Replies

1. 
   zolton | Apr 18, 2009 05:57am | #1

   Country,

   I put the aftermarket Bolt on Riving Knife (BORK) on my Grizzly saw and it works just fine. It's not a true riving knife, as it doesn't go up and down in exact concert with the blade when the blade is raised or lowered. But it's pretty close, and quick and easy to adjust to get the right exposure if needed.

   When I say the knife doesn't go up and down in exact concert with the blade when the blade is raised and lowered, I mean that the blade on my saw travels in an arc when it's raised or lowered. Because the riving knife mounts further out from the pivot point on the end of the arbor arm, as the blade is raised the knife rises faster and further than the blade. When the blade is lowered, the knife falls faster and further than the blade. Hard to explain, but once you see it will become immediately clear.

   To get a better picture, place a circular sawblade lying flat on a 1x2 on your bench. Hold the stick to the bench in one spot about ten inches from the blade and then rotate the stick from that point. The blade rises and falls - and the other end of the stick rises faster and further than the blade... 

   I've had the BORK on my saw since last fall and so far I've had no trouble with it. It's impossible to tell if it's saved me from any kickback situations, but I like having it on there just in case.

   It takes a little while to get it dialed in correctly so it's aligned perfectly behind the blade, but that's a one-time job. The attachment bolt on the version that fits my saw rests just a sixteenth of an inch or so away from the side of the sawblade. This made me uneasy at first, but it has stayed there and has proven to be no problem.

   I shaved some aluminum from the bottom part of the riving knife one day when I changed from a regular kerf blade to a narrow kerf one and forgot to remove the riving knife. The stock I was cutting hit the riving knife with its narrow kert and caused the knife to rotate back a little bit - and the bottom of it contacted the sawblade. Not a big deal - just some aluminum shavings and a weird odor emanating from under the saw. I guess that's why he makes the knife blades out of aluminum; a good design feature for those, like me, who could be expected to make a mistake like this..

   Here's a link to the BORK maker's website. Looks like he's got one that fits your Shop Fox saw..

   http://shop.walnutacrewoodworking.com/product.sc?productId=6&categoryId=2

   Zolton

   If you see a possum running around in here, kill it. It's not a pet. - Jackie Moon

1. 
   Tinkerer3 | Apr 21, 2009 12:52am | #5

   Very good explanation.  I have a question though.  Not having really examined the riving knife closely, Does the blade and riving knife go straight up and down similarly to the table on a thickness planer where all four corners of the table go straight up and down equally to keep the table flat.  That is what I've always imagined.

1. 
   zolton | Apr 21, 2009 02:57pm | #7

   Tink,

   I hope I'm understanding your question correctly.

   No, the blade in a tablesaw (well, those of the most common variety anyway) does not go up and down perfectly vertically the way the bed on a planer does. Because the blade is mounted at the end of an arm that pivots to raise it up and down, the blade actually goes up and down in an arc.

   The arc's circle is determined by where the pivot point is on the arm.

   And, because the riving knife is mounted further out on the arm from the pivot point than the blade, the riving knife rises and falls to a greater degree than does the blade.

   Again, it's hard to describe in words. But if you do the simple experiment with the 1x2 and blade - or even look at your own tablesaw - it will become immediately clear.

   Zolton

    If you see a possum running around in here, kill it. It's not a pet. - Jackie Moon

1. 
   Tinkerer3 | Apr 21, 2009 11:58pm | #8

   I think you got at least part of my thoughts correct.  I know how my saw (PM66) works but it doesn't have a riving knife.  I was speculating on how the arbor of the true riving knife like the PM2000 or the Saw Stop among others is raised or lowered.

1. 
   zolton | Apr 22, 2009 01:16am | #9

   Tink,

   I have no direct knowledge of the two saws you cited that are orginally designed with a riving knife in mind. But I suspect that they have a mechanism where the saw's arbor rises and falls in strict verticality instead of an arc. Again, just speculation on my part though..

   That would make it easy to tie the riving knife directly to the arbor's behavior.  

   Anyone else know about this? Maybe someone owning one of the saws in question?

   Zolton

    If you see a possum running around in here, kill it. It's not a pet. - Jackie Moon

2. 
   Knotscott | Apr 18, 2009 09:42pm | #2

   A "BORK" has been on my Shop Fox 1677 since August, and it works quite well.  It requires a well fitted ZCI, but once installed and adjusted, it works very nicely.  There are models available for several saws, and inventor Bob Ross offers a 100% money back guarantee. 

   View Image

   View ImageView Image

    

   
   

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   Edited 4/18/2009 2:49 pm ET by Knotscott

3. 
   BrianDerr | Apr 20, 2009 08:07am | #3

   I have the Bosch 4000. I just took the whole guard mechanism with the plastic cover and the paws and everything, which I knew I would never really keep on the saw, and cut out the shape of a riving knife from the base of it. It attaches the same way, raises, lowers, tilts. The only time I have to remove it is for the stack dado. Works, really, really well.

   Brian

4. 
   bsutton | Apr 20, 2009 07:59pm | #4

   I made riving knifes from some 1/8" sheet aluminum.  I have one tall one that has a curve matching (approximately) the curve of the blade.  I also have a short one that is maybe 1" above the table surface.  These don't move with the blade but they do the essential thing and that is to hold the work piece against the fence so that it doesn't drift into the back of the blade.  I use the shorter one most of the time because it does the job and I can run my crosscut sled over it without having to remove it every time I need the sled.  The leading edge is beveled to ease entry into the kerf.  I bolted the knife into the mounting bracket behind the saw blade (under the table surface) that factory splitter mounts to (Unisaw).

   It works great and I have never had a problem with kick back when using it.  The main thing is that it needs to be easy to remove and install, otherwise you have a tendency not to use it. 

5. 
   country | Apr 21, 2009 04:31am | #6

   Thanks everyone for the comments and information! I have decided to try inventing my own riving knife retro. Will let you know how it works out when(if) I get it finished.

   Filling my scrap barrel daily!!