Thread: Riving Knife Thickness

The riving Knife should be a tad thinner than the blade in use.

I dont think there is any specific measurement.
But is shouldn't bind in the kerf.

It should be straight & in the centre of the kerf.

Thank you soundman, that's what I would have thought. Mine is about 1.25 mm thinner then the kerf, translating that's not much more then half the kerf width.
Thanks once again. Pat

I don't think that there is any specific thickness for a riving knife. In fact, it could even be thicker than the blade (well, there are reduced kerf blades on the market - one doesn't change the riving knife every time you change your blade).

The purpose of the riving knife is to prevent binding of the timber as it passes the blade, and thereby avoid the threat of kickback. So the primary requirement is that it parts the wood (imitating the parting of the Red Sea). I imagine that as long as the riving knife's leading edge is sharp enough and does not have a too abrupt bevel to jamb the offcut, then it makes no difference how thick the riving knife is.

If I were to build my own (and I am thinking about doing so), then I would design it so that the fence side was flush with the blade.

What do you think?

Regards from Perth

Derek

Derek,

A riving knife wider than the saw kerf could pose a problem in a properly adjusted blade/fence set-up. I experienced binding once on my table saw when ripping. After checking the fence and saw alignment I found that the riving knife was slightly right and causing the problem. Resetting the knife so that it was more in line with the blade eliminated the problem.

Regards

Redneck

I understand. That's why I said "If I were to build my own....then I would design it so that the fence side was flush with the blade ". If you do not do this, you will get kickback. However, it is different on the other side of the blade where the aim is simply to keep the timber apart (i.e. not bind).

Adding thicker or thinner blades would not change this setting since the blade sits up against a stop.

Regards from Perth

Derek

lets cleer up a few things.

A riving knife is mounted at the rear of the blade and usualu fixed to the blade carage. It should rise & fall with the blade.
there are some exceptions (usualy american afterthaught devices) (the yanks still don't get the idea it think)

Common on many machines is an american splitter which is mounted such that it doesn't rise & fall with the blade, it usualy supports the blade guard and may come over the back of the bench typical of stabndard delta and most asian machines.

the splitters will mostly be quite thin & made of light steel plate.

these you would normaly align to the right side of the kerf, asuming using the fence to the right. Can be a bit of a fiddle to get just right.

A riving Knife (propper) is a bit different.
It must be narrower than the kerf but not by much.
Yess it is good practise to change the riving knife with the blade when appropriate.

A propper riving knife should cleer the blade by several milimetres at the rear and fit the diameter of the blade.

In an ideal situation on a machine of good design the riving knife should remain just below the level of the top of the blade thru the blade travel ( many don't)

Statements like.
Blades should only be used with a matching riving knife in place.
are common
In conciencious practise riving knives are machined to match blades.

One point of safety braught up by eastie some months ago.

Ensure that your riving knife (propper) is captive in its mount.
ie if its mounting bolts come loose it can not be pulled out.

aparantly a loose riving knife was pulled onto the back of a rotating blade after it jammed in the kerf. Striking the operator in the chest. Killing, I believe. Eastie may confirm.

Soundman

Ahh. You are saying that a riving knife is dedicated to a blade, while a splitter is part of the saw table.

Got it. The upshot is that the splitter remains at a fixed elevation, while the riving knife moves up and down with the blade. I looked up a similar discussion on the late, lamented Badger Pond archives. It was pointed out that because of this difference "the splitter it has to be mounted farther behind the blade in order to clear the trailing edge of the blade when it's raised; particularly when the blade is lowered for thinner woods, this leaves a substantial area for potential kickback. In contrast, the riving knife rises and lowers with the blade, making it possible to shape it in conformity with the blade's circumference, which keeps it extremely close to the blade's trailing edge all around the periphery and at every blade elevation; this should reduce the potential kickback zone to nil ... Another advantage is that the riving knife can be cut down to just below the blade's top clearance, making it possible to leave it installed for non-through cuts with the standard blade (of course, it still has to be removed when using a dado or other blade of smaller diameter)".

So we would all be better off with dedicated riving knives (for each of our blades). Now we need to consider how this can be done to our USA-designed, Asian-built machines.

Are there aftermarket riving knives available? I'm thinking of how it will rise and fall with the blade. There is the Biesemeyer splitter. Is this similar?

Regards from Perth

Derek

Thanks chasps! all interesting and information that is new to me.

Cheers Electrolad

derick you got the general idea.

My machine has a riving knife but it doesn't track the blade as well as the more expensive machines.

its problem is that the blade carrage swings in an arc from the front of the machine as in the unisaw (or any derived).
the knife therfore rises & falls faster than the blade.
still better than none.

I think there would be great difficulty fitting a propper riving knife where it hasn't been part of the design, for various reasons.

a blade splitter of any (decent) sort is better than none.

I note that the eurapeans are big on riving knives. I know a bloke who has several 7 1/4 inch AEG hand saw machines (european models) that came fitted with a riving knife standard.

The americans seem to be into this splitter thing with anti kick back dogs.

I riving knife is a real blessing for non thru sawing like cutting the tops off boxes.

cheers