Riving Knife - how wide?

[Bruce Thompson]

I'm going to make a riving knife for my old table saw to mount about 1/8" behind the blade, but clearance from the motor mount casting may be a problem, limiting the width of my RK.

How wide is your riving knife?

What is minimum width for a 1/8" kerf riving knife to be effective?

[Mike Henderson]

If it's going on an old saw, it's probably not a riving knife - it's probably a splitter. A riving knife moves with the saw blade and maintains it's position relative to the blade, no matter if you raise or lower the blade or tilt the blade.

In many cases, a splitter does not move with the blade. If it does, it usually tilts with the blade but does not move up and down with the blade.

Mine is 5/64" (on a SawStop saw).

Mike

[Jamie Buxton]

The basic function of a splitter is to keep the kerf from closing if your workpiece has some reaction wood in it. I make the splitter a hair narrower than the kerf. Mine is a steel pin 1/8" diameter and about 3/8" tall. It does what it needs to do.

[johnny means]

I've used a screw sticking out of my throat plate and filed to thickness. Width is super important, as long as it prevents material from rotating into the back of the blade.

[Mark e Kessler]

0.2 mm thicker than the plate


I'm going to make a riving knife for my old table saw to mount about 1/8" behind the blade, but clearance from the motor mount casting may be a problem, limiting the width of my RK.

How wide is your riving knife?

What is minimum width for a 1/8" kerf riving knife to be effective?

[glenn bradley]

Slightly narrower than the kerf. A full kerf blade can run 1/64" over or under 1/8" or more. Thin kerf blades run around 3/32". You want to be a bit thinner than that.

[Frank Pratt]

The basic function of a splitter is to keep the kerf from closing if your workpiece has some reaction wood in it.

Probably even more important is that the splitter or riving knife keeps the board from wandering away from the fence & getting kicked back by the blade.

[Bruce Thompson]

If it's going on an old saw, it's probably not a riving knife - it's probably a splitter. A riving knife moves with the saw blade and maintains it's position relative to the blade, no matter if you raise or lower the blade or tilt the blade.

In many cases, a splitter does not move with the blade. If it does, it usually tilts with the blade but does not move up and down with the blade.

Mine is 5/64" (on a SawStop saw).

Mike
Well, you and everyone else answered the question "How THICK should a riving knife be?". I asked how wide because my old saw will limit width of my RK to 1 1/4" without the back end of it touching the motor mount when cranking the blade up and down. I assume that 1 1/4" will help a lot, but all factory RKs seem to be at least 3" wide. Is that because they need to be that wide to prevent pinching, or maybe just because they also have to support a blade guard?

You said yours is 5/64", but you say nothing about kerf size. 5/64" seems right thickness for a thin kerf blade. Are running a TK blade on a Sawstop?

[Andrew Pitonyak]

Take a look at the Micro Jig Splitter, just for ideas if you are not familiar with it. I was very happy with mine before I purchased my sawstop and did not need it anymore.

[Mike Henderson]

You said yours is 5/64", but you say nothing about kerf size. 5/64" seems right thickness for a thin kerf blade. Are running a TK blade on a Sawstop?

No, that's a standard SawStop riving knife, came standard with the saw. The blade is a standard 1/8" blade. When a piece of wood pinches, the two sides of the wood bend towards each other. Your splitter or riving knife does not have to be the same thickness as the blade, it just has to keep the two pieces from pinching together at the back of the saw blade. Given the length of the riving knife on the SawStop (how far it sticks behind the blade), I assume SawStop did some research and found that 5/64' would work for a standard 1/8" blade and will also work for a thin kerf blade. I've used both on my saw without problems.

Mike

[When describing a riving knife or splitter, I would describe the distance from the table to the top of the riving knife or splitter as the "height". I'd describe how far back behind the blade as the "length". And I'd describe the thickness as the "width". In other words, height, length and width. From the responses you received, it looks like other people looked at it the same way.]

[Jim Becker]

To your specific question that you just reiterated. there's no "standard" for how deep the riving knife goes behind the blade and many are actually curved. That's the case with the riving knife on my slider. It's maybe 2" deep behind the blade max and both the inside and outside follow the curve of the blade so there's very little gap between the teeth on the blade and the riving knife. So yes...it has to actually fit the saw's restrictions on space.

[Vince Shriver]

I'm going to make a riving knife for my old table saw to mount about 1/8" behind the blade, but clearance from the motor mount casting may be a problem, limiting the width of my RK.

How wide is your riving knife?

What is minimum width for a 1/8" kerf riving knife to be effective?

My Jet T/S came with a RK approx 0.100". I cut it down to be slightly lower than my saw blade for non-thru cuts, but have a "stock" one to accommodate the blade guard and prawns (which fit on top of it). BTW, having been the self-inflicted victim of several kickbacks, I can painfully attest to the importance of a splitter or RK.

[Bruce Thompson]

No, that's a standard SawStop riving knife, came standard with the saw. The blade is a standard 1/8" blade. When a piece of wood pinches, the two sides of the wood bend towards each other. Your splitter or riving knife does not have to be the same thickness as the blade, it just has to keep the two pieces from pinching together at the back of the saw blade. Given the length of the riving knife on the SawStop (how far it sticks behind the blade), I assume SawStop did some research and found that 5/64' would work for a standard 1/8" blade and will also work for a thin kerf blade. I've used both on my saw without problems.

Mike

[When describing a riving knife or splitter, I would describe the distance from the table to the top of the riving knife or splitter as the "height". I'd describe how far back behind the blade as the "length". And I'd describe the thickness as the "width". In other words, height, length and width. From the responses you received, it looks like other people looked at it the same way.]

Thanks for your information. Since blade kerfs are referred to as "thin", it seemed natural to refer to that dimension on a RK as thickness. From back edge to cutting edge of a carving knife or hunting knife is always called width, so that seemed natural to me on a RK too.

I looked up Sawstop riving knife and saw it listed as 0.090" (close to 5/64) and it looks to be almost 3" long, as you call it, so would surely handle pinch on a full kerf blade while thin enough to use with a thin kerf. That is actually encouraging information for me.

Mine being limited to 1 1/4" wide/long, using 12ga stainless (0.109") seems likely to give similar anti pinching performance on full kerf as your longer thinner one. I could also get 11ga SS, but at 0.121" thick, that seems too close to kerf size (especially after a blade has been sharpened), requiring extremely precise alignment both vertically and horizontally.

If I ever need to use a thin kerf blade, I'd have to make a thinner RK for it.

[Bill Dufour]

A round steel rod should do it but it may bend a flex a little too much so they are often a plate not just a rod.
Bill D

[Bruce Thompson]

Thanks.
That's very good information for me. If your factory RK is only 2", then my 1 1/4" (maybe 1 1/2" if I can replace the drive belt with a 1" longer one that lets the motor mount drop a little further out of the way of the RK) may work fairly well. Anything is better than nothing, after all.

[Jim Becker]

Are you rigging this up to follow blade tilt? (necessary for a riving knife to not be merely a splitter...)