how close does a blade width have to be to the riving knife's?

[hugh lonner]

Hi all, I noticed that thin kerf doesn't mean the same thing to every manufacturer. How big can the difference in width between the blade and the riving knife be before it matters? (in my case my riving knife is .090, so my specific question is how wide can a blade be without being unsafe with that width?).

A 3/32 blade is .0937..., while other "thin kerf" blades I'm interested in are .104. Does it this small a difference matter? (1/8 is .125 so that is a much bigger difference.)

thanks, Hugh

[Frank Warta]

The blade body should be thinner then the riving knife, but the blade kerf should be wider than the knife. The idea is that so long as the riving knife is in place the wood should not be able to pinch the body of the blade. I know others have posted graphics of this before but I don't have one.

In other words the teeth of the blade must be thicker then the knife but the body of the blade must be thinner than the knife.

Obviously the closer the thickness of the body gets to the thickness of the knife the more things like the total combined run-out becomes a factor. I hope that helps.

[scott spencer]

A blade that's 0.104" should be fine on a splitter that's 0.9. The opposite scenario is the one to be concerned about, as the kerf in the wood will bind on the splitter, possibly forcing it to stop midcut.

[David Cefai]

The purpose of the riving knife is to prevent the wood from pinching the blade. This would cause the wood to be flung off the saw.

So what matters are the width of the blade, the width of the knife and the distance of the knife from the blade. The further away the knife is, the thinner it can be. (I'm ignoring the problems with cutting dados that this would cause).

I doubt that there is a "best" arrangement. To determine the safety of a blade/knife combination one could make a test cut in a narrow piece of wood and then see the effect of pinching the wood with your fingers (with the saw stopped!).

The wood itself also matters. How will it warp?

[John Thompson]

The riving knife must be thinner than the teeth kerf on a blade. Make a practice cut to determine the true width of the kerf cut as it might be slitghtly more than the actual blade tooth width if you have run-out in a blade. At that point the riving knife must be thinner to allow the stock to clear it. Once you determine that the next important thing to do is be sure the riving knive is aligned properly with the blade.

On Euro saws riving knives are usually only a hair under the width of blade kerf. That is ideal but some of the U.S. manufacturers have put thin riving knives on the saw so they don't have to supply one for both full kerf and thin kerf blades. The problem with too thin is it will flex more easily so it is critical to check the alignment to the blade often as yes... most of us bump the splitter and riving knive often and you never know if could have been knocked out of adjustment.

Good luck...

[Sean lennon]

A blade that's 0.104" should be fine on a splitter that's 0.9. The opposite scenario is the one to be concerned about, as the kerf in the wood will bind on the splitter, possibly forcing it to stop midcut.

When i made the knife for my 34-350, I lucked into a piece of stainless that was about that same ratio. seems to work fine for me.

I can see I do have a lot more research to do on this topic .

sean