by a PROPERLY fit riving knife, or from the drag pulling the work piece away from the fence (this is mitigated by technique and tools such as crosscut fences/miter bars, and properly used pushing devices, and also the well fit riving knife) A dado set causes more drag, specifically the type that pulls away from the fence, because it is rarely cutting all the way through a piece. With the riving knife rarely fit to the blade, this adds to the likely hood of a failure. Also, there is a little wiggle room in an open cut where the wood can flex as it goes through and not get caught up in the blade causing a kickback, this wiggle room is completely eliminated when the piece is connected at the top, and worse when the wood is naturally pinching in from both sides.

So.. IMO I cannot agree that a dado set is the same level of danger as a single blade, it is slightly more dangerous… because of the added drag, and can be mitigated by fitting a riving knife that matches the blade. These are hard to come by, and usually only in single purpose machines, but not impossible

The best tool is to be aware of the physics at work in a table saw failure. I and others have posted this before, I may try and link to this thread in a bit.


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## gfadvm (Jan 13, 2011)

rg33, I would NOT use the fence for that dado cut as there is too much chance of it getting away from you and becoming a Frisbee! I would use the miter gauge or a sled.

Since this is a non-through cut, it will get launched if you skew it AT ALL when cutting the dado. Been there, done that, learned my lesson!

Certainly no disrespect to my friend Charlie intended.


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## MrRon (Jul 9, 2009)

After reading all the comments, I conclude that a dado blade is no more dangerous than any other blade. That is my opinion and I am happy to live with it. I understand that we are hearing comments from people with varying amounts of experience and I have taken that into account.

Terry Vaughan; I read the UK regulations pertaining to saws used in commercial service. They are the equivalent to our OSHA regulations. Osha has a bit more power over commercial operations in that it can fine companies if regulations are ignored. (that is a little hard to enforce) It's when a worker gets injured on the job that the lawyers get involved and use ignored OSHA regulations for their case. Home woodworkers don't come under OSHA rules, although the Sawstop inventor would like to see it happen.


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## Surfside (Jun 13, 2012)

Dado blades can be very dangerous. But I think incidents are user error. With this type of tools, extra care, knowledge and concentration are highly required.


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## Bullet (Apr 14, 2009)

Well, the engineer in me is rearing his ugly head. I'm sure what I'm about to write can be disputed, but this is how I see dado safety - with respect to kickback:

If you just look at the physics of what's going on with a dado, the potential for kickback is greater than with a standard blade. 
1. It's generally a smaller diameter, 6" or 8" compared to 10". So the available torque is increased greatly. Compared to a 10" blade, a 8" dado generates 25% more torque and a 6" generates 67% more torque to the workpiece. I know it's not "generating" the torque, but since the diameter is smaller, the available torque is greater. It's harder to loosen a nut with a short handled wrench vs a long handled wrench.
2. The cut is closer to the tangent of the blade. As you raise the blade above the table, the force generated changes direction. The teeth of the blade move down more, in relation to the table, the higher the blade goes. The force that is parallel to the table is the "same" no matter the height of the blade, but the force pushing down, onto the table, increases. With a dado, cuts are with the top of the blade inside the workpiece, keeping the majority the force pushing parallel to the table.








3. Dados take a bigger bite. The volume of material removed by a dado is simply greater than a standard blade. This is why it's safer to take little bites with a dado and do multiple passes. The size of the bite is a huge factor in the safety of the dado (with respect to kickback).

I'm not going to get into twisting the workpiece and binding on the blade since that is with whatever blade, or dado set, you use.

Keep all blades sharp. A dull tooth tears the wood - and tearing wood fibers is more difficult than cutting them. Tearing transfers more of the force of the spinning blade directly to the wood. And with a dull dado, the tearing is in a bigger bite, as in #3 above. It's like cutting a piece of beef jerky with a pair of pliers instead of a wire cutter.

What the heck did I just write? It might not all be perfectly accurate, but it'll do.

With all that said, I don't feel that dados are any less safe than a standard blade. And since the spinning blade is contained within the workpiece, it "lessens" the chance of finger/blade contact.


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## wormil (Nov 19, 2011)

Counterpoint: the most common cause of kickback is wood pinching the back of the blade during a through cut causing the back of the board to ride up the blade. The points you raise would contribute to the force of the kickback but I don't see them as causes of kickback.


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## MrRon (Jul 9, 2009)

Surfside; 100% of all injuries are caused by the operator of the tool. If it's because of a tool that was not properly set up and aligned, the fault lies with the operator. If the saw blade is dull and causes a kickback; again it's the operators fault. The operator is ultimately responsible for his own welfare. Blaming the tool is just a way to cover one's own stupidity. If I get injured, I will blame my own stupidity and not my tools because I keep my tools in top condition. If the Sawstop keeps someone safe from his own stupidity, it's a good chance he will find some other tool to get injured by.


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## darthford (Feb 17, 2013)

Dado's bah, now a shaper…


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## SCOTSMAN (Aug 1, 2008)

Yes it is definitely to do with the removal of riving knives and guards which must be removed to use them the EU European Union doesn't allow them. If however for home use without employees using them then your or should be ok but guess what they don't allow a spindle on E U. machinery long enough to take a dado also the spindles on most saws here is 30 mm or and inch and a quarter+ and dado's correct me if I am wrong are American 5/8ths or thereabouts, so it's definitely safety concerns and nothing else I know I checked it out myself with the government bodies concerned talk about big brother then its to do with getting shop insurance as using them without permission which is not grantable is a serious offence here in Europe very serious they could close you down without delay. and your insurance would be null and void ,without question .Alistair


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## MrRon (Jul 9, 2009)

SCOTSMAN; How do the dado police dress in Scotland and do they carry weapons? Sounds mighty opressive to me. I will have to add my dado blade to my list of things I want the government to keep their hands off of and that includes my guns and my health insurance.


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## shawnmasterson (Jan 24, 2013)

I think it has to do with the removal of the guard/riving knife. There is nothing unsafe about a dado blade, just the uneducated/inexperienced user. since I have no guard/riving knife on any of my 3 TS's there is no problem for me.


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## Tooch (Apr 6, 2013)

I will resaw on my table saws and it work out just fine. those Europeans are crazy…. with their topless beaches, girls with hairy armpits, and admonishment towards dado blades, I have no use for them!

well maybe topless beaches wouldn't be bad


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## Grandpa (Jan 28, 2011)

Splitters and riving knives are supposed to keep a board from closing on the blade and "pinching". This causes the kick back problems. Since the dado doesn't cut completely through the board how can it pinch the blade? The remaining wood should keep this from happening. A riving knife would not add to the safety of a saw using a dado blade (if it were possible). The most dangerous part of using a dado blade is covering it up with the board. It comes from hiding and you have your hand in the wrong place. I don't see how a blade can come off the arbor and fly anywhere unless the arbor nut comes completely off. The nut really should loosen slightly and the blade or dado set should slip and stop turning without flying anywhere. It cant keep turning unless the nut is tight and it can't fly off the arbor unless the nut is completely off the arbor. Arbors are designed to tighten the nut with the force from the blade instead of loosening the blade.


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## TerryV (Jun 30, 2012)

Grandpa, you are exactly right about the board covering the blade - until it doesn't.

The problem with the loosening comes when the saw is stopping, specially in the UK where saws in commercial shops are required to stop rapidly. The blade's momentum tries to keep it spinning and then the force could undo the nut. How likely it is to spin right off the arbor I don't know, but the nut will be close to the end with a dado blade fitted.


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## bannerpond1 (Mar 15, 2013)

I made a dado sled for cutting dadoes on wide boards. If the boards are too long, I use a homemade router jig which is clamped to my board and bench at the same point.

I use a sled for miters, dadoes, and cross cutting batches of identical pieces. It doesn't take long to make the sleds and you can use good scraps of 3/4 ply to make a stable jig.


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## wormil (Nov 19, 2011)

the force could undo the nut.

What? Why would that happen.


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## TerryV (Jun 30, 2012)

When the saw is running up to speed or cutting wood, there is drag on the blade. The force to overcome this drag is applied to the blade by the motor, via the saw spindle, the inner flange and the outer flange and nut. The nut thread is handed so that the drag, if it moves the nut at all, will tighten it.

When the saw is running under power but not cutting, there is no drag and no force acting on the nut.

When the saw is turned off, the momentum of the motor, spindle and blade set makes them want to keep on spinning. Friction overcomes this and the machine comes to a stop. The friction that slows the blade set is applied by the nut. If it is high enough, there is no problem.

But the nut is not handed so as to be self tightening under the forces of slowing down. If the blade set is heavy or the saw motor is braked, the nut tension may not be enough to keep the blade locked to the spindle. Then the blade will spin free and by rubbing on the flange and nut could loosen them further.


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## wormil (Nov 19, 2011)

I understand what you are thinking but it doesn't work like that. Whether electrical power is applied is irrelevant; momentum carries the blade forward while a blade brake applies the same resistance as cutting. As long as the arbor is spinning in the right direction, the nut is self tightening.


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## Grandpa (Jan 28, 2011)

I have to agree with Rick. Think about this some more.


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## TerryV (Jun 30, 2012)

The cutting resistance goes through the blade in the same direction that you tighten the nut. When braking the force is applied to the motor and spindle direct. So the only thing that stops the blade over-running is the nut tension. If the nut is loose the blade will keep spinning in the same direction as you undo the nut.

A brake acting on the blade itself would not cause this.

Anyone else got a view?


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## Grandpa (Jan 28, 2011)

as soon as the nut is loosened say 1/4 turn, the blade should free wheel on the arbor so the nut really wouldn't turn anymore.


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## TerryV (Jun 30, 2012)

Yes, in theory, but there will be vibration and some side to side movement in the blade and flange. It is very likely to push the flange in contact with the nut as it free wheels. So there will be friction trying to undo it. Unless the nut is very free on the thread this might not be a problem in practice, but it will be starting from quite near the end of the thread.


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## wormil (Nov 19, 2011)

Think about applying the brakes in a car, the momentum pushes you forward, not back; same with the blade and nut. Except on a saw the momentum on a nut is resisted by the left handed threads.


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## TerryV (Jun 30, 2012)

OK, let's try an experiment. (I'll make it a thought experiment I think).

I have installed on my saw a heavy dado set with heavy flange washers and a heavy retaining nut that is not fully tight. The spindle is a bit worn so all the components are free-fitting. The saw is running at full speed, but nothing is being cut. I shove a stick in the works so the motor stops dead. What happens? There is not enough grip from the nut to stop the blades and flanges dead along with the motor and spindle, and not enough friction between the nut and spindle thread to stop the nut dead. So all those parts suddenly wrench themselves free and keep on spinning. They spin forwards in the same direction that you turn the nut to undo it. The momentum of the nut causes it to unscrew a bit until it comes to a stop a bit closer to the end of the spindle. The blade set and the outer flange are rattling a bit and still spinning at high speed. They rattle against the nut, rubbing on it and undoing it a bit more.

This doesn't sound safe to me!


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## MrRon (Jul 9, 2009)

Don't left tilt saws have a RH thread? Mine is a right tilt and has a LH thread. Actually I don't think the arbor nut will do anything as long as it is tightened properly. Only if the nut is completely loose allowing the blades to spin freely would there be the tendency for the nut to further loosen up. For the nut to come off completely, I would say it's unlikely to happen.

There was a time way back when cars had LH threads on the wheel studs on one side and RH threads on the other side. Now the wheel nuts are all RH threads. I once had a wheel come off a Mustang, but it wasn't the wheel nuts; the wheel and axle came off as one. I was driving on the freeway; looked in my side mirror and saw the wheel and axle moving away from the car.


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## TerryV (Jun 30, 2012)

I don't think the arbor nut will do anything as long as it is tightened properly

Probably not. But over here the braking force might be higher, to make saws stop quickly. Perhaps the nut will not be properly tightened every time. So that is one reason to say dado blades are more dangerous. How much more dangerous is hard to say. Most times the blade comes loose it will probably just spin to a stop. Out of 1000 saws, all operated by different people, perhaps sometimes the nut will spin right off. Even then, injury may not result. But it seems like a problem if it is possible for the blade to come off.


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## moonie (Jun 18, 2010)

Im I the only preson that is using my TS for a dado saw I have been doing this for a long time and I havent had a nut to lousen or that many kicks backs like you all.


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## wormil (Nov 19, 2011)

So you're saying that dado blades are more dangerous if someone doesn't tighten the arbor nut and jams a stick into the motor. Got it.


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## TerryV (Jun 30, 2012)

So at least we agree on that!

This thread started with the question 'Why are dado blades considered unsafe?'. Some reasons have been suggested, chiefly to do with the difficulty of guarding. This business of stopping times and loose blades is relevant too.

Some people said it is as safe to use unguarded dado blades as it is unguarded standard blades.

There is another question - whether it is best to design out risk from potentially dangerous machinery that employed people may be required to use with minimal training and supervision (a principle of our occupational safety legislation), or to rely on the individual to protect themselves (a principle of your independence).


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## susb8383 (Mar 14, 2021)

> When the saw is turned off, the momentum of the motor, spindle and blade set makes them want to keep on spinning. Friction overcomes this and the machine comes to a stop. The friction that slows the blade set is applied by the nut. If it is high enough, there is no problem.
> 
> But the nut is not handed so as to be self tightening under the forces of slowing down. If the blade set is heavy or the saw motor is braked, the nut tension may not be enough to keep the blade locked to the spindle. Then the blade will spin free and by rubbing on the flange and nut could loosen them further.
> 
> - Terry Vaughan


I know this is an old post but this topic is still relevant.

The discussion above about whether the nut can loosen is mostly theoretical, but I wanted to post that what Terry described is EXACTLY what happened to me.

I'm pretty new to woodworking and went to change my table saw blade for the first time. I watched videos that said not to over tighten the nut, just make it snug because the motion of the spindle will cause the nut to tighten, so that's what I did.

I made a few cuts and turned off my saw. The blade kept spinning even after the spindle was stopped. When I looked at it I found that the nut was about halfway up the spindle.

I made it a little more snug and tried again. The same thing happened but this time the nut had come completely off and I had to fish it out from inside the saw.

In my case it was just a single blade but I've read on other forums that when this happened to other people using a dado stack, the blades were shot across the room.

So how my nut could come loose when the motion of the spindle is supposed to tighten it is a big mystery. I have a theory which is probably a discussion for a different thread but I'll just mention it: my new blade was a Freud that has red paint on it. I think the paint served as a bit of a coating that caused the nut/washer to not be as snug against the metal of the blade as they should have been. The washer had red paint residue on it which is why I think the paint was the culprit. Once the blade rotation was independent of the washer/nut to a small extent, the stopped spindle caused the nut to loosen on the spindle just as Terry described.

I solved my problem by using sandpaper on both the blade and the washer to remove the red paint where they contact. That and I also tightened it a lot more. I haven't had the problem since.

But this experience makes me a little timid to try using dado blades. If the same thing happened with a stack it would really ruin my day.


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## Wood_Scraps (Jan 31, 2021)

> When the saw is turned off, the momentum of the motor, spindle and blade set makes them want to keep on spinning. Friction overcomes this and the machine comes to a stop. The friction that slows the blade set is applied by the nut. If it is high enough, there is no problem.
> 
> But the nut is not handed so as to be self tightening under the forces of slowing down. If the blade set is heavy or the saw motor is braked, the nut tension may not be enough to keep the blade locked to the spindle. Then the blade will spin free and by rubbing on the flange and nut could loosen them further.
> 
> ...


I'd suspect your issue was likely resolved as a result of adequately tightening the arbor nut. With so many out there using Freud/Diablo and other coated blades every day, your experience would be far more common if the coating were the culprit.

As to the OP's question (in this very old thread), I'd imagine dado blades are feared and believed unsafe for the same reason as those who fear black rifles. They look scary and don't understand it's the operator, not the hunk of metal, who's responsible for safety.


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## OldDogNewTricks (Jan 7, 2021)

> I had heard this too, and am interested and agree with what most of the comments on here have said so far. Here are a couple observations from someone who uses my dado set a lot.
> 
> 1. Riving knives and blade guards go out the door pretty much. (+1 PurpLev)
> 2. Removing more material in one swipe can be dangerous if done improperly.
> ...


I've seen this happen (the blade spinning freely) if the arbor isn't tightened sufficiently. Usually the rule of thumb is don't over tighten the arbor because it will get tighter when the saw spins. But with the higher mass of a dado stack, when the saw goes to stop, the blade "unscrews" the arbor when momentum is transferred to the arbor nut.

Mike


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