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Splitter and Riving Knife thicknesses

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Forum topic by ferstler posted 06-23-2009 11:54 PM 1727 views 0 times favorited 18 replies Add to Favorites Watch
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ferstler

333 posts in 2245 days


06-23-2009 11:54 PM

Topic tags/keywords: question tablesaw blade

I have cut a lot of wood on my small table saw and have yet to encounter a workpiece being snagged by the back of the blade and flipped. My saw does not have a riving knife, but it does have a splitter that seems to be doing the protection job OK. Normally, I run the blade a bit more elevated than typical, which may explain how the splitter, thus being reasonably close to the blade edge, has managed to keep things tranquil.

Anyway, I have read here and on other sites about how a splitter or riving knife needs to be THINNER than the blade; specifically, than the blade cutting tips. Some commentators have been pretty emphatic about this. However, the function of those separation devices is to keep the cut outfeed part of the workpiece from squeezing the blade back edge and snagging. Consequently, it appears as if one would want the splitter or riving knife to be slightly THICKER than the blade cutting tips and not thinner.

I’d love some feedback on this.

Howard Ferstler


18 replies so far

View a1Jim's profile

a1Jim

112550 posts in 2302 days


#1 posted 06-24-2009 12:08 AM

Hey Howard
I think your fine with a splitter that’s slightly less than the blade because your trying to stop the wood from pinching totally together behind the blade . If you make it slightly larger you wood will get caught on the splitter

-- http://artisticwoodstudio.com Custom furniture

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ferstler

333 posts in 2245 days


#2 posted 06-24-2009 01:18 AM

Jim, that is the perfect answer. Why didn’t I think of that? It makes absolute sense. After all, my splitter is a tad thinner than my blade, and it has worked just fine. Indeed, it must be just about perfect when it comes to its thickness in comparison to the blade.

Actually, it might be possible to build a splitter or riving knife of advanced design that was somewhat tapered and thin at the front (thinner than the blade), with the thickness increasing rapidly away from that lead-in edge, making that part slightly thicker than the blade. That way, it would not hang up the exiting workpiece, but would also guarantee that the workpiece would not be able to snag the backside of the blade. Heck, maybe some are built that way already.

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niki

426 posts in 2804 days


#3 posted 06-24-2009 09:47 PM

Yeap, Jim is correct…

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niki

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Kindlingmaker

2654 posts in 2251 days


#4 posted 06-24-2009 09:53 PM

...if possible use anti kick back prawns also. I have had two near misses and two dents in a tool box just behind where I normally stand…

-- Never board, always knotty, lots of growth rings

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SCOTSMAN

5538 posts in 2310 days


#5 posted 06-24-2009 10:00 PM

Jim is indeed correct! I set my riving knife just about 1mm below the blade height also ,to allow me to cut grooves without going all the way through the wood.I have an overhead guard etc and it has been sucessful for years,Cutting through the wood with the blade raised and grooves with the blade dropped below the thickness of the wood.Alistair

-- excuse my typing as I have a form of parkinsons disease

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ferstler

333 posts in 2245 days


#6 posted 06-24-2009 10:10 PM

I had anti-kickback hooks come with my saw, but eventually removed them. Invariably, if I was tilting the blade for a bevel cut one of them dug in to the table insert itself. You had to manually pull it out of the way to prevent problems when tilting for bevels, but I regularly forgot to do that. They always seemed to be in the way, too, for 90-degree cuts. As I noted in my original post, I have never had a kickback problem, with or without the anti-kickback devices installed. One thing I never do is stand behind the saw while it is cutting – just in case. I also try to keep that blade nicely centered in front of my splitter.

Howard Ferstler

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SCOTSMAN

5538 posts in 2310 days


#7 posted 06-24-2009 10:36 PM

Quite correct and wise Howard stand well off to the side.I have one of those European saws with a large sliding table which means that once the wood is placed in position it is locked down and all I need to do is walk along this saw, pushing the side handle very well designed and very safe I too have had zero kickbacks with this saw regards Alistair

-- excuse my typing as I have a form of parkinsons disease

View SnowyRiver's profile

SnowyRiver

51450 posts in 2205 days


#8 posted 06-25-2009 07:09 PM

The riving knife should be slightly thinner than the kerf or blade. As others have said, the knife keeps the board from closing on the blade and pinching it. It also keeps the wood from getting caught by the rear of the blade. I use a thin riving knife. It’s .09 in thick. This is perfect for a thin kerf blade and a bit narrow when used with a standard blade, but it works fine for all blades. I have several with a quick release so they can be changed quickly. I have short and tall ones, although I prefer the taller one that looks like a reverse shark fin that comes up the back of the blade and slightly over it. You can see a picture of it in my shop pics.

With a kick-back (and heaven knows I have learned this by experience after nearly being knocked off my feet by getting hit with a board before I added the riving knife) the board is hooked by the rear of the blade and it will pull the board up on the blade and throw it back at you like a frisbee. The riving knife prevents the board from being pulled up on the blade, so the thickness of the knife isnt as important as it is to have it, but it shouldnt be thicker than the blade you are using. You wouldnt want it thicker than the blade as it will then block the wood from sliding by it as it’s cut.

-- Wayne - Plymouth MN

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ferstler

333 posts in 2245 days


#9 posted 06-25-2009 11:40 PM

I read somewhere that a properly set up fence should actually be a tad further from the blade at the rear than at the front, which would eliminate the pinch effect that would cause the outfeed part of a workpiece to be pushed against the rear (and upward swinging) part of the blade. If this were done the splitter or riving knife could be thicker than the blade and still allow for the wood to slide past the blade backside.

In addition, apparently some fences are designed to not extend past the rear part of the blade at all, which would eliminate the pinch situation completely.

Howard

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SnowyRiver

51450 posts in 2205 days


#10 posted 06-25-2009 11:51 PM

I cant imagine not having the fence perfectly parallel to the blade. If it isnt, the cut wont be straight. Also, with a short fence, it would be difficult to cut a long piece since there isnt anything to hold it straight once it passes the blade.

-- Wayne - Plymouth MN

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RedShirt013

219 posts in 2386 days


#11 posted 06-26-2009 12:13 AM

It may be just luck that you haven’t experienced kickback; especially without a riving knife kickback is not a completely preventable occurance. It just happens even when doing everything is done right.

Years ago our shop teacher triggered a kickback on purpose to show us how dangerous it is. The wood shot from the saw, hit a cabinet door ~7 ft away, bounced back at an angle ~6 ft and hit me. No damage but still kind of hurts. Even when you’re not in the line of fire, in a small shop it could get you

That said I removed the anti-kickback pawls on the offcut side of my splitter, which always traps thin offcuts and gets rather scary. But the fence side pawls I kept on, more protection the better.

A fence that’s not full length would help, but I still prefer the stability provided by a full fence, plus I don’t believe it will completely eliminate pinching. I’ve seen some pieces that just bend and close on the kerf itself. Fence or no fence that’s going to pinch the blade.

-- Ed

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ferstler

333 posts in 2245 days


#12 posted 06-26-2009 12:26 AM

I can see the theoretical advantages of a riving knife over a splitter, but given that it is unlikely that the board will pinch together all that close to the rear of the blade a splitter probably can work just fine. After all, we are talking about maybe 1/8 inch from the blade tips with a riving knife, vs maybe a half inch to an inch with a splitter. I will admit that for non-through cuts it is nice to not have to remove a splitter. A riving knife can stay in place, which is a convenience advantage. Actually, in some cases a board could pinch together and snag the rear part of a blade even before reaching either a riving knife or a splitter. Neither device could help in that case. Anti-kickback pawls could help there, but I still do not like the cumbersomeness of the things.

So, with a riving knife you are fairly safe once the workpiece extends 1/8 inch past the back of the blade. With a splitter you have to go another half to one inch, and then you are also safe. I guess that extra fraction of an inch means a lot to some people.

Howard Ferstler

View Damian Penney's profile

Damian Penney

1140 posts in 2716 days


#13 posted 06-26-2009 03:50 PM

A riving knife, unlike a splitter, always stays inline with the blade – even for angled cuts, it also rises and falls with the blade which makes it a better option that a splitter. For cuts at 90 degrees, a splitter does a pretty good job.

-- I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso

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JoeinDE

384 posts in 2048 days


#14 posted 06-26-2009 03:58 PM

I’ve been debating getting a splitter and blade guard for my table saw. I bought a used contractors 10” Craftsman table saw two years ago where the previous owner had removed the safety equipment (and the cover on the drive belt and changed the rip fence). Craftsman is pretty good at allowing you to get parts for old tools, but I wasn’t sure about spending $50 for splitter and blade guard since I have not had any problems with kickback (knock on wood) with my table saw. After reading through this thread and since my tablesaw is the workhorse of my shop, I am going to spend the money. Safety first.

-- A bad craftsmen blames his cheap #$%ing tools

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SnowyRiver

51450 posts in 2205 days


#15 posted 06-26-2009 05:46 PM

I think everyone should have a riving knife on their table saw. I used to poo poo it for years until I got hit in the chest with a drawer front I was cutting on my 3 HP saw. It just about knocked me off my feet, couldnt get my breath for a few seconds, had no feeling in my torso from my neck down, and I still have the mark from my chest to my belt line where the wood hit me. It was pretty scary. I guess I just didnt realize how fast that happens and how hard it hits you. I was lucky that I didnt get hit in the face with it. I typically dont use a blade guard because I like to see what is being cut, but the riving knife is a must for me. There is a guy in Alabama that makes them for most saws. LeeWay Workshop…he made mine, and did a very nice job.

-- Wayne - Plymouth MN

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