Correct thickness of a Riving Knife

[deema]

I would really welcome knowing what the correct thickness of a circular saw riving knife should be. I thought I knew. However, the other day I baught a new circular saw blade and was chatting to the chap who happened to have been in the Royal Navy and a time served wood worker / machine setter. He was informing me that he had been taught that the riving knife should ideally be a 0.1~0.2mm larger on either side of the kerf cut by the blade. So, overall 0.2 to 0.4 larger than the saw kerf. The reason for this was not only to ensure that the stuff did not close up behind the blade causing a kick back, but to ensure that the back edge of the blade as it rises out of the table does not cut the stuff as well as the leading front edge. This would increase the life of the blade and improve the cut edge tremendously.

Well, this was rather contrary to what I had believed, which was that the riving knife should be just slightly thinner than the kerf cut by the blade. Clearly if the saw has a parallel fence such as those favoured by the Americans I can see that a wider riving knife is going to cause a lot of problems. However, my ripping saw which is an old Sedgwick has a short fence so this would not be an issue.

 

[Ttrees]

Does this make it more difficult to push the stock through, I wonder ?
I always ...not that much research done, maybe 2 years on this forum regarding deep interest on tablesaws,
Though it should be somewhere inbetween the thickness of the saw plate and the teeth .
Just thinking about that stainless plate I have in the house with joy.
Thanks Deema,
Tom

 

[memzey]

Timely post as only today I made a splitter/riving knife for my old Wadkin. My saw blade has a 3mm kerf and 2mm plate so I made the knife from 2.5mm stock (stainless steel which is a pig to work by the way). Worked a treat on the test cuts I made afterwards. I can see the logic of your mate's comments but I don't think I much like the thought of the stock being forced against anything while I'm making a cut. Might be safer in theory but feels wrong to me.

 

[Dan j]

Both arguments have their merits, but i definitely prefer the knife slightly narrower than the blade.
Having to force wood through the saw is a recipe for disaster.

The teeth coming up at the back of the blade wont cause kickback as they will simply cut anything in their way. Its the friction on the blade plate that will cause the kick back.
Its why all saws, hand or machine, need offset on the teeth.

 

[custard]

the other day I baught a new circular saw blade and was chatting to the chap who happened to have been in the Royal Navy and a time served wood worker / machine setter. He was informing me that he had been taught that the riving knife should ideally be a 0.1~0.2mm larger on either side of the kerf cut by the blade. So, overall 0.2 to 0.4 larger than the saw kerf.

All due respect to the Senior Service, but that's just plain wrong. If you were ripping a big piece of Oak you wouldn't be able to force it past the riving knife, and if you did it would be acting as a wedge and driving a split ahead of the cut.

The riving knife should be thicker than the saw plate and thinner than the kerf.

 

[meccarroll]

Below is information taken from a HSE data sheet for circular saws:

Here is a link to the HSE data sheet page on the web site:

http://www.hse.gov.uk/pubns/wis16.pdf


Regards Mark