HSE - Very, Very Nice Man & this week's Can of Worms!

[tomatwark]

Thanks very much for that Andy, lots in there to think about. You'll have noticed I'm a bit sceptical of the prevailing wisdom on the topic. I guess I struggle with the idea that so many more people use them in the US than ever could here - in that if there was a significant problem we'd surely have heard of it by now.

While there's a lot of macho stuff that gets talked over there our trans-Atlantic brethren are pretty quick to head for the courts or the media if something goes wrong. They don't seem notably keener than the rest of us to stick their hands in moving cutters either. Nor (despite all the noises about dodgy US practices) do too many seem to be missing fingers and the like.

There is a well documented case recently with the flooring contractor putting his hand in a saw, and winning his case because of the saw not being fitted with a braking system like SawStop.

Will a system like SawStop work with a Dado set, I guess that if it will not and the the US makes fitting that sort of system law, it will put an end to the dado head in the States.

Tom

 

[kirkpoore1]

What's frustrating too C is that the previously mentioned fog of negativity must put many people off dado cutters. Yet when viewed from a 'what do we need to do to make it possible' perspective it seems very much like there's nothing tangible that says it's any less legitimate than using a normal blade:

Pulling together most of the inputs:
...
2 They must be guarded (you can't use a riving knife mounted guard, but there are options, cut closure doesn't happen, and anyway most cuts are covered by the workpiece)
3 The saw must still stop within 10 seconds (normal surely? The weight is likely not a big issue anyway given the smaller 6in and 8in diameters - rotational moment of inertia increases with the square of the radius, so I'd be surprised if they are much different to stop than a 10in blade)
...
Stick your hand in one and its going to be messy, and the wider blade could in a specific situation do more damage - but surely on average not significantly more so than in the case of a normal (much higher) saw blade?

:?: So why the fear of flying and the whiff of gunpowder???? It'd be nice to see the topic treated on the more straightforward basis of practical pros and cons.....

I went out and measured the stop time on my Powermatic 65 cabinet saw with a 10 inch blade, 3 hp motor, 3450 rpm, two belt drive, no brake. Stop time was 4 seconds. I don't have a dado stack, and I didn't have a second 10" blade handy to put on the saw and check, but I'd say it's likely that you'd go over 10 seconds if you were using a 3/4" wide stack. So if you care about this arbitrary time, have some kind of brake or use a narrower stack.

For the cut closure issue, I can only see it coming into play on deep rips on solid wood, and mostly narrow edges. By deep, I mean half or more of the thickness of the wood. In this case, you could be allowing wood which would naturally cup to pinch in.

Again, other than ripping a long dado in the middle of a wide board, I see little need for a dado blade on a tablesaw. I'll use a RAS for crosscuts and a shaper for rabbets & near-edge dados. But that doesn't mean they're any more dangerous than any other blade.

Kirk

 

[ondablade]

That seems to be the point (so far) that's emerging about dado cutters Kirk - of course you can get injured by one as is the case with pretty much all power tools. But there's nothing obviously coming out of this thread to suggest that they make a saw significantly more dangerous than most other woodworking machines.

Thanks for the info on stopping a dado head. A quick calculation (hope my memory is right - and correct me if I'm wrong) suggests that the rotational moments of inertia of 12in (saw blade), 10in (saw blade), 8in (larger dado) and 6in discs (small dado) relate in the ratio of 113:80:50:30. (proportional to the surface area) So that e.g. a ten inch disc has 2.5 times the inertia of a 6 in dia disc, and a 12 in 2.25 times the inertia of an 8in dia disc.

Meaning that in the case of the above two examples you can run something over two discs in both of the smaller sizes (of the same thickness) and still only match the inertia of a regular blade in both cases. A dado uses two discs plus chippers. There's then the question of how much spare braking capacity a given saw has, and how it reacts to the additional inertia.

Smaller saws may be short of braking, but then they probably won't have the power to run a dado anyway.

That US case with the contractors saw was a bit daft Tom - I can't quite remember all the details. The guy did pretty much everything possible to remove all the safety capability of the saw and to misuse it, but the judge ignored this and found the maker in the wrong because they hadn't fitted a Saw Stop type device. (never mind that it's proprietary to Saw Stop - and is far from standard, and not required by any code)

If the case had any value it's that it may encourage makers to fit saws and the like with fast stop capability. The Saw Stop seems a bit crude though (ram a block of aluminium that's been hollowed out to create a crumple zone into the blade) - it could prove to be only the first in a rush of devices that'll hit the market once the factories get serious about it....

 

[tomatwark]

I know that the out come of the court case in the States was daft, the guy did not know what he was doing, I was just interested to know if the system would work with a dado.

I hope that they don't pass a law regarding this device over here, while I can see it has its merits, I think it may make people take less care in what they are doing, and it will be another thing that will get blocked up with sawdust and go wrong and the best way forward is the provision of proper training for Professionals and Hobbists.

Tom

 

[ondablade]

Pardon if the bit about the law case came across wrong Tom - I was just suggesting that it had no specific implications for dado cutters.

There's this feeling of dread that comes over me when the system gets involved in stuff like that too. That's not to argue against effective safety devices, but as before it all ends up so loopy so quickly when authority and anything that eliminates the need for people to stay aware get mixed together....

 

[Sgian Dubh]

Thanks SG, that's good to know. Am I reading you correctly in feeling that it doesn't seem (?) like it puts dado cutters into the sort of high risk territory that the prevailing vibe suggests?

Dado blades, in my opinion, can be used relatively safely with the proviso that they are set up to use in a safe manner. My experience is that dado blades are seldom set up for use in such a manner. Certainly the Americans I worked with, for whom the dado blade was and is a primary tool, never set one up to include such wimpy things as guards or tunnels, or other means to enclose the blade and prevent contact with the hands.

Possibly one of the least safe uses of a dado set I witnessed was cutting shelf housings (dados) in a long bookcase side. The long rip fence was used as the length stop and adjusted for each cut. The long narrow piece was pushed narrow end against the rip fence and guided over the exposed dado set. It didn't surprise me when the bookcase end jumped off the saw table back at the operator. The cause was simple enough because the narrow end of the bookcase drifted away from the rip fence and the rear up cutting teeth of the blade picked up the part and flung it back.

To be honest, I've never needed a dado blade to perform a wood machining operation, even when I lived in the USA where I saw them used daily, and I've been working wood for a living since 1973. I used one perhaps half a dozen times when I worked in Texas, but it wasn't any better at doing the job than alternative tools, eg spindle moulder, overhead router, inverted router or hand held router, etc. Dado blades have a history of causing serious injury to woodworkers as I understand it. The fact that very few table saws sold in the UK will accept a dado blade doesn't bother me. If it ever comes in the future that dado heads can again be fitted to UK sold table saws it wouldn't surprise me to see the number of table saw injuries rise as a consequence. The reason for that would probably be for the same reasons they are likely to have historically been high and significantly injurious, ie, the common habit of using dado blades for speed and convenience, ie, unguarded and sloppily rather than safely, ie, guarded and carefully. Slainte.