Dado cutters - Please, what is so dangerous about them

[johnelliott]

when you want to plow a 2" or deeper groove a router takes too long. I do understand the risks that can be encountered with this kind of cutting (especially the wood closing around the blade) so I stay mindful of the hazards and work accordingly. )

I am very interested to know why you would want to plough a 2" or deeper even groove in hardwood.

I would also be interested to know how exactly one works when mindful of the hazards.

John

 

[wrightclan]

What, to watch me crash and burn?.....

.....I was living in Burnsville at the time.

Might I say, "how appropriate"? :lol: :lol:

Sorry, Mike, OT. I'll get me coat

Scrit

Stepped right into that one :lol:

Brad

It gets worse--I lived on Burnsville Parkway, in Burningham Apartments (affectionately known to some residents as "The Flaming Swine.") :roll:

 

[Inspector]

johnelliott
You asked why I would want to make deep grooves. It's the method I learned from my father (70 years working with wood at this point) when making frame and panel doors. The groove for the panel is cut normally, then instead of mortising for the tenon you raise the blade to the length of the tenon and cut with the dado far enough to accommodate the width of the tenon. The arc after is hidden by the panel when it's all glued together. Modern glues are more than up to the task of holding the joint against the loads encountered unless someone is deliberately trying to break it and they will have to work pretty hard to do that. I will add that I would not use this for an exterior application but for interior doors and cabinet work it's fine, and it's easier for larger doors than for small work.

As for "being mindful of the hazards" I stay out of the line of fire in the event of a kickback (hasn't happened yet with the dado), using push sticks, not putting yourself in a position of being potentially unbalanced over the blade, and not having the hands in such a position as to get pulled back into the blade or over it if the wood isn't suddenly there. One other thing is to be willing to let the wood go and jump back if at any point the 'heebee jeebees' tell you something isn't right. It's better to bail out and replace the wood than to keep going against your instincts and try to overpower a power tool. That may not be a satisfactory answer for you but you are the one to decide what works best for yourself and work accordingly.

 

[SketchUp Guru]

Brad, you might have done so at that.

Say, back on the subject of dadoes, I'm curious as to how one might go about making something such as the grate I drew in Mark's Slatted Mat thread without using a dado set on a saw. This is a traditional way to make grates for boats.

As drawn the notches are 3/4" wide and 3/4" deep. Typically (in the US, anyway) the dadoes would be cut in wider stock and then the stock ripped down to the width of the dadoes. In the case of the grate I drew, and allowing for saw kerfs you would need about 30" of stock width just to make the notched pieces. Lets called it 6 pieces of 5" wide lumber. I drew 13 notches which works out to 390 linear inches or 32.5 feet of cut. Commonly teak would be used for a grate of this sort although other woods such as Ipe or some other tropical hardwood might be used.

Considering that you probably couldn't make a 3/4" x 3/4" cut in one pass, how would you make these? Three passes? Would you set up a box joint sort of registration jig on a router table and make a series of shallow passes and then reset the the cutter height and repeat the passes? Would you use a bit with a 3/4" diameter cut? I'm not trying to be a smart alec. I'd really like to know how you would process all of the wood for that project.

 

[Scrit]

.....I'm curious as to how one might go about making something such as the grate I drew in Mark's Slatted Mat thread without using a dado set on a saw. This is a traditional way to make grates for boats.

The answer is that nowadays a smaller trade workshop would probably use a crosscut saw (much heavier than a radial arm saw) with a dado head or variable groover on it (we used to call them trenching heads), then rip down, whilst the bigger workshops would cut it on a CNC router and again rip down. Another way would be to use a recessor or overhead router with a compound table to do the grooving. All of these ways would give you a 19 x 19mm cut in one pass. Shoving long bits of timber across a table saw sideways on has not really been part of how we do things here in the UK to the same extent as few table saws in trade places had sliding tables and shoving a table or sled is much more physically demanding than pulling a crosscut over IMHO. Most of the established yards I've seen had a Dominion or Wadkin crosscut lurking somewhere set-up for just this task, frequently the had just one machine, a Dominion Elliott combination woodworker (alright I've only seen a few boat builders - but they seemed universally to own a hulking great crosscut).

Above: Wadkin recessor with compound table
Below: Wadkin router (non-compound table version)

Above: Wadkin CD crosscut saw (sans bench - note the home position guard and lack of nose guard on the saw blade)
Below: a Dominion Elliott combination woodworker. Note the swivelling crosscut saw mounted on top

Scrit

 

[SketchUp Guru]

Scrit, that's all fine but what about the rest of us. Your methods are good but leave out the common hobbyist like me.

 

[Scrit]

Scrit, that's all fine but what about the rest of us. Your methods are good but leave out the common hobbyist like me.

OK, so I was trying to show what a boatyard might use, mea culpa

The fact is, Dave, that in the UK RASs aren't that common, many table saws won't take a dado head (and my feelings about the lack of safety/guarding issues on this are well known.....) but many "Average UK Joes" DO have routers. So probably the best way to proceed over here would be to square the end of the timbers and rout the grooves in 2 or 3 passes using a jig like this:

The stick rides against the edge or in the previous groove and the router is screwed to the top. A plane handle and knob could be screwed to the back and front respectively to ease use. By always registering on the previous groove and making the guide stick fit the slot precisely an accurate pattern of grooves could be cut.

Regards

Scrit

 

[Paul Kierstead]

Well, dang, you really do learn something new every day. That is damn cool, don't know why I never seen (or thought!) of that before.

 

[Flyer]

I have used dado blades here in Canada for at least 40 years, in school workshops too, and never experienced any problems. None of the equipment had automatic braking.
I use one on both my own table saw and radial arm saw and wouldn't be without a set.

 

[MikeW]

I have used dado blades here in Canada for at least 40 years, in school workshops too, and never experienced any problems. None of the equipment had automatic braking.
I use one on both my own table saw and radial arm saw and wouldn't be without a set.

Not to pick on you, Flyer, but your post epitomzes our North American work practices and mindset--and this thread also illustrates the divergent mindsets and work practices of both traditions. Neither is inherently wrong. Just different. Both best practices accomplish the same goals and merely go about it differently. Ours does carry with it greater risk. Something which within our tradition is acceptable. But not within the UK and most likely other civilised countries outside the UK.

This discussion is really akin to a debate on religion. Neither point of view will convince the other. It will eventually stalemate--and probably already has.

Take care, Mike
off to count how many angels fit upon the head of a pin...

 

[seaco]

I have a Delta Unisaw and one of the reasons I bought it was that I could use a dado set, I find with careful thought to safety it is a wonderful tool for it's purpose.

Earlier posts say a router is quicker and easier to use well try cutting a 11.5mm wide trench 15mm deep in oak in one pass? I would need a hundred cutters to make up all the combinations of width I can do with my dado set...I know I can do multiple passes but that in itself adds more chance for injury

We all seem to have different reasons to be for or against dado's but in the end it's your own choice you won't suddenly be working in my workshop so if I'm happy to use one so be it, there will never be agreement on this so give it a few months and we will all be here again... :wink:

Lee

 

[johnelliott]

I would need a hundred cutters to make up all the combinations of width I can do with my dado set...I know I can do multiple passes but that in itself adds more chance for injury

Can't imagine how one would use a router in such a way that there is 'more chance for injury with multiple passes'?

John

 

[seaco]

I would need a hundred cutters to make up all the combinations of width I can do with my dado set...I know I can do multiple passes but that in itself adds more chance for injury

Can't imagine how one would use a router in such a way that there is 'more chance for injury with multiple passes'?

John

Well simply because the router would be in use alot longer hence more chance of injury, it's not rocket science... I'm not saying the router is more or less dangerous than a dado but the longer a machine is switched on the more chance of something going wrong...

 

[Scrit]

Well simply because the router would be in use alot longer hence more chance of injury, it's not rocket science... I'm not saying the router is more or less dangerous than a dado but the longer a machine is switched on the more chance of something going wrong...

I don't entirely agree. Time of cut is not the safety issue, it's potential exposure to cutter which is.

Earlier posts say a router is quicker and easier to use well try cutting a 11.5mm wide trench 15mm deep in oak in one pass? I would need a hundred cutters to make up all the combinations of width I can do with my dado set...I know I can do multiple passes but that in itself adds more chance for injury

The majority of housings people work are probably to accommodate the likes of shelves and rails, etc in sheet stock (18mm, 15mm and 12mm) and you can comfortably accommodate an 18mm wide x 9mm deep housing in a single pass with a 1/2in router. To adjust the cut it is probably simpler to add a rebate to the end of shelf, thus (BTW also true for dado heads):

This is a 16 x 9mm housing worked in 19mm stock (because the only cutter available is notionally 16mm) with a rebate in the top edge of the shelf. As the piece is to have a "face-frame" attached it doesn't matter what the end of the housing/shelf looks like - and I'd say that was true for most housed work. Better quality pieces would, in any case, be worked with a stopped housing or a different joint altogether. The jig to cut the housing looks like this:

The gap between the boards is 30mm to accommodate a 30mm O/D guide bush frequently supplied with a 1/2in router (the size normally used for kitchen worktop and stair housing jigs, etc), but there's no reason why a smaller guide bush couldn't be used. As the cut is made into the cross rail, this becomes a "register mark" for cutting the housings:

Total jig cost, circa £6 (nil if scrap used) - total cutter cost, circa £25 (for 12mm and 16mm) - total time to make, circa 15 minutes. set-up time is just your marking-out time really...... And because your hands are always above the cutter holding the router probably a heck of a lot safer that the dado head. Noise? Buy a Bosch or Mafell or Festool router and they are considerably quieter than the DW625 I use, but in reality the majority of the noise is made by the cutter on the timber in either case - so wear ear defenders.

There is also another fact to consider - that housings rob strength from chipboard, MFC and MDF and thus aren't suitable for use with those materials.

My experience of using stuff like trenching heads is that they can be a royal time-consuming pain to set to the right width and are only worth considering if you have a lot of identical cuts to make.

So, if not sheet materials what exactly do you use your dado head for?

Scrit

 

[seaco]

Hi Scrit

I use one of those jigs myself and very good it is, as I've already said we won't all agree on the best way to do this so we will all be here again soon... :wink:

I think we will all have to agree to disagree...

 

[johnelliott]

I think we will all have to agree to disagree...

Especially about this, from your previous post

I'm not saying the router is more or less dangerous than a dado but the longer a machine is switched on the more chance of something going wrong......

I am saying that a router is less dangerous than a dado.

John

 

[Scrit]

I'm not saying the router is more or less dangerous than a dado but the longer a machine is switched on the more chance of something going wrong......

I am saying that a router is less dangerous than a dodo.

Considering the above (the duration bit), I'm probably dead several times over! 8) - for that matter so are you, John!

Scrit

 

[Alf]

I'm inclined to think that if the dado head doesn't kill you, this thread might... :lol:

I'm going to go and watch England stuff up against Ecuador now, for a little stress and danger of a different sort. Be kind to us poor football-watching saps when Ecuador go through, won't you? :roll:

Cheers, Alf

Putting on The Lucky Shirt [-o<

 

[seaco]

I agree I'm getting so bored with this now...

Simple if you don't want to use a dado don't buy one...

 

[seaco]

Be kind to us poor football-watching saps when Ecuador go through, won't you? :roll:

Cheers, Alf

Putting on The Lucky Shirt [-o<

You were saying Alf, come on England....