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Thread: The Sawstop debate rages on

  1. #31
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    Yes, my example was a full-force slam into the saw blade. I doubt you can do much worse.

    As for the gash, it is 3cm deep, but at that depth, a 10 inch diameter blade makes a 6.5" long gash. To put it another way, if you have a zero-clearance insert and raise the blade up 3cm, you will have made a 6.5" long cut in the insert.
    Last edited by Ron Wessels; 02-05-2007 at 7:16 PM.

  2. #32
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    Ah, I get it...it is Monday after the Super Bowl after all!
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  3. #33
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    Thanks, appears under normal useage hitting the blade will just cost you a blade and brake, where jaming the fingers in would cost probably a bunch of stiches, still better than having to go look for your fingers on a sawdust covered floor...pretty impressive.

    Thanks.
    Al

  4. #34
    OK, so the blade STOPS in 3 to 5 ms, but it's also travelling DOWN and AWAY from your precious hand/fingers for most of this time too, by virtue of the huge angular momentum of the blade, according to the SS website.

    The SS DSP system detects human contact and triggers the stop mechanism within about 300ns if I recall correctly - there used to be a paper on the SS website that showed this but I can't find it now.

    Can someone who knows all about angular momentum do the calcs to tell us how fast the blade moves down and away from your finger? Then I think we can do some better estimates as to the length and depth of the cut vs. the maximum speed a hand can humanly attain.

    Also, what I'd like to see is the result of a test where the blade is raised fairly high, and the hotdog is slammed right into the TOP of the blade (kind of "flicked" onto the top of the blade real fast) rather than being run in horizontally with the wood.

    Even without this info, my old Jet TS/Incra Fence will be FS very soon now
    Dave Fifield

    XYZ Laser - 45W Epilog 36EXT, Rotary, Corel X4, Photograv

  5. #35
    Fellas,

    Never mind that the saw's safety feature works.

    Who cares if its the best made North American style saw

    on the market today.

    Money? Heck I spent that much monthly at Clancy's when I

    was drinking.

    Nope, we bought ours because its black.

    Perfectly match's our new company polo shirts.

    As they say, if ya gonna do it...

    Do it with style.


    Per
    "all men dream: but not equally. Those who dream by night....wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible."
    T.E. Lawrence

  6. #36
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    Per, they have that saw in "Early garage"?

    Al...who thinks that saw is to pretty for his garage.

  7. #37
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    My calculations assume 3ms between first touch and start of blade "removal". I also assumed instantaneous blade removal.

    There is insufficient information to calculate how fast the blade drops below the table. Amazingly enough, nowhere in the SawStop documentation does it say how fast the blade rotates. But more importantly, there is no information regarding the mass of the mechanism that must be moved to drop the blade, nor how much force is required to overcome whatever is holding the blade in place in the first place.

    While the processor may decide to fire the brake in 300ns, I would really hope that they take readings for much longer before deciding to fire. At 300ns, one glitch in the analog-to-digital readout will result in a mis-fire. Besides, they are designing around an accidental "normal" feed into the blade, not some moron slamming his hand into it.

    Although I can't find the reference, they talk about 2 blade teeth contacting before the blade is removed. Assuming 4000 RPM and a 60 tooth blade, that requires between 0.25ms (250000ns) and 0.5ms (500000ns) of contact, depending on the "width" of the teeth.

    So, taking Dave's points into consideration, and going back to my extreme example, in 0.5ms at 10m/s, your hand has travelled 5mm or 1/512 inch (about 2 thou). If the brake has fired and the retraction is in progress, arguably your hand is now assisting in pushing the blade down with significantly less damage being done.

    My gut says that the actual answer is that you will still have a significant wound requiring medical attention. You might even lose a finger or two (there's not a whole lot of cutting that needs to be done for that to happen). But what you will not get is the significant additional damage caused by you removing your hand in the less-than-perfectly-optimal direction as your reactions kick in.

    Besides, there has to be a reason why they don't demo the hot dog being flicked into the blade.

    Oh, and yes, the saw is hansome.

  8. #38
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    Ron,

    I think your extreme example is a bit way out there...knock off a magnitude and think it is a more realistic extreme.

    However, email Mr. Steve Gass...he has been quite responsive in the past and even has posted on SMC a time or two when called upon to do so. I bet he'll be happy to give you all the numbers you desire.

    Here is his profile: http://www.sawmillcreek.org/member.php?u=2829
    Last edited by Chris Padilla; 02-06-2007 at 4:36 PM.
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  9. #39
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    Slamming might be the wrong term, I'd think as fast as your hand would be going if you slipped or the saw kickbacked and somehow your hand hit the blade, not quite slamming, but probably a bit faster than the test?
    I think slamming your hand into a stopped blade would probaly leave you with the need for more than a couple band aids, I'd rather not be the one to test it, but I bet you could drive a blade a ways into your hand just by slamming the still blade?

    Al

  10. #40
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    I agree that my extreme example is extreme. But I do think that it's not too far off the maximum speed that you can impact the saw blade in the worst case.

    I assumed that people were curious as to the "maximum" amount of damage you can do to yourself with a SawStop. And in no way am I trying to downplay the SawStop. In fact, it's top of my list for an upcoming tablesaw upgrade. I just wanted to point out that you can still hurt yourself quite badly if you're being an idiot with the saw.

  11. #41
    You can not move your hand faster then that blade drops below the table.
    "all men dream: but not equally. Those who dream by night....wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes, to make it possible."
    T.E. Lawrence

  12. #42
    Math is great, but I can have trouble intrpreting the numbers into reality, it's easier for me to understand something I can see.

    I mention again the demonstration/test that the Minnesota Woodworkers Guild did last year. A 2' long summer sausage was swung into the spinning blade (vertically, about 45 degrees to the blade) like a baseball bat. (I don't know how fast that is, but I don't see how you could get yourself into the blade much faster) The blade was MOST THE WAY UP...~2.5". The resulting cut was about 3/4 of an inch long, maybe 3/8" deep. A nasty gash for sure, but on any other tablesaw that would have been 2 half sausages...or an arm and a hand.

    Also again, here is a video at WOOD magazine of a similar, but less agressive test.

    http://miniurl.org/BE6

    http://www.woodmagazine.com/wood/sto..._highspeed.xml

    BTW, I hear from SawStop that they are working on a smarter brake that will be more effective in differentiating between meat and metal.




    Last edited by Kevin Groenke; 02-06-2007 at 10:54 PM. Reason: edit URL

  13. #43
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    Thanks Kevin for injecting some reality in what has been an academic exercise up to now. I hadn't seen the Wood Magazine tests previously, nor had I seen your original report of the Minnesota test. But I think your results can be called definative.

  14. #44
    Thanks Kevin!
    Dave Fifield

    XYZ Laser - 45W Epilog 36EXT, Rotary, Corel X4, Photograv

  15. #45
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    Yep, we're done! Good reportin', Kevin!
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

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