Dado cutters - Please, what is so dangerous about them

[Sgian Dubh]

Kane, ancient style UK ripsaws had long fences that stretched the full length of the table alongside the saw blade. Typically there was a rail front and back and the fence stretched from rail to rail. It locked in place on these rails with a cam action lever on the infeed side. Decades ago when I started in this game they were still quite common on older pre-WW2, WW2 and 50's Wadkins for example.

Similar long fences are the most common type in the US with the most popular brand being the T locking style Beisemeyer (sp?) fence itself and a bunch of clones based on it.

The problem with this kind of fence in ripping is that when the saw kerf in the wood opens after the cut due to the release of internal stresses this can force the dimensioned piece of timber on the right side of the blade tight against the rear upcutting teeth. This is kickback territory. Where a riving knife is fitted and a crown guard is in use the kickback is less likely to occur because the riving knife helps prevent the wood making firm contact with the rising rear teeth. However, in the US most users use neither a splitter (riving knife equivalent but iffy) nor a crown guard. The wood in the situation I described is forced into tight contact with those rear upcutting teeth which can easily result in kickback.

A short ripfence (the style used in the UK) allows a piece of wood similarly bending to bend away from the blade.

I witnessed kickback off dado blades too. The wood closed on the blade after internal stresses were released resulting in the wood firing back at the operator. Similarly, wood that drifted away from the long rip fence kicked back at the operator-- it's almost all down to those upcutting rear teeth. True, hold downs and other safety gear could have likely prevented the mishaps in both cases. The operator chose not to set any up.

I do say if anyone wants to use a dado blade, do at least be very wary of them. Slainte.

 

[Noel]

adam all i was saying that it seemed to be getting to my risks are
bigger than your risks, and that is where the contest seems to be.

having driven at over 200 mph, and pulled large wheelies on
bikes i understand risks, but that was on machines i had
built not ones i had bought and wood i knew nothing about.

paul :wink:

Interesting comparison as Marco Melandri might understand.
These days a stacked dado is waaay safer that travelling at 2 ton.

Noel, who hasn't exceeded 185, in a car.

 

[engineer one]

yea but i did it on proper tracks and roads, not
overtaking some horse and cart in the middle of derry :lol: :lol: :lol: :lol:

and boy those autobahns in the old days :twisted: :twisted: :twisted:
paul :wink:

 

[Noel]

Autobahns were and still are fun, although the de-restricted bits are few and far between these days.
That horse and cart you mention, what about it? Too fast for you was it?

Noel

 

[engineer one]

no mate but it was like the old story,
you know if i were you i would not be starting from here.

sadly it happened to me in dublin from a hotel :lol:

actually it was when the horse pulled a wheelie that i got really
scared :twisted: :twisted: :lol: :lol:

and coming down the mountains from strasbourg along to luxembourg
now that can be fun in the fog and ice [-X [-X

paul :wink:

 

[Anonymous]

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[wrightclan]

Kane, ancient style UK ripsaws had long fences that stretched the full length of the table alongside the saw blade. Typically there was a rail front and back and the fence stretched from rail to rail. It locked in place on these rails with a cam action lever on the infeed side. Decades ago when I started in this game they were still quite common on older pre-WW2, WW2 and 50's Wadkins for example.

Similar long fences are the most common type in the US with the most popular brand being the T locking style Beisemeyer (sp?) fence itself and a bunch of clones based on it.

Where a riving knife is fitted and a crown guard is in use the kickback is less likely to occur because the riving knife helps prevent the wood making firm contact with the rising rear teeth. However, in the US most users use neither a splitter (riving knife equivalent but iffy) nor a crown guard. The wood in the situation I described is forced into tight contact with those rear upcutting teeth which can easily result in kickback.

Slainte.

Not going to break my :-# on the D issue.

Just replying to some general tablesaw comments. I have a UK saw which is nowhere near as old as Sgian Dubh mentions, and it has a full-length fence. I've also seen alot of new saws marketed in the UK, which do, and not just American clones.

I really think that if American saws had proper riving knives and guards which detach and attach easily to the riving knife; then they would get used a lot more. You have to realise how poorly designed and unnecessarily complex American style guards/splitters are to understand why no one uses them.

Those Americans who know what a proper riving knife is, are begging for them. I don't know why more manufacturers aren't doing it. BTW at least one American company--Laguna, is doing it. Oh, I just remembered, Sawstop is, as well.

Brad

 

[Sgian Dubh]

SawStop is a new'ish brand in the US offering table saws with a riving knife and crown guard. The other element in their package is the almost instant braking device available should flesh come into contact with the blade. By all acounts most reviewers and/or users are happy with the tool. There's some whinges by some potential buyers about price, but that's a different issue.

Powermatic (and Grizzly I think) are both now offering an improved riving knife and crown guard configuration for the US market. Certainly both are now offering new developments such as sliding table saw that would be familiar to European woodworkers.

I have seen some saws at the low end here in the UK with long rip fences as you mention. Personally I wouldn't touch one with a barge pole unless there is a configuration where the fence can be set up for the short rip style. I see that some have that capability, but I can't say for all of them. Slainte.

 

[wrightclan]

Personally I wouldn't touch one with a barge pole unless there is a configuration where the fence can be set up for the short rip style. I see that some have that capability, but I can't say for all of them. Slainte.

Simple solution: a facing of ply or MDF which does not go the full length of the fence.

BTW,after my last post I remembered some of the high end Grizzlies have riving knives. What I can't understand, is why they don't fit them to all their saws; presumably it's a cheaper option as it's a much simpler device with fewer parts, and it's attached to the trunnions.

Brad

 

[Alf]

Personally I wouldn't touch one with a barge pole unless there is a configuration where the fence can be set up for the short rip style. I see that some have that capability, but I can't say for all of them. Slainte.

Simple solution: a facing of ply or MDF which does not go the full length of the fence.

The Maxi (cough, spit) solves the problem with a little adjustable L-shaped length of plastic held with a thumbscrew to the main fence. Only needs one hole tapped in the fence iirc, if anyone feels like applying the modification themselves.

Cheers, Alf

 

[wrightclan]

I have seen some saws at the low end here in the UK with long rip fences as you mention. Personally I wouldn't touch one with a barge pole unless there is a configuration where the fence can be set up for the short rip style. I see that some have that capability, but I can't say for all of them. Slainte.

I have a Startrite. Not sure of the age, but quite sure it's well post-50's. Misterfish has a Wadkin, which is surely well post-50's. ( He has a recent post with a photo). Both of our saws have full-length fences. I wouldn't call them high-end, but I also, certainly wouldn't classify them as low-end. They're both well-made solid British saws. Perhaps, you having worked in industrial settings, your idea of low-end and mine are different. (By the way, I have worked in industrial settings, repairing and installing safety equipment for metalworking machines, just not an industrial woodworking setting.)

Brad

 

[wrightclan]

Is this a low-end saw?

http://www.axminster.co.uk/recno/2/product-Rojek-KPF300-Saw-and-Spindle-Moulder-32087.htm :-k :?

 

[Freetochat]

Not trolling! Just want to point out that a wobble saw such as this http://www.axminster.co.uk/name/wobble+ ... -20237.htm does everything that a dado set does AFAICS but with absolutely non of the problems - real or imaginary.
I always find it trouble free and a pleasure to use. I use it mostly for slots 13x13mm in panel door styles and rails.
Fast , quiet, clean cutting, precise, easily adjustable, dust free, no kick back risk and more. Everyone should have one!

cheers
Jacob

But isn't this wobble saw only advised for a spindle moulder. That being the case, there are many groovers, adjustable or fixed, available. Therefore it will not do the same job as a dado which seems to primarly do crosscut housings.

 

[johnelliott]

Is this a low-end saw?

http://www.axminster.co.uk/recno/2/product-Rojek-KPF300-Saw-and-Spindle-Moulder-32087.htm :-k :?

From the context of your previous post I presume you are asking the question from the POV that the fence appears to be of the full length variety.
I have a recent Startrite saw (made by Rojek) which is similar (without the spindle moulder) to the model you are asking about. I would say that it is not low-end. Also the alloy extrusion which is fitted to the fabricated steel fence can be adjusted so that the it stops wherever one wishes in relation to the blade. When ripping hardwood I set it so that it stops in line with the back of the blade. This means that in this case it is a short fence. When cutting plywood I normally set it so that it is in effect a long fence

John

 

[Scrit]

My, haven't I missed some fun! But I'd still like to add a few of comments:

...., although I fail to see why, if a wheels can stay on a car under heavy braking (eg emergency stop with the wheels locked up), manufacturers can't make a blade stay on a saw where the braking is pathetic anyway.

Because a car has 4 or more nuts to hold it on - a blade has one, designed in such a way that when the blade is accellerated from rest the centrifigal force will tend to tighten the nut onto the blade. Brake a blade and it will undo the nut - which is why ALL industrial/larger saws now have pinned arbors to stop the unscrewing of the nut by the blade under braking. Under 10 inches there is generally insufficient kinetic energy stored in the blade for this to happen. And my saws, including a 16in rip saw all brake to stop in under 5 seconds.

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.

That and the little question of stacked dado heads over 15.5mm (BSI standard) not being of anti-kickback design (mandatory on most tooling sold in the EU since 2000). The other thing to quote from the HSE is "Tools which belong to a tool set, or are part of a stacked tool..... .....should be designed in such a way as to prevent the parts being used individually, eg by using pins". This also makes the sale and use of stacked dado sets questionable. Oh, and Norm generally doesn't discuss guarding, either.

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.

On saws with suspended crown guards where you have a short riving knife, such as panel saws, which do not extend above the blade (rather like those on a hand circular saws) the riving knife serves another function - to minimise the risk of picking-up on rising teeth if the work is accidentally tipped, something Sgian also mentions. Hence my preference for a Shaw-type down pressure guard or power feeder.

What I find odd is that the use of dado cutters in the US is so high - surely in the land of litigation if a tool was causing a lot of injuries because it's design was so inherently dangerous someone would have sued a manufacturer by now (maybe they have lol)

My understanding is that American firms work on the basis that they can legally defend the status quo at lower cost than a novelty (i.e. a new concept). This has been done to death on a number of fora in the USA, such Taunton's Knots. There are genuinely an increasing number of people in the USA who are aware of safety issues and who are actively seeking more European style safety solutions.

Personally, I think that Sgians comments on the subject of dados sum it up very well indeed.

Of anyone is interested in the topic of short rip fences Barb Siddiqui and Richard Jones published an excellent article subject on Badger Pond a few years back. The same site also has good article on DIY overarm guards here

Scrit

 

[Sgian Dubh]

Rojek don't make low end machines. They make lower middle range professional or upper range amateur use saws. Hammer is in about the same bracket, probably a bit lower. Hammers' big brother, Felder, makes upper mid range kit, SCMI about the same and perhaps slightly above and, of course, Altendorf are top end in the dedicated panel handling sliding table saw bracket-- they're actually pretty poor for ripping solid wood due to access problems. Slainte.

 

[Kane]

Scrit,
I was thinking more of individuals rather than businesses - just trying to get into woodwork so this is the only forum I've been on I think most of us will be familiar with individuals in the US carrying out some blatantly ridiculous practice with something then suing the maker for millions of dollars, or do the dado suppliers in the US emphasise the need for appropriate guards etc?

 

[Jake]

Scrit,
I was thinking more of individuals rather than businesses - just trying to get into woodwork so this is the only forum I've been on I think most of us will be familiar with individuals in the US carrying out some blatantly ridiculous practice with something then suing the maker for millions of dollars, or do the dado suppliers in the US emphasise the need for appropriate guards etc?

US woodworking industrial injury statistics (deaths/100,000 workers) are worse than in the UK by a factor of about 2, at least for fatal accidents. There were no UK stats for non-fatal injuries in the document I was looking at, so no comparison available there. I can't now find the document, but it is buried in the HSE site somewhere.

 

[Sawdust]

My, haven't I missed some fun! But I'd still like to add a few of comments:

...., although I fail to see why, if a wheels can stay on a car under heavy braking (eg emergency stop with the wheels locked up), manufacturers can't make a blade stay on a saw where the braking is pathetic anyway.

Because a car has 4 or more nuts to hold it on - a blade has one, designed in such a way that when the blade is accellerated from rest the centrifigal force will tend to tighten the nut onto the blade. Brake a blade and it will undo the nut - which is why ALL industrial/larger saws now have pinned arbors to stop the unscrewing of the nut by the blade under braking. Under 10 inches there is generally insufficient kinetic energy stored in the blade for this to happen. And my saws, including a 16in rip saw all brake to stop in under 5 seconds.

Actually those nuts hold the wheel onto the hub, the hub is held in place with a single (castellated I believe it's called) nut. Nit picking I know but from an engineering perspective, it could be achieved on a table saw arbour if the manufacturers chose to do so.

It has been an interesting couple of days and I'm glad I started the thread!

My initial question was an attempt to find out if I was completely overlooking something in terms of dado safety (or lack of it) but it seems in summary the issues are:

Potentially coming off a braked arbor.
The standard guard cannot be used.
The riving knife is ineffective.

It seems to me that the only one which cannot be overcome is the riving knife issue which as I understand it, leads to potential kickback dangers which I completely agree should not be taken lightly.

Having said that, the reason I asked in the first place was that the overwhelming dislike for dado cutters was because there really was something I had overlooked.

Having read all I've read, I do intend to go ahead and buy one, try it out on the RAS and see how I get on.

Cheers
Mike

 

[RogerS]

It seems to me that the only one which cannot be overcome is the riving knife issue which as I understand it, leads to potential kickback dangers which I completely agree should not be taken lightly.

I may have got the wrong end of the stick here but isn't the point of the riving knife to keep the two pieces of wood on either side of the cut apart when you are cutting completely through the stock? So that the rising blade doesn't kick back the wood.

But when you use a dado you are only cutting through part of the stock and so a riving knife isn't needed in this instance?