Dado cutters - Please, what is so dangerous about them

[Sawdust]

the router would fly, more likely than the wood.

by its very design, you tend to stand behind the wood when using a
table saw, on a router table or freehand you stand to one side
thus reducing the personal, but not the workshop risk.

paul :wink:

Flying oak is dangerous, but a flying router, now that would be fun

 

[Kane]

I think I'll switch to hand tools!!!

 

[Adam]

Flying oak is dangerous, but a flying router, now that would be fun

I do not believe the momentum in a router bit, transfered to the weight of a router, could propel it to any degree. This is due to the (relatively) low weight, and close proximity of the cutting surfaces to the centre of the spin of the spindle, compared to the reasonably heavy weight of a router. The router bits are normally only weighing in the order of grams, they simply do not contain much energy. Even adding in the spinning weight of the motor of the router, they are still small and lightweight - they are designed to be "portable". The momentum of a dado is much greater, and the cutting edge acts at a much greater distance. The weight of wood is not to be ignored, and when launched at speed at you, will cause injury. Additionally, table saws have much much higher power motors, and the momentum in those, the spindle etc is much more significant, as they have to cope with deep rip cuts. Perhaps thats the best reason I can think of.... the amount of stored energy in a router at cutting speed compared to a tablesaw at cutting speed.

Adam

 

[Sawdust]

However, would a big router cutter be any better in similar circumstances, or what if a planer hits the same shake or knot.
Mike

Yes, it would be much better surely. A) The mass of the cutter is much less B) the rotational speed of the cutter is much less, especially if its a physically larger cutter C) the user is normally holding the router with two hands D) if its on a router table, then more than likely then holddowns are being used. (or are at least available). With only the depth of the router bit itself in the wood, once that is lifted (forced) ripped, or however it exits, it is doesn;t continue to exert any force on the router, and hence its safer. The user normally has access to the power switch, possibly quicker than getting a hand on the off button. The router cannot "pickup" and smash the wood into the user. Just a few reasons - not neccasarily all true, but all possibilities at least.

Adam

On a planer, the the infeed and outfeed tables are set to a different height, the wood cannot be dragged into the cutter as the tables prevent this, and the balde cannot normally be signficiantly exposed - so its only taking light cuts

Adam,

To take things to extremes, compare a raised panel cutter in a router table to a dado cutter in a table saw taking a very thin and shallow cut, extreme yes, but which is the most scary/dangerous? Also a router on its slow setting is faster than a table saw.

As for a planer, according to the specs, mine can take a 3mm cut off a 10 inch wide board (sorry for mixing my units), that's a lot of wood and my opinion, the guard is not great (and no I haven't removed it). If that hit the same knot there would be wood everywhere. This hasn't happened to me but has to a friend and it had a similar effect on him to the one Scrit describes with the dado.

Mike

 

[wrightclan]

Yes, it would be much better surely. A) The mass of the cutter is much less B) the rotational speed of the cutter is much less, especially if its a physically larger cutter C) the user is normally holding the router with two hands D) if its on a router table, then more than likely then holddowns are being used. (or are at least available). With only the depth of the router bit itself in the wood, once that is lifted (forced) ripped, or however it exits, it is doesn;t continue to exert any force on the router, and hence its safer. The user normally has access to the power switch, possibly quicker than getting a hand on the off button. The router cannot "pickup" and smash the wood into the user. Just a few reasons - not neccasarily all true, but all possibilities at least.

Adam

On a planer, the the infeed and outfeed tables are set to a different height, the wood cannot be dragged into the cutter as the tables prevent this, and the balde cannot normally be signficiantly exposed - so its only taking light cuts

I'm sorry, but I have to break my self-imposed silence on the issue. The rotational speed of a router is much higher than a sawblade. Most tablesaws go no higher than 4,000rpm. Most routers go no lower than 8,000 rpm. If you use appropriate pushers and hold-downs with the dado, it will not '"pickup" and smash the wood into the user.' Remember, as well, that in a dado blade most of the 'mass' that everyone is concerned about is in the form of two tooth chippers. The fewer the teeth (and the shallower the cut), the less resistance. That's why you don't use an 80 tooth blade for ripping. I have had some gnarly bits thrown at me from a router in a table. Understanding how wood works and how forces of machinery work in relation to the wood, will keep you far safer than all the guards in the world.

By the way, I do use a dado cutter, but not really that much--I just don't do a lot of work where it would be an advantage. Now and then, it is an advantage, and I use it.

Brad

 

[Anonymous]

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[Sawdust]

Yes, it would be much better surely. A) The mass of the cutter is much less B) the rotational speed of the cutter is much less, especially if its a physically larger cutter C) the user is normally holding the router with two hands D) if its on a router table, then more than likely then holddowns are being used. (or are at least available). With only the depth of the router bit itself in the wood, once that is lifted (forced) ripped, or however it exits, it is doesn;t continue to exert any force on the router, and hence its safer. The user normally has access to the power switch, possibly quicker than getting a hand on the off button. The router cannot "pickup" and smash the wood into the user. Just a few reasons - not neccasarily all true, but all possibilities at least.

Adam

On a planer, the the infeed and outfeed tables are set to a different height, the wood cannot be dragged into the cutter as the tables prevent this, and the balde cannot normally be signficiantly exposed - so its only taking light cuts

I'm sorry, but I have to break my self-imposed silence on the issue. The rotational speed of a router is much higher than a sawblade. Most tablesaws go no higher than 4,000rpm. Most routers go no lower than 8,000 rpm. If you use appropriate pushers and hold-downs with the dado, it will not '"pickup" and smash the wood into the user.' Remember, as well, that in a dado blade most of the 'mass' that everyone is concerned about is in the form of two tooth chippers. The fewer the teeth (and the shallower the cut), the less resistance. That's why you don't use an 80 tooth blade for ripping. I have had some gnarly bits thrown at me from a router in a table. Understanding how wood works and how forces of machinery work in relation to the wood, will keep you far safer than all the guards in the world.

Brad

Brad,

There's probably an emoticon for loud applause but I don't know it so I'll just say thanks.

Cheers
Mike

 

[Adam]

Most tablesaws go no higher than 4,000rpm. Most routers go no lower than 8,000 rpm.

OK, but rotation speed of the spindle has no relation to the speed of at the cutting tips. Thats a function of RPM but the RPM itself is no guide.

For example. Assuming a 250mm diameter table saw blade, that is operating at 4000 rpm as you indicate. That means its speed is

66 revolutions per second, at (pi x 250mm) = 0.78meters per turn,

So the speed of the dado blade is 51 meters per second with lots of momentum.

Lets assume a 1inch dado, and you are using a 1 inch diameter cutter (large I know). therefore, lets use 8000rpm

25 millimeters x pi = 0.0785398163 meters = 10meters per second with much less momentum.

So, as I said, the router goes a lot slower, with a lot less momentum.

Adam

If you use a more realistic 12mm cutter on the router, and wind it up to 12000rpm it drops to 7.53meters per second.

 

[wrightclan]

Most tablesaws go no higher than 4,000rpm. Most routers go no lower than 8,000 rpm.

OK, but rotation speed of the spindle has no relation to the speed of at the cutting tips. Thats a function of RPM but the RPM itself is no guide.

For example. Assuming a 250mm diameter table saw blade, that is operating at 4000 rpm as you indicate. That means its speed is

66 revolutions per second, at (pi x 250mm) = 0.78meters per turn,

So the speed of the dado blade is 51 meters per second with lots of momentum.

Lets assume a 1inch dado, and you are using a 1 inch diameter cutter (large I know). therefore, lets use 8000rpm

25 millimeters x pi = 0.0785398163 meters = 10meters per second with much less momentum.

So, as I said, the router goes a lot slower, with a lot less momentum.

Adam

If you use a more realistic 12mm cutter on the router, and wind it up to 12000rpm it drops to 7.53meters per second.

My router goes up to 32,000 rpm. You also won't find a 10 inch (250mm) dado blade anywhere--they're usually either 6inch or 8 inch. My tablesaw turns at 2800rpm that's 29.8 metres per second. A 1/2 inch bit at 32,000 (which is not unreasonable) travels at 20.9 metres per second--not that far off now. But they are turning in different planes, so the forces are different.

But that still does not address the issue that each of the teeth of a dado cutter are taking relatively small individual cuts, with relatively little resistance. And further, it does not address my ultimate point: Understanding how wood works and how forces of machinery work in relation to the wood, will keep you far safer than all the guards in the world. Perhaps I should qualify this by saying it will keep you safer than just using guards without the aforementioned understanding.

Brad

 

[johnelliott]

Visiblity not an issue when in use as the blade is out of sight under the workpiece - which also makes it very safe.

There is the 'small' matter of when the blade is exposed at the start and end of the cut.

John

 

[johnelliott]

,

Understanding how wood works and how forces of machinery work in relation to the wood, will keep you far safer than all the guards in the world. Perhaps I should qualify this by saying it will keep you safer than just using guards without the aforementioned understanding.

Understanding that people sometimes slip, especially on sawdusty floors, and that sometimes people feel a little dizzy, without warning, or that they can be distracted, or that sometimes bad stuff happens, and that therefore one should keep guards in place will keep you much safer than knowing how wood works and the how the forces of machinery work in relation to wood.
John

 

[wrightclan]

,

Understanding how wood works and how forces of machinery work in relation to the wood, will keep you far safer than all the guards in the world. Perhaps I should qualify this by saying it will keep you safer than just using guards without the aforementioned understanding.

Understanding that people sometimes slip, especially on sawdusty floors, and that sometimes people feel a little dizzy, without warning, or that they can be distracted, or that sometimes bad stuff happens, and that therefore one should keep guards in place will keep you much safer than knowing how wood works and the how the forces of machinery work in relation to wood.
John

Did I ever advocate removing guards? OK, you need to remove factory-fitted guards to use a dado, but I did mention using appropriate pushers (not those silly plastic things that come with tablesaws) and hold-downs--these are in effect guards. As far as your **** happens, etc., this is an issue for knowing your limits and using a safe stance, etc., not relevant to whether dado's can be used safely.

Brad

 

[Noel]

Overhead guard works well.

 

[matthew]

I'm probably missing something 'cos I'm still relatively new to this, but I don't really see the attraction of a dado set?

Perhaps for those in production environments - but they don't have the option anyway, what with H& S regs.

For the amateurs among us, are you really cutting that many dados to make it worthwhile? The expense of the set, the time spent changing the blades? Can't it be done just as easily with a router and clamp guide, or by making multiple passes with the normal table saw blade?

Matthew

 

[johnelliott]

As far as your **** happens, etc., this is an issue for knowing your limits and using a safe stance, etc., not relevant to whether dado's can be used safely.

Well, there we will have to agree to disagree.

I would be interested to know what the others who are reading this think about this, though. Do they think that knowing their own limits is going to save them in a **** happens scenario?
I thought that **** happening was something that, in itself, couldn't be prevented. I thought that was what **** happening meant.
The point I was trying to make was that one should strive to lessen the impact of the **** by chosing to avoid unsafe working methods.

John

 

[JPEC]

Refering to questions posed on Norm's site, the only reason dado cutters do not conform to European standards is that they take longer to come to a stop after the saw is switched off, than is permissable.

Julian

 

[Sawdust]

All,

This has been an interesting debate and I thank everyone who has contributed and I'm sorry if I've raked over old ground or touched a few nerves. I feel I know a lot more about dado safety than I did this morning and it seems to me that the major concerns are:

The saw's braking mechanism allowing the blade to come off, this would definitely put me off using one on a braked saw.

The inability to use the saw's standard guards, but I think this could be overcome with suitable overhead guarding.

It's not possible to use a riving knife. As far as I can see, there is no way round this and I'm unsure how much of a risk this is.

It appears that a RAS is much more suitable than a table saw for using a dado cutter and I'm still very tempted to get one and use it on the RAS and once I feel comfortable with how it cuts I will probably use it on a table saw with a good overhead guard and hold down.

Thanks again for all the advice and comments.

Mike

 

[Anonymous]

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[wrightclan]

Visiblity not an issue when in use as the blade is out of sight under the workpiece - which also makes it very safe.

There is the 'small' matter of when the blade is exposed at the start and end of the cut.

John

Well it is a 'small' matter. I don't know why wobble saws cause so much paranoia. A wobble saw is very safe.
For that matter if a dado cutter is as dangerous as some say (I've never used one) well I'd seriously recommend the wobble saw which appears to do just the same job but safely. And they are cheaper.

cheers
Jacob
PS why the mention of 'riving knife' with ref to a dado cutter - it wouldn't serve any purpose even if you could fit one. These cutters make a slot, not a through cut, so there is no risk of the work binding on the blade as the sides can't spring together.

You can solve the visibility issues by making a zero clearance insert for your saw, and get cleaner cuts, as well. If you think you need a riving knife, you can make your own wooden one that fits into the insert.

Brad

 

[wrightclan]

As far as your **** happens, etc., this is an issue for knowing your limits and using a safe stance, etc., not relevant to whether dado's can be used safely.

Well, there we will have to agree to disagree.

I would be interested to know what the others who are reading this think about this, though. Do they think that knowing their own limits is going to save them in a **** happens scenario?
I thought that **** happening was something that, in itself, couldn't be prevented. I thought that was what **** happening meant.
The point I was trying to make was that one should strive to lessen the impact of the **** by chosing to avoid unsafe working methods.

John

No offense, but maybe you shouldn't drive a car, or even leave your own house. Or use powertools at all, if you want to keep yourself from all conceivable risks.

I thought I just described how to 'avoid unsafe working methods' when using dado cutters.


Brad