Riving Knives

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I was just reading about Powermatics new table saw, the PM2000. One of the new features highlighted was a riving knife, a feature that the predicted would become mandatory in the next ten years. To me it looks like a splitter only it is attached to the trunnion rather than the fence. Is there something more to the difference or is the name change just to differentiate the mounting location?
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A riving knife is a common feature on European saws. Its main attribute is that it rises and falls and tilts with the blade, allowing you pretty much use it for almost all cuts. Its more complicated mechanically and more expensive to manufacture. I looked into buying parts from Europe to add a riving knife to my table saw. I finally gave up. One of the barriers to making such a device standard in the USA is working through the safety and legal barriers.
Bob
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snipped-for-privacy@yahoo.com wrote:

It's actually pretty simple and inexpensive. I've got an Old (~8yrs) Ryobi BT3000 that came with one and All the Ryobi BTXX saws have them.
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The BT3000 implementation is an American bastardized implementation. Its got those dreadful anit-kickback pawls and its taller than the blade. These facets prevent using leaving the knife in place for a number of cuts, including tenon cuts. Admittedly the BT3000 is ahead of its time in the US marketplace in this particular area.
Bob
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BillyBob wrote:

An inventor and user of the BT came out with a much better version. The shark gaurd, the reason IT is taller, is due to it being the place to mount the blade gaurd to. I've thought about getting his and modifying the original as a more normal riving knife.
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On Tue, 13 Sep 2005 05:01:55 GMT, Lobby Dosser

As do shopsmiths (Models 510 and 520 since the mid 1980s, not the old no longer made model 500s).
Dave Hall Dave Hall
"The power of accurate observation is commonly called cynicism by those who have not got it." -- G.B. Shaw
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wrote:

I'm not certain how this applies, regarding the Shopsmith. The Shopsmith uses a tilting _table_, rather than an arbor, and otherwise has a blade guard just as clunky as any US-delivered Delta or Powermatic. The tilting table arrangement makes for some high pucker factor mitered cross cuts, and effectively precludes its use on anything longer than about 12".
Patriarch, embarrassed owner of a Model 520, who learned better...
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On Tue, 13 Sep 2005 11:00:22 -0500, Patriarch

While I understand that you do not like your Shopsmith there are lots of people who have made very nice furniture and other projects with them. I can assure you that they often have to make mitered crosscuts on boards longer than 12". My crosscut sled is wider than 12" and it works quite well on mitered crosscuts. In fact I would not be concerned in the least in making a 45 degree mitered crosscut on boards 4 or 5 foot long. After that the physics do limit you since the other end of the board might drag on the floor or hit the ceiling, so I use either my compound miter saw or my RAS. Contrary to popular belief, you can also make mitered rip cuts on long boards quite well on a Shopsmith. In any case, the issue was riving knives - and Shopsmiths have them. They stay the same distance from the blade no matter the depth, they are in place for all miter cuts and they are extremely easy to take off and reinstall as needed. If a tool as lowly in some people's eyes as a Shopsmith can have a functioning riving kinife, then why can't a $2,000 Powermatic? (Said with a wink since a new Shopsmith costs more than $2,000). Dave Hall
"The power of accurate observation is commonly called cynicism by those who have not got it." -- G.B. Shaw
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Or even lower, the BTXX. I'm a real sucker for gadgets and the BT sliding table reeled me in.
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Not to drift TOO far off topic, but...
Maybe it's a user error. Tilt the table to 45 degrees, down on the right. Can't go left, because the motor unit's there. At some, fairly quick length limitation, you run into the tubes and/or right table support. Move everything to the end, like one would on a bowl lathe? On that undersized table? Clamping everything to a sled, so it doesn't slide off? Get me a freakin' hand saw & a good plane!
Again, a riving knife on a tilting TABLE is a piece of cake. It's the tilting TABLE that is an obsolete, questionable design.
What really pissed me off about the Shopsmith really was that I got taken in by the hype, and bought at a home show. I paid way more than Unisaw money, and should have just walked away. The 'only works on Shopsmith' accessories were a rude surprise, too. Every needed add-on piece required another mail order, with a 10 day delay, and an expensive charge.
Yes, folks can really do nice work on a Shopsmith. I did, too, actually. But it was WAY more work than it needed to be, with a lot more scrap. The Shopsmith sits in storage, replaced by real tools. One of my sons wants it, when he gets out of his apartment space limits.
There. Sorry. That feels better. I'm going to the shop now.
Patriarch
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On Wed, 14 Sep 2005 10:22:58 -0500, Patriarch

Guess I didn't say it didn't take a moment or two to set up, a little planning and some fine grit sandpaper on the fence of your sled to keep things from sliding. BTW you can go left because you can extend the quill to get the table far enough away from the headstock to clear it. I don't know if you can get the full 45 degrees though.

No argument that if you were buying a saw that a tilting table would be a poor design. If you bought a Shopsmith, however, you were not buying a saw, you were buying a multi-purpose tool. As with any such beast some design compromises are requied for each purpose in order to allow for the other purposes. There is just no way to produce a machine that does those specific 5 functions without a tilting table. I agree that if a person has the room for all stand alone tools and the desire to dedicate that space to woodworking tools then a Shopsmith is clearly not their best choice.

I can understand that! Too many things need Shopsmith specific stuff, and they do seem quite proud of their stuff given the price. Actually that would be expected for a niche product with a small market and small volumes.

;-) Dave Hall
"The power of accurate observation is commonly called cynicism by those who have not got it." -- G.B. Shaw
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Woops. I meant blade guard, not fence.
Ken
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Does anyone know of a source for riving knives that one could adapt for the US made (or sold!) saws? I too am most interested in installing such a beast but don't have the patience (read: time) to try to figure one out at the moment. Cheers, cc
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On 13/09/2005 11:38 AM, James "Cubby" Culbertson wrote:

You might also be interested in microjig splitters:
http://www.microjig.com /
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I've got one but haven't yet installed it. I figured I'd better get an overhead guard build first but am looking forward to using it. Cheers, cc
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the
at
I'll be so bold as to say there are none. Adding one requires machining or replacement of existing parts. Its not a simple bolt-on affair. A well designed riving knife has mechanical linkages that keep its position and distance from the blade constant, as the blade is raised and lowered. This is a non-linear linkage, since the back edge of the blade-table intersection shifts forward as the blade is lowered. Jet makes commercial parts to support a Riving knife on some of their saws. I actually got the manual and parts numbers through a contact in Ireland. But actually buying and getting the parts is an impossible task. The european and american operations have no relationship with each other. I gave up.
Bob
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Take a look at the BTXX mount. Two bolts and some shims to center the knife on the blade. The distance between the knife and blade is fixed and it moves up and down and tilts With the blade. No complexity.
Here's a link to the manual: <http://www.bt3central.com/articles/layoutpage.asp?ArticleIde

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With simpleness comes compromise in function. I described a riving knife that does more. Its not so complex if its built from the factory to begin with. But retrofitting requires disassembley of many things and replacement of some major cast parts.
Bob
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BillyBob wrote:

no compromise with that mechanism. arbor travel is linear in that saw, rather than pivot. it works fine.
the problems with it are from the castings being aluminum, rather than from configuration.
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Hmmm, I lived in Ireland for 3.5 years and my wife is from there. Might have to look into this a bit. It actually might be easier for me to just make my own in the long run. I've got a Griz. cabinet saw so not sure if the Jet stuff is interchangeable. Cheers, cc
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