Non-Thru-Cut Riving Knife

[bobgroh]

The riving knife is NOT supposed to be as thick as the saw blade - just the opposite - it needs to be thinner.

It's purpose is keep the rear of the saw blade (which is moving upward relative to the wood) from catching the wood at the rear of the blade which would (in a heart beat) lift the wood up over the top of the blade and throw it backwards.

So the 0.075" is a good compromise - thick enough to be stiff enough yet thinner than a thin kerf saw blade.

[charlese]

My rip fence is always on the right of the blade, so I set the riving knife to be even with the fence side of the blade. That way there are no little waves in the cut.

[algale]

The riving knife is NOT supposed to be as thick as the saw blade - just the opposite - it needs to be thinner.

It's purpose is keep the rear of the saw blade (which is moving upward relative to the wood) from catching the wood at the rear of the blade which would (in a heart beat) lift the wood up over the top of the blade and throw it backwards.

So the 0.075" is a good compromise - thick enough to be stiff enough yet thinner than a thin kerf saw blade.

Agreed. So why is the non-through cut riving knife 0.075 and the upper saw guard riving knife 0.073? Shouldn't they be the same?

[BuckeyeDennis]

Agreed. So why is the non-through cut riving knife 0.075 and the upper saw guard riving knife 0.073? Shouldn't they be the same?

That difference is more likely to be due to a variation in manufacturing tolerance, or an to alternate material source, than to an actual design change. The particular type of steel used would have a much greater effect on strength and stiffness than would a 0.002" variation in thickness.

[dusty]

I suggest that the deviations are there because this is NOT a critical dimension. In this specific application a few thousandths is unimportant so long as that deviation does not result in the riving knife being thicker than the mounted saw blade.

I disagree with some of the comments here that the riving knife must be thinner than the blade. It must not be thicker but equal to is not, in my mind, a problem.

BTW, I received my Shopsmith riving knife today. I can now retire my homemade riving knife to the "hard to reach" tool board.

It is about the same thickness as the riving knife on the lower saw guard but I believe it is more rigid. It looks good, feels good and is mounted. Time will tell but I propose that it is going to do the job well.

Can you believe, though, that it came with a five page instruction sheet. I hope that all of the instruction sheets that accompany items ordered from Shopsmith are now this adequate. I have received some in the past that would not pass muster.

[algale]

I suggest that the deviations are there because this is NOT a critical dimension. In this specific application a few thousandths is unimportant so long as that deviation does not result in the riving knife being thicker than the mounted saw blade.

I disagree with some of the comments here that the riving knife must be thinner than the blade. It must not be thicker but equal to is not, in my mind, a problem.

BTW, I received my Shopsmith riving knife today. I can now retire my homemade riving knife to the "hard to reach" tool board.

It is about the same thickness as the riving knife on the lower saw guard but I believe it is more rigid. It looks good, feels good and is mounted. Time will tell but I propose that it is going to do the job well.

I am glad you like your non-through cut riving knife. I like mine too. I agree it seems more rigid. But I have come to believe that both are made from the same material and that the main reason the non-through cut riving knife seems more rigid is that it doesn't get subjected to the same lateral forces being applied to the regular upper saw guard riving knife through the attaching mechanism for the blade guard. But what do I know, I'm not an engineer.

[dusty]

I am glad you like your non-through cut riving knife. I like mine too. I agree it seems more rigid. But I have come to believe that both are made from the same material and that the main reason the non-through cut riving knife seems more rigid is that it doesn't get subjected to the same lateral forces being applied to the regular upper saw guard riving knife through the attaching mechanism for the blade guard. But what do I know, I'm not an engineer.

My homemade riving knife resided on the table saw. For all practical purposes, it took the place of the upper saw guard. This one will too.

No lectures, please. I know that this riving knife is intended for "non-through cuts".:)

PS: I made some saw dust last night and again this morning. The new riving knife works well but there is a "humming" sort of noise when it is installed that goes away when I remove it. I have not determined what causes it yet but I think the riving knife might be vibrating against my ZCI. I do not consider this an issue; I would just like to know what it is.

[Deicer]

Hi, Sorry to revive this thread on riving knife. I have been using my shopsmith Mark 7 when ripping with my Grr-ripper pushblocks.( I use two) Of course I have to take off the upper guard and riving knife. I have been looking at getting the Non-Through-Cut Riving Knife. I know it says for "Non - through cuts Only" I am correct in thinking that this is for the lawyers. It will still provide the protection from the wood coming together beyond the blade. The Grr-ripper protects my hands from the top of the blade on the through cut. Is there any other reasons for "non through cuts only"?
PS. I am solely responsible for the use of my SS Mark 7 and all of it's functions. Any advice given and used by me is entirely my decision and responsibility. Thanks Jim

[BuckeyeDennis]

Hi, Sorry to revive this thread on riving knife. I have been using my shopsmith Mark 7 when ripping with my Grr-ripper pushblocks.( I use two) Of course I have to take off the upper guard and riving knife. I have been looking at getting the Non-Through-Cut Riving Knife. I know it says for "Non - through cuts Only" I am correct in thinking that this is for the lawyers. It will still provide the protection from the wood coming together beyond the blade. The Grr-ripper protects my hands from the top of the blade on the through cut. Is there any other reasons for "non through cuts only"?
PS. I am solely responsible for the use of my SS Mark 7 and all of it's functions. Any advice given and used by me is entirely my decision and responsibility. Thanks Jim

I often use my "non-through" riving knife for through cuts, although for a different reason. I like to use a sacrificial miter gauge fence, which gives cleaner cuts and better workpiece control. You can't use one with the upper guard installed, but the riving knife is not a problem.

[dusty]

Prudent advice would be to use the upper saw guard at all times possible. My upper saw guard has been stored in the shop equipment cabinet for years. I have a riving knife installed on the table saw and hardly ever remove it. Yes, it serves the purpose of a riving knife for all cuts even though the probability of the work piece closing on the saw blade is unlikely.