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PostPosted: 06 Dec 2003, 16:47 
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Midnight wrote:
OK..... call me a trouble maker if you like... but I'm gonna play Devil's advocate here..
Exactly what IS the prob re a stack head dado cutter??

The biggest single objection must be that there are very few saws out there with the necessary top-supported crown guard to safely guard the cutter set from above.

The second objection is that, with modern (i.e. CE-marked) saws requiring a motor brake (either mechanical or electronic) to stop the blade in 10 seconds of hitting the stop button you have a problem with the dado head - the extra kinetic energy stored in a dado head over a conventional saw blade makes it likely that the arbor will stop, but the dado head will try to continue spinning resulting in the arbor nut unscrewing (LH thread, remember) and the potential of bits of metal coming adrift (as stated by Neil above). There are remedies to this - you can either pin the blade set (the "standard" commercial sawbench approach to this is to add two extra locating pins on either side of the arbor and drill all the blades to match) or you can fit a locknut on the end of the arbor and make sure it is REALLY tight. The former method is good, but I have yet to see a dado set with a set of pinned raker blades, the latter method is really a bit hit and miss in terms of a safety assessment to consider using it in a table saw. i.e. there is no way to guarantee that stopping the blade will not result in BOTH nuts being unscrewed - then we are back to bits of loose metal being propelled from the arbor :shock:

For good measure there is a third objection - ever wondered why Norm uses dados (rebates or housings) on plywood in the main? The answer is that when you hit a knot (as in solid wood) with a dado head the width of the cutter being greater there is a greater tendency for the work to kickback, even more so if the cutter set is blunt, combine that with no adequate top guarding and you have a potential amputation situation.

Lastly, have you ever noticed the difference between using a long cutter on a 1/4in router as opposed to using the same cutter on a 1/2in router? The larger router has more power and will therefore tend to stall or kickback a lot less. You can overcome this tendency with the smaller router by reducing the depth of cut and utilising an anti-kickback design of cutter, but that in turn leads to other compromises - especially in terms of repeatability of cut. The same is true of table saws - some small saws are hard pressed to do deep ripping and my feeling is that such saws are fundamentally unsuited for use with a dado head as their lack of power makes them more prone to stalling and in some cases kickback.

However, I am not completely against the use of the dado head. On crosscut saws or radial arms they can have their uses. In that instance the blade guard in conjunction with the table ensures safer working conditions as it is almost impossible to get ones hand near to the blade (a kickback and fall on blade scenario is not possible). The saw should be fitted with adequate guarding (i.e. a guard designed specifically designed for the task), have a guarded "home" position as well as a spring return mechanism to meet legislation - if that is done I am informed that the saw does not need to have a motor brake as releasing the handle ensures that the blade is safely withdrawn away from the operator.

I hope that you don't consider this a bawling out, I am just trying to point out the downsides of the dado head. In any case, when doing a risk assessment (now a statutory obligation for employers) you are obliged to find the lowest risk solution from your available equipment - or if there isn't one reject the job or find a safer method of work - surely home woodworkers should apply the same sort of logic to their personal well being and safety.

In terms of safety there are books on the subject, most notably F.E.Sherlock's "Machine Woodworking for Hand Woodworkers" (Stobart Davies ISBN 0 85442 041 X) and Nigel Voisey's "Wood Machining - A Complete Guide to Effective and Safe Working Practices" (Stobart Davies ISBN 0 85442 032 0) although it should be bourne in mind that both of these books are now getting quite old and in the main refer to the 1974 legislation (superceded by PUWER 98), so if you do decide to read them do so in conjunction with the factsheets available free on the HSE website mentioned above. That advice is excellent, current and best of all free!

Have a good weekend

Scrit

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PostPosted: 06 Dec 2003, 18:48 
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Hi Scrit

Thank you for taking the time to post your reply to Midnight. The background you have given is excellent.

I came to woodworking just over a year ago, via Norm, and I was amazed that I couldn't buy a saw that would take a dado head. (Apart from NMA who offered to sell me their Scheppach ts315 and assured me I could fit a dado head).

I learnt from this group and also from ukww that the safest way to cut dadoes is to use a router with a simple jig. It was Jester who pointed me in the right direction and I will be forever grateful.

If I was to carry out a risk assessment on cutting dadoes in my workshop the safest option would have to be with a router.

As you rightly point out you can still legally fit a dado head to a RAS, albeit with some slight modifications (Freud dado to a DW720). I decided that I didn't even want to go down that path and I bought a cheap dedicated router and some Wealden 8mm cutters (thanks Scrit) and spent a little time and money making a jig. This set up has the advantage of being simple, very quick and far cheaper than a dado head set.

Sorry Norm. :wink: :wink: :wink:

Cheers

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PostPosted: 06 Dec 2003, 19:26 
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Probably staying out of this would be most sensible :wink: , but two aspects of using a dado head (not safety related in any way) have bothered me for some time. Perhaps someone who's used/using one could tell me?

Firstly, exactly how long is the set up time for a dado head?
My limited exposure to Norm hasn't shown me if he ever shows that bit, but I'm guessing not. :lol: But I can't believe it's not for nothing that I've seen pictures of Unisaws with a second bench top saw built into the extension table with a dado head permanently fitted.

Secondly, what's the finished dado like? Is it clean and square etc etc or what?
As I've never seen one, I'm curious, and no one ever seems to mention it. How does it compare to a router cut one?

Enquiringly, Alf

P.S. Neil, should have got you onto dado or combination planes instead. D'oh! :oops: :lol:


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PostPosted: 06 Dec 2003, 19:59 
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alf whould those planes have motors :D

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PostPosted: 06 Dec 2003, 21:03 
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Hi Alf

Oh well, here goes, time for complete honesty. :? :?

I do own a plane, but it is made by Makita. :oops: :oops:

There, I've done it. :roll: :roll:

Oh no, now I find I have another one. No, it's ok it's a Record. Very old!!!

I also spy a L-N or is it a low angle? (very small one bought when the pound had a really good exchange rate, just so that I could see what all of the fuss was about).


I hereby tender my resignation from this most venerable of groups for being found in possession of a power plane.

A very sad Neil

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PostPosted: 06 Dec 2003, 21:45 
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Hey Alf,

BIL uses one on his Tyzac regulary.

Like most things when you first get them setup is slow.
however once its been used a few times and you have
built up a chart of what chipper, spacer combos to use
its really quite quick, quicker than I can set up the router
for the same task.

Cuts are clean and crisp .

However he is very aware of the dangers and has made a
kind of sled which the workpiece is clamped to and has a
guard area over the blade and to the non fence side of the
blade.

In essence, for batch work it seems great, once set up speed
and repeatability are excellent. For the one off stuff that I and
I dare say a good deal of us in the group its just not worth the
hassles or the risks IMHO.

Cheers

Signal


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PostPosted: 06 Dec 2003, 21:50 
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<Firstly, exactly how long is the set up time for a dado head?
Enquiringly, Alf>

Hi Alf - I have a Dewalt 720 RAS that I occasionally use with a Freud Dado set. It takes about 5 to 8 minutes to remove the guard and normal blade, fit the dado set (using a keyed adapter ring), refit the guard and set the depth etc. Refitting the normal blade is also about 5 to 8 minutes.

Only makes sense if there are a number of rebates to cut.

Cheers,

John


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PostPosted: 06 Dec 2003, 23:55 
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Firstly… Scrit.. thanks for taking the time to answer my question, I appreciate it. Please, DON’T take the following as a personal attack, that is NOT my intension; like I said in my last post, I’m simply playing Devil’s advocate here. I don’t have the shop space nor the budget for the machines capable of handling a dado cutter.

Your first point, the crown guard. Surely the best remedy to this would be something as simple as fitting one..? In my own set up, that’s nothing more technical than drilling and tapping something like 4 off M6 or M8 threads into the fence and adding a plate extending over the cutter; initial thoughts for suitable material would be a 6x12x0.25” aluminium plate. Hardly rocket science.

Your second point, runaway cutters. My initial reaction here was…. “but what about the guys who built their own saw to put their safety brake into production??” Forgive me, I canna remember their name, but you’ll know who I mean; when a finger contacts the blade, the brake kicks in, killing rotation in a fraction of a second. The saw they built is aimed at the US market i.e. a market where use of a dado cutter is considered normal if not routine. Surely if the cutter can stay on the arbour with no adverse reaction to blade retention under vastly higher decelerative forces than our 10 second braking time, there has to be a workable solution. You mentioned the chances of even a double nut set up working loose, why not use an aircraft nut, or failing that, cross drill the arbour to suit a retaining pin of some sort. Hardly rocket science. In my minds eye I tried to picture exactly what would happen with a run away cutter. First thought here was what happens when the cutter hits the throat plate?? Surely the abrasion of the throat plate material would be sufficient to bring the blade to a rather sudden stop, all the more so if it’s loose enough to be independent of the decelerative force of the speed brake. Before it sees the end of the arbour, it has to eat it’s way through practically the entire width of the throat plate, and all without any power from the motor; some task for a 215mm blade.

Your third point, kickback. Surely better stock selection is the answer here…??

Personally, I don’t buy the “routers are safer” argument. I mean think about it. For rebate cutting, you’re working with a highly unstable machine on the edge of the board. Less than half of the machine is supported by the board. The chances of a slip sending the bit into a sudden deep lateral movement are pretty high. The chances of that sudden movement causing a fracture in the cutter are similarly high, more so if the cutter is on a ¼” or 6mm shaft; even more if the cutter is made of lesser quality steel. Pause to consider the popularity of ¼” machines and budget sets of cutters to appreciate the chances of that happening. Need I go into the likely effect of a fractured router bit going ballistic with up to 27,000RPM’s worth of momentum behind it…???

Like I said at the start…. This is NOT a personal attack against Scrit. I’m simply trying to illustrate the half ass’d nature of this kind of legislation. Speed brakes I’m all in favour of, likewise with EFFECTIVE blade guards and riving knives. Stupidity however is something that I have a low tolerance for, and I’m afraid that this type of legislation IS, quite frankly, stupid.
Surely the safest way to plough rabbets and dado’s is with a shoulder plane…????


Ohhhhh..... and ummmm.... Neil.....

wash your mouth with soap.....
Makita.... sheesh.........

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PostPosted: 07 Dec 2003, 08:59 
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Midnight wrote:
Personally, I don’t buy the “routers are safer” argument.


Have a look at this to get an idea of the sort of router dado jig that can be made http://benchnotes.com/Router%20Dado%20Guide/router_dado_guide.htm

This is not exactly the jig that I have, but it gives you a good idea. In use, the router is fully supported at all times. Set up time is less than a minute as I have a cheap dedicated router with a Freud cutter. As I am never cutting huge quantities there is no contest in terms of speed.

Midnight wrote:
Surely the safest way to plough rabbets and dado’s is with a shoulder plane…????


Mike, I couldn't agree more. The limiting factor, sadly, is my distinct lack of hand skills. :cry: :cry:

Cheers

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Sig, John,

Thanks for that. I only wondered about the finish, as I notice one of Lee Valley's selling points for their shoulder plane is that it'll clean up the bottom of 3/4" dados. Waste of a good plane to my mind, but still... :lol:

Neil, Neil, Neil... What can I say? We'll pretend you never said that for your own sake... :wink:

Midnight wrote:
Forgive me, I canna remember their name, but you’ll know who I mean; when a finger contacts the blade, the brake kicks in, killing rotation in a fraction of a second.

Saw Stop?

Midnight wrote:
Surely the safest way to plough rabbets and dado’s is with a shoulder plane…????

Umm, just for the sake of accuracy, you'd be better off using a rebate plane for rebates, and a dado plane for dados. Or a combination plane that does both. Shoulder planes are really more for fine cuts to clean up or trim. Not that you can't use them for that, but it's a bit like using a mitre plane for shooting boards... Ah, erm... :oops: :wink:

Cheers, Alf


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PostPosted: 07 Dec 2003, 17:43 
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Midnight wrote:
DON’T take the following as a personal attack, that is NOT my intension;

Wouldn't dream of it. :lol: This whole thing is making me think about the subject afresh :idea:
Quote:
..... the crown guard. Surely the best remedy to this would be something as simple as fitting one..?

I think I intimated the same, with an overhead crown guard you are generally pretty safe, although the absence of a riving knife and the manner in which a dado head makes its cut means that even with a reduced depth of cut per pass a dado head is always going to be more inclined to kick-back than a conventional saw blade used with a riving knife. I have web references to DIY crown guards in the past, but your method would seem to involve moving the guard each time you made a different cut - and how do you handle a long job, say the housings in the side of a bookcase? If a guard is awkward to adjust or use it is normally the first thing to be jetisoned :oops:
Quote:
... runaway cutters...... “but what about the guys who built their own saw to put their safety brake into production??”

This is called the SawStop http://www.sawstop.com/home.htm and is actually quite a neat idea. It apparently works by passing an electrical current through the blade. If anything contacts the blade which can form an earth (e.g. a finger) it is detected (shorts to earth) and the unit kills the power and brakes the blade to a stop. Kickback is frequently caused by the workpiece pinching on the rear upcutting teeth as they emerge from the table. There are no fingers near the blade but there is nonetheless danger. As far as I can see SawStop cannot address this problem. Personally, I wouldn't fancy using a saw where I had to take my rubber-soled boots off every time I used it :lol:
Quote:
.... why not use an aircraft nut, or failing that, cross drill the arbour to suit a retaining pin of some sort

Cross pin a variable width dado set? Hmmm... But aren't we now getting into curing the symptoms, rather than the cause? I don't know about you but the chances of getting everyone in industry to agree a standard for doing this sort of thing for the benefit of a relatively small market isn't so great.
Quote:
...before it sees the end of the arbor, it has to eat it’s way through practically the entire width of the throat plate, and all without any power from the motor; some task for a 215mm blade.

A dado set weighs a LOT more than and therefore has a lot more kinetic energy stored in it than a similarly sized sawblade. I was once "fortunate" enough in the days of square cutter blocks (on spindle moulders) to witness first hand the result of a 3 or 4 oz brazed tip breaking off a forged steel cutter after one nut had loosened and the cutter had slid out and struck a cast-iron fence wing. The trajectory was random, but the tip buried itself more than an inch into a large softwood roof beam (we are talking 16 x 9in or so and more than 100 years old, therefore HARD) and the body went out through the open window. I've also seen a 300mm blade come adrift on a panel saw under braking (not mine, I hasten to add), bend and chew a 4in long gash through a 6mm thick aluminium sliding carraige, fortunately without hitting any steel which might have shed teeth. When blades start to come off arbors at speed there is a major risk of the blade simply breaking up as soon as it contacts something hard, and that is the real danger - it's why I always double check tightness of nuts, etc.
Quote:
... routers.... I mean think about it. For rebate cutting, you’re working with a highly unstable machine on the edge of the board. Less than half of the machine is supported by the board. The chances of a slip sending the bit into a sudden deep lateral movement are pretty high.

I take it from that that you would not consider adding a sub-base to support the router and make it more stable? There are good examples all over the place - see Bill Hylton's "Router Magic" for example, or here is a commercial example http://megproducts.com/edgetrimrouterbase.html. If the tool is unstable doesn't one stop and ask oneself "why?" or "how can I work safer?". Just because it is a router doesn't mean that there are no safety issues - only that they are different.
Quote:
Need I go into the likely effect of a fractured router bit going ballistic with up to 27,000RPM’s worth of momentum behind it…???

Router cutters are generally of small diameter and when used vertically the axis of rotation generally dictates that the cutter will be expelled in a downwards direction. Additionally the smaller diameter (say 12 to 20 mm as opposed to 215mm) together with the much lower mass of the cutter would tend to indicate that the router cutter had much lower stored kinetic energy - if there any physicists out there...... From experience, if you are using a dust extraction hood on your router this should be enough to absorb the impact
Quote:
I’m simply trying to illustrate the half ass’d nature of this kind of legislation. Speed brakes I’m all in favour of, likewise with EFFECTIVE blade guards and riving knives. Stupidity however is something that I have a low tolerance for, and I’m afraid that this type of legislation IS, quite frankly, stupid.

As I have stated the legislation doesn't ban dado heads or many other questionable practices per se. It does try to protect individuals from inflicting potentially dangerous situations on themselves, their employees or their customers. Without adequate education (even self-education) who is to say what are safe practices - what is stupid or not. As a sometime employer I DO NOT think the legislation is half-assed at all although at times some of it exasperates me). It does, however, form a useful BASELINE for me in determining safe working practices, and if the HSE wants to give me free safety ADVICE, who am I to complain.
Quote:
Surely the safest way to plough rabbets and dado’s is with a shoulder plane…????

Yes, however in a commercial world.... :cry:

Scrit

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Last edited by Scrit on 07 Dec 2003, 18:43, edited 2 times in total.

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PostPosted: 07 Dec 2003, 17:48 
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Alf

Not all dado sets are made equal. Some do, indeed leave a nice relatively smooth bottom to a housing, some less so, but they all seem to have spurs on the outer teeth which means that the bottom corners will tend to exhibit a slight vee cut below the level of the main housing. This may not be acceptable in certain situations.

Scrit

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PostPosted: 07 Dec 2003, 21:32 
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Just to keep things interesting on the subject of spinning blades, brakes and the 'sawstop' in particular perhaps you would like to know that it does not rely on earthing at all. It measures the resistance of the object being cut. It will cut the power, but the clever bit is that as it brakes the blade it drops it below the table - that is why it is so fast! It removes that spinning blade from harms so quickly 'simply' by recognising a foreign object at the front of the blade, i.e. not a bit of wood or plastic.
Cheers.
S

By the way, I got all this from the sales videos! I wouldn't want to trust it all that much. How do you know it's going to work next time? The time your finger is in the way! Bit like trusting an air bag, perhaps.


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Scrit.. yet again, thanks for taking the time to reply. As before, this is NOT intended as a personal attack, I assure you. I’m simply trying to illustrate that valid safety concerns needn’t involve legislation that makes outlaws of otherwise honest craftsmen, and that given some long overdue thinking time, proper sensible measures can be taken to make a potentially lethal machine far safer without too much additional cost.


but your method would seem to involve moving the guard each time you made a different cut - and how do you handle a long job, say the housings in the side of a bookcase? If a guard is awkward to adjust or use it is normally the first thing to be jettisoned

Sorry.. I should have put this better last night. That plate bolted to the fence was what sprang to mind to remedy the overhead crown guard problem when milling rebates close to the fence. For conventional dado’s, the overhead crown guard comes into it’s own.

and how do you handle a long job, say the housings in the side of a bookcase?

Simply put, one of 3 ways. Firstly, exactly the same way as I do now; hand held router and jig/guide collar. Secondly, provided the work piece in question wasn’t excessively long, on the table saw using a dedicated crosscut sled. Lastly, as you pointed out in your last post, using a RAS.


This is called the SawStop

Yea.. that’s the pipper.. memory like a sieve. Impressive sounding piece of kit, more so with the retracting blade too. However, I didn’t mention them as a remedy to kickback. The point I was making was that as their brake is FAR faster reacting than the 10 secs that the new regs impose, they MUST have had to find an effective blade retention solution. Near as I can figure, a doubled lock nut, the second being a nyloc is as close to bomb proof as it gets. The cross drilled and lock pinned arbour is a last gasp measure to ensure that NOTHING gets past that pin without it’s prior removal. As for kickback… I thought about that off and on all afternoon (waiting for glue to dry). Would the solution not lie in the problem…? If a stack head cutter makes the kickback potential worse, why not remedy it by stacking splitters too….?? Obviously they’d need to be no higher than the top of the blade. OK, it’s hardly conventional, but then, neither is a stack of cutters, so why not…???? Couple that to a cutter set that utilises an anti-kickback design (Freud’s chip limiting pattern for instance). As I understand it, the design physically limits your feed rate to that with the blade can handle safely by pushing the stock back before the cutter advances into the cut. They work too; I’ve used one for over a year without so much as a hint at kickback. The same can’t be said for the blade supplied with my saw.
A later thinking session (more glue drying time) had me thinking about power feeders. If the rollers were slightly skewed to pull work into the fence as well as along, surely that in itself negates kickback? I’m guessing here, I’ve never seen one much less used one.
3 of the above 4 measures could be used full time with a conventional blade, further reducing the risk under ordinary conditions.
As for taking off your rubber…. I ummmmmmm…. Think fetishes are best left for another forum… Ahem…

I hear what you’re saying about getting manufacturers to agree on a set of specs. If they’re anything like politicians, it’d take them a year to agree the table shape that they sit at, much less who’s sat next to who… but THERE’S where legislation should be used. “Your machinery WILL conform to these specifications or it will NOT receive an approval certificate.” Last I heard the European market was a sizeable one, not something to sneeze at at any rate.

I take your point on board re the dangers of a run-away blade impacting on surroundings hard enough to cause either partial of full failure of the blade. All the more reason to tighten up specifications for throat plates. Thoughts here were along the lines of a material tough enough to withstand the rigours of day to day use, soft enough to be sacrificial in the event of the blade striking it while being substantial enough to be able to absorb all the kinetic energy in the blade. Something like Oak would be ideal. Tough as old boots yet cheap enough to be seen as a consumable as the need arises. Add a stipulation that it MUST be a flush fit with the surrounding table and that alone would force the likes of Ferm to pull their socks up.


I take it from that that you would not consider adding a sub-base to support the router and make it more stable? There are good examples all over the place –

I came across these at Pat Warner’s site… initial reaction was why in god’s name aren’t they supplied as STANDARD? The down side to them as I see them, again with no hands on experience, is that although the increase the footprint of the machine, they do nothing to improve the weight distribution, and it’s that distribution that causes the instability. Personally I prefer to take the time to set up the router table to do as much as I can. These days virtually all of my edge routing is on the table.

Router cutters are generally of small diameter and when used vertically the axis of rotation generally dictates that the cutter will be expelled in a downwards direction.

Have to differ with you here. Centrifugal force causes an object to be expelled in an outward direction, in this instance at a random ballistic trajectory. The vastly higher RPM’s more than compensate for the lack of mass. Basic slingshot theory, yea..?? The only way I can visualise an instant downward vector is if the bit in question was spiral ground although I can never work out if they’re up or down sheer. Either way they’re unsuitable for hand held cutting (see the Freud catalogue).

Now my conscience is bothering me. These last 2 posts paint me as a thoroughly argumentative pipper at best. Well maybe so, but not just for the sake of it. Like I said at the top of my last post, I don’t have nor do I see me having the capability to use a stack head cutter. That doesn’t detract from my resentment of legislation putting me at a potential commercial disadvantage with a manufacturer who CAN use a tool that, when PROPERLY set up, can make short work of cuts such as this. I resent the fact that even if I took the time to retro-fit a machine with every bell and whistle designed to eradicate kickback, I STILL can’t legally use the cutter in a commercial application. THAT’S why I say the regs are half baked. Personally I’d love to see the responsibility for fitting the bells and whistles dumped fairly and squarely on the machine manufacturers. Doing so should guarantee the compatibility of the various measures through thorough testing. Additionally, I’d love to see the return of safety certification that actually MEANS something. When a piece of junk such as the saw I’ve ended up with qualifies for CE certification, it nullifies the credibility of quality manufacturers, if there are any left that is. Whatever happened to the days when the British Standards kite mark MEANT quality…?? If the cost of carrying proper safety gear drove the cheaper tools off the market would that REALLY be such a bad thing??
Last part of the rant, promise. Manuals…. Surely if they’re worth printing at all, they should at LEAST carry a meaningful guide for their safe and proper use. By that, I do NOT mean the current accepted practice of three sentences in pigeon English, translated into 312 languages.

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Mike

Stay safe... Have fun


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PostPosted: 08 Dec 2003, 09:50 
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Hi again

I think the guarding thing still boils down to a proper suspended crown guard - a device useable for almost all cuts. They exist now, are available in the aftermarket, and I can testify personally (as can many other woodworkers) that they are effective. They are also offered either as standard or as an option on every panel and most rip saws I know of.
Midnight wrote:
...The point I was making was that as their brake is FAR faster reacting than the 10 secs that the new regs impose, they MUST have had to find an effective blade retention solution.

Maybe they have, but their saws are no bigger than 10in whereas I (and many other people) use a saw with a 12in (or larger blade). The bigger the blade, the bigger the problem, and there a lot of amateurs out there using machines such as the Felder, etc. which come as standard with a 12in blade. As to using Nylocs, these are really designed for one-time use. In an average day I can easily have to change blades 8 or 9 times depending on work mix (of for a rip saw...) - that would mean 8 or 9 new Nylocs a day! (not cheap) As industrial machines now come with two extra pins on the arbor (and indeed have done so for about 8 to 10 years - German CE marking from 1994) why not extend that to all saws benches?
The SawStop has attracted some serious criticism in the USA for a couple of reasons, first it depends on the charge in the blade being discharged to earth which may or may not work if you are wearing gloves or rubber-soled shoes (and in any case how will that work 10 years down the line?) and secondly, surely you are depending on the machine to safeguard your safety when you should be depending upon your own safety assessment and training, first and foremost, and taking the appropriate primary safety precautions. It's probably analageous to the air bags vs. better driver training question in cars.
Quote:
If a stack head cutter makes the kickback potential worse, why not remedy it by stacking splitters too….??

Or why not just choose a method which doesn't require the reinvention of the wheel? I think you may be trying to solve a problem which is much more easily resolved by simply choosing an alternative approach. A pro shop doing trenching would probably tend to look at using a crosscut saw (RAS) with a trenching (dado) head or a hand router/jig combination.
Quote:
(chip limiter blades) As I understand it, the design physically limits your feed rate to that with the blade can handle safely by pushing the stock back before the cutter advances into the cut.

There is a major difference between chip limitation on a 60 tooth combination blade and a 2- (or at best 4-) tooth raker blade in the middle of a dado set. With only 2 or 4 teeth to clear the waste you either have to take a very shallow cut (say 5 or 6mm) or pass the work over the cutter very slowly (a more dangerous approach as kick-back is more likely to be encountered). Remember that here we are talking in the main about 1 or 1-1/2HP home shop machines - unlike the large industrial saws of 5 or even 10HP the small saws do not have the margin of power to overcome resistance in the cut and are more likely to stall or kickback during heavy cuts. As you correctly surmise power feeders are another solution used in industry - partly for reasons of safety, partly for reasons of improved throughput - but you can still experience kick-back with them if you are running an underpowered saw, it's just that the effect is less noticeable. However they won't be much help if you are trying to trench across the middle of a 12in wide board as you'd really struggle to hold the work at 90 degrees to the fence. Somehow I can't see many people here flashing out the £400 or so a full-size feeder and stand costs. Oh, and I do use feeders in the shop - on the spindle moulder and the edge sander (ripping tends to be done on the bandsaw) - they need to be set up with a few degrees toe-in against the fence to ensure straight feeding which makes them suited to ripping-type longitudinal cuts but not for feeding across the narrowest part of a board. They are, also, unfortunately too heavy to lug around between machines, especially at chest height, so they stay attached to the same machine all the time.
Quote:
... All the more reason to tighten up specifications for throat plates....

But how do you deal with panel or dimension saws which have and can have NO throat plate? (I'd love to see how Felder have managed this on the K900 series for the USA) Sorry, Mike, still think you're trying to reinvent the wheel here :wink: Yes, you can make dado heads on a table saw safe - but at what cost? (and is it really worth it when there are other solutions already available)

Your comments about sub-bases are interesting. Elu used to make two routers for edging work which were specifically made with offset baseplates to address this problem - the MKF67 and the MOF 69. Balance doesn't seem to be too much of a problem with them, but then they are only 1HP routers. The MKF67 has been re-introduced as the DW609 and once more I can testify to the fact that these routers work and work well. So, why not try an offset baseplate for yourself?

As to router bit breakages - have you experienced any yourself? I have, quite a few over the last 25 years or so of router ownership, but I was only speaking from personal experience - with a dust extraction boot in place the broken cutter seems rarely to be ejected. Same goes for our pin router in the shop. Maybe I have been lucky.

Quote:
These last 2 posts paint me as a thoroughly argumentative pipper at best.

Ermmm.... well, yes :lol: But then that makes two of us..... :wink:
Quote:
I resent the fact that even if I took the time to retro-fit a machine with every bell and whistle designed to eradicate kickback, I STILL can’t legally use the cutter in a commercial application.

Not true. As I stated there is a Duty of Care placed on employers (and in many cases on the self-employeed by their insurers) which requires us to take steps to ensure best working practice. I feel that the same approach should be considered by amateurs - after all none of us can regrow fingers after amputation...

One thing we can agree on, however, is the quality of most manuals.... Generally quite dreadful (including the Italian ones)

Have fun, stay safe

Scrit

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