Zero Clearance Insert for Riving Knife

Yes. The problem is cutting such a long slot results
in some flex of the insert. Use stiffer material than
hardboard and the insert will do a better job
reducing chip-out.

Thanks Loren, what are you using to cut the riving knife slot? are you cutting it with a router or something?

WLuke

When I made mine, I lowered the riving knife down out of the way, then cut the slot using the usual method of clamping down the insert and slowly raising the blade. Then I used my jig saw to extend the slot back far enough to clear the knife.

When I made mine, I lowered the riving knife down out of the way, then cut the slot using the usual method of clamping down the insert and slowly raising the blade. Then I used my jig saw to extend the slot back far enough to clear the knife

Thanks Lifesaver2000

That’s how I’ve been doing mine also

Like these guys said. Make the slot for the blade then
draw some lines and extend the slot for the knife
using a jig saw or hand saw.

thanks for the reply Loren

WLuke

I made ZCIs for my R4512 with 1/4” MDF, with a rabbet around the edge so they sit flush in the throat. I tried using a jigsaw to lengthen the slot for the riving knife, but found that to be a little cumbersome. So I tried a few different methods:

(1) I routed out the knife slot on one ZCI with a 1/8” router bit.
(2) I used a standard hand saw to rough cut a knife slot on another ZCI.
(3) I flipped a third ZCI end for end on the table saw, clamped it down, and raised the blade through it again to lengthen the slot (but I don’t think this made a long enough slot).

Honestly I don’t remember which of these methods worked best, but if you find that the jigsaw is a little wonky these may be viable alternatives. Realistically, I don’t think you need the riving knife slot to be perfectly zero-clearance since that isn’t where you’re going to get chip-out, so even a rough slot should suffice as long as it doesn’t reduce the structural integrity of the insert.

-- Dan in Minneapolis, woodworking since 11/11.

I cut the ZCI slot by raising the blade to full height through the insert, then shut it down and finish the RK slot with a jig saw.

It’s very important that a throat insert is stiff and doesn’t flex, or you’ve negated a lot of precision….1/2” phenolic works great.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

I made my ZCI for my R4512 out of 1/8” hardboard, and as you can see I just extended the slot all the way to the back of the insert. The ZCI rests on a lip all the way around its perimeter and honestly, it’s pretty solid even with the cut going all the way through.

-- John, BC, Canada

nwbusa – that looks very nice.

Here are some pictures of my ZCIs. I also added a “catch” to the back with some scrap hardwood – you can’t tell from this angle, but there’s a short piece of oak separating the longer piece from the base; the longer piece catches the back of the throat. (I hadn’t drilled through for set screws in these pics.)

-- Dan in Minneapolis, woodworking since 11/11.

I’m assuming that each of you are using full kerf blades on the saw. Is there any way to use a thin kerf blade with the riving knife and even go so far as to add the use of a ZCI?

-- Russell Pitner Hixson, TN 37343 bassboy40@msn.com

I use a thin-kerf blade with the riving knife (and I have a ZCI for that blade). Haven’t had any problems so far.

My theory is that (to the extent the R4512 riving knife is barely thicker than the blade), the knife flexes away from the fence as the workpiece passes through, which would wedge the non-trapped side away from the blade. But I haven’t tested this scientifically; all I know is that I’ve been able to make smooth thin-kerf cuts with no ill effects so far. I’d be interested to know if anyone thinks this is a bad idea.

-- Dan in Minneapolis, woodworking since 11/11.

I use thin kerf blades as well. As Dan notes, the riving knife is barely thicker than the blade. I measured it a while ago, I think it was .005” or so thicker, leaving little margin for error when aligning the riving knife to the blade. But it can be done.

-- John, BC, Canada