-------------------------------------------------- From: "Oli Glaser" Sent: Tuesday, July 13, 2010 3:23 AM To: "Jake Anderson" Subject: Re: [TECH]:: Auto stop table saw - demo with real finger > > > -------------------------------------------------- > From: "Jake Anderson" > Sent: Tuesday, July 13, 2010 2:34 AM > To: "Microcontroller discussion list - Public." > Cc: "Oli Glaser" > Subject: Re: [TECH]:: Auto stop table saw - demo with real finger > >> On 13/07/10 06:11, Oli Glaser wrote: >>> >>> -------------------------------------------------- >>> From: "Olin Lathrop" >>> Sent: Monday, July 12, 2010 8:19 PM >>> To: "Microcontroller discussion list - Public." >>> Subject: Re: [TECH]:: Auto stop table saw - demo with real finger >>> >>> >>>> If the system is cheap enough and >>>> the cost+hassle of resetting it is minimal, then it will be more widely >>>> deployed and thereby save more injury than a fancy system nobody >>>> installs. >>>> It also wouldn't give a false sense of security and invite sloppiness >>>> like >>>> SawStop may in some cases. >>>> >>>> So maybe the target should be to do what you can for a reasonable cost >>>> that >>>> can be reset in one minute or less with no consumables to replace. >>>> >>> Yes that sounds like a reasonable target, at least to start with, and if >>> it >>> achieves better results then it's a bonus. The main reason it occurred >>> to me >>> in the first place (as I'm sure it occurred to many others) was the cost >>> of >>> resetting/replacing the SawStop system seems (to me) like it's biggest >>> problem, and possibly the main reason for people avoiding it (apart from >>> the >>> fact that it cannot prevent injury completely as a guard if used >>> correctly >>> will). >>> Something that works as a good backup system to a proper guard, is >>> reasonably cheap/simple to manufacture and install, resets quickly with >>> no >>> extra cost, sounds quite attractive from a consumers point of view and >>> as >>> you say would be less likely to invite sloppiness etc. >>> I think it makes sense that such a system would always have to have >>> something else in place that's non-reliant on a circuit performing it's >>> duty >>> correctly, so backup rather than main safety feature sounds like a good >>> idea, especially for the times when people need to remove the guard for >>> some >>> reason, or do something accidental or stupid. >>> >> The field of stopping a rotating metal disk is a fairly thoroughly >> explored field, they are called car brakes. >> I'd wager with a hydraulic accumulator, shop air, and some ABS/brake >> components you could stop the blade near arbitraily fast. >> damage to the blade would be minimal, though you would want to check it >> for warping if it got used often. Yes indeed. However, we were talking of *moving* the entire metal disk itself very quickly - to remove it from the immediate area to which a finger/hand/random body part may be approaching. Actually stopping the disk *rotating* quickly may not be necessary, in contrast with the SawStop system which does exactly that. The discs in car brakes are a lot more sturdy and designed to withstand the extreme forces applied during braking. I imagine it would be a far bigger challenge to stop a disc blade quickly enough without damaging it due to the material being a lot thinner and the equivalent forces being higher - it seems logical that if it was possible easily/cheaply the SawStop system would probably do it that way to avoid the cost of replacement parts. I find it hard to believe the inventor did not try it this way first, but you never know.. Or maybe he considered it not to be certain enough that way, the chances of failure to stop in time to be unacceptable - or something along those lines. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist