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Thread: Riving Knife solution for cabinet saw?

  1. #1

    Riving Knife solution for cabinet saw?

    All,

    Reading the thread on blade guards got me to thinking. Is there a solution out there for adding a riving knife to a cabinet saw?

    I understand that it's mostly found on Euro saws, but it looks like a nice added safety device beyond what a traditional splitter achieves.

    Given the average person's love of life and limbs in general, I'm surprised to no be able to find anyone selling them for all the Unisaws, PM66's, General, etc saws that pepper the countryside.

    I guess it begs the question, if one was sold at a relatively acceptable price, would _you_ buy one for your cabinet saw?

    That and of course, do you know where I can find one?

    Thanks,
    /Kevin

  2. #2
    I don't think it can be done becuase a riving knife goes up and down with the blade so that the blade cut out part stays about 1/4" from the blade at all times. With all the cab and contractor saws I have looked at the splitter mounts permanently to a mount that does not move


    I used to have a Ryobi BT3100 with this feature and have used a MJ splitter and can honestly say that there is really only a minor enhancement in safety going from a splitter to a true riving knife. There is a definate difference in having a riving knife, but this is only evident in a small number of situations. The only difference is that your danger zone extends about 1/2-3/4" longer with a splitter vs. a riving knife. Usually the feed rate is quick enough that this danger time is minimal with a splitter. The only time it could be a proble is if you have a board that has some wicked internal stresses and starts twisting immdiately after being ripped.

  3. #3
    Join Date
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    Not a simple addition

    The way in which a riving knife works, the knife lowers and raises right along with the blade. I have one on my Festool circular saw so I see this action just about every day.

    I can't see how this could be done as an after-market addition to the typical North American table saw. Maybe someoe really smart can figure out how to do it -and it they can I would pay a lot to get their device.

  4. #4
    Join Date
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    Kevin,

    The problem is that a Unisaw changes blade height by rotating around a pivot. The arbor carriage angle is constantly changing. A crescent moon shaped knife bolted to this shifting carriage would not stay level with the top of the blade.

    You might be able to come up with a Rube Goldberg style armature that articulates to solve this problem. I bet it would be expensive and flexible - both bad features.

    European saws, and the Ryobi, move vertically by a totally different mechanism. Instead of a pivot they use vertical ways or rods, and are moved up and down by a threaded rod. That's more expensive to make. I'm not sure how the Ryobi does it, but suspect that it's not as smooth, rigid, or durable as the European or SawStop versions.

    Seems to me that the solution is in the table top insert around the blade. You might be able to design an insert plate with a knife right behind the blade that can be moved up and down easily and locked in place solidly. In use you would slide the wood next to the knife, unlock it, move it up or down to match the stock, and lock it. You would then separately adjust the blade to cut slightly deeper than the stock. Presto. Gotta be some way to do this with reasonable economy.

    Regards,

    Dave

  5. #5
    Quote Originally Posted by Dave Wright #2
    Kevin,
    European saws, and the Ryobi, move vertically by a totally different mechanism. Instead of a pivot they use vertical ways or rods, and are moved up and down by a threaded rod. That's more expensive to make. I'm not sure how the Ryobi does it, but suspect that it's not as smooth, rigid, or durable as the European or SawStop versions.
    Having just taken a Ryobi apart to sell in parts I can tell you that it is similar to the post mechanism of a euro saw. Basically there is an aluminum channel with some metal shims and a metal arbor rides in the channel and the motor, pulleys and arbor mount onto. It moves up and down on a screw drive mechanism. I'll see if I have some pics somewhere

  6. #6
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    Oct 2004
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    Brad,

    I'd like to see the mechanism. Does the female thread that rides on the threaded rod fully capture it? That's how it is on my SawStop. I don't know how the full Euros do it. I note that good quality conventional North American style contractor and cabinet saws adjust height and blade tilt with an open worm screw that cannot get clogged by sawdust. Did dust clogging interfere with vertical movement of your Ryobi's carriage? Maybe the integral dust collection on these saws takes care of that.

    Thanks, Dave

  7. #7
    Quote Originally Posted by Dave Wright #2
    Brad,

    I'd like to see the mechanism. Does the female thread that rides on the threaded rod fully capture it? That's how it is on my SawStop. I don't know how the full Euros do it. I note that good quality conventional North American style contractor and cabinet saws adjust height and blade tilt with an open worm screw that cannot get clogged by sawdust. Did dust clogging interfere with vertical movement of your Ryobi's carriage? Maybe the integral dust collection on these saws takes care of that.

    Thanks, Dave
    Here is an annotated pic of where the blade goes (the arbor is pointed toward you). On the back side of this assembly is the motor, belts and pulleys as well as the lift mechanism. The lift is simply a screw drive and the arbor assembly in the middle has a square nut that seats in it to raise and lower the blade. Basically the arbor mechanism rides in that aluminum chanel on a set of metal shims. Not as nice as the euro saws, but accomplishes the ability to have a riving knife.

    You can also see how the riving knife attachment at directly attached to the arbor, much different that a cabinet or contractor saw.
    Attached Images Attached Images

  8. #8
    I got up in to my 66 today, and while looking it over, I decided that it would be easy enough to mount a riving knife. The problem would be getting the knife lined up with the blade, and keeping it lined up at all times.

    I don't know about other brands of cabinet saws, but the Powermatic looks like it would work with a little bit more brain power then what I have.

  9. #9
    Join Date
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    Attached is a picture of how the riving knife mounts in a Felder saw. Note that the trunnion is a rather massive chunk of iron. Arrows point to the 2 acme threads used for raising/tilting the trunnion/blade assembly.

    The riving knife is replaceable with knives of varying thicknesses to match the blade kerf and can be moved closer to the blade if running a smaller than 12" blade. An example of when you'd do that is if using the scoring blade - in that case the largest blade I can run is a 10" main blade with the scoring blade.

    Hope the picture helps.

    Rob
    Attached Images Attached Images

  10. #10
    Quote Originally Posted by Rob Russell
    Attached is a picture of how the riving knife mounts in a Felder saw. Note that the trunnion is a rather massive chunk of iron. Arrows point to the 2 acme threads used for raising/tilting the trunnion/blade assembly.

    The riving knife is replaceable with knives of varying thicknesses to match the blade kerf and can be moved closer to the blade if running a smaller than 12" blade. An example of when you'd do that is if using the scoring blade - in that case the largest blade I can run is a 10" main blade with the scoring blade.

    Hope the picture helps.

    Rob
    I have a sneaking suspicion that the arbor on that felder weighs more than my entire old Ryobi!

    I tried putting my new PM64A onto my old base I made for my Ryobi and it wouldn't move an inch, it caused one of the stretchers to sag onto the floor and thus prevent free movement. I'm in the market for a good universal base if anyone is getting rid of one since I discovered this issue!

    As to putting a riving knife on an American saw, I think the best bet might be a guy who is making a thing called the shark guard. He was making stuf for the Ryobi, but has branched out into other saw since he upgraded

    http://www.leestyron.com/index.php
    Last edited by Brad Olson; 01-03-2005 at 6:16 PM.

  11. #11
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    I was just looking at the "Shark Guard" and don't believe it would qualify as a "riving knife" in the way that is really desirable...two things that make a riving knife wonderful are the ablity to raise and lower it so you can keep it on the saw for non-through cuts and the fast that it's designed to stay close to the blade consistantly no matter what height you have the blade set to. The OEM splitter systems (and what the Shark Guard appears to be in the pictures, at least for the cabinet saws) don't do either. Even the great Biesemeyer splitter I use does not meet either of those features.
    --

    The most expensive tool is the one you buy "cheaply" and often...

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