table saw riving knife design

[lou sansone]

good evening ww's
this morning I asked about splitters for table saws and some possible types that are out there. Some of those who responded mentioned that some european saws use riving knives. Well as I looked at my table saw I realized that what I thought was a missing splitter was a missing riving knife ( for those interested my saw is a rockwell / delta RT-40 ).

So I have come up with what some folks showed me in their responses and I wanted to get some feedback from the group before making the little guy. What you see are just cardboard mock ups. The red one is sort of skinney and the orange one is a little stouter. I am only running a 12" blade at this time so things look a little out of proportion. The saw is made to take from a 12" to 16" blade so the riving knife holder is held in a slotted fixture. I took some of the advise offered and tried to make the knife no taller than the blade.

thanks in advance
lou

[Greg Mann]

Looks like original equipment, Lou. :cool: Very nice.

Greg

[Mark Singer]

Lou,
That is the correct shape. years ago I woked with a guy that was German and he had a similar one with a board monted on top. This helps with kick back. The knife should be just under the blade kerf in thickness.

[lou sansone]

Hi mark

which one looks better ? I am tending toward the orange one.

My blade is 0.125" thick and I was going to make the riving knife about 0.120" is that too tight?

lou

[Jim Becker]

Orange one, Lou...the other one will be "too delicate" for the job. I'd actually make it even "deeper" behind the blade for maximum stiffess. You really lucked out with that RT being designed for a riving knife!! Wonderful!

[Mark Singer]

I think the gold one is better. I will Mic my Beismeyer and give you the thickness...I am BBQing at the moment. If you have Tage Frids Book he has a picture of his on page 21 or 22...it is similar to the old one I used 30 years ago. Maybe Fritz and Tage went to the same school in Europe?
Hi mark

which one looks better ? I am tending toward the orange one.

My blade is 0.125" thick and I was going to make the riving knife about 0.120" is that too tight?

lou

[lou sansone]

Orange one, Lou...the other one will be "too delicate" for the job. I'd actually make it even "deeper" behind the blade for maximum stiffess. You really lucked out with that RT being designed for a riving knife!! Wonderful!

hi jim
thanks for the feedback.. I feel sort of stupid that for the last 3 years I had no idea what that darn thing was for!:confused: I was also thinking about making "deeper" in the back so it does not get bent somehow.



The reason that I have started to give this safety thing more thought is this semester with my young student will probably be the time he starts to learn how to use the TS. I think that having this riving knife installed will be a big help with my worry. Maybe I will post a new thread asking for advise in teaching the fundamentials of teaching about a TS.

lou

[Mark Singer]

Lou,

It is 0.1 inches. I think that is good. You should bevel the curved part toward the blade...like a dull knife to allow easy entry.

[lou sansone]

Lou,

It is 0.1 inches. I think that is good. You should bevel the curved part toward the blade...like a dull knife to allow easy entry.

thanks mark.

I was worried that if I made it too thin it wouldn't do its job. Looks like a good job for a bridgeport !
lou

[Jim Becker]

The reason that I have started to give this safety thing more thought is this semester with my young student will probably be the time he starts to learn how to use the TS. I think that having this riving knife installed will be a big help with my worry. Maybe I will post a new thread asking for advise in teaching the fundamentials of teaching about a TS.

I applaud you for your forethought on this subject. Should I be so lucky that "A" and/or "J" become interested in woodworking someday, safety will always be where things start and where things end.

[CPeter James]

Does the knife move with the blade or does the blade come up under it and the relationship between the knife and the blade change with blade height?


CPeter

[Glen Blanchard]

Okay, I don't get it. What's the difference between a riving knife and a splitter?

[Jim Becker]

Okay, I don't get it. What's the difference between a riving knife and a splitter?

A riving knife follows the blade up and down as it's adjusted for height and stays exactly the same distance away from the blade...it's attached to the same stuff that the arbor is and moves with the arbor in all directions. A splitter only tilts with the arbor and is closer or farther from the blade, depending on where the blade hight is set. It does not move up and down with the blade.

I guess technically you could call a riving knife a splitter...but the terms kinda are used to differentiate between there capablities.

[Bruce Page]

A riving knife follows the blade up and down as it's adjusted for height and stays exactly the same distance away from the blade...it's attached to the same stuff that the arbor is and moves with the arbor in all directions. A splitter only tilts with the arbor and is closer or farther from the blade, depending on where the blade hight is set. It does not move up and down with the blade.

I guess technically you could call a riving knife a splitter...but the terms kinda are used to differentiate between there capablities.
I did not know that.
I love this place, I learn something new everyday.

[Ian Barley]

Lou

The orange one looks more the part. Most original riving knives have some sort of arrangement in the top (hole, slot etc...) which is used to mount the blade guard. Also the mounting slot at the base includes some adjustment capacity.

The following link http://www.hse.gov.uk/pubns/wis16.pdf takes you to the HSE (kinda like OSHA) page dealing with table saws. Figure 4 on page 3 tells you about thickness relative to blade.

[lou sansone]

Does the knife move with the blade or does the blade come up under it and the relationship between the knife and the blade change with blade height?


CPeter

the knife moves with the blade both in height and tilt.

lou

[Glen Blanchard]

A riving knife follows the blade up and down as it's adjusted for height and stays exactly the same distance away from the blade...it's attached to the same stuff that the arbor is and moves with the arbor in all directions. A splitter only tilts with the arbor and is closer or farther from the blade, depending on where the blade hight is set. It does not move up and down with the blade.

What is the practical difference then? Does this design (moving in all planes with the blade) make it safer then a simple splitter? I am having a difficult time grasping the distinction in practical terms.

[Jim Becker]

What is the practical difference then? Does this design (moving in all planes with the blade) make it safer then a simple splitter? I am having a difficult time grasping the distinction in practical terms.

Yes, the riving knife that moves in all planes with the blade is essentially safer since it can stay on the saw pretty much 100% of the time. For non-through cuts, you can position the top of the splitter just a hair lower than blade height and you still get the benefits of a splitter, although they are less needed for that type of work. Further, the design of the riving knife keeps it close to the back of the blade all the time...a constant distance, as a matter of fact. You get the same benefit there as you do with a zero clearance insert...less space for material to get caught. With a "traditional NA splitter", when the blade is low, the distance between the back of the blade and the front of the splitter is a much greater distance than when the blade is raised up. Etc. Riving knives are a significant advantage in safey which is why they are mandated in Europe. Heck, even the Festool ATF55 plunge saw has one!

[Michael Sloan]

Hi Lou,

I'm going to propose an extension of your riving knife. The structure for holding your riving knife looks strong enough to hold a full size riving knife that you can attach an over-the-blade dust collection blade guard to. The blade guard would be bolted to the riving knife through a single hole drilled near the top of the knife.

My Mini-max slider, and I believe all of the Felder sliders come with this approach. You can buy a blade guard that attaches to the riving knife from Felder, and probably from other places as well. Also would not be too difficult to build one, although the Felder is clear plastic which is nice. Also, you might check, the Felder accessory riving knives could possibly fit on the saw with minor modifications.

Mike

[Bill Simmeth]

Hi Lou and other Creekers!

Lou, I thought I'd post a pic of the riving knife on my Oliver 260. By the Oliver Green overspray on it, I'm guessing it's an original. I know the one on the second arbor (Gawd I love saying that! :D ) is a shop-made replacement. The knife is 3/32" thick which works well with 16" blades that are 5/32".

You probably know this, but thought I'd point it out anyway, the leading edge is ground to a point (much like a scythe blade but not that sharp) to encourage stock to slide past it should they meet. (I'm guessing that's where the "knife" part of the name comes from).

Bill Simmeth
Delaplane, VA