It's worth mentioning that the shape of the exponential (Bernoulli) spiral has a particular property useful for this application. To wit, there is a constant amount of squeeze applied for a given (small) motion of the clamped board, regardless of what the opening is. The spiral is given as r = r_0 * exp(k*theta), with theta given in radians and r_0 being the starting radius. Small k gives a slowly growing spiral, and large k gives a fast growing spiral.
To calculate your own spiral, here's an expression to run in Excel. Adjust r_0 and k to suit your own table's separation of holes and how hard you want to squeeze (smaller k is harder squeeze but less clamp range).
where k is stored in B1, r_0 in B2, and column A has the angles in degrees. Here's an example:
k = 0.6
r_0 = 1
Implements r = r_0 exp(k*theta*pi/180)
angle (deg) radius
Wow. What a lot of entries! This will be lost in the crowd, but I too feel impelled to offer my thoughts, since I had an almost visceral experience watching the video.
After reading my eyes sore, I finally found what Wade01 wrote, that is very much to the point: that unless the teeth of the blade are designed and sharpened for side-cutting (e.g. the Freud Fusion), you are in trouble. And even at that, with too great a bite you are feeding wood into the blade body rather than into the teeth. Neither of these conditions pertain to the tenon jig or the router table, where this job can be done not only more safely but with smoother results. If I were fitting barn timbers maybe this is a valid technique, but in doing *fine woodworking* I want a flat, not scalloped, finish on my tenons.
I share with Hal_in_Houston the experience of being a NASA engineer (also with JSC, but retired, in my case), and I strongly second his suggestion of a safety article (maybe even a regular column?). Journals in other disciplines I am familiar with (scuba, climbing) regularly publish articles along the line of "what went wrong here, and what should have happened instead?" In woodworking, simple things can go badly, and rapidly, but mostly avoidably, wrong. Anybody here with no scars at all?
Foresight really trumps retrospect; I kinda wish I'd seen a column about the inadvisability of cutting a triangular wedge out of a board inverted on the tablesaw, for example. Fortunately, I have often enough read of the inadvisability of standing in line with the blade. Consequently he nasty bruise occurred to my shop wall, not to my waist line. So, how about a video series on safety, similar to one I saw in which the dynamics of pinched tablesaw cuts and kickback were demonstrated using polystyrene foam?
-- Richard Juday, Longmont CO
Hey, I've got next year's April tech improvement here... All the problems with kickback would be ameliorated were the PUSH stick to be replaced with a PULL stick. Can't say I really like the pink color, but add a little weight to keep the end of the stick down, reconfigure the push notch into a pull notch, and you get to stand on the safe side of the blade.
For the random physicist who might be reading this note, it is occasioned by my memory of a lecture from years back. Speaker drew the classical picture of the positively-charged alpha particle having its path curved to the right, the negatively-charged beta particle being directed to the left, and the neutral gamma shooting straight up. "The only safe place is right beneath the atom," the speaker informed his rapt audience.
Thanks for the informative and entertaining note, FWW! And raspberries to those commentors who have lost their ability to smile.
-- Richard Juday
Hopefully new comments in a passionate stream:
1. Gass would do well to emulate Bose and their sound system noise reduction technology. Bose continues its research and writing new patents. But significantly, Bose licenses their technology cheaply enough that others are not tempted to "design around" the Bose patents. Bose does not price itself out of the market or spend a lot defending patents against infringement, licensees spend less. Everyone comes out ahead.
2. I have no problem with Gass's providing draft language to the feds regarding specifications for a safer saw. Although the language indeed appears tailored to his system, I think his system was actually designed around the application's technical requirements rather than the draft's merely being blindly adherent to his product. The specs look fine to me.
3. To get into the market Gass intelligently began with a well-built high-end cabinet saw so that the incremental percentage cost of the flesh-sensing was reduced. Only recently is he moving into lower-end saws. I surmise that his amortized cost per cartridge is now reduced enough to make it accessible to a wider market. Smart!
4. SawStop technologists have a good product, know it well, and provide good customer service. I sent my fired cartridge back to them, puzzled as to why it activated. "Look at your miter gauge," they said, "the data show the blade hit metal." Sure enough, there was a very tiny nick in it -- applied to skin, it would hardly have bled. I'm sold.
5. Being dumb can prevail, of course. I cut a V-shaped slot in a 2x4 that dropped the cutoff into the blade, shot it across the shop, and shattered the cutoff. Habitually I stand outside the blade's line of fire, and since I like my bellybutton I'll continue that habit! The point is that all the electronic technology and riving knives in the world do not substitute for inherently safe practices.
Richard Juday, Longmont CO
OK, so I read through the comments and what I find missing is any mention of the SawStop. Lots of encomiums for the favored Unisaw with a Biesmeier fence, much moaning about cost of Felder, Festool, etc. But let me tell you, I am exceedingly pleased with the AMERICAN MADE and US Patented SawStop! I sold my (pre-2010) Unisaw, bought the SawStop, and haven't looked back. It's a great saw, well justifying the somewhat expensive Incra fence I added with its 0.001" precision. The saw is solid, easily adjusted and maintained, plenty of power, on-board kickback prevention, etc. With respect to other manufacturers, there was some complaint about various customer service experiences; I have had one experience with SawStop, and it was most competent. My cartridge fired for no reason I could divine, so I sent the spent cartridge and the chunk of wood to Oregon. Here's their response: "Um, we looked at the wood and noticed that the cartridge fired just as the blade was leaving the wood, and the data saved in the electronics indicated it hit metal. Check your miter gauge." Sure enough, there was a teeny nick in it; nothing to blame here except operator error -- I had not left sufficient clearance between gauge and blade. I feel all the more safe for having had the $75 experience of having had it activate. (Maybe that's $175, actually; I replaced the SawStop blade with a Freud Fusion, but it's a really fine blade -- even better than the SawStop factory blade.) I think the tablesaw is the most potentially dangerous tool in the shop, especially given its frequency of use, and I am very glad to have that danger minimized, especially embodied in a fine AMERICAN woodworking tool.
Oops, I meant to sign my previous comment.
The Carvewright (q.v. at carvewright.com) is notably missing from the list. Starting at $1600, it is priced well below the prices quoted for the other four. For several years I worked in the same group at NASA Johnson Space Center with the Carvewright's developer, Chris Lovchick, before he left to form this company. (I have no connection with the company, by the way.) When you see on their website that the system was developed by NASA engineers, it is absolutely true. Chris is the best mechanical engineer I have seen at work, and that's saying a mouthful. He designed and built superb robotic hands at NASA, and interestingly his prototypes were always of a LEFT robotic hand since Chris is himself left-handed. As a friend and former colleague I watched as he developed intricate elements of the Carvewright, such as a zero-play low-force collet to enable automated change of router bits. I have seen the Carvewright operate at woodworking shows in Denver, which I live near now, and though I do not have personal hands-on experience myself, I am impressed that it is easy to operate and has plenty of accuracy built in. Carvewright has a crew of folks working on advances in software, including enlarging the catalog of objects that the machine can spit out. And they have been around long enough to convince me that (A) they are stable in the business, and (B) I should have invested! I am not likely to buy a CNC machine for my workshop, but the Carvewright is the first one I would look at. Fine Woodworking should definitely include it in their list of CNC tools.
Regarding jewelry... I certainly noticed the ring, but for reasons other than ordinarily found in a wood shop. In college I spent a delightful summer working in a full machine shop, and I heard more scary stories than woodworkers tell. Hand smashed in a die press on a guy's first day at work, not using the wrist straps. Being casual with a circular saw with a carbide blade cutting aluminum plate, having it jump, and opening the miscreant's abdomen; "I've killed myself!" he said, and he was right. But the welders told of a guy whose jealous wife insisted he wear his wedding ring. One day he caught it between electrode and ground, and it flashed to white hot in an instant. As he shook his hand the ring slid down the finger, stripping all the skin off the finger along the way. We woodworkers must be careful -- I've jammed a thumb owing to a poor molding-head cutter setup, and I've been stitched up once from a kickback -- but we do have a somewhat limited set of ways to damage ourselves.
Two things left strong impressions with me. First is that these guys still have all their digits and aren't wearing bandages. And second, with the tools they had, they were in no danger of inhaling too much fine sawdust. Who needs a Tucker vise when you have a leather apron? And without random orbital sanders or high-speed circular saws, who needs dust collection?
This suit is precisely an example of why the manufacturers refused to license the technology now seen in SawStop. To have licensed and used the technology as a manufacturer would be taken by lawyers as an admission that he had previously been building an unsafe product -- essentially a prima facie admission of liability. Sure, as woodworkers we all know the dangers inherent to our beloved practice. That's different than the attitude that a persuasive lawyer can create in a pliable jury. I'd wager that there was not an experienced woodworker on the jury, because otherwise the verdict would have been different.
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