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.
MrRon
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.
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.
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!
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!
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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.
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.
Attachments
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.
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.
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
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.
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
well maybe topless beaches wouldn't be bad
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.
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.
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.
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.
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.
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.
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.
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.
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?
A brake acting on the blade itself would not cause this.
Anyone else got a view?
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